Add a test for multiple whitespaces between hash and header

plugins/base/src/test/kotlin/markdown/ParserTest.kt

@@ -1573,7 +1573,23 @@ class ParserTest : KDocTest() {
             P(listOf(Text(" sdsdsds sdd"))),
             P(listOf(Text(" eweww  ")))
         )
-        print(expectedDocumentationNode)
+        assertEquals(actualDocumentationNode, expectedDocumentationNode)
+    }
+
+    @Test // exists due to #3231
+    fun `should ignore the first whitespace in header in-between the hash symbol and header text`() {
+        val markdown = """
+        | #   first header
+        | ##     second header
+        | ###                third header
+        | 
+        """.trimMargin()
+        val actualDocumentationNode = parseMarkdownToDocNode(markdown).children
+        val expectedDocumentationNode = listOf(
+            H1(listOf(Text("first header"))),
+            H2(listOf(Text("second header"))),
+            H3(listOf(Text("third header"))),
+        )
         assertEquals(actualDocumentationNode, expectedDocumentationNode)
     }
 }

subprojects/analysis-markdown-jb/src/main/kotlin/org/jetbrains/dokka/analysis/markdown/jb/MarkdownParser.kt

@@ -90,6 +90,8 @@ public open class MarkdownParser(
         // in-between the `#` symbol and the text (like `# header`), it will be present here too.
         // However, we don't need the first space between the `#` symbol and the text,
         // so we just skip it (otherwise the header text will be parsed as `<whitespace>header` instead of `header`).
+        // If there's more space between `#` and text, like `#     header`, it will still be a single WHITE_SPACE
+        // element, but it will be wider, so the solution below should still hold.
         val textStartsWithWhitespace = node.children.firstOrNull()?.type == MarkdownTokenTypes.WHITE_SPACE
         val children = if (textStartsWithWhitespace) node.children.subList(1, node.children.size) else node.children