New timeline event renderer: add new modules (#7721)

* Added HTML parser to abstract tree nodes

* Add HTML renderer using `HtmlMessageContent`

* Add custom rendering for inline code nodes besides the monospace font

* Support `<s>` and `<strike>` too

* Add `ContentAvoidingLayoutData` support

* Improve the last block node behaviour and its integration with `ContentAvoidingLayout`

* Move `ContentAvoidingLayout` to `:libraries:ui-common` so it can be shared

* Add missing `:libraries:htmlrenderer:impl` entry in `DependencyHandlerScope.allLibrariesImpl`

* Update screenshots

---------

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

libraries/htmlrenderer/api/build.gradle.kts

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+plugins {
+    id("io.element.android-compose-library")
+}
+
+android {
+    namespace = "io.element.android.libraries.htmlrenderer.api"
+}
+
+dependencies {
+    api(projects.libraries.matrix.api)
+    api(libs.jsoup)
+}

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

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.htmlrenderer.api
+
+import org.jsoup.nodes.Document
+
+/**
+ * Parses the HTML [Document] of a formatted message body into a tree of [MessageNode]s
+ * that a Compose renderer can turn into composables.
+ *
+ * The [Document] is expected to have already been sanitized (e.g. via
+ * `FormattedBody.toHtmlDocument`) so that only supported tags remain.
+ */
+interface HtmlMessageParser {
+    /**
+     * Converts [document] into a [DocumentNode]. Never throws: unknown or empty content
+     * yields a [DocumentNode] with no children.
+     */
+    fun parse(document: Document): DocumentNode
+
+    companion object {
+        /**
+         * Tag used for the string annotation attached to link (`<a href>`) text ranges in a
+         * [ParagraphNode.text]. The annotation value is the link target URL.
+         */
+        const val LINK_ANNOTATION_TAG = "url"
+
+        /**
+         * Tag used for the string annotation attached to inline code (`<code>`) text ranges in a
+         * [ParagraphNode.text]. The annotation value is empty; only the range matters. A `<code>`
+         * nested inside a `<pre>` is part of the [CodeBlockNode] and is never annotated this way.
+         */
+        const val INLINE_CODE_ANNOTATION_TAG = "inline_code"
+    }
+}

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

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.htmlrenderer.api
+
+import androidx.compose.runtime.Immutable
+import io.element.android.libraries.matrix.api.core.RoomIdOrAlias
+import io.element.android.libraries.matrix.api.core.UserId
+
+/**
+ * Describes a mention "pill" referenced from a [ParagraphNode].
+ *
+ * Each mention occupies an inline-content placeholder inside the paragraph's
+ * [ParagraphNode.text]; the renderer looks the id up in [ParagraphNode.inlineContent]
+ * and draws the corresponding pill.
+ */
+@Immutable
+sealed interface MentionNodeContent {
+    /** The text shown inside the pill (e.g. a display name, prefixed with `@` for users). */
+    val displayText: String
+
+    /** A mention of a specific user (`<a href="matrix.to/#/@user:server">`). */
+    data class User(
+        override val displayText: String,
+        val userId: UserId,
+    ) : MentionNodeContent
+
+    /** A mention of a room (`<a href="matrix.to/#/#room:server">`). */
+    data class Room(
+        override val displayText: String,
+        val roomIdOrAlias: RoomIdOrAlias,
+    ) : MentionNodeContent
+
+    /** An `@room` mention notifying everyone in the room. */
+    data class Everyone(
+        override val displayText: String,
+    ) : MentionNodeContent
+}

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

@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.htmlrenderer.api
+
+import androidx.compose.runtime.Immutable
+import androidx.compose.ui.text.AnnotatedString
+import kotlinx.collections.immutable.ImmutableList
+import kotlinx.collections.immutable.ImmutableMap
+import kotlinx.collections.immutable.persistentMapOf
+
+/**
+ * A node in the parsed representation of a formatted (HTML) message body.
+ *
+ * The tree is produced by [HtmlMessageParser] and consumed by a Compose renderer.
+ * Block-level nodes ([BlockNode]) either contain other block nodes (nested lists, a
+ * quote containing paragraphs, ...) or terminate in a [ParagraphNode] / [CodeBlockNode]
+ * that carries the actual text.
+ */
+@Immutable
+sealed interface MessageNode
+
+/** A block-level node, laid out vertically by the renderer. */
+@Immutable
+sealed interface BlockNode : MessageNode
+
+/**
+ * The root of a parsed message: an ordered list of block-level children.
+ */
+@Immutable
+data class DocumentNode(
+    val children: ImmutableList<BlockNode>,
+) : BlockNode
+
+/**
+ * A run of inline content (text with inline formatting) already flattened to an
+ * [AnnotatedString]. This is the only leaf that carries styled text.
+ *
+ * Inline formatting (`<b>`, `<i>`, `<u>`, `<del>`, inline `<code>`) is encoded as
+ * [androidx.compose.ui.text.SpanStyle] ranges, and links (`<a>`) as string annotations
+ * tagged [HtmlMessageParser.LINK_ANNOTATION_TAG].
+ *
+ * Mentions (pills) are encoded as inline-content placeholders inside [text] (see
+ * [androidx.compose.foundation.text.appendInlineContent]); [inlineContent] maps each
+ * placeholder id to the [MentionNodeContent] the renderer needs to draw the pill.
+ */
+@Immutable
+data class ParagraphNode(
+    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.
+ */
+@Immutable
+data class CodeBlockNode(
+    val code: String,
+) : BlockNode
+
+/**
+ * A block quote (`<blockquote>`). Quotes can nest and can contain any block content.
+ */
+@Immutable
+data class QuoteNode(
+    val children: ImmutableList<BlockNode>,
+) : BlockNode
+
+/**
+ * An ordered (`<ol>`) or unordered (`<ul>`) list.
+ *
+ * @param ordered whether the list is numbered (`<ol>`) or bulleted (`<ul>`).
+ * @param startIndex the number the first item of an ordered list starts at (honors `ol[start]`, default 1).
+ * @param items the list items, in document order.
+ */
+@Immutable
+data class ListNode(
+    val ordered: Boolean,
+    val startIndex: Int,
+    val items: ImmutableList<ListItemNode>,
+) : BlockNode
+
+/**
+ * A single list item (`<li>`). Being a block container, an item can itself hold
+ * paragraphs, nested lists or quotes.
+ */
+@Immutable
+data class ListItemNode(
+    val children: ImmutableList<BlockNode>,
+) : MessageNode