Render maths with respect to data-mx-maths

(matrix-org/matrix-spec-proposals#2191)

Firstly, this implements a commonmark-java plugin which is solely used to parse
LaTeX input in the composer box, so that they can be rendered into
`<span data-mx-maths=...>fallback</span>` and `<div
data-mx-maths=...>fallback</div>` for inline and display maths
respectively in the sent message.

Secondly, received messages of this form are pre-processed by a simple
regex into a form which markwon (which performs the rendering) expects.

matrix-sdk-android/src/main/java/org/commonmark/ext/maths/DisplayMaths.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2020 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.commonmark.ext.maths;
+
+import org.commonmark.node.CustomBlock;
+
+public class DisplayMaths extends CustomBlock {
+    public enum DisplayDelimiter {
+        DOUBLE_DOLLAR,
+        SQUARE_BRACKET_ESCAPED
+    };
+
+    private DisplayDelimiter delimiter;
+
+    public DisplayMaths(DisplayDelimiter delimiter) {
+        this.delimiter = delimiter;
+    }
+}

matrix-sdk-android/src/main/java/org/commonmark/ext/maths/InlineMaths.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2020 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.commonmark.ext.maths;
+
+import org.commonmark.node.CustomNode;
+import org.commonmark.node.Delimited;
+
+public class InlineMaths extends CustomNode implements Delimited {
+    public enum InlineDelimiter {
+        SINGLE_DOLLAR,
+        ROUND_BRACKET_ESCAPED
+    };
+
+    private InlineDelimiter delimiter;
+
+    public InlineMaths(InlineDelimiter delimiter) {
+        this.delimiter = delimiter;
+    }
+
+    @Override
+    public String getOpeningDelimiter() {
+        switch (delimiter) {
+            case SINGLE_DOLLAR:
+                return "$";
+            case ROUND_BRACKET_ESCAPED:
+                return "\\(";
+        }
+        return null;
+    }
+
+    @Override
+    public String getClosingDelimiter() {
+        switch (delimiter) {
+            case SINGLE_DOLLAR:
+                return "$";
+            case ROUND_BRACKET_ESCAPED:
+                return "\\)";
+        }
+        return null;
+    }
+}

matrix-sdk-android/src/main/java/org/commonmark/ext/maths/MathsExtension.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2020 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.commonmark.ext.maths;
+
+import org.commonmark.Extension;
+import org.commonmark.ext.maths.internal.DollarMathsDelimiterProcessor;
+import org.commonmark.ext.maths.internal.MathsHtmlNodeRenderer;
+import org.commonmark.parser.Parser;
+import org.commonmark.renderer.NodeRenderer;
+import org.commonmark.renderer.html.HtmlNodeRendererContext;
+import org.commonmark.renderer.html.HtmlNodeRendererFactory;
+import org.commonmark.renderer.html.HtmlRenderer;
+
+public class MathsExtension implements Parser.ParserExtension, HtmlRenderer.HtmlRendererExtension {
+
+    private MathsExtension() {
+    }
+
+    public static Extension create() {
+        return new MathsExtension();
+    }
+
+    @Override
+    public void extend(Parser.Builder parserBuilder) {
+        parserBuilder.customDelimiterProcessor(new DollarMathsDelimiterProcessor());
+    }
+
+    @Override
+    public void extend(HtmlRenderer.Builder rendererBuilder) {
+        rendererBuilder.nodeRendererFactory(new HtmlNodeRendererFactory() {
+            @Override
+            public NodeRenderer create(HtmlNodeRendererContext context) {
+                return new MathsHtmlNodeRenderer(context);
+            }
+        });
+    }
+}

matrix-sdk-android/src/main/java/org/commonmark/ext/maths/internal/DollarMathsDelimiterProcessor.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2020 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.commonmark.ext.maths.internal;
+
+import org.commonmark.ext.maths.DisplayMaths;
+import org.commonmark.ext.maths.InlineMaths;
+import org.commonmark.node.Node;
+import org.commonmark.node.Text;
+import org.commonmark.parser.delimiter.DelimiterProcessor;
+import org.commonmark.parser.delimiter.DelimiterRun;
+
+public class DollarMathsDelimiterProcessor implements DelimiterProcessor {
+    @Override
+    public char getOpeningCharacter() {
+        return '$';
+    }
+
+    @Override
+    public char getClosingCharacter() {
+        return '$';
+    }
+
+    @Override
+    public int getMinLength() {
+        return 1;
+    }
+
+    @Override
+    public int getDelimiterUse(DelimiterRun opener, DelimiterRun closer) {
+        if (opener.length() == 1 && closer.length() == 1)
+            return 1; // inline
+        else if (opener.length() == 2 && closer.length() == 2)
+            return 2; // display
+        else
+            return 0;
+    }
+
+    @Override
+    public void process(Text opener, Text closer, int delimiterUse) {
+        Node maths = delimiterUse == 1 ? new InlineMaths(InlineMaths.InlineDelimiter.SINGLE_DOLLAR) :
+                new DisplayMaths(DisplayMaths.DisplayDelimiter.DOUBLE_DOLLAR);
+
+        Node tmp = opener.getNext();
+        while (tmp != null && tmp != closer) {
+            Node next = tmp.getNext();
+            maths.appendChild(tmp);
+            tmp = next;
+        }
+
+        opener.insertAfter(maths);
+    }
+}

matrix-sdk-android/src/main/java/org/commonmark/ext/maths/internal/MathsHtmlNodeRenderer.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2020 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.commonmark.ext.maths.internal;
+
+import org.commonmark.ext.maths.DisplayMaths;
+import org.commonmark.node.Node;
+import org.commonmark.node.Text;
+import org.commonmark.renderer.html.HtmlNodeRendererContext;
+import org.commonmark.renderer.html.HtmlWriter;
+
+import java.util.Collections;
+import java.util.Map;
+
+public class MathsHtmlNodeRenderer extends MathsNodeRenderer {
+    private final HtmlNodeRendererContext context;
+    private final HtmlWriter html;
+
+    public MathsHtmlNodeRenderer(HtmlNodeRendererContext context) {
+        this.context = context;
+        this.html = context.getWriter();
+    }
+
+    @Override
+    public void render(Node node) {
+        boolean display = node.getClass() == DisplayMaths.class;
+        Node contents = node.getFirstChild(); // should be the only child
+        String latex = ((Text) contents).getLiteral();
+        Map<String, String> attributes = context.extendAttributes(node, display ? "div" : "span", Collections.<String, String>singletonMap("data-mx-maths",
+                latex));
+        html.tag(display ? "div" : "span", attributes);
+        html.tag("code");
+        context.render(contents);
+        html.tag("/code");
+        html.tag(display ? "/div" : "/span");
+    }
+}

matrix-sdk-android/src/main/java/org/commonmark/ext/maths/internal/MathsNodeRenderer.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2020 New Vector Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.commonmark.ext.maths.internal;
+
+import org.commonmark.ext.maths.DisplayMaths;
+import org.commonmark.ext.maths.InlineMaths;
+import org.commonmark.node.Node;
+import org.commonmark.renderer.NodeRenderer;
+
+import java.util.HashSet;
+import java.util.Set;
+
+abstract class MathsNodeRenderer implements NodeRenderer {
+    @Override
+    public Set<Class<? extends Node>> getNodeTypes() {
+        final Set<Class<? extends Node>> types = new HashSet<Class<? extends Node>>();
+        types.add(InlineMaths.class);
+        types.add(DisplayMaths.class);
+        return types;
+    }
+}

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/RoomModule.kt

@@ -20,6 +20,8 @@ package org.matrix.android.sdk.internal.session.room
 import dagger.Binds
 import dagger.Module
 import dagger.Provides
+import org.commonmark.Extension
+import org.commonmark.ext.maths.MathsExtension
 import org.commonmark.parser.Parser
 import org.commonmark.renderer.html.HtmlRenderer
 import org.matrix.android.sdk.api.session.file.FileService
@@ -84,6 +86,7 @@ internal abstract class RoomModule {
 
     @Module
     companion object {
+        private val extensions : List<Extension> = listOf(MathsExtension.create())
         @Provides
         @JvmStatic
         @SessionScope
@@ -94,14 +97,15 @@ internal abstract class RoomModule {
         @Provides
         @JvmStatic
         fun providesParser(): Parser {
-            return Parser.builder().build()
+            return Parser.builder().extensions(extensions).build()
         }
 
         @Provides
         @JvmStatic
         fun providesHtmlRenderer(): HtmlRenderer {
             return HtmlRenderer
                     .builder()
+                    .extensions(extensions)
                     .build()
         }
     }

matrix-sdk-android/src/main/java/org/matrix/android/sdk/internal/session/room/send/MarkdownParser.kt

@@ -31,7 +31,7 @@ internal class MarkdownParser @Inject constructor(
         private val htmlRenderer: HtmlRenderer
 ) {
 
-    private val mdSpecialChars = "[`_\\-*>.\\[\\]#~]".toRegex()
+    private val mdSpecialChars = "[`_\\-*>.\\[\\]#~$]".toRegex()
 
     fun parse(text: String): TextContent {
         // If no special char are detected, just return plain text

vector/src/main/java/im/vector/app/features/html/EventHtmlRenderer.kt

@@ -21,6 +21,7 @@ import im.vector.app.core.di.ActiveSessionHolder
 import im.vector.app.core.glide.GlideApp
 import im.vector.app.core.resources.ColorProvider
 import im.vector.app.features.home.AvatarRenderer
+import io.noties.markwon.AbstractMarkwonPlugin
 import io.noties.markwon.Markwon
 import io.noties.markwon.MarkwonPlugin
 import io.noties.markwon.ext.latex.JLatexMathPlugin
@@ -39,6 +40,13 @@ class EventHtmlRenderer @Inject constructor(context: Context,
 
     private val markwon = Markwon.builder(context)
             .usePlugin(HtmlPlugin.create(htmlConfigure))
+            .usePlugin(object : AbstractMarkwonPlugin() { // Markwon expects maths to be in a specific format: https://noties.io/Markwon/docs/v4/ext-latex
+                override fun processMarkdown(markdown: String): String {
+                    return markdown
+                            .replace(Regex("""<span\s+data-mx-maths="([^"]*)">.*?</span>""")) { matchResult -> "$$" + matchResult.groupValues[1] + "$$" }
+                            .replace(Regex("""<div\s+data-mx-maths="([^"]*)">.*?</div>""")) { matchResult -> "\n$$\n" + matchResult.groupValues[1] + "\n$$\n" }
+                }
+            })
             .usePlugin(MarkwonInlineParserPlugin.create())
             .usePlugin(JLatexMathPlugin.create(44F) { builder ->
                 builder.inlinesEnabled(true)