client: Implement auto syntax highlighting

src/public/app/services/mime_types.js

@@ -1,5 +1,10 @@
 import options from "./options.js";
 
+/**
+ * A pseudo-MIME type which is used in the editor to automatically determine the language used in code blocks via heuristics.
+ */
+const MIME_TYPE_AUTO = "text-x-trilium-auto";
+
 const MIME_TYPES_DICT = [
     { default: true, title: "Plain text", mime: "text/plain", highlightJs: "plaintext" },
     { title: "APL", mime: "text/apl" },
@@ -218,6 +223,7 @@ function normalizeMimeTypeForCKEditor(mimeType) {
 }
 
 export default {
+    MIME_TYPE_AUTO,
     getMimeTypes,
     loadMimeTypes,
     getHighlightJsNameForMime,

src/public/app/widgets/type_widgets/ckeditor/syntax_highlight.js

@@ -171,7 +171,7 @@ function highlightCodeBlock(codeBlock, writer) {
     // Find the corresponding language for the given mimetype.
     const highlightJsLanguage = mime_types.getHighlightJsNameForMime(mimeType);
 
-    if (!highlightJsLanguage) {
+    if (mimeType !== mime_types.MIME_TYPE_AUTO && !highlightJsLanguage) {
         console.warn(`Unsupported highlight.js for mime type ${mimeType}.`);
         return;
     }
@@ -221,13 +221,12 @@ function highlightCodeBlock(codeBlock, writer) {
         }
     }
 
-    // XXX This auto-detects the language, if we want to honor the language
-    //     attribute we can do
-    //     let html = hljs.highlight(text, {language: 'python'});
-    //     If that is done, it would also be interesting to have an
-    //     auto-detect option. See language mime types at
-    //     https://github.com/zadam/trilium/blob/dbd312c88db2b000ec0ce18c95bc8a27c0e621a1/src/public/app/widgets/type_widgets/editable_text.js#L104    
-    let highlightRes = hljs.highlight(text, { language: highlightJsLanguage });
+    let highlightRes;
+    if (mimeType === mime_types.MIME_TYPE_AUTO) {
+        highlightRes = hljs.highlightAuto(text);
+    } else {
+        highlightRes = hljs.highlight(text, { language: highlightJsLanguage });
+    }
     dbg("text\n" + text);
     dbg("html\n" + highlightRes.value);
 

src/public/app/widgets/type_widgets/editable_text.js

@@ -88,6 +88,23 @@ const TPL = `
 </div>
 `;
 
+function buildListOfLanguages() {
+    const userLanguages = (mimeTypesService.getMimeTypes())
+        .filter(mt => mt.enabled)
+        .map(mt => ({
+                language: mimeTypesService.normalizeMimeTypeForCKEditor(mt.mime),
+                label: mt.title
+            }));
+
+    return [
+        {
+            language: mimeTypesService.MIME_TYPE_AUTO,
+            label: "Auto"
+        },
+        ...userLanguages
+    ];
+}
+
 export default class EditableTextTypeWidget extends AbstractTextTypeWidget {
     static getType() { return "editableText"; }
 
@@ -108,13 +125,7 @@ export default class EditableTextTypeWidget extends AbstractTextTypeWidget {
         await libraryLoader.requireLibrary(libraryLoader.CKEDITOR);
         await libraryLoader.requireLibrary(libraryLoader.HIGHLIGHT_JS);
 
-        const codeBlockLanguages =
-            (mimeTypesService.getMimeTypes())
-                .filter(mt => mt.enabled)
-                .map(mt => ({
-                        language: mimeTypesService.normalizeMimeTypeForCKEditor(mt.mime),
-                        label: mt.title
-                    }));
+        const codeBlockLanguages = buildListOfLanguages();
 
         // CKEditor since version 12 needs the element to be visible before initialization. At the same time,
         // we want to avoid flicker - i.e., show editor only once everything is ready. That's why we have separate