Function parseGitDiffHeader

src/patch/parse.ts:266–334

* Parses the old and new filenames from a `diff --git` header line. * * The format is: * diff --git a/ b/ * * When filenames contain special characters (including newlines, tabs, * backslashes, or double quotes), Git quotes them with C-style escaping: *

(line: string)

   * undefined in the output.
   */
  function parseGitDiffHeader(line: string): { oldFileName: string, newFileName: string } | null {
    // Strip the "diff --git " prefix
    const rest = line.substring('diff --git '.length);

    // Handle quoted paths: "a/path" "b/path"
    // Git quotes paths when they contain characters like newlines, tabs,
    // backslashes, or double quotes (but notably not spaces).
    if (rest.startsWith('"')) {
      const oldPath = parseQuotedFileName(rest);
      if (oldPath === null) { return null; }
      const afterOld = rest.substring(oldPath.rawLength + 1); // +1 for space
      let newFileName: string;
      if (afterOld.startsWith('"')) {
        const newPath = parseQuotedFileName(afterOld);
        if (newPath === null) { return null; }
        newFileName = newPath.fileName;
      } else {
        newFileName = afterOld;
      }
      return {
        oldFileName: oldPath.fileName,
        newFileName
      };
    }

    // Check if the second path is quoted
    // e.g. diff --git a/simple "b/renamed\nnewline.txt"
    const quoteIdx = rest.indexOf('"');
    if (quoteIdx > 0) {
      const oldFileName = rest.substring(0, quoteIdx - 1);
      const newPath = parseQuotedFileName(rest.substring(quoteIdx));
      if (newPath === null) { return null; }
      return {
        oldFileName,
        newFileName: newPath.fileName
      };
    }

    // Unquoted paths. Try to find the split point.
    // The format is: a/<old-path> b/<new-path>
    //
    // Note the potential ambiguity caused by the possibility of the file paths
    // themselves containing the substring ` b/`, plus the pathological case
    // described in the comment above.
    //
    // Strategy: find all occurrences of " b/" and split on the middle
    // one. When old and new names are the same (which is the only case where
    // we can't rely on extended headers later in the patch so HAVE to get
    // this right), this will always be the correct split.
    if (rest.startsWith('a/')) {
      const splits = [];
      let idx = 0;
      while (true) {
        idx = rest.indexOf(' b/', idx + 1);
        if (idx === -1) { break; }
        splits.push(idx);
      }
      if (splits.length > 0) {