[Markdown][IDEA-305524] Add support for MS Azure mermaid code fences

GitOrigin-RevId: e2ec0fa87fba5abd147187bf14163fe382a764a9

plugins/markdown/core/src/org/intellij/plugins/markdown/lang/parser/MarkdownDefaultMarkerProcessor.kt

@@ -15,6 +15,7 @@ import org.intellij.markdown.parser.constraints.getCharsEaten
 import org.intellij.markdown.parser.markerblocks.MarkerBlockProvider
 import org.intellij.markdown.parser.markerblocks.providers.*
 import org.intellij.markdown.parser.sequentialparsers.SequentialParser
+import org.intellij.plugins.markdown.lang.parser.blocks.CodeFenceMarkerProvider
 import org.intellij.plugins.markdown.lang.parser.blocks.CommentAwareLinkReferenceDefinitionProvider
 import org.intellij.plugins.markdown.lang.parser.blocks.DefinitionListMarkerProvider
 import org.intellij.plugins.markdown.lang.parser.blocks.frontmatter.FrontMatterHeaderMarkerProvider
@@ -62,7 +63,7 @@ open class MarkdownDefaultMarkerProcessor(
   override fun getMarkerBlockProviders(): List<MarkerBlockProvider<StateInfo>> {
     return buildList {
       add(CodeBlockProvider())
-      add(CodeFenceProvider())
+      add(CodeFenceMarkerProvider())
       add(SetextHeaderProvider())
       add(BlockQuoteProvider())
       add(ListMarkerProvider())

plugins/markdown/core/src/org/intellij/plugins/markdown/lang/parser/blocks/CodeFenceMarkerProvider.kt

@@ -0,0 +1,39 @@
+package org.intellij.plugins.markdown.lang.parser.blocks
+
+import org.intellij.markdown.parser.LookaheadText
+import org.intellij.markdown.parser.constraints.MarkdownConstraints
+import org.intellij.markdown.parser.markerblocks.MarkerBlockProvider
+import org.intellij.markdown.parser.markerblocks.providers.CodeFenceProvider
+import org.jetbrains.annotations.ApiStatus
+
+/**
+ * Extends default [CodeFenceProvider] to support additional MS Azure code fence syntax
+ * for Mermaid.js fences.
+ *
+ * ```markdown
+ * ::: mermaid
+ * <mermaid diagram syntax>
+ * :::
+ * ```
+ */
+@ApiStatus.Experimental
+open class CodeFenceMarkerProvider: CodeFenceProvider() {
+  override fun obtainFenceOpeningInfo(pos: LookaheadText.Position, constraints: MarkdownConstraints): OpeningInfo? {
+    if (!MarkerBlockProvider.isStartOfLineWithConstraints(pos, constraints)) {
+      return null
+    }
+    val matchResult = openingRegex.find(pos.currentLineFromPosition) ?: return null
+    val delimiter = matchResult.groups[1]?.value
+    checkNotNull(delimiter) { "Failed to obtain delimiter group value from match result" }
+    val info = matchResult.groups[2]?.value
+    checkNotNull(info) { "Failed to obtain info string group value form match result" }
+    if (delimiter.startsWith(":::") && info.trim().lowercase() != "mermaid") {
+      return null
+    }
+    return OpeningInfo(delimiter, info)
+  }
+
+  companion object {
+    private val openingRegex = Regex("^ {0,3}(~~~+|```+|:::+)([^`]*)\$")
+  }
+}

plugins/markdown/test/src/org/intellij/plugins/markdown/parser/MarkdownCodeFenceFlavourParserTest.kt

@@ -0,0 +1,36 @@
+package org.intellij.plugins.markdown.parser
+
+import com.intellij.psi.SyntaxTraverser
+import com.intellij.testFramework.LightPlatformCodeInsightTestCase
+import junit.framework.TestCase
+import org.intellij.plugins.markdown.lang.psi.impl.MarkdownCodeFence
+
+class MarkdownCodeFenceFlavourParserTest: LightPlatformCodeInsightTestCase() {
+  fun `test valid mermaid fence`() {
+    val content = """
+    ::: mermaid
+    :::
+    """.trimIndent()
+    configureFromFileText("some.md", content)
+    val fence = findFence()
+    TestCase.assertNotNull("Failed to find a fence", fence)
+    checkNotNull(fence)
+    val language = fence.fenceLanguage?.trim()
+    TestCase.assertEquals("mermaid", language)
+  }
+
+  fun `test delimiter syntax with non mermaid info string`() {
+    val content = """
+    ::: java
+    :::
+    """.trimIndent()
+    configureFromFileText("some.md", content)
+    val fence = findFence()
+    TestCase.assertNull("This fragment should not be parsed as a fence", fence)
+  }
+
+  private fun findFence(): MarkdownCodeFence? {
+    val elements = SyntaxTraverser.psiTraverser(file).asSequence()
+    return elements.filterIsInstance<MarkdownCodeFence>().firstOrNull()
+  }
+}