fix(v2): fix title logic (meta vs heading) + ignore fixed anchor id syntax (#4688)

* parseMarkdownContentTitle should ignore {#my-anchor-id} syntax

* use frontMatter.title in priority for page meta title

* parseMarkdownString should ignore fixed anchor ids syntax

* docs: make the distinction between headingTitle + metaTitle more clear + add useful todo

* docs: make the distinction between headingTitle + metaTitle more clear + add useful todo

* writeHeadingIds should ignore top-level md title like "# Title"
=> we are not supposed to create anchor links for h1 headers

* update tests

* fix doc tests

packages/docusaurus-plugin-content-docs/src/__tests__/__snapshots__/index.test.ts.snap

@@ -146,7 +146,7 @@ Object {
   \\"unversionedId\\": \\"foo/bar\\",
   \\"id\\": \\"foo/bar\\",
   \\"isDocsHomePage\\": false,
-  \\"title\\": \\"Bar\\",
+  \\"title\\": \\"Remarkable\\",
   \\"description\\": \\"This is custom description\\",
   \\"source\\": \\"@site/docs/foo/bar.md\\",
   \\"sourceDirName\\": \\"foo\\",
@@ -182,7 +182,7 @@ Object {
   },
   \\"sidebar\\": \\"docs\\",
   \\"previous\\": {
-    \\"title\\": \\"Bar\\",
+    \\"title\\": \\"Remarkable\\",
     \\"permalink\\": \\"/docs/foo/bar\\"
   },
   \\"next\\": {
@@ -396,7 +396,7 @@ Object {
             \\"items\\": [
               {
                 \\"type\\": \\"link\\",
-                \\"label\\": \\"Bar\\",
+                \\"label\\": \\"Remarkable\\",
                 \\"href\\": \\"/docs/foo/bar\\"
               },
               {

packages/docusaurus-plugin-content-docs/src/__tests__/docs.test.ts

@@ -181,7 +181,7 @@ describe('simple site', () => {
       isDocsHomePage: false,
       permalink: '/docs/foo/bar',
       slug: '/foo/bar',
-      title: 'Bar',
+      title: 'Remarkable',
       description: 'This is custom description',
       frontMatter: {
         description: 'This is custom description',
@@ -255,7 +255,7 @@ describe('simple site', () => {
       isDocsHomePage: true,
       permalink: '/docs/',
       slug: '/',
-      title: 'Bar',
+      title: 'Remarkable',
       description: 'This is custom description',
       frontMatter: {
         description: 'This is custom description',

packages/docusaurus-plugin-content-docs/src/__tests__/index.test.ts

@@ -309,7 +309,7 @@ describe('simple website', () => {
         'foo',
         'bar.md',
       ),
-      title: 'Bar',
+      title: 'Remarkable',
       description: 'This is custom description',
       frontMatter: {
         description: 'This is custom description',

packages/docusaurus-plugin-content-docs/src/docs.ts

@@ -121,9 +121,7 @@ export function processDocMetadata({
     frontMatter: unsafeFrontMatter,
     contentTitle,
     excerpt,
-  } = parseMarkdownString(content, {
-    source,
-  });
+  } = parseMarkdownString(content);
   const frontMatter = validateDocFrontMatter(unsafeFrontMatter);
 
   const {
@@ -205,8 +203,11 @@ export function processDocMetadata({
         numberPrefixParser: options.numberPrefixParser,
       });
 
-  // Default title is the id.
-  const title: string = frontMatter.title ?? contentTitle ?? baseID;
+  // TODO expose both headingTitle+metaTitle to theme?
+  // Different fallbacks order on purpose!
+  // See https://github.com/facebook/docusaurus/issues/4665#issuecomment-825831367
+  const headingTitle: string = contentTitle ?? frontMatter.title ?? baseID;
+  // const metaTitle: string = frontMatter.title ?? contentTitle  ?? baseID;
 
   const description: string = frontMatter.description ?? excerpt ?? '';
 
@@ -245,7 +246,7 @@ export function processDocMetadata({
     unversionedId,
     id,
     isDocsHomePage,
-    title,
+    title: headingTitle,
     description,
     source: aliasedSitePath(filePath, siteDir),
     sourceDirName,