Fix HTML comments bug - ignore headings inside HTML comments for TOC generation

src/commonMain/kotlin/ch/derlin/bitdowntoc/BitGenerator.kt

@@ -76,6 +76,10 @@ object BitGenerator {
             val codeMarker = listOf('`', '~').firstNotNullOfOrNull { line.getCodeStart(it) }
 
             if (!codeMarker.isNullOrBlank()) iter.consumeCode(codeMarker)
+            else if (line.isCompleteHtmlComment()) {
+                // Single-line HTML comment, keep in output but don't process for TOC
+            }
+            else if (line.isHtmlCommentStart()) iter.consumeHtmlComment()
             else if (commenter.isAnchor(line)) iter.remove()
             else {
                 line.parseHeader(toc)?.let {
@@ -122,10 +126,25 @@ object BitGenerator {
             .takeIf { it.startsWith("$char".repeat(3)) }
             ?.let { trimmedLine -> trimmedLine.takeWhile { it == char } }
 
+    private fun String.isHtmlCommentStart(): Boolean {
+        val trimmed = this.trim()
+        return trimmed.startsWith("<!--") && !trimmed.contains("TOC")
+    }
+
+    private fun String.isCompleteHtmlComment(): Boolean {
+        val trimmed = this.trim()
+        return trimmed.startsWith("<!--") && trimmed.endsWith("-->") && !trimmed.contains("TOC")
+    }
 
     private fun Iterator<String>.consumeCode(codeMarker: String) {
         while (this.hasNext() && !this.next().trim().startsWith(codeMarker));
     }
 
+    private fun Iterator<String>.consumeHtmlComment() {
+        while (this.hasNext()) {
+            if (this.next().trim().endsWith("-->")) break
+        }
+    }
+
     private fun Iterable<String>.asText() = this.joinToString(NL)
 }

src/commonTest/kotlin/ch.derlin.bitdowntoc/HtmlCommentsTest.kt

@@ -0,0 +1,174 @@
+package ch.derlin.bitdowntoc
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+import kotlin.test.assertFalse
+
+class HtmlCommentsTest {
+
+    @Test
+    fun testHtmlCommentsAreIgnored() {
+        val input = """
+        # Example
+
+        [TOC]
+
+        ## Section A
+
+        TODO
+
+        <!--
+        ### Placeholder SubSection
+        -->
+
+        ## Section B
+
+        TODO
+        """.trimIndent()
+
+        val expected = """
+        # Example
+
+        <!-- TOC start (generated with $BITDOWNTOC_URL) -->
+
+        - [Section A](#section-a)
+        - [Section B](#section-b)
+
+        <!-- TOC end -->
+
+        ## Section A
+
+        TODO
+
+        <!--
+        ### Placeholder SubSection
+        -->
+
+        ## Section B
+
+        TODO
+        """.trimIndent()
+
+        assertEquals(
+            expected,
+            BitGenerator.generate(input, BitGenerator.Params(generateAnchors = false))
+        )
+    }
+
+    @Test
+    fun testSingleLineHtmlCommentsAreIgnored() {
+        val input = """
+        # Example
+
+        [TOC]
+
+        ## Section A
+
+        <!-- ### Commented out heading -->
+
+        ## Section B
+        """.trimIndent()
+
+        val expected = """
+        # Example
+
+        <!-- TOC start (generated with $BITDOWNTOC_URL) -->
+
+        - [Section A](#section-a)
+        - [Section B](#section-b)
+
+        <!-- TOC end -->
+
+        ## Section A
+
+        <!-- ### Commented out heading -->
+
+        ## Section B
+        """.trimIndent()
+
+        assertEquals(
+            expected,
+            BitGenerator.generate(input, BitGenerator.Params(generateAnchors = false))
+        )
+    }
+
+    @Test
+    fun testMultipleHeadingsInHtmlCommentsAreIgnored() {
+        val input = """
+        # Example
+
+        [TOC]
+
+        ## Section A
+
+        <!--
+        ### First commented heading
+        #### Second commented heading
+        ##### Third commented heading
+        -->
+
+        ## Section B
+        """.trimIndent()
+
+        val expected = """
+        # Example
+
+        <!-- TOC start (generated with $BITDOWNTOC_URL) -->
+
+        - [Section A](#section-a)
+        - [Section B](#section-b)
+
+        <!-- TOC end -->
+
+        ## Section A
+
+        <!--
+        ### First commented heading
+        #### Second commented heading
+        ##### Third commented heading
+        -->
+
+        ## Section B
+        """.trimIndent()
+
+        assertEquals(
+            expected,
+            BitGenerator.generate(input, BitGenerator.Params(generateAnchors = false))
+        )
+    }
+
+    @Test
+    fun testBitDownTocCommentsAreNotIgnored() {
+        val input = """
+        # Example
+
+        [TOC]
+
+        ## Section A
+
+        <!--
+        ### Placeholder SubSection
+        -->
+
+        ## Section B
+        """.trimIndent()
+
+        val result = BitGenerator.generate(input, BitGenerator.Params(generateAnchors = true))
+
+        // Check that HTML comments are preserved in output
+        assertTrue(result.contains("<!--"), "HTML comments should be preserved in output")
+        assertTrue(result.contains("### Placeholder SubSection"), "HTML comment content should be preserved in output")
+        assertTrue(result.contains("-->"), "HTML comments should be preserved in output")
+
+        // Check that TOC only contains Section A and Section B, not Placeholder SubSection
+        val tocLines = result.lines().dropWhile { !it.contains("TOC start") }.takeWhile { !it.contains("TOC end") }
+        val tocContent = tocLines.joinToString("\n")
+        assertTrue(tocContent.contains("Section A"), "TOC should contain Section A")
+        assertTrue(tocContent.contains("Section B"), "TOC should contain Section B")
+        assertFalse(tocContent.contains("Placeholder SubSection"), "TOC should NOT contain Placeholder SubSection")
+
+        // Check that BitDownToc comments are preserved
+        assertTrue(result.contains("<!-- TOC -->"), "BitDownToc comments should be preserved")
+    }
+}