fix(docs-infra): apply custom `autoLinkCode` filters to single-word `<code>` elements (#41709)

Previously, the `autoLinkCode` Dgeni post-processor would not apply the
custom filters when matching the whole contents of a `<code>` element.
This meant that custom filters would not be applied to single-word
`<code>` elements.

You can see occurrences of this issue in the following sections of the
"Reactive forms" guide:
- [Creating nested form groups][1]
  (look for `street, city, state, and zip controls`)
- [Using the FormBuilder service to generate controls][2]
  (look for `group method`)

This commit fixes this by also applying the custom filters when
processing the whole contents of a `<code>` element.

This commit also updates the `filterPipes` custom filter to allow
matching a pipe's name in a single-word `<code>` element (where there is
no preceeding `|` character).

[1]: https://v10.angular.io/guide/reactive-forms#creating-nested-form-groups
[2]: https://v10.angular.io/guide/reactive-forms#using-the-formbuilder-service-to-generate-controls

PR Close #41709

aio/tools/transforms/angular-base-package/post-processors/auto-link-code.js

@@ -55,7 +55,7 @@ module.exports = function autoLinkCode(getDocFromAlias) {
           const index = parent.children.indexOf(node);
 
           // Can we convert the whole text node into a doc link?
-          const docs = getDocFromAlias(node.value);
+          const docs = getFilteredDocsFromAlias([node.value], 0);
           if (foundValidDoc(docs, node.value, file)) {
             parent.children.splice(index, 1, createLinkNode(docs[0], node.value));
           } else {
@@ -89,14 +89,18 @@ module.exports = function autoLinkCode(getDocFromAlias) {
     return ancestors.some(ancestor => is(ancestor, 'a'));
   }
 
+  function getFilteredDocsFromAlias(words, index) {
+    // Remove docs that fail the custom filter tests.
+    return autoLinkCodeImpl.customFilters.reduce(
+        (docs, filter) => filter(docs, words, index), getDocFromAlias(words[index]));
+  }
+
   function getNodes(node, file) {
     return textContent(node)
         .split(/([A-Za-z0-9_.-]+)/)
         .filter(word => word.length)
         .map((word, index, words) => {
-          // remove docs that fail the custom filter tests
-          const filteredDocs = autoLinkCodeImpl.customFilters.reduce(
-              (docs, filter) => filter(docs, words, index), getDocFromAlias(word));
+          const filteredDocs = getFilteredDocsFromAlias(words, index);
 
           return foundValidDoc(filteredDocs, word, file) ?
               // Create a link wrapping the text node.

aio/tools/transforms/angular-base-package/post-processors/auto-link-code.spec.js

@@ -89,7 +89,7 @@ describe('autoLinkCode post-processor', () => {
        expect(doc.renderedContent).toEqual('<code>xyz-MyClass</code>');
      });
 
-  it('should ignore code items that are filtered out by custom filters', () => {
+  it('should ignore code items that are filtered out by custom filters (multiple words)', () => {
     autoLinkCode.customFilters = [filterPipes];
     aliasMap.addDoc({
       docType: 'pipe',
@@ -115,6 +115,27 @@ describe('autoLinkCode post-processor', () => {
             '</code>');
   });
 
+  it('should ignore code items that are filtered out by custom filters (single word)', () => {
+    const filterAnchors = (docs, words, index) => (words[index].toLowerCase() === 'a') ? [] : docs;
+    autoLinkCode.customFilters = [filterAnchors];
+    autoLinkCode.docTypes = ['directive'];
+
+    aliasMap.addDoc({
+      docType: 'directive',
+      id: 'MyAnchorDirective',
+      aliases: ['MyAnchorDirective', 'a'],
+      path: 'a/b/my-anchor-directive',
+    });
+    const doc = {
+      docType: 'test-doc',
+      renderedContent: '<code>a</code>',
+    };
+
+    processor.$process([doc]);
+
+    expect(doc.renderedContent).toBe('<code>a</code>');
+  });
+
   it('should ignore generated nodes', () => {
     const filterAnchors = (docs, words, index) => (words[index].toLowerCase() === 'a') ? [] : docs;
     autoLinkCode.customFilters = [filterAnchors];

aio/tools/transforms/angular-base-package/services/auto-link-filters/filterPipes.js

@@ -8,5 +8,6 @@ module.exports = function filterPipes() {
     docs.filter(doc =>
       doc.docType !== 'pipe' ||
       doc.pipeOptions.name !== '\'' + words[index] + '\'' ||
-      index > 0 && words[index - 1].trim() === '|');
+      index === 0 ||
+      words[index - 1].trim() === '|');
 };