Custom doctag extension (#2343)

* Add an extension point for rendering custom doc tags

* Iterate over documentable sourcesets when building custom tags

* Extract a nested custom tags brief block into a separate method

* Filter out tag content providers and make since kotlin brief a one-liner

* Add padding to "Since Kotlin" block in brief description

6 files changed, 150 insertions, 24 deletions

diff --git a/plugins/base/src/main/kotlin/DokkaBase.kt b/plugins/base/src/main/kotlin/DokkaBase.kt
index a26f6dcd..0443b136 100644
--- a/plugins/base/src/main/kotlin/DokkaBase.kt
+++ b/plugins/base/src/main/kotlin/DokkaBase.kt
@@ -29,6 +29,8 @@ import org.jetbrains.dokka.base.translators.documentables.DefaultDocumentableToP
 import org.jetbrains.dokka.base.translators.psi.DefaultPsiToDocumentableTranslator
 import org.jetbrains.dokka.base.generation.SingleModuleGeneration
 import org.jetbrains.dokka.base.renderers.html.command.consumers.ReplaceVersionsConsumer
+import org.jetbrains.dokka.base.transformers.pages.tags.CustomTagContentProvider
+import org.jetbrains.dokka.base.transformers.pages.tags.SinceKotlinTagContentProvider
 import org.jetbrains.dokka.base.translators.descriptors.DefaultExternalDocumentablesProvider
 import org.jetbrains.dokka.base.translators.descriptors.ExternalClasslikesTranslator
 import org.jetbrains.dokka.base.translators.descriptors.ExternalDocumentablesProvider
@@ -41,6 +43,7 @@ class DokkaBase : DokkaPlugin() {
     val preMergeDocumentableTransformer by extensionPoint<PreMergeDocumentableTransformer>()
     val pageMergerStrategy by extensionPoint<PageMergerStrategy>()
     val commentsToContentConverter by extensionPoint<CommentsToContentConverter>()
+    val customTagContentProvider by extensionPoint<CustomTagContentProvider>()
     val signatureProvider by extensionPoint<SignatureProvider>()
     val locationProviderFactory by extensionPoint<LocationProviderFactory>()
     val externalLocationProviderFactory by extensionPoint<ExternalLocationProviderFactory>()
@@ -151,6 +154,10 @@ class DokkaBase : DokkaPlugin() {
         commentsToContentConverter with DocTagToContentConverter()
     }
 
+    val sinceKotlinTagContentProvider by extending {
+        customTagContentProvider with SinceKotlinTagContentProvider
+    }
+
     val pageMerger by extending {
         CoreExtensions.pageTransformer providing ::PageMerger
     }
diff --git a/plugins/base/src/main/kotlin/renderers/html/HtmlRenderer.kt b/plugins/base/src/main/kotlin/renderers/html/HtmlRenderer.kt
index 2906e8f2..2d8f88a6 100644
--- a/plugins/base/src/main/kotlin/renderers/html/HtmlRenderer.kt
+++ b/plugins/base/src/main/kotlin/renderers/html/HtmlRenderer.kt
@@ -113,6 +113,7 @@ open class HtmlRenderer(
                     childrenCallback()
                 }
             }
+            node.hasStyle(TextStyle.InlineComment) -> div("inline-comment") { childrenCallback() }
             node.dci.kind == ContentKind.BriefComment -> div("brief $additionalClasses") { childrenCallback() }
             node.dci.kind == ContentKind.Cover -> div("cover $additionalClasses") { //TODO this can be removed
                 childrenCallback()
diff --git a/plugins/base/src/main/kotlin/transformers/pages/tags/CustomTagContentProvider.kt b/plugins/base/src/main/kotlin/transformers/pages/tags/CustomTagContentProvider.kt
new file mode 100644
index 00000000..e818ef1d
--- /dev/null
+++ b/plugins/base/src/main/kotlin/transformers/pages/tags/CustomTagContentProvider.kt
@@ -0,0 +1,59 @@
+package org.jetbrains.dokka.base.transformers.pages.tags
+
+import org.jetbrains.dokka.DokkaConfiguration.DokkaSourceSet
+import org.jetbrains.dokka.base.translators.documentables.PageContentBuilder.DocumentableContentBuilder
+import org.jetbrains.dokka.model.doc.CustomTagWrapper
+import org.jetbrains.dokka.model.doc.DocTag
+
+/**
+ * Provides an ability to render custom doc tags
+ *
+ * Custom tags can be generated during build, for instance via transformers from converting an annotation
+ * (such as in [org.jetbrains.dokka.base.transformers.pages.annotations.SinceKotlinTransformer])
+ *
+ * Also, custom tags can come from the kdoc itself, where "custom" is defined as unknown to the compiler/spec.
+ * `@property` and `@throws` are not custom tags - they are defined by the spec and have special meaning
+ * and separate blocks on the documentation page, it's clear how to render it. Whereas `@usesMathJax` is
+ * a custom tag - it's application/plugin specific and is not handled by dokka by default.
+ *
+ * Using this provider, we can map custom tags  (such as `@usesMathJax`) and generate content for it that
+ * will be displayed on the pages.
+ */
+interface CustomTagContentProvider {
+
+    /**
+     * Whether this content provider supports given [CustomTagWrapper].
+     *
+     * Tags can be filtered out either by name or by nested [DocTag] type
+     */
+    fun isApplicable(customTag: CustomTagWrapper): Boolean
+
+    /**
+     * Full blown content description, most likely to be on a separate page
+     * dedicated to just one element (i.e one class/function), so any
+     * amount of detail should be fine.
+     */
+    fun DocumentableContentBuilder.contentForDescription(
+        sourceSet: DokkaSourceSet,
+        customTag: CustomTagWrapper
+    ) {}
+
+    /**
+     * Brief comment section, usually displayed as a summary/preview.
+     *
+     * For instance, when listing all functions of a class on one page,
+     * it'll be too much to display complete documentation for each function.
+     * Instead, a small brief is shown for each one (i.e the first paragraph
+     * or some other important information) - the user can go to the dedicated
+     * page for more details if they find the brief interesting.
+     *
+     * Tag-wise, it would make sense to include `Since Kotlin`, since it's
+     * important information for the users of stdlib. It would make little
+     * sense to include `@usesMathjax` here, as this information seems
+     * to be more specific and detailed than is needed for a brief.
+     */
+    fun DocumentableContentBuilder.contentForBrief(
+        sourceSet: DokkaSourceSet,
+        customTag: CustomTagWrapper
+    ) {}
+}
diff --git a/plugins/base/src/main/kotlin/transformers/pages/tags/SinceKotlinTagContentProvider.kt b/plugins/base/src/main/kotlin/transformers/pages/tags/SinceKotlinTagContentProvider.kt
new file mode 100644
index 00000000..c9010421
--- /dev/null
+++ b/plugins/base/src/main/kotlin/transformers/pages/tags/SinceKotlinTagContentProvider.kt
@@ -0,0 +1,34 @@
+package org.jetbrains.dokka.base.transformers.pages.tags
+
+import org.jetbrains.dokka.DokkaConfiguration
+import org.jetbrains.dokka.base.translators.documentables.PageContentBuilder.DocumentableContentBuilder
+import org.jetbrains.dokka.model.doc.CustomTagWrapper
+import org.jetbrains.dokka.pages.ContentKind
+import org.jetbrains.dokka.pages.TextStyle
+
+object SinceKotlinTagContentProvider : CustomTagContentProvider {
+
+    private const val SINCE_KOTLIN_TAG_NAME = "Since Kotlin"
+
+    override fun isApplicable(customTag: CustomTagWrapper) = customTag.name == SINCE_KOTLIN_TAG_NAME
+
+    override fun DocumentableContentBuilder.contentForDescription(
+        sourceSet: DokkaConfiguration.DokkaSourceSet,
+        customTag: CustomTagWrapper
+    ) {
+        group(sourceSets = setOf(sourceSet), kind = ContentKind.Comment, styles = setOf(TextStyle.Block)) {
+            header(4, customTag.name)
+            comment(customTag.root)
+        }
+    }
+
+    override fun DocumentableContentBuilder.contentForBrief(
+        sourceSet: DokkaConfiguration.DokkaSourceSet,
+        customTag: CustomTagWrapper
+    ) {
+        group(sourceSets = setOf(sourceSet), styles = setOf(TextStyle.InlineComment)) {
+            text(customTag.name + " ", styles = setOf(TextStyle.Bold))
+            comment(customTag.root, styles = emptySet())
+        }
+    }
+}
\ No newline at end of file
diff --git a/plugins/base/src/main/kotlin/translators/documentables/DefaultDocumentableToPageTranslator.kt b/plugins/base/src/main/kotlin/translators/documentables/DefaultDocumentableToPageTranslator.kt
index 18647207..a385e0e4 100644
--- a/plugins/base/src/main/kotlin/translators/documentables/DefaultDocumentableToPageTranslator.kt
+++ b/plugins/base/src/main/kotlin/translators/documentables/DefaultDocumentableToPageTranslator.kt
@@ -4,10 +4,7 @@ import org.jetbrains.dokka.base.DokkaBase
 import org.jetbrains.dokka.base.DokkaBaseConfiguration
 import org.jetbrains.dokka.model.DModule
 import org.jetbrains.dokka.pages.ModulePageNode
-import org.jetbrains.dokka.plugability.configuration
-import org.jetbrains.dokka.plugability.DokkaContext
-import org.jetbrains.dokka.plugability.plugin
-import org.jetbrains.dokka.plugability.querySingle
+import org.jetbrains.dokka.plugability.*
 import org.jetbrains.dokka.transformers.documentation.DocumentableToPageTranslator
 
 class DefaultDocumentableToPageTranslator(
@@ -16,8 +13,15 @@ class DefaultDocumentableToPageTranslator(
     private val configuration = configuration<DokkaBase, DokkaBaseConfiguration>(context)
     private val commentsToContentConverter = context.plugin<DokkaBase>().querySingle { commentsToContentConverter }
     private val signatureProvider = context.plugin<DokkaBase>().querySingle { signatureProvider }
+    private val customTagContentProviders = context.plugin<DokkaBase>().query { customTagContentProvider }
     private val logger = context.logger
 
     override fun invoke(module: DModule): ModulePageNode =
-        DefaultPageCreator(configuration, commentsToContentConverter, signatureProvider, logger).pageForModule(module)
+        DefaultPageCreator(
+            configuration,
+            commentsToContentConverter,
+            signatureProvider,
+            logger,
+            customTagContentProviders
+        ).pageForModule(module)
 }
\ No newline at end of file
diff --git a/plugins/base/src/main/kotlin/translators/documentables/DefaultPageCreator.kt b/plugins/base/src/main/kotlin/translators/documentables/DefaultPageCreator.kt
index c16996a0..946d6416 100644
--- a/plugins/base/src/main/kotlin/translators/documentables/DefaultPageCreator.kt
+++ b/plugins/base/src/main/kotlin/translators/documentables/DefaultPageCreator.kt
@@ -19,6 +19,7 @@ import org.jetbrains.dokka.DokkaConfiguration.DokkaSourceSet
 import org.jetbrains.dokka.base.DokkaBaseConfiguration
 import org.jetbrains.dokka.base.resolvers.anchors.SymbolAnchorHint
 import org.jetbrains.dokka.base.transformers.documentables.ClashingDriIdentifier
+import org.jetbrains.dokka.base.transformers.pages.tags.CustomTagContentProvider
 
 private typealias GroupedTags = Map<KClass<out TagWrapper>, List<Pair<DokkaSourceSet?, TagWrapper>>>
 
@@ -29,7 +30,8 @@ open class DefaultPageCreator(
     configuration: DokkaBaseConfiguration?,
     commentsToContentConverter: CommentsToContentConverter,
     signatureProvider: SignatureProvider,
-    val logger: DokkaLogger
+    val logger: DokkaLogger,
+    val customTagContentProviders: List<CustomTagContentProvider> = emptyList()
 ) {
     protected open val contentBuilder = PageContentBuilder(commentsToContentConverter, signatureProvider, logger)
 
@@ -341,6 +343,23 @@ open class DefaultPageCreator(
                 }
             }
 
+            val customTags = d.customTags
+            if (customTags.isNotEmpty()) {
+                group(styles = setOf(TextStyle.Block)) {
+                    platforms.forEach { platform ->
+                        customTags.forEach { (tagName, sourceSetTag) ->
+                            sourceSetTag[platform]?.let { tag ->
+                                customTagContentProviders.filter { it.isApplicable(tag) }.forEach { provider ->
+                                    with(provider) {
+                                        contentForDescription(platform, tag)
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
             val unnamedTags = tags.filterNot { (k, _) -> k.isSubclassOf(NamedTagWrapper::class) || k in specialTags }
                 .values.flatten().groupBy { it.first }.mapValues { it.value.map { it.second } }
             if (unnamedTags.isNotEmpty()) {
@@ -357,8 +376,6 @@ open class DefaultPageCreator(
                     }
                 }
             }
-
-            contentForSinceKotlin(d)
         }.children
     }
 
@@ -560,21 +577,6 @@ open class DefaultPageCreator(
         } ?: firstParagraphComment(tag.root)
     }
 
-    protected open fun DocumentableContentBuilder.contentForSinceKotlin(documentable: Documentable) {
-        documentable.documentation.mapValues {
-            it.value.children.find { it is CustomTagWrapper && it.name == "Since Kotlin" } as CustomTagWrapper?
-        }.run {
-            documentable.sourceSets.forEach { sourceSet ->
-                this[sourceSet]?.also { tag ->
-                    group(sourceSets = setOf(sourceSet), kind = ContentKind.Comment, styles = setOf(TextStyle.Block)) {
-                        header(4, tag.name)
-                        comment(tag.root)
-                    }
-                }
-            }
-        }
-    }
-
     protected open fun contentForFunction(f: DFunction) = contentForMember(f)
 
     protected open fun contentForProperty(p: DProperty) = contentForMember(p)
@@ -681,7 +683,7 @@ open class DefaultPageCreator(
                                         }
                                         after(extra = PropertyContainer.empty()) {
                                             contentForBrief(it)
-                                            contentForSinceKotlin(it)
+                                            contentForCustomTagsBrief(it)
                                         }
                                     }
                                 }
@@ -692,6 +694,22 @@ open class DefaultPageCreator(
         }
     }
 
+    private fun DocumentableContentBuilder.contentForCustomTagsBrief(documentable: Documentable) {
+        val customTags = documentable.customTags
+        if (customTags.isEmpty()) return
+
+        documentable.sourceSets.forEach { sourceSet ->
+            customTags.forEach { (tagName, sourceSetTag) ->
+                sourceSetTag[sourceSet]?.let { tag ->
+                    customTagContentProviders.filter { it.isApplicable(tag) }.forEach { provider ->
+                        with(provider) {
+                            contentForBrief(sourceSet, tag)
+                        }
+                    }
+                }
+            }
+        }
+    }
 
     protected open fun TagWrapper.toHeaderString() = this.javaClass.toGenericString().split('.').last()
 
@@ -706,6 +724,9 @@ open class DefaultPageCreator(
     private val Documentable.descriptions: SourceSetDependent<Description>
         get() = groupedTags.withTypeUnnamed<Description>()
 
+    private val Documentable.customTags: Map<String, SourceSetDependent<CustomTagWrapper>>
+        get() = groupedTags.withTypeNamed()
+
     private val Documentable.hasSeparatePage: Boolean
         get() = this !is DTypeAlias