add --log-path argument to specify SMAPI log path during testing

4 files changed, 30 insertions, 7 deletions

diff --git a/README.md b/README.md
index c90e62cc..74388144 100644
--- a/README.md
+++ b/README.md
@@ -145,9 +145,10 @@ field | purpose
 `ModCompatibility` | A list of mod versions SMAPI should consider compatible or broken regardless of whether it detects incompatible code. Each record can be set to `AssumeCompatible` or `AssumeBroken`. Changing this field is not recommended and may destabilise your game.
 
 ### Command-line arguments
-SMAPI recognises the following command-line arguments. These are intended for internal use and may
-change without warning.
+SMAPI recognises the following command-line arguments. These are intended for internal use or
+testing and may change without warning.
 
 argument | purpose
 -------- | -------
+`--log path "path"` | The relative or absolute path of the log file SMAPI should write.
 `--no-terminal` | SMAPI won't write anything to the console window. (Messages will still be written to the log file.)
diff --git a/release-notes.md b/release-notes.md
index bde3e4b0..a5ef4a0b 100644
--- a/release-notes.md
+++ b/release-notes.md
@@ -43,6 +43,7 @@ For mod developers:
 * Added `ContentEvents.AfterLocaleChanged` event triggered when the player changes the content language (for the upcoming Stardew Valley 1.2).
 * Added `SaveEvents.AfterReturnToTitle` event triggered when the player returns to the title screen (for the upcoming Stardew Valley 1.2).
 * Added `helper.Reflection.GetPrivateProperty` method.
+* Added a `--log-path` argument to specify the SMAPI log path during testing.
 * SMAPI now writes XNA input enums (`Buttons` and `Keys`) to JSON as strings automatically, so mods no longer need to add a `StringEnumConverter` themselves for those.
 * The SMAPI log now has a simpler filename.
 * The SMAPI log now shows the OS caption (like "Windows 10") instead of its internal version when available.
diff --git a/src/StardewModdingAPI/Constants.cs b/src/StardewModdingAPI/Constants.cs
index e28b33d7..4a036cd0 100644
--- a/src/StardewModdingAPI/Constants.cs
+++ b/src/StardewModdingAPI/Constants.cs
@@ -69,7 +69,7 @@ namespace StardewModdingAPI
         internal static string ApiConfigPath => Path.Combine(Constants.ExecutionPath, $"{typeof(Program).Assembly.GetName().Name}.config.json");
 
         /// <summary>The file path to the log where the latest output should be saved.</summary>
-        internal static string LogPath => Path.Combine(Constants.LogDir, "SMAPI-latest.txt");
+        internal static string DefaultLogPath => Path.Combine(Constants.LogDir, "SMAPI-latest.txt");
 
         /// <summary>The full path to the folder containing mods.</summary>
         internal static string ModPath { get; } = Path.Combine(Constants.ExecutionPath, "Mods");
diff --git a/src/StardewModdingAPI/Program.cs b/src/StardewModdingAPI/Program.cs
index ac98f2e4..58850dc3 100644
--- a/src/StardewModdingAPI/Program.cs
+++ b/src/StardewModdingAPI/Program.cs
@@ -30,7 +30,7 @@ namespace StardewModdingAPI
         ** Properties
         *********/
         /// <summary>The log file to which to write messages.</summary>
-        private readonly LogFileManager LogFile = new LogFileManager(Constants.LogPath);
+        private readonly LogFileManager LogFile;
 
         /// <summary>Manages console output interception.</summary>
         private readonly ConsoleInterceptionManager ConsoleManager = new ConsoleInterceptionManager();
@@ -67,17 +67,38 @@ namespace StardewModdingAPI
         /// <param name="args">The command-line arguments.</param>
         private static void Main(string[] args)
         {
-            new Program(writeToConsole: !args.Contains("--no-terminal"))
+            // get flags from arguments
+            bool writeToConsole = !args.Contains("--no-terminal");
+
+            // get log path from arguments
+            string logPath = null;
+            {
+                int pathIndex = Array.LastIndexOf(args, "--log-path") + 1;
+                if (pathIndex >= 1 && args.Length >= pathIndex)
+                {
+                    logPath = args[pathIndex];
+                    if (!Path.IsPathRooted(logPath))
+                        logPath = Path.Combine(Constants.LogDir, logPath);
+                }
+            }
+            if (string.IsNullOrWhiteSpace(logPath))
+                logPath = Constants.DefaultLogPath;
+
+            // load SMAPI
+            new Program(writeToConsole, logPath)
                 .LaunchInteractively();
         }
 
         /// <summary>Construct an instance.</summary>
-        internal Program(bool writeToConsole)
+        /// <param name="writeToConsole">Whether to output log messages to the console.</param>
+        /// <param name="logPath">The full file path to which to write log messages.</param>
+        internal Program(bool writeToConsole, string logPath)
         {
             // load settings
             this.Settings = JsonConvert.DeserializeObject<SConfig>(File.ReadAllText(Constants.ApiConfigPath));
 
             // initialise
+            this.LogFile = new LogFileManager(logPath);
             this.Monitor = new Monitor("SMAPI", this.ConsoleManager, this.LogFile, this.ExitGameImmediately) { WriteToConsole = writeToConsole };
             this.ModRegistry = new ModRegistry(this.Settings.ModCompatibility);
             this.DeprecationManager = new DeprecationManager(this.Monitor, this.ModRegistry);
@@ -460,7 +481,7 @@ namespace StardewModdingAPI
                 try
                 {
                     int modEntries = modAssembly.DefinedTypes.Count(type => typeof(Mod).IsAssignableFrom(type) && !type.IsAbstract);
-                    if(modEntries == 0)
+                    if (modEntries == 0)
                     {
                         this.Monitor.Log($"{skippedPrefix} because its DLL has no '{nameof(Mod)}' subclass.", LogLevel.Error);
                         continue;