Function applyUnifiedDiff

core/edit/lazy/unifiedDiffApply.ts:43–93

(
  sourceCode: string,
  unifiedDiffText: string,
)

 * @throws Error if the diff cannot be cleanly applied to the source
 */
export function applyUnifiedDiff(
  sourceCode: string,
  unifiedDiffText: string,
): DiffLine[] {
  const sourceLines = sourceCode.split(/\r?\n/);
  const hunks = parseUnifiedDiff(unifiedDiffText);
  const diffResult: DiffLine[] = [];
  let currentPos = 0; // pointer in sourceLines

  for (const hunk of hunks) {
    const hunkBeforeLines = extractBeforeLines(hunk.lines);
    const hunkStart = findHunkInSource(
      sourceLines,
      hunkBeforeLines,
      currentPos,
    );
    if (hunkStart === -1) {
      // All hunks must be found in the source code. If not, throw an error.
      throw new Error("Hunk could not be applied cleanly to source code.");
    }

    // Emit any unchanged lines that come before this hunk.
    for (let i = currentPos; i < hunkStart; i++) {
      diffResult.push({ type: "same", line: sourceLines[i] });
    }
    let hunkSourcePos = hunkStart;

    for (const dline of hunk.lines) {
      const srcLine = sourceLines[hunkSourcePos];
      if (dline.startsWith("+")) {
        // Insertion: output new line (strip the '+' marker)
        diffResult.push({ type: "new", line: dline.substring(1) });
      } else if (dline.startsWith("-")) {
        // Removal: output the removed (old) line and advance the pointer.
        diffResult.push({ type: "old", line: srcLine });
        hunkSourcePos++;
      } else {
        // Context line: use the source line (in case the diff’s context has a minor whitespace error)
        // and advance the pointer.
        diffResult.push({ type: "same", line: srcLine });
        hunkSourcePos++;
      }
    }
    currentPos = hunkSourcePos;
  }

  for (let i = currentPos; i < sourceLines.length; i++) {
    diffResult.push({ type: "same", line: sourceLines[i] });
  }
  return diffResult;
}

interface Hunk {
  lines: string[];