Merge branch 'feature/mod-code-analysis' into develop

30 files changed, 1523 insertions, 41 deletions

diff --git a/build/prepare-nuget-package.targets b/build/prepare-nuget-package.targets
new file mode 100644
index 00000000..5dbc5508
--- /dev/null
+++ b/build/prepare-nuget-package.targets
@@ -0,0 +1,20 @@
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <!--
+  
+  This build task is run from the ModBuildConfig project after it's been compiled, and copies the
+  package files to the bin\Pathoschild.Stardew.ModBuildConfig folder.
+  
+  -->
+  <Target Name="AfterBuild">
+    <PropertyGroup>
+      <PackagePath>$(SolutionDir)\..\bin\Pathoschild.Stardew.ModBuildConfig</PackagePath>
+    </PropertyGroup>
+    <RemoveDir Directories="$(PackagePath)" />
+    <Copy SourceFiles="$(ProjectDir)/package.nuspec" DestinationFolder="$(PackagePath)" />
+    <Copy SourceFiles="$(ProjectDir)/build/smapi.targets" DestinationFiles="$(PackagePath)/build/Pathoschild.Stardew.ModBuildConfig.targets" />
+    <Copy SourceFiles="$(TargetDir)/StardewModdingAPI.ModBuildConfig.dll" DestinationFiles="$(PackagePath)/build/StardewModdingAPI.ModBuildConfig.dll" />
+    <Copy SourceFiles="$(SolutionDir)/SMAPI.ModBuildConfig.Analyzer/bin/netstandard1.3/StardewModdingAPI.ModBuildConfig.Analyzer.dll" DestinationFiles="$(PackagePath)/analyzers/dotnet/cs/StardewModdingAPI.ModBuildConfig.Analyzer.dll" />
+    <Copy SourceFiles="$(SolutionDir)/SMAPI.ModBuildConfig.Analyzer/tools/install.ps1" DestinationFiles="$(PackagePath)/tools/install.ps1" />
+    <Copy SourceFiles="$(SolutionDir)/SMAPI.ModBuildConfig.Analyzer/tools/uninstall.ps1" DestinationFiles="$(PackagePath)/tools/uninstall.ps1" />
+  </Target>
+</Project>
diff --git a/docs/mod-build-config.md b/docs/mod-build-config.md
index 0d72e4d9..99a567f2 100644
--- a/docs/mod-build-config.md
+++ b/docs/mod-build-config.md
@@ -3,15 +3,16 @@ for SMAPI mods.
 
 The package...
 
-* lets your code compile on any computer (Linux/Mac/Windows) without needing to change the assembly
-  references or game path.
-* packages the mod into the game's `Mods` folder when you rebuild the code (configurable).
-* configures Visual Studio so you can debug into the mod code when the game is running (_Windows
-  only_).
+* detects your game install path;
+* adds the assembly references you need (with automatic support for Linux/Mac/Windows);
+* packages the mod into your `Mods` folder when you rebuild the code (configurable);
+* configures Visual Studio to enable debugging into the code when the game is running (_Windows only_);
+* adds C# analyzers to warn for Stardew Valley-specific issues.
 
 ## Contents
 * [Install](#install)
 * [Configure](#configure)
+* [Code analysis warnings](#code-analysis-warnings)
 * [Troubleshoot](#troubleshoot)
 * [Release notes](#release-notes)
 
@@ -121,7 +122,7 @@ The configuration will check your custom path first, then fall back to the defau
 still compile on a different computer).
 
 ### Unit test projects
-**(upcoming in 2.0.3)**
+**(upcoming in 2.1)**
 
 You can use the package in unit test projects too. Its optional unit test mode...
 
@@ -134,15 +135,81 @@ To enable it, add this above the first `</PropertyGroup>` in your `.csproj`:
 <ModUnitTests>True</ModUnitTests>
 ```
 
+## Code warnings
+### Overview
+The NuGet package adds code warnings in Visual Studio specific to Stardew Valley. For example:  
+![](screenshots/code-analyzer-example.png)
+
+You can hide the warnings...
+* [for specific code](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/preprocessor-directives/preprocessor-pragma-warning);
+* for a method using this attribute:
+  ```cs
+  [System.Diagnostics.CodeAnalysis.SuppressMessage("SMAPI.CommonErrors", "SMAPI001")] // implicit net field conversion
+  ```
+* for an entire project:
+  1. Expand the _References_ node for the project in Visual Studio.
+  2. Right-click on _Analyzers_ and choose _Open Active Rule Set_.
+  4. Expand _StardewModdingAPI.ModBuildConfig.Analyzer_ and uncheck the warnings you want to hide.
+
+See below for help with each specific warning.
+
+### SMAPI001
+**Implicit net field conversion:**
+> This implicitly converts '{{expression}}' from {{net type}} to {{other type}}, but
+> {{net type}} has unintuitive implicit conversion rules. Consider comparing against the actual
+> value instead to avoid bugs.
+
+Stardew Valley uses net types (like `NetBool` and `NetInt`) to handle multiplayer sync. These types
+can implicitly convert to their equivalent normal values (like `bool x = new NetBool()`), but their
+conversion rules are unintuitive and error-prone. For example,
+`item?.category == null && item?.category != null` can both be true at once, and
+`building.indoors != null` will be true for a null value in some cases.
+
+Suggested fix:
+* Some net fields have an equivalent non-net property like `monster.Health` (`int`) instead of
+  `monster.health` (`NetInt`). The package will add a separate [SMAPI002](#smapi002) warning for
+  these. Use the suggested property instead.
+* For a reference type (i.e. one that can contain `null`), you can use the `.Value` property:
+  ```c#
+  if (building.indoors.Value == null)
+  ```
+  Or convert the value before comparison:
+  ```c#
+  GameLocation indoors = building.indoors;
+  if(indoors == null)
+     // ...
+  ```
+* For a value type (i.e. one that can't contain `null`), check if the object is null (if applicable)
+  and compare with `.Value`:
+  ```cs
+  if (item != null && item.category.Value == 0)
+  ```
+
+### SMAPI002
+**Avoid net fields when possible:**
+> '{{expression}}' is a {{net type}} field; consider using the {{property name}} property instead.
+
+Your code accesses a net field, which has some unusual behavior (see [SMAPI001](#smapi001)). This
+field has an equivalent non-net property that avoids those issues.
+
+Suggested fix: access the suggested property name instead.
+
+### SMAPI003
+**Avoid obsolete fields:**
+> The '{{old field}}' field is obsolete and should be replaced with '{{new field}}'.
+
+Your code accesses a field which is obsolete or no longer works. Use the suggested field instead.
+
 ## Troubleshoot
 ### "Failed to find the game install path"
 That error means the package couldn't find your game. You can specify the game path yourself; see
 _[Game path](#game-path)_ above.
 
 ## Release notes
-### 2.0.3 alpha
+### 2.1 alpha
 * Added support for Stardew Valley 1.3.
 * Added support for unit test projects.
+* Added C# analyzers to warn about implicit conversions of Netcode fields in Stardew Valley 1.3.
 
 ### 2.0.2
 * Fixed compatibility issue on Linux.
diff --git a/docs/release-notes.md b/docs/release-notes.md
index c04b6bdf..c65d6e0d 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -8,6 +8,7 @@
   * Fixed SMAPI update checks not showing newer beta versions when using a beta version.
 
 * For modders:
+  * Added code analysis to mod build config package to flag common issues as warnings.
   * Dropped some deprecated APIs.
   * Fixed assets loaded by temporary content managers not being editable.
   * Fixed issue where assets didn't reload correctly when the player switches language.
diff --git a/docs/screenshots/code-analyzer-example.png b/docs/screenshots/code-analyzer-example.png
new file mode 100644
index 00000000..3b930dc5
--- /dev/null
+++ b/docs/screenshots/code-analyzer-example.png
diff --git a/docs/technical-docs.md b/docs/technical-docs.md
index 37ec7f69..9e1a49e7 100644
--- a/docs/technical-docs.md
+++ b/docs/technical-docs.md
@@ -20,6 +20,7 @@ mods, this section isn't relevant to you; see the main README to use or create m
   * [Development](#development-2)
     * [Local development](#local-development)
     * [Deploying to Amazon Beanstalk](#deploying-to-amazon-beanstalk)
+* [Mod build config package](#mod-build-config-package)
 
 # SMAPI
 ## Development
@@ -222,3 +223,31 @@ property name                   | description
 `LogParser:SectionUrl`          | The root URL of the log page, like `https://log.smapi.io/`.
 `ModUpdateCheck:GitHubPassword` | The password with which to authenticate to GitHub when fetching release info.
 `ModUpdateCheck:GitHubUsername` | The username with which to authenticate to GitHub when fetching release info.
+
+## Mod build config package
+### Overview
+The mod build config package is a NuGet package that mods reference to automatically set up
+references, configure the build, and add analyzers specific to Stardew Valley mods.
+
+This involves three projects:
+
+project                                           | purpose
+------------------------------------------------- | ----------------
+`StardewModdingAPI.ModBuildConfig`                | Configures the build (references, deploying the mod files, setting up debugging, etc).
+`StardewModdingAPI.ModBuildConfig.Analyzer`       | Adds C# analyzers which show code warnings in Visual Studio.
+`StardewModdingAPI.ModBuildConfig.Analyzer.Tests` | Unit tests for the C# analyzers.
+
+When the projects are built, the relevant files are copied into `bin/Pathoschild.Stardew.ModBuildConfig`.
+
+### Preparing a build
+To prepare a build of the NuGet package:
+1. Install the [NuGet CLI](https://docs.microsoft.com/en-us/nuget/install-nuget-client-tools#nugetexe-cli).
+1. Change the version and release notes in `package.nuspec`.
+2. Rebuild the solution in _Release_ mode.
+3. Open a terminal in the `bin/Pathoschild.Stardew.ModBuildConfig` package and run this command:
+   ```bash
+   nuget.exe pack
+   ```
+
+That will create a `Pathoschild.Stardew.ModBuildConfig-<version>.nupkg` file in the same directory
+which can be uploaded to NuGet or referenced directly.
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticResult.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticResult.cs
new file mode 100644
index 00000000..896c2cb8
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticResult.cs
@@ -0,0 +1,88 @@
+// <generated />
+using Microsoft.CodeAnalysis;
+using System;
+
+namespace SMAPI.ModBuildConfig.Analyzer.Tests.Framework
+{
+    /// <summary>
+    /// Location where the diagnostic appears, as determined by path, line number, and column number.
+    /// </summary>
+    public struct DiagnosticResultLocation
+    {
+        public DiagnosticResultLocation(string path, int line, int column)
+        {
+            if (line < -1)
+            {
+                throw new ArgumentOutOfRangeException(nameof(line), "line must be >= -1");
+            }
+
+            if (column < -1)
+            {
+                throw new ArgumentOutOfRangeException(nameof(column), "column must be >= -1");
+            }
+
+            this.Path = path;
+            this.Line = line;
+            this.Column = column;
+        }
+
+        public string Path { get; }
+        public int Line { get; }
+        public int Column { get; }
+    }
+
+    /// <summary>
+    /// Struct that stores information about a Diagnostic appearing in a source
+    /// </summary>
+    public struct DiagnosticResult
+    {
+        private DiagnosticResultLocation[] locations;
+
+        public DiagnosticResultLocation[] Locations
+        {
+            get
+            {
+                if (this.locations == null)
+                {
+                    this.locations = new DiagnosticResultLocation[] { };
+                }
+                return this.locations;
+            }
+
+            set
+            {
+                this.locations = value;
+            }
+        }
+
+        public DiagnosticSeverity Severity { get; set; }
+
+        public string Id { get; set; }
+
+        public string Message { get; set; }
+
+        public string Path
+        {
+            get
+            {
+                return this.Locations.Length > 0 ? this.Locations[0].Path : "";
+            }
+        }
+
+        public int Line
+        {
+            get
+            {
+                return this.Locations.Length > 0 ? this.Locations[0].Line : -1;
+            }
+        }
+
+        public int Column
+        {
+            get
+            {
+                return this.Locations.Length > 0 ? this.Locations[0].Column : -1;
+            }
+        }
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticVerifier.Helper.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticVerifier.Helper.cs
new file mode 100644
index 00000000..0247288e
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticVerifier.Helper.cs
@@ -0,0 +1,173 @@
+// <generated />
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Text;
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Linq;
+
+namespace SMAPI.ModBuildConfig.Analyzer.Tests.Framework
+{
+    /// <summary>
+    /// Class for turning strings into documents and getting the diagnostics on them
+    /// All methods are static
+    /// </summary>
+    public abstract partial class DiagnosticVerifier
+    {
+        private static readonly MetadataReference CorlibReference = MetadataReference.CreateFromFile(typeof(object).Assembly.Location);
+        private static readonly MetadataReference SystemCoreReference = MetadataReference.CreateFromFile(typeof(Enumerable).Assembly.Location);
+        private static readonly MetadataReference CSharpSymbolsReference = MetadataReference.CreateFromFile(typeof(CSharpCompilation).Assembly.Location);
+        private static readonly MetadataReference CodeAnalysisReference = MetadataReference.CreateFromFile(typeof(Compilation).Assembly.Location);
+        private static readonly MetadataReference SelfReference = MetadataReference.CreateFromFile(typeof(DiagnosticVerifier).Assembly.Location);
+
+        internal static string DefaultFilePathPrefix = "Test";
+        internal static string CSharpDefaultFileExt = "cs";
+        internal static string VisualBasicDefaultExt = "vb";
+        internal static string TestProjectName = "TestProject";
+
+        #region  Get Diagnostics
+
+        /// <summary>
+        /// Given classes in the form of strings, their language, and an IDiagnosticAnalyzer to apply to it, return the diagnostics found in the string after converting it to a document.
+        /// </summary>
+        /// <param name="sources">Classes in the form of strings</param>
+        /// <param name="language">The language the source classes are in</param>
+        /// <param name="analyzer">The analyzer to be run on the sources</param>
+        /// <returns>An IEnumerable of Diagnostics that surfaced in the source code, sorted by Location</returns>
+        private static Diagnostic[] GetSortedDiagnostics(string[] sources, string language, DiagnosticAnalyzer analyzer)
+        {
+            return GetSortedDiagnosticsFromDocuments(analyzer, GetDocuments(sources, language));
+        }
+
+        /// <summary>
+        /// Given an analyzer and a document to apply it to, run the analyzer and gather an array of diagnostics found in it.
+        /// The returned diagnostics are then ordered by location in the source document.
+        /// </summary>
+        /// <param name="analyzer">The analyzer to run on the documents</param>
+        /// <param name="documents">The Documents that the analyzer will be run on</param>
+        /// <returns>An IEnumerable of Diagnostics that surfaced in the source code, sorted by Location</returns>
+        protected static Diagnostic[] GetSortedDiagnosticsFromDocuments(DiagnosticAnalyzer analyzer, Document[] documents)
+        {
+            var projects = new HashSet<Project>();
+            foreach (var document in documents)
+            {
+                projects.Add(document.Project);
+            }
+
+            var diagnostics = new List<Diagnostic>();
+            foreach (var project in projects)
+            {
+                var compilationWithAnalyzers = project.GetCompilationAsync().Result.WithAnalyzers(ImmutableArray.Create(analyzer));
+                var diags = compilationWithAnalyzers.GetAnalyzerDiagnosticsAsync().Result;
+                foreach (var diag in diags)
+                {
+                    if (diag.Location == Location.None || diag.Location.IsInMetadata)
+                    {
+                        diagnostics.Add(diag);
+                    }
+                    else
+                    {
+                        for (int i = 0; i < documents.Length; i++)
+                        {
+                            var document = documents[i];
+                            var tree = document.GetSyntaxTreeAsync().Result;
+                            if (tree == diag.Location.SourceTree)
+                            {
+                                diagnostics.Add(diag);
+                            }
+                        }
+                    }
+                }
+            }
+
+            var results = SortDiagnostics(diagnostics);
+            diagnostics.Clear();
+            return results;
+        }
+
+        /// <summary>
+        /// Sort diagnostics by location in source document
+        /// </summary>
+        /// <param name="diagnostics">The list of Diagnostics to be sorted</param>
+        /// <returns>An IEnumerable containing the Diagnostics in order of Location</returns>
+        private static Diagnostic[] SortDiagnostics(IEnumerable<Diagnostic> diagnostics)
+        {
+            return diagnostics.OrderBy(d => d.Location.SourceSpan.Start).ToArray();
+        }
+
+        #endregion
+
+        #region Set up compilation and documents
+        /// <summary>
+        /// Given an array of strings as sources and a language, turn them into a project and return the documents and spans of it.
+        /// </summary>
+        /// <param name="sources">Classes in the form of strings</param>
+        /// <param name="language">The language the source code is in</param>
+        /// <returns>A Tuple containing the Documents produced from the sources and their TextSpans if relevant</returns>
+        private static Document[] GetDocuments(string[] sources, string language)
+        {
+            if (language != LanguageNames.CSharp && language != LanguageNames.VisualBasic)
+            {
+                throw new ArgumentException("Unsupported Language");
+            }
+
+            var project = CreateProject(sources, language);
+            var documents = project.Documents.ToArray();
+
+            if (sources.Length != documents.Length)
+            {
+                throw new InvalidOperationException("Amount of sources did not match amount of Documents created");
+            }
+
+            return documents;
+        }
+
+        /// <summary>
+        /// Create a Document from a string through creating a project that contains it.
+        /// </summary>
+        /// <param name="source">Classes in the form of a string</param>
+        /// <param name="language">The language the source code is in</param>
+        /// <returns>A Document created from the source string</returns>
+        protected static Document CreateDocument(string source, string language = LanguageNames.CSharp)
+        {
+            return CreateProject(new[] { source }, language).Documents.First();
+        }
+
+        /// <summary>
+        /// Create a project using the inputted strings as sources.
+        /// </summary>
+        /// <param name="sources">Classes in the form of strings</param>
+        /// <param name="language">The language the source code is in</param>
+        /// <returns>A Project created out of the Documents created from the source strings</returns>
+        private static Project CreateProject(string[] sources, string language = LanguageNames.CSharp)
+        {
+            string fileNamePrefix = DefaultFilePathPrefix;
+            string fileExt = language == LanguageNames.CSharp ? CSharpDefaultFileExt : VisualBasicDefaultExt;
+
+            var projectId = ProjectId.CreateNewId(debugName: TestProjectName);
+
+            var solution = new AdhocWorkspace()
+                .CurrentSolution
+                .AddProject(projectId, TestProjectName, TestProjectName, language)
+                .AddMetadataReference(projectId, DiagnosticVerifier.SelfReference)
+                .AddMetadataReference(projectId, CorlibReference)
+                .AddMetadataReference(projectId, SystemCoreReference)
+                .AddMetadataReference(projectId, CSharpSymbolsReference)
+                .AddMetadataReference(projectId, CodeAnalysisReference);
+
+            int count = 0;
+            foreach (var source in sources)
+            {
+                var newFileName = fileNamePrefix + count + "." + fileExt;
+                var documentId = DocumentId.CreateNewId(projectId, debugName: newFileName);
+                solution = solution.AddDocument(documentId, newFileName, SourceText.From(source));
+                count++;
+            }
+            return solution.GetProject(projectId);
+        }
+        #endregion
+    }
+}
+
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticVerifier.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticVerifier.cs
new file mode 100644
index 00000000..edaaabd4
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Framework/DiagnosticVerifier.cs
@@ -0,0 +1,248 @@
+// <generated />
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using NUnit.Framework;
+
+namespace SMAPI.ModBuildConfig.Analyzer.Tests.Framework
+{
+    /// <summary>
+    /// Superclass of all Unit Tests for DiagnosticAnalyzers
+    /// </summary>
+    public abstract partial class DiagnosticVerifier
+    {
+        #region To be implemented by Test classes
+        /// <summary>
+        /// Get the CSharp analyzer being tested - to be implemented in non-abstract class
+        /// </summary>
+        protected virtual DiagnosticAnalyzer GetCSharpDiagnosticAnalyzer()
+        {
+            return null;
+        }
+
+        /// <summary>
+        /// Get the Visual Basic analyzer being tested (C#) - to be implemented in non-abstract class
+        /// </summary>
+        protected virtual DiagnosticAnalyzer GetBasicDiagnosticAnalyzer()
+        {
+            return null;
+        }
+        #endregion
+
+        #region Verifier wrappers
+
+        /// <summary>
+        /// Called to test a C# DiagnosticAnalyzer when applied on the single inputted string as a source
+        /// Note: input a DiagnosticResult for each Diagnostic expected
+        /// </summary>
+        /// <param name="source">A class in the form of a string to run the analyzer on</param>
+        /// <param name="expected"> DiagnosticResults that should appear after the analyzer is run on the source</param>
+        protected void VerifyCSharpDiagnostic(string source, params DiagnosticResult[] expected)
+        {
+            VerifyDiagnostics(new[] { source }, LanguageNames.CSharp, GetCSharpDiagnosticAnalyzer(), expected);
+        }
+
+        /// <summary>
+        /// Called to test a C# DiagnosticAnalyzer when applied on the inputted strings as a source
+        /// Note: input a DiagnosticResult for each Diagnostic expected
+        /// </summary>
+        /// <param name="sources">An array of strings to create source documents from to run the analyzers on</param>
+        /// <param name="expected">DiagnosticResults that should appear after the analyzer is run on the sources</param>
+        protected void VerifyCSharpDiagnostic(string[] sources, params DiagnosticResult[] expected)
+        {
+            VerifyDiagnostics(sources, LanguageNames.CSharp, GetCSharpDiagnosticAnalyzer(), expected);
+        }
+
+        /// <summary>
+        /// General method that gets a collection of actual diagnostics found in the source after the analyzer is run, 
+        /// then verifies each of them.
+        /// </summary>
+        /// <param name="sources">An array of strings to create source documents from to run the analyzers on</param>
+        /// <param name="language">The language of the classes represented by the source strings</param>
+        /// <param name="analyzer">The analyzer to be run on the source code</param>
+        /// <param name="expected">DiagnosticResults that should appear after the analyzer is run on the sources</param>
+        private void VerifyDiagnostics(string[] sources, string language, DiagnosticAnalyzer analyzer, params DiagnosticResult[] expected)
+        {
+            var diagnostics = GetSortedDiagnostics(sources, language, analyzer);
+            VerifyDiagnosticResults(diagnostics, analyzer, expected);
+        }
+
+        #endregion
+
+        #region Actual comparisons and verifications
+        /// <summary>
+        /// Checks each of the actual Diagnostics found and compares them with the corresponding DiagnosticResult in the array of expected results.
+        /// Diagnostics are considered equal only if the DiagnosticResultLocation, Id, Severity, and Message of the DiagnosticResult match the actual diagnostic.
+        /// </summary>
+        /// <param name="actualResults">The Diagnostics found by the compiler after running the analyzer on the source code</param>
+        /// <param name="analyzer">The analyzer that was being run on the sources</param>
+        /// <param name="expectedResults">Diagnostic Results that should have appeared in the code</param>
+        private static void VerifyDiagnosticResults(IEnumerable<Diagnostic> actualResults, DiagnosticAnalyzer analyzer, params DiagnosticResult[] expectedResults)
+        {
+            int expectedCount = expectedResults.Count();
+            int actualCount = actualResults.Count();
+
+            if (expectedCount != actualCount)
+            {
+                string diagnosticsOutput = actualResults.Any() ? FormatDiagnostics(analyzer, actualResults.ToArray()) : "    NONE.";
+
+                Assert.IsTrue(false,
+                    string.Format("Mismatch between number of diagnostics returned, expected \"{0}\" actual \"{1}\"\r\n\r\nDiagnostics:\r\n{2}\r\n", expectedCount, actualCount, diagnosticsOutput));
+            }
+
+            for (int i = 0; i < expectedResults.Length; i++)
+            {
+                var actual = actualResults.ElementAt(i);
+                var expected = expectedResults[i];
+
+                if (expected.Line == -1 && expected.Column == -1)
+                {
+                    if (actual.Location != Location.None)
+                    {
+                        Assert.IsTrue(false,
+                            string.Format("Expected:\nA project diagnostic with No location\nActual:\n{0}",
+                            FormatDiagnostics(analyzer, actual)));
+                    }
+                }
+                else
+                {
+                    VerifyDiagnosticLocation(analyzer, actual, actual.Location, expected.Locations.First());
+                    var additionalLocations = actual.AdditionalLocations.ToArray();
+
+                    if (additionalLocations.Length != expected.Locations.Length - 1)
+                    {
+                        Assert.IsTrue(false,
+                            string.Format("Expected {0} additional locations but got {1} for Diagnostic:\r\n    {2}\r\n",
+                                expected.Locations.Length - 1, additionalLocations.Length,
+                                FormatDiagnostics(analyzer, actual)));
+                    }
+
+                    for (int j = 0; j < additionalLocations.Length; ++j)
+                    {
+                        VerifyDiagnosticLocation(analyzer, actual, additionalLocations[j], expected.Locations[j + 1]);
+                    }
+                }
+
+                if (actual.Id != expected.Id)
+                {
+                    Assert.IsTrue(false,
+                        string.Format("Expected diagnostic id to be \"{0}\" was \"{1}\"\r\n\r\nDiagnostic:\r\n    {2}\r\n",
+                            expected.Id, actual.Id, FormatDiagnostics(analyzer, actual)));
+                }
+
+                if (actual.Severity != expected.Severity)
+                {
+                    Assert.IsTrue(false,
+                        string.Format("Expected diagnostic severity to be \"{0}\" was \"{1}\"\r\n\r\nDiagnostic:\r\n    {2}\r\n",
+                            expected.Severity, actual.Severity, FormatDiagnostics(analyzer, actual)));
+                }
+
+                if (actual.GetMessage() != expected.Message)
+                {
+                    Assert.IsTrue(false,
+                        string.Format("Expected diagnostic message to be \"{0}\" was \"{1}\"\r\n\r\nDiagnostic:\r\n    {2}\r\n",
+                            expected.Message, actual.GetMessage(), FormatDiagnostics(analyzer, actual)));
+                }
+            }
+        }
+
+        /// <summary>
+        /// Helper method to VerifyDiagnosticResult that checks the location of a diagnostic and compares it with the location in the expected DiagnosticResult.
+        /// </summary>
+        /// <param name="analyzer">The analyzer that was being run on the sources</param>
+        /// <param name="diagnostic">The diagnostic that was found in the code</param>
+        /// <param name="actual">The Location of the Diagnostic found in the code</param>
+        /// <param name="expected">The DiagnosticResultLocation that should have been found</param>
+        private static void VerifyDiagnosticLocation(DiagnosticAnalyzer analyzer, Diagnostic diagnostic, Location actual, DiagnosticResultLocation expected)
+        {
+            var actualSpan = actual.GetLineSpan();
+
+            Assert.IsTrue(actualSpan.Path == expected.Path || (actualSpan.Path != null && actualSpan.Path.Contains("Test0.") && expected.Path.Contains("Test.")),
+                string.Format("Expected diagnostic to be in file \"{0}\" was actually in file \"{1}\"\r\n\r\nDiagnostic:\r\n    {2}\r\n",
+                    expected.Path, actualSpan.Path, FormatDiagnostics(analyzer, diagnostic)));
+
+            var actualLinePosition = actualSpan.StartLinePosition;
+
+            // Only check line position if there is an actual line in the real diagnostic
+            if (actualLinePosition.Line > 0)
+            {
+                if (actualLinePosition.Line + 1 != expected.Line)
+                {
+                    Assert.IsTrue(false,
+                        string.Format("Expected diagnostic to be on line \"{0}\" was actually on line \"{1}\"\r\n\r\nDiagnostic:\r\n    {2}\r\n",
+                            expected.Line, actualLinePosition.Line + 1, FormatDiagnostics(analyzer, diagnostic)));
+                }
+            }
+
+            // Only check column position if there is an actual column position in the real diagnostic
+            if (actualLinePosition.Character > 0)
+            {
+                if (actualLinePosition.Character + 1 != expected.Column)
+                {
+                    Assert.IsTrue(false,
+                        string.Format("Expected diagnostic to start at column \"{0}\" was actually at column \"{1}\"\r\n\r\nDiagnostic:\r\n    {2}\r\n",
+                            expected.Column, actualLinePosition.Character + 1, FormatDiagnostics(analyzer, diagnostic)));
+                }
+            }
+        }
+        #endregion
+
+        #region Formatting Diagnostics
+        /// <summary>
+        /// Helper method to format a Diagnostic into an easily readable string
+        /// </summary>
+        /// <param name="analyzer">The analyzer that this verifier tests</param>
+        /// <param name="diagnostics">The Diagnostics to be formatted</param>
+        /// <returns>The Diagnostics formatted as a string</returns>
+        private static string FormatDiagnostics(DiagnosticAnalyzer analyzer, params Diagnostic[] diagnostics)
+        {
+            var builder = new StringBuilder();
+            for (int i = 0; i < diagnostics.Length; ++i)
+            {
+                builder.AppendLine("// " + diagnostics[i].ToString());
+
+                var analyzerType = analyzer.GetType();
+                var rules = analyzer.SupportedDiagnostics;
+
+                foreach (var rule in rules)
+                {
+                    if (rule != null && rule.Id == diagnostics[i].Id)
+                    {
+                        var location = diagnostics[i].Location;
+                        if (location == Location.None)
+                        {
+                            builder.AppendFormat("GetGlobalResult({0}.{1})", analyzerType.Name, rule.Id);
+                        }
+                        else
+                        {
+                            Assert.IsTrue(location.IsInSource,
+                                $"Test base does not currently handle diagnostics in metadata locations. Diagnostic in metadata: {diagnostics[i]}\r\n");
+
+                            string resultMethodName = diagnostics[i].Location.SourceTree.FilePath.EndsWith(".cs") ? "GetCSharpResultAt" : "GetBasicResultAt";
+                            var linePosition = diagnostics[i].Location.GetLineSpan().StartLinePosition;
+
+                            builder.AppendFormat("{0}({1}, {2}, {3}.{4})",
+                                resultMethodName,
+                                linePosition.Line + 1,
+                                linePosition.Character + 1,
+                                analyzerType.Name,
+                                rule.Id);
+                        }
+
+                        if (i != diagnostics.Length - 1)
+                        {
+                            builder.Append(',');
+                        }
+
+                        builder.AppendLine();
+                        break;
+                    }
+                }
+            }
+            return builder.ToString();
+        }
+        #endregion
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetFieldBase.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetFieldBase.cs
new file mode 100644
index 00000000..1684229a
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetFieldBase.cs
@@ -0,0 +1,16 @@
+// ReSharper disable CheckNamespace -- matches Stardew Valley's code
+namespace Netcode
+{
+    /// <summary>A simplified version of Stardew Valley's <c>Netcode.NetFieldBase</c> for unit testing.</summary>
+    /// <typeparam name="T">The type of the synchronised value.</typeparam>
+    /// <typeparam name="TSelf">The type of the current instance.</typeparam>
+    public class NetFieldBase<T, TSelf> where TSelf : NetFieldBase<T, TSelf>
+    {
+        /// <summary>The synchronised value.</summary>
+        public T Value { get; set; }
+
+        /// <summary>Implicitly convert a net field to the its type.</summary>
+        /// <param name="field">The field to convert.</param>
+        public static implicit operator T(NetFieldBase<T, TSelf> field) => field.Value;
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetInt.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetInt.cs
new file mode 100644
index 00000000..b3abc467
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetInt.cs
@@ -0,0 +1,6 @@
+// ReSharper disable CheckNamespace -- matches Stardew Valley's code
+namespace Netcode
+{
+    /// <summary>A simplified version of Stardew Valley's <c>Netcode.NetInt</c> for unit testing.</summary>
+    public class NetInt : NetFieldBase<int, NetInt> { }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetRef.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetRef.cs
new file mode 100644
index 00000000..be2459cc
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/Netcode/NetRef.cs
@@ -0,0 +1,6 @@
+// ReSharper disable CheckNamespace -- matches Stardew Valley's code
+namespace Netcode
+{
+    /// <summary>A simplified version of Stardew Valley's <c>Netcode.NetRef</c> for unit testing.</summary>
+    public class NetRef<T> : NetFieldBase<T, NetRef<T>> where T : class { }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Farmer.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Farmer.cs
new file mode 100644
index 00000000..e0f0e30c
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Farmer.cs
@@ -0,0 +1,11 @@
+// ReSharper disable CheckNamespace, InconsistentNaming -- matches Stardew Valley's code
+using System.Collections.Generic;
+
+namespace StardewValley
+{
+    /// <summary>A simplified version of Stardew Valley's <c>StardewValley.Farmer</c> class for unit testing.</summary>
+    internal class Farmer
+    {
+        public IDictionary<string, int[]> friendships;
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Item.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Item.cs
new file mode 100644
index 00000000..386767d7
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Item.cs
@@ -0,0 +1,24 @@
+// ReSharper disable CheckNamespace, InconsistentNaming -- matches Stardew Valley's code
+using Netcode;
+
+namespace StardewValley
+{
+    /// <summary>A simplified version of Stardew Valley's <c>StardewValley.Item</c> class for unit testing.</summary>
+    public class Item
+    {
+        /// <summary>A net int field with an equivalent non-net <c>Category</c> property.</summary>
+        public readonly NetInt category = new NetInt { Value = 42 };
+
+        /// <summary>A generic net int field with no equivalent non-net property.</summary>
+        public readonly NetInt netIntField = new NetInt { Value = 42 };
+
+        /// <summary>A generic net ref field with no equivalent non-net property.</summary>
+        public readonly NetRef<object> netRefField = new NetRef<object>();
+
+        /// <summary>A generic net int property with no equivalent non-net property.</summary>
+        public NetInt netIntProperty = new NetInt { Value = 42 };
+
+        /// <summary>A generic net ref property with no equivalent non-net property.</summary>
+        public NetRef<object> netRefProperty { get; } = new NetRef<object>();
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Object.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Object.cs
new file mode 100644
index 00000000..3dd66a6d
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/Mock/StardewValley/Object.cs
@@ -0,0 +1,12 @@
+// ReSharper disable CheckNamespace, InconsistentNaming -- matches Stardew Valley's code
+using Netcode;
+
+namespace StardewValley
+{
+    /// <summary>A simplified version of Stardew Valley's <c>StardewValley.Object</c> class for unit testing.</summary>
+    public class Object : Item
+    {
+        /// <summary>A net int field with an equivalent non-net property.</summary>
+        public NetInt type = new NetInt { Value = 42 };
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/NetFieldAnalyzerTests.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/NetFieldAnalyzerTests.cs
new file mode 100644
index 00000000..101f4c21
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/NetFieldAnalyzerTests.cs
@@ -0,0 +1,140 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using NUnit.Framework;
+using SMAPI.ModBuildConfig.Analyzer.Tests.Framework;
+using StardewModdingAPI.ModBuildConfig.Analyzer;
+
+namespace SMAPI.ModBuildConfig.Analyzer.Tests
+{
+    /// <summary>Unit tests for <see cref="NetFieldAnalyzer"/>.</summary>
+    [TestFixture]
+    public class NetFieldAnalyzerTests : DiagnosticVerifier
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>Sample C# mod code, with a {{test-code}} placeholder for the code in the Entry method to test.</summary>
+        const string SampleProgram = @"
+            using System;
+            using StardewValley;
+            using Netcode;
+            using SObject = StardewValley.Object;
+
+            namespace SampleMod
+            {
+                class ModEntry
+                {
+                    public void Entry()
+                    {
+                        {{test-code}}
+                    }
+                }
+            }
+        ";
+
+        /// <summary>The line number where the unit tested code is injected into <see cref="SampleProgram"/>.</summary>
+        private const int SampleCodeLine = 13;
+
+        /// <summary>The column number where the unit tested code is injected into <see cref="SampleProgram"/>.</summary>
+        private const int SampleCodeColumn = 25;
+
+
+        /*********
+        ** Unit tests
+        *********/
+        /// <summary>Test that no diagnostics are raised for an empty code block.</summary>
+        [TestCase]
+        public void EmptyCode_HasNoDiagnostics()
+        {
+            // arrange
+            string test = @"";
+
+            // assert
+            this.VerifyCSharpDiagnostic(test);
+        }
+
+        /// <summary>Test that the expected diagnostic message is raised for implicit net field comparisons.</summary>
+        /// <param name="codeText">The code line to test.</param>
+        /// <param name="column">The column within the code line where the diagnostic message should be reported.</param>
+        /// <param name="expression">The expression which should be reported.</param>
+        /// <param name="fromType">The source type name which should be reported.</param>
+        /// <param name="toType">The target type name which should be reported.</param>
+        [TestCase("Item item = null; if (item.netIntField < 42);", 22, "item.netIntField", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntField <= 42);", 22, "item.netIntField", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntField > 42);", 22, "item.netIntField", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntField >= 42);", 22, "item.netIntField", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntField == 42);", 22, "item.netIntField", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntField != 42);", 22, "item.netIntField", "NetInt", "int")]
+        [TestCase("Item item = null; if (item?.netIntField != 42);", 22, "item?.netIntField", "NetInt", "int")]
+        [TestCase("Item item = null; if (item?.netIntField != null);", 22, "item?.netIntField", "NetInt", "object")]
+        [TestCase("Item item = null; if (item.netIntProperty < 42);", 22, "item.netIntProperty", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntProperty <= 42);", 22, "item.netIntProperty", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntProperty > 42);", 22, "item.netIntProperty", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntProperty >= 42);", 22, "item.netIntProperty", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntProperty == 42);", 22, "item.netIntProperty", "NetInt", "int")]
+        [TestCase("Item item = null; if (item.netIntProperty != 42);", 22, "item.netIntProperty", "NetInt", "int")]
+        [TestCase("Item item = null; if (item?.netIntProperty != 42);", 22, "item?.netIntProperty", "NetInt", "int")]
+        [TestCase("Item item = null; if (item?.netIntProperty != null);", 22, "item?.netIntProperty", "NetInt", "object")]
+        [TestCase("Item item = null; if (item.netRefField == null);", 22, "item.netRefField", "NetRef", "object")]
+        [TestCase("Item item = null; if (item.netRefField != null);", 22, "item.netRefField", "NetRef", "object")]
+        [TestCase("Item item = null; if (item.netRefProperty == null);", 22, "item.netRefProperty", "NetRef", "object")]
+        [TestCase("Item item = null; if (item.netRefProperty != null);", 22, "item.netRefProperty", "NetRef", "object")]
+        [TestCase("SObject obj = null; if (obj.netIntField != 42);", 24, "obj.netIntField", "NetInt", "int")] // ↓ same as above, but inherited from base class
+        [TestCase("SObject obj = null; if (obj.netIntProperty != 42);", 24, "obj.netIntProperty", "NetInt", "int")]
+        [TestCase("SObject obj = null; if (obj.netRefField == null);", 24, "obj.netRefField", "NetRef", "object")]
+        [TestCase("SObject obj = null; if (obj.netRefField != null);", 24, "obj.netRefField", "NetRef", "object")]
+        [TestCase("SObject obj = null; if (obj.netRefProperty == null);", 24, "obj.netRefProperty", "NetRef", "object")]
+        [TestCase("SObject obj = null; if (obj.netRefProperty != null);", 24, "obj.netRefProperty", "NetRef", "object")]
+        public void AvoidImplicitNetFieldComparisons_RaisesDiagnostic(string codeText, int column, string expression, string fromType, string toType)
+        {
+            // arrange
+            string code = NetFieldAnalyzerTests.SampleProgram.Replace("{{test-code}}", codeText);
+            DiagnosticResult expected = new DiagnosticResult
+            {
+                Id = "SMAPI001",
+                Message = $"This implicitly converts '{expression}' from {fromType} to {toType}, but {fromType} has unintuitive implicit conversion rules. Consider comparing against the actual value instead to avoid bugs. See https://smapi.io/buildmsg/smapi001 for details.",
+                Severity = DiagnosticSeverity.Warning,
+                Locations = new[] { new DiagnosticResultLocation("Test0.cs", NetFieldAnalyzerTests.SampleCodeLine, NetFieldAnalyzerTests.SampleCodeColumn + column) }
+            };
+
+            // assert
+            this.VerifyCSharpDiagnostic(code, expected);
+        }
+
+        /// <summary>Test that the expected diagnostic message is raised for avoidable net field references.</summary>
+        /// <param name="codeText">The code line to test.</param>
+        /// <param name="column">The column within the code line where the diagnostic message should be reported.</param>
+        /// <param name="expression">The expression which should be reported.</param>
+        /// <param name="netType">The net type name which should be reported.</param>
+        /// <param name="suggestedProperty">The suggested property name which should be reported.</param>
+        [TestCase("Item item = null; int category = item.category;", 33, "item.category", "NetInt", "Category")]
+        [TestCase("Item item = null; int category = (item).category;", 33, "(item).category", "NetInt", "Category")]
+        [TestCase("Item item = null; int category = ((Item)item).category;", 33, "((Item)item).category", "NetInt", "Category")]
+        [TestCase("SObject obj = null; int category = obj.category;", 35, "obj.category", "NetInt", "Category")]
+        public void AvoidNetFields_RaisesDiagnostic(string codeText, int column, string expression, string netType, string suggestedProperty)
+        {
+            // arrange
+            string code = NetFieldAnalyzerTests.SampleProgram.Replace("{{test-code}}", codeText);
+            DiagnosticResult expected = new DiagnosticResult
+            {
+                Id = "SMAPI002",
+                Message = $"'{expression}' is a {netType} field; consider using the {suggestedProperty} property instead. See https://smapi.io/buildmsg/smapi002 for details.",
+                Severity = DiagnosticSeverity.Warning,
+                Locations = new[] { new DiagnosticResultLocation("Test0.cs", NetFieldAnalyzerTests.SampleCodeLine, NetFieldAnalyzerTests.SampleCodeColumn + column) }
+            };
+
+            // assert
+            this.VerifyCSharpDiagnostic(code, expected);
+        }
+
+
+        /*********
+        ** Helpers
+        *********/
+        /// <summary>Get the analyzer being tested.</summary>
+        protected override DiagnosticAnalyzer GetCSharpDiagnosticAnalyzer()
+        {
+            return new NetFieldAnalyzer();
+        }
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/ObsoleteFieldAnalyzerTests.cs b/src/SMAPI.ModBuildConfig.Analyzer.Tests/ObsoleteFieldAnalyzerTests.cs
new file mode 100644
index 00000000..dc7476ef
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/ObsoleteFieldAnalyzerTests.cs
@@ -0,0 +1,88 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using NUnit.Framework;
+using SMAPI.ModBuildConfig.Analyzer.Tests.Framework;
+using StardewModdingAPI.ModBuildConfig.Analyzer;
+
+namespace SMAPI.ModBuildConfig.Analyzer.Tests
+{
+    /// <summary>Unit tests for <see cref="ObsoleteFieldAnalyzer"/>.</summary>
+    [TestFixture]
+    public class ObsoleteFieldAnalyzerTests : DiagnosticVerifier
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>Sample C# mod code, with a {{test-code}} placeholder for the code in the Entry method to test.</summary>
+        const string SampleProgram = @"
+            using System;
+            using StardewValley;
+            using Netcode;
+            using SObject = StardewValley.Object;
+
+            namespace SampleMod
+            {
+                class ModEntry
+                {
+                    public void Entry()
+                    {
+                        {{test-code}}
+                    }
+                }
+            }
+        ";
+
+        /// <summary>The line number where the unit tested code is injected into <see cref="SampleProgram"/>.</summary>
+        private const int SampleCodeLine = 13;
+
+        /// <summary>The column number where the unit tested code is injected into <see cref="SampleProgram"/>.</summary>
+        private const int SampleCodeColumn = 25;
+
+
+        /*********
+        ** Unit tests
+        *********/
+        /// <summary>Test that no diagnostics are raised for an empty code block.</summary>
+        [TestCase]
+        public void EmptyCode_HasNoDiagnostics()
+        {
+            // arrange
+            string test = @"";
+
+            // assert
+            this.VerifyCSharpDiagnostic(test);
+        }
+
+        /// <summary>Test that the expected diagnostic message is raised for an obsolete field reference.</summary>
+        /// <param name="codeText">The code line to test.</param>
+        /// <param name="column">The column within the code line where the diagnostic message should be reported.</param>
+        /// <param name="oldName">The old field name which should be reported.</param>
+        /// <param name="newName">The new field name which should be reported.</param>
+        [TestCase("var x = new Farmer().friendships;", 8, "StardewValley.Farmer.friendships", "friendshipData")]
+        public void AvoidObsoleteField_RaisesDiagnostic(string codeText, int column, string oldName, string newName)
+        {
+            // arrange
+            string code = ObsoleteFieldAnalyzerTests.SampleProgram.Replace("{{test-code}}", codeText);
+            DiagnosticResult expected = new DiagnosticResult
+            {
+                Id = "SMAPI003",
+                Message = $"The '{oldName}' field is obsolete and should be replaced with '{newName}'. See https://smapi.io/buildmsg/smapi003 for details.",
+                Severity = DiagnosticSeverity.Warning,
+                Locations = new[] { new DiagnosticResultLocation("Test0.cs", ObsoleteFieldAnalyzerTests.SampleCodeLine, ObsoleteFieldAnalyzerTests.SampleCodeColumn + column) }
+            };
+
+            // assert
+            this.VerifyCSharpDiagnostic(code, expected);
+        }
+
+
+        /*********
+        ** Helpers
+        *********/
+        /// <summary>Get the analyzer being tested.</summary>
+        protected override DiagnosticAnalyzer GetCSharpDiagnosticAnalyzer()
+        {
+            return new ObsoleteFieldAnalyzer();
+        }
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer.Tests/SMAPI.ModBuildConfig.Analyzer.Tests.csproj b/src/SMAPI.ModBuildConfig.Analyzer.Tests/SMAPI.ModBuildConfig.Analyzer.Tests.csproj
new file mode 100644
index 00000000..8d3815c3
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer.Tests/SMAPI.ModBuildConfig.Analyzer.Tests.csproj
@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="2.4.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.3.0" />
+    <PackageReference Include="NUnit" Version="3.10.1" />
+    <PackageReference Include="NUnit3TestAdapter" Version="3.10.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\SMAPI.ModBuildConfig.Analyzer\StardewModdingAPI.ModBuildConfig.Analyzer.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/SMAPI.ModBuildConfig.Analyzer/NetFieldAnalyzer.cs b/src/SMAPI.ModBuildConfig.Analyzer/NetFieldAnalyzer.cs
new file mode 100644
index 00000000..915a50e8
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer/NetFieldAnalyzer.cs
@@ -0,0 +1,271 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace StardewModdingAPI.ModBuildConfig.Analyzer
+{
+    /// <summary>Detects implicit conversion from Stardew Valley's <c>Netcode</c> types. These have very unintuitive implicit conversion rules, so mod authors should always explicitly convert the type with appropriate null checks.</summary>
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public class NetFieldAnalyzer : DiagnosticAnalyzer
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The namespace for Stardew Valley's <c>Netcode</c> types.</summary>
+        private const string NetcodeNamespace = "Netcode";
+
+        /// <summary>Maps net fields to their equivalent non-net properties where available.</summary>
+        private readonly IDictionary<string, string> NetFieldWrapperProperties = new Dictionary<string, string>
+        {
+            // Character
+            ["StardewValley.Character::currentLocationRef"] = "currentLocation",
+            ["StardewValley.Character::facingDirection"] = "FacingDirection",
+            ["StardewValley.Character::name"] = "Name",
+            ["StardewValley.Character::position"] = "Position",
+            ["StardewValley.Character::scale"] = "Scale",
+            ["StardewValley.Character::speed"] = "Speed",
+            ["StardewValley.Character::sprite"] = "Sprite",
+
+            // Chest
+            ["StardewValley.Objects.Chest::tint"] = "Tint",
+
+            // Farmer
+            ["StardewValley.Farmer::houseUpgradeLevel"] = "HouseUpgradeLevel",
+            ["StardewValley.Farmer::isMale"] = "IsMale",
+            ["StardewValley.Farmer::items"] = "Items",
+            ["StardewValley.Farmer::magneticRadius"] = "MagneticRadius",
+            ["StardewValley.Farmer::stamina"] = "Stamina",
+            ["StardewValley.Farmer::uniqueMultiplayerID"] = "UniqueMultiplayerID",
+            ["StardewValley.Farmer::usingTool"] = "UsingTool",
+
+            // Forest
+            ["StardewValley.Locations.Forest::netTravelingMerchantDay"] = "travelingMerchantDay",
+            ["StardewValley.Locations.Forest::netLog"] = "log",
+
+            // FruitTree
+            ["StardewValley.TerrainFeatures.FruitTree::greenHouseTileTree"] = "GreenHouseTileTree",
+            ["StardewValley.TerrainFeatures.FruitTree::greenHouseTree"] = "GreenHouseTree",
+
+            // GameLocation
+            ["StardewValley.GameLocation::isFarm"] = "IsFarm",
+            ["StardewValley.GameLocation::isOutdoors"] = "IsOutdoors",
+            ["StardewValley.GameLocation::lightLevel"] = "LightLevel",
+            ["StardewValley.GameLocation::name"] = "Name",
+
+            // Item
+            ["StardewValley.Item::category"] = "Category",
+            ["StardewValley.Item::netName"] = "Name",
+            ["StardewValley.Item::parentSheetIndex"] = "ParentSheetIndex",
+            ["StardewValley.Item::specialVariable"] = "SpecialVariable",
+
+            // Junimo
+            ["StardewValley.Characters.Junimo::eventActor"] = "EventActor",
+
+            // LightSource
+            ["StardewValley.LightSource::identifier"] = "Identifier",
+
+            // Monster
+            ["StardewValley.Monsters.Monster::damageToFarmer"] = "DamageToFarmer",
+            ["StardewValley.Monsters.Monster::experienceGained"] = "ExperienceGained",
+            ["StardewValley.Monsters.Monster::health"] = "Health",
+            ["StardewValley.Monsters.Monster::maxHealth"] = "MaxHealth",
+            ["StardewValley.Monsters.Monster::netFocusedOnFarmers"] = "focusedOnFarmers",
+            ["StardewValley.Monsters.Monster::netWildernessFarmMonster"] = "wildernessFarmMonster",
+            ["StardewValley.Monsters.Monster::slipperiness"] = "Slipperiness",
+
+            // NPC
+            ["StardewValley.NPC::age"] = "Age",
+            ["StardewValley.NPC::birthday_Day"] = "Birthday_Day",
+            ["StardewValley.NPC::birthday_Season"] = "Birthday_Season",
+            ["StardewValley.NPC::breather"] = "Breather",
+            ["StardewValley.NPC::defaultMap"] = "DefaultMap",
+            ["StardewValley.NPC::gender"] = "Gender",
+            ["StardewValley.NPC::hideShadow"] = "HideShadow",
+            ["StardewValley.NPC::isInvisible"] = "IsInvisible",
+            ["StardewValley.NPC::isWalkingTowardPlayer"] = "IsWalkingTowardPlayer",
+            ["StardewValley.NPC::manners"] = "Manners",
+            ["StardewValley.NPC::optimism"] = "Optimism",
+            ["StardewValley.NPC::socialAnxiety"] = "SocialAnxiety",
+
+            // Object
+            ["StardewValley.Object::canBeGrabbed"] = "CanBeGrabbed",
+            ["StardewValley.Object::canBeSetDown"] = "CanBeSetDown",
+            ["StardewValley.Object::edibility"] = "Edibility",
+            ["StardewValley.Object::flipped"] = "Flipped",
+            ["StardewValley.Object::fragility"] = "Fragility",
+            ["StardewValley.Object::hasBeenPickedUpByFarmer"] = "HasBeenPickedUpByFarmer",
+            ["StardewValley.Object::isHoedirt"] = "IsHoeDirt",
+            ["StardewValley.Object::isOn"] = "IsOn",
+            ["StardewValley.Object::isRecipe"] = "IsRecipe",
+            ["StardewValley.Object::isSpawnedObject"] = "IsSpawnedObject",
+            ["StardewValley.Object::minutesUntilReady"] = "MinutesUntilReady",
+            ["StardewValley.Object::netName"] = "name",
+            ["StardewValley.Object::price"] = "Price",
+            ["StardewValley.Object::quality"] = "Quality",
+            ["StardewValley.Object::scale"] = "Scale",
+            ["StardewValley.Object::stack"] = "Stack",
+            ["StardewValley.Object::tileLocation"] = "TileLocation",
+            ["StardewValley.Object::type"] = "Type",
+
+            // Projectile
+            ["StardewValley.Projectiles.Projectile::ignoreLocationCollision"] = "IgnoreLocationCollision",
+
+            // Tool
+            ["StardewValley.Tool::currentParentTileIndex"] = "CurrentParentTileIndex",
+            ["StardewValley.Tool::indexOfMenuItemView"] = "IndexOfMenuItemView",
+            ["StardewValley.Tool::initialParentTileIndex"] = "InitialParentTileIndex",
+            ["StardewValley.Tool::instantUse"] = "InstantUse",
+            ["StardewValley.Tool::netName"] = "BaseName",
+            ["StardewValley.Tool::stackable"] = "Stackable",
+            ["StardewValley.Tool::upgradeLevel"] = "UpgradeLevel"
+        };
+
+        /// <summary>Describes the diagnostic rule covered by the analyzer.</summary>
+        private readonly IDictionary<string, DiagnosticDescriptor> Rules = new Dictionary<string, DiagnosticDescriptor>
+        {
+            ["SMAPI001"] = new DiagnosticDescriptor(
+                id: "SMAPI001",
+                title: "Netcode types shouldn't be implicitly converted",
+                messageFormat: "This implicitly converts '{0}' from {1} to {2}, but {1} has unintuitive implicit conversion rules. Consider comparing against the actual value instead to avoid bugs. See https://smapi.io/buildmsg/smapi001 for details.",
+                category: "SMAPI.CommonErrors",
+                defaultSeverity: DiagnosticSeverity.Warning,
+                isEnabledByDefault: true,
+                helpLinkUri: "https://smapi.io/buildmsg/smapi001"
+            ),
+            ["SMAPI002"] = new DiagnosticDescriptor(
+                id: "SMAPI002",
+                title: "Avoid Netcode types when possible",
+                messageFormat: "'{0}' is a {1} field; consider using the {2} property instead. See https://smapi.io/buildmsg/smapi002 for details.",
+                category: "SMAPI.CommonErrors",
+                defaultSeverity: DiagnosticSeverity.Warning,
+                isEnabledByDefault: true,
+                helpLinkUri: "https://smapi.io/buildmsg/smapi001"
+            )
+        };
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The descriptors for the diagnostics that this analyzer is capable of producing.</summary>
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        public NetFieldAnalyzer()
+        {
+            this.SupportedDiagnostics = ImmutableArray.CreateRange(this.Rules.Values);
+        }
+
+        /// <summary>Called once at session start to register actions in the analysis context.</summary>
+        /// <param name="context">The analysis context.</param>
+        public override void Initialize(AnalysisContext context)
+        {
+            // SMAPI002: avoid net fields if possible
+            context.RegisterSyntaxNodeAction(
+                this.AnalyzeAvoidableNetField,
+                SyntaxKind.SimpleMemberAccessExpression
+            );
+
+            // SMAPI001: avoid implicit net field conversion
+            context.RegisterSyntaxNodeAction(
+                this.AnalyseNetFieldConversions,
+                SyntaxKind.EqualsExpression,
+                SyntaxKind.NotEqualsExpression,
+                SyntaxKind.GreaterThanExpression,
+                SyntaxKind.GreaterThanOrEqualExpression,
+                SyntaxKind.LessThanExpression,
+                SyntaxKind.LessThanOrEqualExpression
+            );
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Analyse a syntax node and add a diagnostic message if it references a net field when there's a non-net equivalent available.</summary>
+        /// <param name="context">The analysis context.</param>
+        private void AnalyzeAvoidableNetField(SyntaxNodeAnalysisContext context)
+        {
+            try
+            {
+                // check member type
+                MemberAccessExpressionSyntax node = (MemberAccessExpressionSyntax)context.Node;
+                TypeInfo memberType = context.SemanticModel.GetTypeInfo(node);
+                if (!this.IsNetType(memberType.Type))
+                    return;
+
+                // get reference info
+                ITypeSymbol declaringType = context.SemanticModel.GetTypeInfo(node.Expression).Type;
+                string propertyName = node.Name.Identifier.Text;
+
+                // suggest replacement
+                for (ITypeSymbol type = declaringType; type != null; type = type.BaseType)
+                {
+                    if (this.NetFieldWrapperProperties.TryGetValue($"{type}::{propertyName}", out string suggestedPropertyName))
+                    {
+                        context.ReportDiagnostic(Diagnostic.Create(this.Rules["SMAPI002"], context.Node.GetLocation(), node, memberType.Type.Name, suggestedPropertyName));
+                        break;
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                throw new InvalidOperationException($"Failed processing expression: '{context.Node}'. Exception details: {ex.ToString().Replace('\r', ' ').Replace('\n', ' ')}");
+            }
+        }
+
+        /// <summary>Analyse a syntax node and add a diagnostic message if it implicitly converts a net field.</summary>
+        /// <param name="context">The analysis context.</param>
+        private void AnalyseNetFieldConversions(SyntaxNodeAnalysisContext context)
+        {
+            try
+            {
+                BinaryExpressionSyntax binaryExpression = (BinaryExpressionSyntax)context.Node;
+                foreach (var pair in new[] { Tuple.Create(binaryExpression.Left, binaryExpression.Right), Tuple.Create(binaryExpression.Right, binaryExpression.Left) })
+                {
+                    // get node info
+                    ExpressionSyntax curExpression = pair.Item1; // the side of the comparison being examined
+                    ExpressionSyntax otherExpression = pair.Item2; // the other side
+                    TypeInfo typeInfo = context.SemanticModel.GetTypeInfo(curExpression);
+                    if (!this.IsNetType(typeInfo.Type))
+                        continue;
+
+                    // warn for implicit conversion
+                    if (!this.IsNetType(typeInfo.ConvertedType))
+                    {
+                        context.ReportDiagnostic(Diagnostic.Create(this.Rules["SMAPI001"], context.Node.GetLocation(), curExpression, typeInfo.Type.Name, typeInfo.ConvertedType));
+                        break;
+                    }
+
+                    // warn for comparison to null
+                    // An expression like `building.indoors != null` will sometimes convert `building.indoors` to NetFieldBase instead of object before comparison. Haven't reproduced this in unit tests yet.
+                    Optional<object> otherValue = context.SemanticModel.GetConstantValue(otherExpression);
+                    if (otherValue.HasValue && otherValue.Value == null)
+                    {
+                        context.ReportDiagnostic(Diagnostic.Create(this.Rules["SMAPI001"], context.Node.GetLocation(), curExpression, typeInfo.Type.Name, "null"));
+                        break;
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                throw new InvalidOperationException($"Failed processing expression: '{context.Node}'. Exception details: {ex.ToString().Replace('\r', ' ').Replace('\n', ' ')}");
+            }
+        }
+
+        /// <summary>Get whether a type symbol references a <c>Netcode</c> type.</summary>
+        /// <param name="typeSymbol">The type symbol.</param>
+        private bool IsNetType(ITypeSymbol typeSymbol)
+        {
+            return typeSymbol?.ContainingNamespace?.Name == NetFieldAnalyzer.NetcodeNamespace;
+        }
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer/ObsoleteFieldAnalyzer.cs b/src/SMAPI.ModBuildConfig.Analyzer/ObsoleteFieldAnalyzer.cs
new file mode 100644
index 00000000..00565329
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer/ObsoleteFieldAnalyzer.cs
@@ -0,0 +1,98 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace StardewModdingAPI.ModBuildConfig.Analyzer
+{
+    /// <summary>Detects references to a field which has been replaced.</summary>
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public class ObsoleteFieldAnalyzer : DiagnosticAnalyzer
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>Maps obsolete fields/properties to their non-obsolete equivalent.</summary>
+        private readonly IDictionary<string, string> ReplacedFields = new Dictionary<string, string>
+        {
+            // Farmer
+            ["StardewValley.Farmer::friendships"] = "friendshipData"
+        };
+
+        /// <summary>Describes the diagnostic rule covered by the analyzer.</summary>
+        private readonly IDictionary<string, DiagnosticDescriptor> Rules = new Dictionary<string, DiagnosticDescriptor>
+        {
+            ["SMAPI003"] = new DiagnosticDescriptor(
+                id: "SMAPI003",
+                title: "Reference to obsolete field",
+                messageFormat: "The '{0}' field is obsolete and should be replaced with '{1}'. See https://smapi.io/buildmsg/smapi003 for details.",
+                category: "SMAPI.CommonErrors",
+                defaultSeverity: DiagnosticSeverity.Warning,
+                isEnabledByDefault: true,
+                helpLinkUri: "https://smapi.io/buildmsg/smapi003"
+            )
+        };
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>The descriptors for the diagnostics that this analyzer is capable of producing.</summary>
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        public ObsoleteFieldAnalyzer()
+        {
+            this.SupportedDiagnostics = ImmutableArray.CreateRange(this.Rules.Values);
+        }
+
+        /// <summary>Called once at session start to register actions in the analysis context.</summary>
+        /// <param name="context">The analysis context.</param>
+        public override void Initialize(AnalysisContext context)
+        {
+            // SMAPI003: avoid obsolete fields
+            context.RegisterSyntaxNodeAction(
+                this.AnalyzeObsoleteFields,
+                SyntaxKind.SimpleMemberAccessExpression
+            );
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Analyse a syntax node and add a diagnostic message if it references an obsolete field.</summary>
+        /// <param name="context">The analysis context.</param>
+        private void AnalyzeObsoleteFields(SyntaxNodeAnalysisContext context)
+        {
+            try
+            {
+                // get reference info
+                MemberAccessExpressionSyntax node = (MemberAccessExpressionSyntax)context.Node;
+                ITypeSymbol declaringType = context.SemanticModel.GetTypeInfo(node.Expression).Type;
+                string propertyName = node.Name.Identifier.Text;
+
+                // suggest replacement
+                for (ITypeSymbol type = declaringType; type != null; type = type.BaseType)
+                {
+                    if (this.ReplacedFields.TryGetValue($"{type}::{propertyName}", out string replacement))
+                    {
+                        context.ReportDiagnostic(Diagnostic.Create(this.Rules["SMAPI003"], context.Node.GetLocation(), $"{type}.{propertyName}", replacement));
+                        break;
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                throw new InvalidOperationException($"Failed processing expression: '{context.Node}'. Exception details: {ex.ToString().Replace('\r', ' ').Replace('\n', ' ')}");
+            }
+        }
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer/Properties/AssemblyInfo.cs b/src/SMAPI.ModBuildConfig.Analyzer/Properties/AssemblyInfo.cs
new file mode 100644
index 00000000..1cc41000
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer/Properties/AssemblyInfo.cs
@@ -0,0 +1,4 @@
+using System.Reflection;
+
+[assembly: AssemblyTitle("SMAPI.ModBuildConfig.Analyzer")]
+[assembly: AssemblyDescription("")]
diff --git a/src/SMAPI.ModBuildConfig.Analyzer/StardewModdingAPI.ModBuildConfig.Analyzer.csproj b/src/SMAPI.ModBuildConfig.Analyzer/StardewModdingAPI.ModBuildConfig.Analyzer.csproj
new file mode 100644
index 00000000..c32343e3
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer/StardewModdingAPI.ModBuildConfig.Analyzer.csproj
@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netstandard1.3</TargetFramework>
+    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
+    <IncludeBuildOutput>false</IncludeBuildOutput>
+    <OutputPath>bin</OutputPath>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="..\..\build\GlobalAssemblyInfo.cs" Link="Properties\GlobalAssemblyInfo.cs" />
+  </ItemGroup>
+   
+  <ItemGroup>
+    <PackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="2.4.0" PrivateAssets="all" />
+    <PackageReference Update="NETStandard.Library" PrivateAssets="all" />
+  </ItemGroup>
+  
+  <ItemGroup>
+    <None Include="$(OutputPath)\$(AssemblyName).dll" Pack="true" PackagePath="analyzers/dotnet/cs" Visible="false" />
+  </ItemGroup>
+
+</Project>
diff --git a/src/SMAPI.ModBuildConfig.Analyzer/tools/install.ps1 b/src/SMAPI.ModBuildConfig.Analyzer/tools/install.ps1
new file mode 100644
index 00000000..ff051759
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer/tools/install.ps1
@@ -0,0 +1,58 @@
+param($installPath, $toolsPath, $package, $project)
+
+if($project.Object.SupportsPackageDependencyResolution)
+{
+    if($project.Object.SupportsPackageDependencyResolution())
+    {
+        # Do not install analyzers via install.ps1, instead let the project system handle it.
+        return
+    }
+}
+
+$analyzersPaths = Join-Path (Join-Path (Split-Path -Path $toolsPath -Parent) "analyzers") * -Resolve
+
+foreach($analyzersPath in $analyzersPaths)
+{
+    if (Test-Path $analyzersPath)
+    {
+        # Install the language agnostic analyzers.
+        foreach ($analyzerFilePath in Get-ChildItem -Path "$analyzersPath\*.dll" -Exclude *.resources.dll)
+        {
+            if($project.Object.AnalyzerReferences)
+            {
+                $project.Object.AnalyzerReferences.Add($analyzerFilePath.FullName)
+            }
+        }
+    }
+}
+
+# $project.Type gives the language name like (C# or VB.NET)
+$languageFolder = ""
+if($project.Type -eq "C#")
+{
+    $languageFolder = "cs"
+}
+if($project.Type -eq "VB.NET")
+{
+    $languageFolder = "vb"
+}
+if($languageFolder -eq "")
+{
+    return
+}
+
+foreach($analyzersPath in $analyzersPaths)
+{
+    # Install language specific analyzers.
+    $languageAnalyzersPath = join-path $analyzersPath $languageFolder
+    if (Test-Path $languageAnalyzersPath)
+    {
+        foreach ($analyzerFilePath in Get-ChildItem -Path "$languageAnalyzersPath\*.dll" -Exclude *.resources.dll)
+        {
+            if($project.Object.AnalyzerReferences)
+            {
+                $project.Object.AnalyzerReferences.Add($analyzerFilePath.FullName)
+            }
+        }
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig.Analyzer/tools/uninstall.ps1 b/src/SMAPI.ModBuildConfig.Analyzer/tools/uninstall.ps1
new file mode 100644
index 00000000..4bed3337
--- /dev/null
+++ b/src/SMAPI.ModBuildConfig.Analyzer/tools/uninstall.ps1
@@ -0,0 +1,65 @@
+param($installPath, $toolsPath, $package, $project)
+
+if($project.Object.SupportsPackageDependencyResolution)
+{
+    if($project.Object.SupportsPackageDependencyResolution())
+    {
+        # Do not uninstall analyzers via uninstall.ps1, instead let the project system handle it.
+        return
+    }
+}
+
+$analyzersPaths = Join-Path (Join-Path (Split-Path -Path $toolsPath -Parent) "analyzers") * -Resolve
+
+foreach($analyzersPath in $analyzersPaths)
+{
+    # Uninstall the language agnostic analyzers.
+    if (Test-Path $analyzersPath)
+    {
+        foreach ($analyzerFilePath in Get-ChildItem -Path "$analyzersPath\*.dll" -Exclude *.resources.dll)
+        {
+            if($project.Object.AnalyzerReferences)
+            {
+                $project.Object.AnalyzerReferences.Remove($analyzerFilePath.FullName)
+            }
+        }
+    }
+}
+
+# $project.Type gives the language name like (C# or VB.NET)
+$languageFolder = ""
+if($project.Type -eq "C#")
+{
+    $languageFolder = "cs"
+}
+if($project.Type -eq "VB.NET")
+{
+    $languageFolder = "vb"
+}
+if($languageFolder -eq "")
+{
+    return
+}
+
+foreach($analyzersPath in $analyzersPaths)
+{
+    # Uninstall language specific analyzers.
+    $languageAnalyzersPath = join-path $analyzersPath $languageFolder
+    if (Test-Path $languageAnalyzersPath)
+    {
+        foreach ($analyzerFilePath in Get-ChildItem -Path "$languageAnalyzersPath\*.dll" -Exclude *.resources.dll)
+        {
+            if($project.Object.AnalyzerReferences)
+            {
+                try
+                {
+                    $project.Object.AnalyzerReferences.Remove($analyzerFilePath.FullName)
+                }
+                catch
+                {
+
+                }
+            }
+        }
+    }
+}
diff --git a/src/SMAPI.ModBuildConfig/StardewModdingAPI.ModBuildConfig.csproj b/src/SMAPI.ModBuildConfig/StardewModdingAPI.ModBuildConfig.csproj
index d2e06e05..2e3ba356 100644
--- a/src/SMAPI.ModBuildConfig/StardewModdingAPI.ModBuildConfig.csproj
+++ b/src/SMAPI.ModBuildConfig/StardewModdingAPI.ModBuildConfig.csproj
@@ -57,4 +57,5 @@
   </ItemGroup>
   <Import Project="..\SMAPI.Common\StardewModdingAPI.Common.projitems" Label="Shared" />
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <Import Project="..\..\build\prepare-nuget-package.targets" />
 </Project>
\ No newline at end of file
diff --git a/src/SMAPI.ModBuildConfig/build/smapi.targets b/src/SMAPI.ModBuildConfig/build/smapi.targets
index d2e37101..a177840c 100644
--- a/src/SMAPI.ModBuildConfig/build/smapi.targets
+++ b/src/SMAPI.ModBuildConfig/build/smapi.targets
@@ -142,7 +142,7 @@
   <Target Name="BeforeBuild">
     <Error Condition="'$(OS)' != 'OSX' AND '$(OS)' != 'Unix' AND '$(OS)' != 'Windows_NT'" Text="The mod build package doesn't recognise OS type '$(OS)'." />
 
-    <Error Condition="!Exists('$(GamePath)')" Text="The mod build package can't find your game folder. You can specify where to find it; see details at https://github.com/Pathoschild/SMAPI/blob/develop/docs/mod-build-config.md#game-path." />
+    <Error Condition="!Exists('$(GamePath)')" Text="The mod build package can't find your game folder. You can specify where to find it; see https://smapi.io/buildmsg/game-path." />
     <Error Condition="'$(OS)' == 'Windows_NT' AND !Exists('$(GamePath)\Stardew Valley.exe')" Text="The mod build package found a game folder at $(GamePath), but it doesn't contain the Stardew Valley.exe file. If this folder is invalid, delete it and the package will autodetect another game install path." />
     <Error Condition="'$(OS)' != 'Windows_NT' AND !Exists('$(GamePath)\StardewValley.exe')" Text="The mod build package found a game folder at $(GamePath), but it doesn't contain the StardewValley.exe file. If this folder is invalid, delete it and the package will autodetect another game install path." />
     <Error Condition="!Exists('$(GamePath)\StardewModdingAPI.exe')" Text="The mod build package found a game folder at $(GamePath), but it doesn't contain SMAPI. You need to install SMAPI before building the mod." />
diff --git a/src/SMAPI.ModBuildConfig/package.nuspec b/src/SMAPI.ModBuildConfig/package.nuspec
index d24e15be..a280a268 100644
--- a/src/SMAPI.ModBuildConfig/package.nuspec
+++ b/src/SMAPI.ModBuildConfig/package.nuspec
@@ -2,7 +2,7 @@
 <package xmlns="http://schemas.microsoft.com/packaging/2013/05/nuspec.xsd">
   <metadata>
     <id>Pathoschild.Stardew.ModBuildConfig</id>
-    <version>2.0.3-alpha20180325</version>
+    <version>2.1-alpha20180409</version>
     <title>Build package for SMAPI mods</title>
     <authors>Pathoschild</authors>
     <owners>Pathoschild</owners>
@@ -12,28 +12,10 @@
     <iconUrl>https://raw.githubusercontent.com/Pathoschild/SMAPI/develop/src/SMAPI.ModBuildConfig/assets/nuget-icon.png</iconUrl>
     <description>Automates the build configuration for crossplatform Stardew Valley SMAPI mods.</description>
     <releaseNotes>
-      2.0:
-      - Added: mods are now copied into the `Mods` folder automatically (configurable).
-      - Added: release zips are now created automatically in your build output folder (configurable).
-      - Added: mod deploy and release zips now exclude Json.NET automatically, since it's provided by SMAPI.
-      - Added mod's version to release zip filename.
-      - Improved errors to simplify troubleshooting.
-      - Fixed release zip not having a mod folder.
-      - Fixed release zip failing if mod name contains characters that aren't valid in a filename.
-
-      2.0.1:
-      - Fixed mod deploy failing to create subfolders if they don't already exist.
-
-      2.0.2:
-      - Fixed compatibility issue on Linux.
-
-      2.0.3:
+      2.1:
       - Added support for Stardew Valley 1.3.
       - Added support for unit test projects.
+      - Added C# analyzers to warn about implicit conversions of Netcode fields in Stardew Valley 1.3.
     </releaseNotes>
   </metadata>
-  <files>
-    <file src="build/smapi.targets" target="build/Pathoschild.Stardew.ModBuildConfig.targets" />
-    <file src="bin/StardewModdingAPI.ModBuildConfig.dll" target="build/StardewModdingAPI.ModBuildConfig.dll" />
-  </files>
 </package>
diff --git a/src/SMAPI.Tests/StardewModdingAPI.Tests.csproj b/src/SMAPI.Tests/StardewModdingAPI.Tests.csproj
index e4b2c8c6..858a0d4a 100644
--- a/src/SMAPI.Tests/StardewModdingAPI.Tests.csproj
+++ b/src/SMAPI.Tests/StardewModdingAPI.Tests.csproj
@@ -66,6 +66,9 @@
       <Name>StardewModdingAPI</Name>
     </ProjectReference>
   </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Import Project="..\..\build\common.targets" />
 </Project>
\ No newline at end of file
diff --git a/src/SMAPI.Web/Framework/RewriteRules/RedirectToUrlRule.cs b/src/SMAPI.Web/Framework/RewriteRules/RedirectToUrlRule.cs
index 0719e311..4bae0b4c 100644
--- a/src/SMAPI.Web/Framework/RewriteRules/RedirectToUrlRule.cs
+++ b/src/SMAPI.Web/Framework/RewriteRules/RedirectToUrlRule.cs
@@ -12,11 +12,8 @@ namespace StardewModdingAPI.Web.Framework.RewriteRules
         /*********
         ** Properties
         *********/
-        /// <summary>A predicate which indicates when the rule should be applied.</summary>
-        private readonly Func<HttpRequest, bool> ShouldRewrite;
-
-        /// <summary>The new URL to which to redirect.</summary>
-        private readonly string NewUrl;
+        /// <summary>Get the new URL to which to redirect (or <c>null</c> to skip).</summary>
+        private readonly Func<HttpRequest, string> NewUrl;
 
 
         /*********
@@ -27,8 +24,7 @@ namespace StardewModdingAPI.Web.Framework.RewriteRules
         /// <param name="url">The new URL to which to redirect.</param>
         public RedirectToUrlRule(Func<HttpRequest, bool> shouldRewrite, string url)
         {
-            this.ShouldRewrite = shouldRewrite ?? (req => true);
-            this.NewUrl = url;
+            this.NewUrl = req => shouldRewrite(req) ? url : null;
         }
 
         /// <summary>Construct an instance.</summary>
@@ -37,8 +33,7 @@ namespace StardewModdingAPI.Web.Framework.RewriteRules
         public RedirectToUrlRule(string pathRegex, string url)
         {
             Regex regex = new Regex(pathRegex, RegexOptions.IgnoreCase | RegexOptions.Compiled);
-            this.ShouldRewrite = req => req.Path.HasValue && regex.IsMatch(req.Path.Value);
-            this.NewUrl = url;
+            this.NewUrl = req => req.Path.HasValue ? regex.Replace(req.Path.Value, url) : null;
         }
 
         /// <summary>Applies the rule. Implementations of ApplyRule should set the value for <see cref="RewriteContext.Result" /> (defaults to RuleResult.ContinueRules).</summary>
@@ -47,14 +42,15 @@ namespace StardewModdingAPI.Web.Framework.RewriteRules
         {
             HttpRequest request = context.HttpContext.Request;
 
-            // check condition
-            if (!this.ShouldRewrite(request))
+            // check rewrite
+            string newUrl = this.NewUrl(request);
+            if (newUrl == null || newUrl == request.Path.Value)
                 return;
 
             // redirect request
             HttpResponse response = context.HttpContext.Response;
             response.StatusCode = (int)HttpStatusCode.Redirect;
-            response.Headers["Location"] = this.NewUrl;
+            response.Headers["Location"] = newUrl;
             context.Result = RuleResult.EndResponse;
         }
     }
diff --git a/src/SMAPI.Web/Startup.cs b/src/SMAPI.Web/Startup.cs
index 47102e5c..6c7ccecd 100644
--- a/src/SMAPI.Web/Startup.cs
+++ b/src/SMAPI.Web/Startup.cs
@@ -155,6 +155,7 @@ namespace StardewModdingAPI.Web
             // shortcut redirects
             redirects.Add(new RedirectToUrlRule(@"^/compat\.?$", "https://stardewvalleywiki.com/Modding:SMAPI_compatibility"));
             redirects.Add(new RedirectToUrlRule(@"^/docs\.?$", "https://stardewvalleywiki.com/Modding:Index"));
+            redirects.Add(new RedirectToUrlRule(@"^/buildmsg(?:/?(.*))$", "https://github.com/Pathoschild/SMAPI/blob/develop/docs/mod-build-config.md#$1"));
 
             // redirect legacy canimod.com URLs
             var wikiRedirects = new Dictionary<string, string[]>
diff --git a/src/SMAPI.sln b/src/SMAPI.sln
index 6577b42e..56898a32 100644
--- a/src/SMAPI.sln
+++ b/src/SMAPI.sln
@@ -45,9 +45,17 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "build", "build", "{09CF91E5
 		..\build\common.targets = ..\build\common.targets
 		..\build\GlobalAssemblyInfo.cs = ..\build\GlobalAssemblyInfo.cs
 		..\build\prepare-install-package.targets = ..\build\prepare-install-package.targets
+		..\build\prepare-nuget-package.targets = ..\build\prepare-nuget-package.targets
 	EndProjectSection
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "StardewModdingAPI.ModBuildConfig", "SMAPI.ModBuildConfig\StardewModdingAPI.ModBuildConfig.csproj", "{EA4F1E80-743F-4A1D-9757-AE66904A196A}"
+	ProjectSection(ProjectDependencies) = postProject
+		{80AD8528-AA49-4731-B4A6-C691845815A1} = {80AD8528-AA49-4731-B4A6-C691845815A1}
+	EndProjectSection
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "StardewModdingAPI.ModBuildConfig.Analyzer", "SMAPI.ModBuildConfig.Analyzer\StardewModdingAPI.ModBuildConfig.Analyzer.csproj", "{80AD8528-AA49-4731-B4A6-C691845815A1}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "SMAPI.ModBuildConfig.Analyzer.Tests", "SMAPI.ModBuildConfig.Analyzer.Tests\SMAPI.ModBuildConfig.Analyzer.Tests.csproj", "{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}"
 EndProject
 Global
 	GlobalSection(SharedMSBuildProjectFiles) = preSolution
@@ -137,6 +145,30 @@ Global
 		{EA4F1E80-743F-4A1D-9757-AE66904A196A}.Release|Mixed Platforms.Build.0 = Release|x86
 		{EA4F1E80-743F-4A1D-9757-AE66904A196A}.Release|x86.ActiveCfg = Release|x86
 		{EA4F1E80-743F-4A1D-9757-AE66904A196A}.Release|x86.Build.0 = Release|x86
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Debug|Mixed Platforms.ActiveCfg = Debug|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Debug|Mixed Platforms.Build.0 = Debug|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Debug|x86.Build.0 = Debug|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Release|Any CPU.Build.0 = Release|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Release|Mixed Platforms.ActiveCfg = Release|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Release|Mixed Platforms.Build.0 = Release|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Release|x86.ActiveCfg = Release|Any CPU
+		{80AD8528-AA49-4731-B4A6-C691845815A1}.Release|x86.Build.0 = Release|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Debug|Mixed Platforms.ActiveCfg = Debug|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Debug|Mixed Platforms.Build.0 = Debug|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Debug|x86.Build.0 = Debug|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Release|Any CPU.Build.0 = Release|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Release|Mixed Platforms.ActiveCfg = Release|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Release|Mixed Platforms.Build.0 = Release|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Release|x86.ActiveCfg = Release|Any CPU
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -147,6 +179,7 @@ Global
 		{2AA02FB6-FF03-41CF-A215-2EE60AB4F5DC} = {82D22ED7-A0A7-4D64-8E92-4B6A5E74ED11}
 		{EB35A917-67B9-4EFA-8DFC-4FB49B3949BB} = {86C452BE-D2D8-45B4-B63F-E329EB06CEDA}
 		{09CF91E5-5BAB-4650-A200-E5EA9A633046} = {86C452BE-D2D8-45B4-B63F-E329EB06CEDA}
+		{0CF97929-B0D0-4D73-B7BF-4FF7191035F9} = {82D22ED7-A0A7-4D64-8E92-4B6A5E74ED11}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {70143042-A862-47A8-A677-7C819DDC90DC}