Function getChangesInLine

src/highlightChangesInLine.ts:16–51

* Given a pair of lines from a diff, returns more granular changes to the * lines. Attempts to only return changes that are useful. The current heuristic * is to only show granular changes if the ratio of change to unchanged parts in * the line is below a threshold, otherwise the lines have chang

(
    context: Context,
    lineA: string | null,
    lineB: string | null
)

 * enough for the granular diffs to not be useful.
 */
function getChangesInLine(
    context: Context,
    lineA: string | null,
    lineB: string | null
): Change[] | null {
    const { HIGHLIGHT_LINE_CHANGES } = context;

    if (!HIGHLIGHT_LINE_CHANGES || lineA === null || lineB === null) {
        return null;
    }

    // Drop the prefix
    const lineTextA = lineA.slice(1);
    const lineTextB = lineB.slice(1);
    const changes = diffWords(lineTextA, lineTextB, {
        ignoreCase: false,
        ignoreWhitespace: false,
    });

    // Count how many words changed vs total words. Note that a replacement gets
    // double counted.
    let changedWords = 0;
    let totalWords = 0;
    for (const { added, removed, count } of changes) {
        if (added || removed) {
            changedWords += count ?? 0;
        } else {
            totalWords += count ?? 0;
        }
    }
    if (changedWords > totalWords * HIGHLIGHT_CHANGE_RATIO) {
        return null;
    }

    return changes;
}

export function getChangesInLines(
    context: Context,