Add headers (h1-h6) tag support for the new timeline renderer (#7754)

* Add headers (`h1-h6`) tag support for the new timeline renderer

* Make H1 and H2 use the same (smaller) style

* Update screenshots

---------

Co-authored-by: ElementBot <android@element.io>

libraries/htmlrenderer/api/src/main/kotlin/io/element/android/libraries/htmlrenderer/api/MessageNode.kt

@@ -54,6 +54,18 @@ data class ParagraphNode(
     val inlineContent: ImmutableMap<String, MentionNodeContent> = persistentMapOf(),
 ) : BlockNode
 
+/**
+ * A heading (`<h1>`–`<h6>`). Like a [ParagraphNode] it carries inline content ([text] and
+ * [inlineContent]), plus the heading [level] from 1 (largest) to 6 (smallest), used by the renderer
+ * to pick the typography.
+ */
+@Immutable
+data class HeaderNode(
+    val level: Int,
+    val text: AnnotatedString,
+    val inlineContent: ImmutableMap<String, MentionNodeContent> = persistentMapOf(),
+) : BlockNode
+
 /**
  * A preformatted code block (`<pre>`). Rendered in a monospaced, horizontally
  * scrollable container. The text is kept raw: no inline styling is applied inside it.

libraries/htmlrenderer/api/src/main/kotlin/io/element/android/libraries/htmlrenderer/api/ui/HtmlMessageContent.kt

@@ -62,6 +62,7 @@ import androidx.compose.ui.text.Placeholder
 import androidx.compose.ui.text.PlaceholderVerticalAlign
 import androidx.compose.ui.text.SpanStyle
 import androidx.compose.ui.text.TextLayoutResult
+import androidx.compose.ui.text.TextStyle
 import androidx.compose.ui.text.buildAnnotatedString
 import androidx.compose.ui.text.font.FontFamily
 import androidx.compose.ui.text.rememberTextMeasurer
@@ -76,6 +77,7 @@ import io.element.android.libraries.designsystem.theme.components.Text
 import io.element.android.libraries.htmlrenderer.api.BlockNode
 import io.element.android.libraries.htmlrenderer.api.CodeBlockNode
 import io.element.android.libraries.htmlrenderer.api.DocumentNode
+import io.element.android.libraries.htmlrenderer.api.HeaderNode
 import io.element.android.libraries.htmlrenderer.api.HtmlMessageParser.Companion.INLINE_CODE_ANNOTATION_TAG
 import io.element.android.libraries.htmlrenderer.api.HtmlMessageParser.Companion.LINK_ANNOTATION_TAG
 import io.element.android.libraries.htmlrenderer.api.ListNode
@@ -158,6 +160,7 @@ internal fun BlockNode.lastBlockNode(): BlockNode? = when (this) {
     is ListNode -> this
     is QuoteNode -> this
     is CodeBlockNode -> this
+    is HeaderNode -> this
 }
 
 @Composable
@@ -180,7 +183,7 @@ private fun BlockNodeView(
     context: RenderContext,
     modifier: Modifier = Modifier,
 ) {
-    if (node === context.lastBlockNode && node !is ParagraphNode) {
+    if (node === context.lastBlockNode && node !is ParagraphNode && node !is HeaderNode) {
         SideEffect { context.onContentLayoutChange(ContentAvoidingLayoutData.NotOverlapping) }
     }
 
@@ -189,6 +192,7 @@ private fun BlockNodeView(
         is ParagraphNode -> {
             ParagraphView(node = node, context = context, modifier = modifier)
         }
+        is HeaderNode -> HeaderView(node = node, context = context, modifier = modifier)
         is CodeBlockNode -> CodeBlockView(node = node, modifier = modifier)
         is QuoteNode -> QuoteView(node = node, context = context, modifier = modifier)
         is ListNode -> ListView(node = node, context = context, modifier = modifier)
@@ -201,16 +205,6 @@ private fun ParagraphView(
     context: RenderContext,
     modifier: Modifier = Modifier,
 ) {
-    val linkColor = ElementTheme.colors.textLinkExternal
-    val codeBackgroundColor = ElementTheme.colors.bgSubtleSecondary
-    val codeBorderColor = ElementTheme.colors.borderInteractiveSecondary
-    val styledText = remember(node.text, linkColor) {
-        node.text
-            .linkify(SpanStyle(color = linkColor))
-            .applyLinkStyles(linkColor = linkColor)
-    }
-    val inlineContent = rememberMentionInlineContent(node.inlineContent, context)
-    val layoutResult = remember { mutableStateOf<TextLayoutResult?>(null) }
     // Only the last rendered paragraph (and only when not inside a code block / quote) reports its
     // measured last line to the timeline.
     val measureLastLine = if (node === context.lastBlockNode) {
@@ -218,21 +212,87 @@ private fun ParagraphView(
     } else {
         null
     }
+    TextBlock(
+        text = node.text,
+        inlineContent = node.inlineContent,
+        textStyle = ElementTheme.typography.fontBodyMdRegular,
+        context = context,
+        modifier = modifier,
+        onTextLayout = { measureLastLine?.invoke(it) },
+    )
+}
+
+@Composable
+private fun HeaderView(
+    node: HeaderNode,
+    context: RenderContext,
+    modifier: Modifier = Modifier,
+) {
+    // Only the last rendered paragraph (and only when not inside a code block / quote) reports its
+    // measured last line to the timeline.
+    val measureLastLine = if (node === context.lastBlockNode) {
+        ContentAvoidingLayout.measureLastTextLine(onContentLayoutChange = context.onContentLayoutChange)
+    } else {
+        null
+    }
+    TextBlock(
+        text = node.text,
+        inlineContent = node.inlineContent,
+        textStyle = headerTextStyle(node.level),
+        context = context,
+        modifier = modifier,
+        onTextLayout = { measureLastLine?.invoke(it) }
+    )
+}
+
+/**
+ * Renders an inline-content block (a paragraph or a header) as a [Text] with [textStyle], applying
+ * link styling, the inline-code background boxes, mention/image inline content and link taps.
+ */
+@Composable
+private fun TextBlock(
+    text: AnnotatedString,
+    inlineContent: ImmutableMap<String, MentionNodeContent>,
+    textStyle: TextStyle,
+    context: RenderContext,
+    modifier: Modifier = Modifier,
+    onTextLayout: (TextLayoutResult) -> Unit = {},
+) {
+    val linkColor = ElementTheme.colors.textLinkExternal
+    val codeBackgroundColor = ElementTheme.colors.bgSubtleSecondary
+    val codeBorderColor = ElementTheme.colors.borderInteractiveSecondary
+    val styledText = remember(text, linkColor) {
+        text.linkify(SpanStyle(color = linkColor))
+            .applyLinkStyles(linkColor = linkColor)
+    }
+    val resolvedInlineContent = rememberMentionInlineContent(inlineContent, context)
+    val layoutResult = remember { mutableStateOf<TextLayoutResult?>(null) }
     Text(
         text = styledText,
         modifier = modifier
             .drawInlineCodeBackgrounds(styledText, layoutResult, codeBackgroundColor, codeBorderColor, LocalDensity.current)
             .linkTapHandler(styledText, layoutResult, context),
-        style = ElementTheme.typography.fontBodyMdRegular,
+        style = textStyle,
         color = ElementTheme.colors.textPrimary,
-        inlineContent = inlineContent,
+        inlineContent = resolvedInlineContent,
         onTextLayout = { result ->
             layoutResult.value = result
-            measureLastLine?.invoke(result)
+            onTextLayout(result)
         },
     )
 }
 
+/** Maps an `<h1>`–`<h6>` [level] to a Compound typography style, largest first. */
+@Composable
+private fun headerTextStyle(level: Int): TextStyle = when (level) {
+    // For safety reasons, use the same style for H1 and H2, to avoid people using H1 for 'shouting' spam that fills the timeline with huge text
+    1, 2 -> ElementTheme.typography.fontHeadingLgBold
+    3 -> ElementTheme.typography.fontHeadingMdBold
+    4 -> ElementTheme.typography.fontHeadingSmMedium
+    5 -> ElementTheme.typography.fontBodyLgMedium
+    else -> ElementTheme.typography.fontBodyMdMedium
+}
+
 @Composable
 private fun CodeBlockView(
     node: CodeBlockNode,

libraries/htmlrenderer/api/src/main/kotlin/io/element/android/libraries/htmlrenderer/api/ui/HtmlMessageContentPreview.kt

@@ -26,6 +26,7 @@ import io.element.android.libraries.designsystem.preview.PreviewsDayNight
 import io.element.android.libraries.htmlrenderer.api.BlockNode
 import io.element.android.libraries.htmlrenderer.api.CodeBlockNode
 import io.element.android.libraries.htmlrenderer.api.DocumentNode
+import io.element.android.libraries.htmlrenderer.api.HeaderNode
 import io.element.android.libraries.htmlrenderer.api.HtmlMessageParser.Companion.INLINE_CODE_ANNOTATION_TAG
 import io.element.android.libraries.htmlrenderer.api.HtmlMessageParser.Companion.LINK_ANNOTATION_TAG
 import io.element.android.libraries.htmlrenderer.api.ListItemNode
@@ -55,6 +56,7 @@ internal fun HtmlMessageContentPreview(
 internal class HtmlMessageContentPreviewParam : PreviewParameterProvider<DocumentNode> {
     override val values: Sequence<DocumentNode>
         get() = sequenceOf(
+            headers(),
             richParagraph(),
             inlineCode(),
             multilineInlineCode(),
@@ -237,6 +239,16 @@ internal class HtmlMessageContentPreviewParam : PreviewParameterProvider<Documen
         ),
     )
 
+    private fun headers() = document(
+        HeaderNode(level = 1, text = AnnotatedString("Heading 1")),
+        HeaderNode(level = 2, text = AnnotatedString("Heading 2")),
+        HeaderNode(level = 3, text = AnnotatedString("Heading 3")),
+        HeaderNode(level = 4, text = AnnotatedString("Heading 4")),
+        HeaderNode(level = 5, text = AnnotatedString("Heading 5")),
+        HeaderNode(level = 6, text = AnnotatedString("Heading 6")),
+        paragraph(AnnotatedString("Body text under the headings.")),
+    )
+
     private fun document(vararg blocks: BlockNode) = DocumentNode(blocks.toList().toImmutableList())
 
     private fun paragraph(

libraries/htmlrenderer/impl/src/main/kotlin/io/element/android/libraries/htmlrenderer/impl/DefaultHtmlMessageParser.kt

@@ -18,6 +18,7 @@ import dev.zacsweers.metro.ContributesBinding
 import io.element.android.libraries.htmlrenderer.api.BlockNode
 import io.element.android.libraries.htmlrenderer.api.CodeBlockNode
 import io.element.android.libraries.htmlrenderer.api.DocumentNode
+import io.element.android.libraries.htmlrenderer.api.HeaderNode
 import io.element.android.libraries.htmlrenderer.api.HtmlMessageParser
 import io.element.android.libraries.htmlrenderer.api.HtmlMessageParser.Companion.INLINE_CODE_ANNOTATION_TAG
 import io.element.android.libraries.htmlrenderer.api.HtmlMessageParser.Companion.LINK_ANNOTATION_TAG
@@ -30,6 +31,7 @@ import io.element.android.libraries.htmlrenderer.api.spans.InlineCodeSpanStyle
 import io.element.android.libraries.matrix.api.permalink.PermalinkData
 import io.element.android.libraries.matrix.api.permalink.PermalinkParser
 import kotlinx.collections.immutable.ImmutableList
+import kotlinx.collections.immutable.ImmutableMap
 import kotlinx.collections.immutable.toImmutableList
 import kotlinx.collections.immutable.toImmutableMap
 import org.jsoup.nodes.Document
@@ -81,12 +83,13 @@ class DefaultHtmlMessageParser(
         return blocks.toImmutableList()
     }
 
-    private fun parseBlock(element: Element): BlockNode? = when (element.tagName()) {
+    private fun parseBlock(element: Element): BlockNode? = when (val tag = element.tagName()) {
         TAG_P -> buildParagraph(element.childNodes())
         TAG_PRE -> CodeBlockNode(code = element.wholeText().trimEnd('\n'))
         TAG_BLOCKQUOTE -> QuoteNode(children = parseBlocks(element))
         TAG_UL -> buildList(element, ordered = false)
         TAG_OL -> buildList(element, ordered = true)
+        in HEADER_TAGS -> buildHeader(element, level = tag.removePrefix("h").toInt())
         else -> null
     }
 
@@ -102,6 +105,17 @@ class DefaultHtmlMessageParser(
 
     /** Builds a [ParagraphNode] from a run of inline [nodes], or `null` if it holds no content. */
     private fun buildParagraph(nodes: List<Node>): ParagraphNode? {
+        return buildInlineContent(nodes)?.let { ParagraphNode(text = it.text, inlineContent = it.inlineContent) }
+    }
+
+    /** Builds a [HeaderNode] of the given [level] from the inline content of [element], or `null` if empty. */
+    private fun buildHeader(element: Element, level: Int): HeaderNode? {
+        return buildInlineContent(element.childNodes())?.let {
+            HeaderNode(level = level, text = it.text, inlineContent = it.inlineContent)
+        }
+    }
+
+    private fun buildInlineContent(nodes: List<Node>): InlineContentBuilder.Result? {
         val builder = InlineContentBuilder()
         nodes.forEach { builder.append(it) }
         return builder.build()
@@ -199,21 +213,29 @@ class DefaultHtmlMessageParser(
             }
         }
 
-        fun build(): ParagraphNode? {
+        fun build(): Result? {
             val text = builder.toAnnotatedString()
             if (text.isBlank() && mentions.isEmpty()) return null
-            return ParagraphNode(
+            return Result(
                 text = text,
                 inlineContent = mentions.toImmutableMap(),
             )
         }
+
+        /** The flattened inline content of a block: styled text plus its inline-content placeholders. */
+        inner class Result(
+            val text: AnnotatedString,
+            val inlineContent: ImmutableMap<String, MentionNodeContent>,
+        )
     }
 }
 
 /** Tags that start a new block-level node. Anything else is treated as inline content. */
 private fun Element.isBlockLevel(): Boolean = tagName() in BLOCK_TAGS
 
-private val BLOCK_TAGS = setOf(TAG_P, TAG_PRE, TAG_BLOCKQUOTE, TAG_UL, TAG_OL)
+private val HEADER_TAGS = setOf("h1", "h2", "h3", "h4", "h5", "h6")
+
+private val BLOCK_TAGS = setOf(TAG_P, TAG_PRE, TAG_BLOCKQUOTE, TAG_UL, TAG_OL) + HEADER_TAGS
 
 private const val TAG_P = "p"
 private const val TAG_PRE = "pre"

libraries/htmlrenderer/impl/src/test/kotlin/io/element/android/libraries/htmlrenderer/impl/DefaultHtmlMessageParserTest.kt

@@ -12,6 +12,7 @@ import androidx.compose.ui.text.font.FontStyle
 import androidx.compose.ui.text.font.FontWeight
 import com.google.common.truth.Truth.assertThat
 import io.element.android.libraries.htmlrenderer.api.CodeBlockNode
+import io.element.android.libraries.htmlrenderer.api.HeaderNode
 import io.element.android.libraries.htmlrenderer.api.HtmlMessageParser
 import io.element.android.libraries.htmlrenderer.api.ListNode
 import io.element.android.libraries.htmlrenderer.api.MentionNodeContent
@@ -191,6 +192,24 @@ class DefaultHtmlMessageParserTest : RobolectricTest() {
         assertThat(paragraph.text.text).isEqualTo("Actual message")
     }
 
+    @Test
+    fun `headers become HeaderNodes with their level and inline content`() {
+        val document = parse("<h1>Title</h1><h3>Subtitle with <strong>bold</strong></h3><h6>Small</h6>")
+        assertThat(document.children).hasSize(3)
+
+        val h1 = document.children[0] as HeaderNode
+        assertThat(h1.level).isEqualTo(1)
+        assertThat(h1.text.text).isEqualTo("Title")
+
+        val h3 = document.children[1] as HeaderNode
+        assertThat(h3.level).isEqualTo(3)
+        assertThat(h3.text.text).isEqualTo("Subtitle with bold")
+
+        val h6 = document.children[2] as HeaderNode
+        assertThat(h6.level).isEqualTo(6)
+        assertThat(h6.text.text).isEqualTo("Small")
+    }
+
     @Test
     fun `blank input produces an empty document`() {
         val document = parse("   ")