feat(linter/plugins): implement SourceCode#getTokenBefore() (#15956)

- Part of
#14829 (comment).
- Follow up to #15861.

Author: lilnasy

apps/oxlint/src-js/plugins/tokens.ts

@@ -319,14 +319,93 @@ export function getLastTokens(node: Node, countOptions?: CountOptions | number |
  * @param skipOptions? - Options object. Same options as `getFirstToken()`.
  * @returns `Token`, or `null` if all were skipped.
  */
-/* oxlint-disable no-unused-vars */
 export function getTokenBefore(
   nodeOrToken: NodeOrToken | Comment,
   skipOptions?: SkipOptions | number | FilterFn | null,
 ): Token | null {
-  throw new Error('`sourceCode.getTokenBefore` not implemented yet'); // TODO
+  if (tokens === null) initTokens();
+  debugAssertIsNonNull(tokens);
+  debugAssertIsNonNull(comments);
+
+  // Number of tokens preceding the given node to skip
+  let skip =
+    typeof skipOptions === 'number'
+      ? skipOptions
+      : typeof skipOptions === 'object' && skipOptions !== null
+        ? skipOptions.skip
+        : null;
+
+  const filter =
+    typeof skipOptions === 'function'
+      ? skipOptions
+      : typeof skipOptions === 'object' && skipOptions !== null
+        ? skipOptions.filter
+        : null;
+
+  // Whether to return comment tokens
+  const includeComments =
+    typeof skipOptions === 'object' &&
+    skipOptions !== null &&
+    'includeComments' in skipOptions &&
+    skipOptions.includeComments;
+
+  // Source array of tokens to search in
+  let nodeTokens: Token[] | null = null;
+  if (includeComments) {
+    if (tokensWithComments === null) {
+      tokensWithComments = [...tokens, ...comments].sort((a, b) => a.range[0] - b.range[0]);
+    }
+    nodeTokens = tokensWithComments;
+  } else {
+    nodeTokens = tokens;
+  }
+
+  const nodeStart = nodeOrToken.range[0];
+
+  // Index of the token immediately before the given node, token, or comment.
+  let beforeIndex = 0;
+  let hi = nodeTokens.length;
+
+  while (beforeIndex < hi) {
+    const mid = (beforeIndex + hi) >> 1;
+    if (nodeTokens[mid].range[0] < nodeStart) {
+      beforeIndex = mid + 1;
+    } else {
+      hi = mid;
+    }
+  }
+
+  beforeIndex -= 1;
+
+  if (typeof filter !== 'function') {
+    if (typeof skip !== 'number') {
+      return nodeTokens[beforeIndex] ?? null;
+    } else {
+      return nodeTokens[beforeIndex - skip] ?? null;
+    }
+  } else {
+    if (typeof skip !== 'number') {
+      while (beforeIndex >= 0) {
+        const token = nodeTokens[beforeIndex];
+        if (filter(token)) {
+          return token;
+        }
+        beforeIndex -= 1;
+      }
+    } else {
+      while (beforeIndex >= 0) {
+        const token = nodeTokens[beforeIndex];
+        if (filter(token)) {
+          if (skip === 0) return token;
+          skip -= 1;
+        }
+        beforeIndex -= 1;
+      }
+    }
+  }
+
+  return null;
 }
-/* oxlint-enable no-unused-vars */
 
 /**
  * Get the token that precedes a given node or token.

apps/oxlint/test/tokens.test.ts

@@ -209,12 +209,93 @@ describe('when calling getTokensBefore', () => {
 });
 
 describe('when calling getTokenBefore', () => {
-  /* oxlint-disable-next-line no-disabled-tests expect-expect */
-  it('is to be implemented');
-  /* oxlint-disable-next-line no-unused-expressions */
-  getTokenBefore;
-  /* oxlint-disable-next-line no-unused-expressions */
-  resetSourceAndAst;
+  it('should retrieve one token before a node', () => {
+    assert.strictEqual(getTokenBefore(BinaryExpression)!.value, '=');
+  });
+
+  it('should skip a given number of tokens', () => {
+    assert.strictEqual(getTokenBefore(BinaryExpression, 1)!.value, 'answer');
+    assert.strictEqual(getTokenBefore(BinaryExpression, 2)!.value, 'var');
+  });
+
+  it('should skip a given number of tokens with skip option', () => {
+    assert.strictEqual(getTokenBefore(BinaryExpression, { skip: 1 })!.value, 'answer');
+    assert.strictEqual(getTokenBefore(BinaryExpression, { skip: 2 })!.value, 'var');
+  });
+
+  it('should retrieve matched token with filter option', () => {
+    assert.strictEqual(getTokenBefore(BinaryExpression, (t) => t.value !== '=')!.value, 'answer');
+  });
+
+  it('should retrieve matched token with skip and filter options', () => {
+    assert.strictEqual(
+      getTokenBefore(BinaryExpression, {
+        skip: 1,
+        filter: (t) => t.value !== '=',
+      })!.value,
+      'var',
+    );
+  });
+
+  it('should retrieve one token or comment before a node with includeComments option', () => {
+    assert.strictEqual(
+      getTokenBefore(BinaryExpression, {
+        includeComments: true,
+      })!.value,
+      'C',
+    );
+  });
+
+  it('should retrieve one token or comment before a node with includeComments and skip options', () => {
+    assert.strictEqual(
+      getTokenBefore(BinaryExpression, {
+        includeComments: true,
+        skip: 1,
+      })!.value,
+      '=',
+    );
+  });
+
+  it('should retrieve one token or comment before a node with includeComments and skip and filter options', () => {
+    assert.strictEqual(
+      getTokenBefore(BinaryExpression, {
+        includeComments: true,
+        skip: 1,
+        filter: (t) => t.type.startsWith('Block'),
+      })!.value,
+      'B',
+    );
+  });
+
+  it('should retrieve the previous node if the comment at the end of source code is specified.', () => {
+    resetSourceAndAst();
+    sourceText = 'a + b /*comment*/';
+    // TODO: this verbatim range should be replaced with `ast.comments[0]`
+    const token = getTokenBefore({ range: [6, 17] } as Node);
+
+    assert.strictEqual(token!.value, 'b');
+    resetSourceAndAst();
+  });
+
+  it('should retrieve the previous comment if the first token is specified.', () => {
+    resetSourceAndAst();
+    sourceText = '/*comment*/ a + b';
+    // TODO: this verbatim range should be replaced with `ast.tokens[0]`
+    const token = getTokenBefore({ range: [12, 13] } as Node, { includeComments: true });
+
+    assert.strictEqual(token!.value, 'comment');
+    resetSourceAndAst();
+  });
+
+  it('should retrieve null if the first comment is specified.', () => {
+    resetSourceAndAst();
+    sourceText = '/*comment*/ a + b';
+    // TODO: this verbatim range should be replaced with `ast.comments[0]`
+    const token = getTokenBefore({ range: [0, 11] } as Node, { includeComments: true });
+
+    assert.strictEqual(token, null);
+    resetSourceAndAst();
+  });
 });
 
 describe('when calling getTokenAfter', () => {