Function matchLine

core/diff/util.ts:48–95

(
  newLine: string,
  oldLines: string[],
  permissiveAboutIndentation = false,
)

 * Also return a version of the line with correct indentation if needs fixing
 */
export function matchLine(
  newLine: string,
  oldLines: string[],
  permissiveAboutIndentation = false,
): MatchLineResult {
  // Only match empty lines if it's the next one:
  if (newLine.trim() === "" && oldLines[0]?.trim() === "") {
    return {
      matchIndex: 0,
      isPerfectMatch: true,
      newLine: newLine.trim(),
    };
  }

  const isEndBracket = END_BRACKETS.includes(newLine.trim());

  for (let i = 0; i < oldLines.length; i++) {
    // trims trailing whitespaces from the lines before comparison
    //this ensures trailing spaces don't affect matching.
    const oldLineTrimmed = oldLines[i].trimEnd();
    const newLineTrimmed = newLine.trimEnd();

    // Don't match end bracket lines if too far away
    if (i > 4 && isEndBracket) {
      return { matchIndex: -1, isPerfectMatch: false, newLine };
    }

    if (linesMatchPerfectly(newLineTrimmed, oldLineTrimmed)) {
      return { matchIndex: i, isPerfectMatch: true, newLine };
    }
    if (linesMatch(newLineTrimmed, oldLineTrimmed, i)) {
      // This is a way to fix indentation, but only for sufficiently long lines to avoid matching whitespace or short lines
      if (
        newLineTrimmed.trimStart() === oldLineTrimmed.trimStart() &&
        (permissiveAboutIndentation || newLine.trim().length > 8)
      ) {
        return {
          matchIndex: i,
          isPerfectMatch: true,
          newLine: oldLines[i],
        };
      }
      return { matchIndex: i, isPerfectMatch: false, newLine };
    }
  }

  return { matchIndex: -1, isPerfectMatch: false, newLine };
}

/**
 * Convert a stream of arbitrary chunks to a stream of lines