chrome-devtools-frontend/front_end/ui/components/text_editor/AiCodeGenerationParser.ts

Chrome DevTools UI

// Copyright 2025 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import * as CodeMirror from '../../../third_party/codemirror.next/codemirror.next.js';

const LINE_COMMENT_PATTERN = /^(?:\/\/|#)\s*/;
const BLOCK_COMMENT_START_PATTERN = /^\/\*+\s*/;
const BLOCK_COMMENT_END_PATTERN = /\s*\*+\/$/;
const BLOCK_COMMENT_LINE_PREFIX_PATTERN = /^\s*\*\s?/;

function findLastNonWhitespacePos(state: CodeMirror.EditorState, cursorPosition: number): number {
  const line = state.doc.lineAt(cursorPosition);
  const textBefore = line.text.substring(0, cursorPosition - line.from);
  const effectiveEnd = line.from + textBefore.trimEnd().length;
  return effectiveEnd;
}

function resolveCommentNode(state: CodeMirror.EditorState, cursorPosition: number): CodeMirror.SyntaxNode|undefined {
  const tree = CodeMirror.syntaxTree(state);
  const lookupPos = findLastNonWhitespacePos(state, cursorPosition);
  // Find the innermost syntax node at the last non-whitespace character position.
  // The bias of -1 makes it check the character to the left of the position.
  const node = tree.resolveInner(lookupPos, -1);
  const nodeType = node.type.name;
  // Check if the node type is a comment AND the cursor is within the node's range.
  if (nodeType.includes('Comment') && cursorPosition >= node.to) {
    if (!nodeType.includes('BlockComment')) {
      return node;
    }
    // An unclosed block comment can result in the parser inserting an error.
    let hasInternalError = false;
    tree.iterate({
      from: node.from,
      to: node.to,
      enter: n => {
        if (n.type.isError) {
          hasInternalError = true;
          return false;
        }
        return true;
      },
    });
    return hasInternalError ? undefined : node;
  }
  return;
}

function extractBlockComment(rawText: string): string|undefined {
  // Remove /* and */, whitespace, and common leading asterisks on new lines
  let cleaned = rawText.replace(BLOCK_COMMENT_START_PATTERN, '').replace(BLOCK_COMMENT_END_PATTERN, '');
  // Remove leading " * " from multi-line block comments
  cleaned = cleaned.split('\n').map(line => line.replace(BLOCK_COMMENT_LINE_PREFIX_PATTERN, '')).join('\n').trim();
  return cleaned;
}

function extractLineComment(rawText: string): string {
  return rawText.replace(LINE_COMMENT_PATTERN, '').trim();
}

export class AiCodeGenerationParser {
  static extractCommentText(state: CodeMirror.EditorState, cursorPosition: number): string|undefined {
    const node = resolveCommentNode(state, cursorPosition);
    if (!node) {
      return;
    }
    const nodeType = node.type.name;
    const rawText = state.doc.sliceString(node.from, node.to);
    if (nodeType.includes('LineComment')) {
      return extractLineComment(rawText);
    }
    if (nodeType.includes('BlockComment')) {
      return extractBlockComment(rawText);
    }
    return rawText;
  }
}