Update regex for more robust detection of tags

Update the regex used for more robust detection of tags. Replace the
negative lookahead assertion `\s` with `[ \t]` (allow for `\n`), and
add `#` to the class so that `##` is ignored.

Attempted to add the negation `^[0-9p{L}p{Emoji}p{N}-/]` to the
negative look ahead. This was to exclude items like `#$`, `#&` that
can't be tags. However my regex-fu was insufficient.

Instead, if the regex match is to a single `#`, ensure it is the
character to the left of the cursor. Example

  `this is text #%|`

where the `|` represents the cursor. The `TAG_REGEX`
will match the `#` at index 13. However since the cursor is at 15, the
Completion provider will not run.

Update the tests to cover these situations and add them all to a sub-
`describe` block labeled by the bug issue number #1189

packages/foam-vscode/src/features/tag-completion.spec.ts

@@ -66,36 +66,6 @@ describe('Tag Completion', () => {
     expect(tags).toBeNull();
   });
 
-  it('should provide multiple suggestions when typing #, issue #1189', async () => {
-    const { uri } = await createFile(`# Title
-
-#`);
-    const { doc } = await showInEditor(uri);
-    const provider = new TagCompletionProvider(foamTags);
-
-    const tags = await provider.provideCompletionItems(
-      doc,
-      new vscode.Position(2, 1)
-    );
-    expect(tags.items.length).toEqual(3);
-  });
-
-  it('should not provide a suggestion when typing `# `, issue #1189', async () => {
-    const { uri } = await createFile(`# Title
-
-# `);
-    const { doc } = await showInEditor(uri);
-    const provider = new TagCompletionProvider(foamTags);
-
-    const tags = await provider.provideCompletionItems(
-      doc,
-      new vscode.Position(2, 2)
-    );
-
-    expect(foamTags.tags.get('primary')).toBeTruthy();
-    expect(tags).toBeNull();
-  });
-
   it('should provide a suggestion when typing #prim', async () => {
     const { uri } = await createFile('#prim');
     const { doc } = await showInEditor(uri);
@@ -137,4 +107,84 @@ describe('Tag Completion', () => {
     expect(foamTags.tags.get('primary')).toBeTruthy();
     expect(tags).toBeNull();
   });
+
+  describe('has robust triggering #1189', () => {
+    it('should provide multiple suggestions when typing #', async () => {
+      const { uri } = await createFile(`# Title
+
+#`);
+      const { doc } = await showInEditor(uri);
+      const provider = new TagCompletionProvider(foamTags);
+
+      const tags = await provider.provideCompletionItems(
+        doc,
+        new vscode.Position(2, 1)
+      );
+      expect(tags.items.length).toEqual(3);
+    });
+
+    it('should provide multiple suggestions when typing # at EOL', async () => {
+      const { uri } = await createFile(`# Title
+
+#
+more text
+`);
+      const { doc } = await showInEditor(uri);
+      const provider = new TagCompletionProvider(foamTags);
+
+      const tags = await provider.provideCompletionItems(
+        doc,
+        new vscode.Position(2, 1)
+      );
+      expect(tags.items.length).toEqual(3);
+    });
+
+    it('should not provide a suggestion when typing `# `', async () => {
+      const { uri } = await createFile(`# Title
+
+# `);
+      const { doc } = await showInEditor(uri);
+      const provider = new TagCompletionProvider(foamTags);
+
+      const tags = await provider.provideCompletionItems(
+        doc,
+        new vscode.Position(2, 2)
+      );
+
+      expect(foamTags.tags.get('primary')).toBeTruthy();
+      expect(tags).toBeNull();
+    });
+
+    it('should not provide a suggestion when typing `#{non-match}`', async () => {
+      const { uri } = await createFile(`# Title
+
+#$`);
+      const { doc } = await showInEditor(uri);
+      const provider = new TagCompletionProvider(foamTags);
+
+      const tags = await provider.provideCompletionItems(
+        doc,
+        new vscode.Position(2, 2)
+      );
+
+      expect(foamTags.tags.get('primary')).toBeTruthy();
+      expect(tags).toBeNull();
+    });
+
+    it('should not provide a suggestion when typing `##`', async () => {
+      const { uri } = await createFile(`# Title
+
+##`);
+      const { doc } = await showInEditor(uri);
+      const provider = new TagCompletionProvider(foamTags);
+
+      const tags = await provider.provideCompletionItems(
+        doc,
+        new vscode.Position(2, 2)
+      );
+
+      expect(foamTags.tags.get('primary')).toBeTruthy();
+      expect(tags).toBeNull();
+    });
+  });
 });

packages/foam-vscode/src/features/tag-completion.ts

@@ -7,7 +7,7 @@ import { mdDocSelector } from '../utils';
 // this regex is different from HASHTAG_REGEX in that it does not look for a
 // #+character. It uses a negative look-ahead for `# `
 const TAG_REGEX =
-  /(?<=^|\s)#(?!(\s+))([0-9]*[\p{L}\p{Emoji_Presentation}\p{N}/_-]*)/gmu;
+  /(?<=^|\s)#(?![ \t#])([0-9]*[\p{L}\p{Emoji_Presentation}\p{N}/_-]*)/gu;
 
 const feature: FoamFeature = {
   activate: async (
@@ -44,6 +44,19 @@ export class TagCompletionProvider
       return null;
     }
 
+    // check the match group length.
+    // if the match is only '#', the character to the left of cursor should
+    // also be `#`. If it isn't, we didn't match the
+    // `[0-9]*[\p{L}\p{Emoji_Presentation}\p{N}/_-]` group
+    // This excludes things like `#&`
+    const matchText = requiresAutocomplete[requiresAutocomplete.length - 1];
+    if (
+      matchText === '#' &&
+      cursorPrefix.charAt(position.character - 1) !== '#'
+    ) {
+      return null;
+    }
+
     const completionTags = [];
     [...this.foamTags.tags].forEach(([tag]) => {
       const item = new vscode.CompletionItem(