Rework incremental diffing (#499)
* Improve our deepening logic * Use consistent SHA for PR-related operations in CheckoutPrTool * compute `deepenDepth` at more appropriate time * fix stale comment * add comments for `alreadyOnBranch` * ensure before sha is available * small cleanup * computeIncrementalDiff * move the util * improve algorithm * improve algorithm further * get rid of temp result array * add comment * compute incremental diff and updte instructions * add comment * update stale comment * get rid of redundant rev-parse call * improve comment * strenghten the instructions * make diff paths unique
This commit is contained in:
Mateusz Burzyński
committed by
pullfrog[bot]
pullfrog[bot]
parent
248d11d73d
commit
a7b8dcbced
@@ -0,0 +1,182 @@
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import { log } from "./cli.ts";
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import { $ } from "./shell.ts";
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type ComputeIncrementalDiffParams = {
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baseBranch: string;
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beforeSha: string;
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headSha: string;
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};
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/**
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* computes the incremental diff between two versions of a PR using range-diff
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* on virtual squash commits created via `git commit-tree`.
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*
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* each PR version is squashed into a single synthetic commit (merge-base → tip tree),
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* then range-diff compares those two single-commit ranges. this:
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* - isolates each version's net effect (base branch noise eliminated via per-version merge bases)
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* - avoids commit-matching issues that raw range-diff has with rebases/squashes/reordering
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* - creates only loose git objects, no branches or refs (unlike temp-branch squash approaches)
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*
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* unlike fetchAndFormatPrDiff/formatFilesWithLineNumbers, this output has no line numbers.
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* range-diff compares *patches* (diffs-of-diffs), not file trees — its hunk headers are
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* `@@ file.ts` breadcrumbs, not positional `@@ -X,Y +A,B @@` markers. reconstructing
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* line numbers would require cross-referencing with the v2 diff or content-matching against
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* file trees, both of which are fragile (duplicate lines, hunk boundary shifts after rebase).
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* a structured interdiff approach (diff two parsed patches, compare only +/- keys via Myers)
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* could approximate line numbers but loses semantic precision: range-diff understands patch
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* structure natively (rename detection, hunk-aware matching, dual-prefix inner/outer changes),
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* while flat key-sequence comparison can misalign duplicate lines and can't distinguish
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* "new addition to the PR" from "existing code newly modified by the PR". range-diff is the
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* right abstraction here — the incremental diff answers "how did the changeset evolve?",
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* not "where in the file is this?", and forcing positional line numbers onto it would be
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* semantically misleading.
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*
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* alternatives considered:
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* - plain git diff (two-tree or three-dot): includes base branch changes, no PR isolation
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* - patch-text diffing (interdiff / diff-of-diffs): fragile, hunk offset noise on rebase
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* - range-diff on raw commit ranges: confused by commit reorganization across force-pushes
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*/
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export function computeIncrementalDiff(params: ComputeIncrementalDiffParams): string | null {
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try {
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// $1=beforeSha, $2=baseBranch, $3=headSha
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const raw = $(
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"sh",
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[
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"-c",
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'old_base=$(git merge-base "$1" "origin/$2") && ' +
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'new_base=$(git merge-base "$3" "origin/$2") && ' +
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"git range-diff --no-color " +
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'"$old_base..$(git commit-tree "$1^{tree}" -p "$old_base" -m x)" ' +
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'"$new_base..$(git commit-tree "$3^{tree}" -p "$new_base" -m x)"',
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"--",
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params.beforeSha,
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params.baseBranch,
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params.headSha,
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],
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{ log: false }
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);
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return postProcessRangeDiff(raw);
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} catch (e) {
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log.debug(`» range-diff failed: ${e instanceof Error ? e.message : String(e)}`);
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return null;
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}
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}
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function isDiffPrefix(ch: string): boolean {
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return ch === " " || ch === "+" || ch === "-";
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}
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/**
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* transforms git range-diff output into a clean incremental diff.
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*
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* range-diff content lines have two prefix characters:
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* 1st (outer): range-diff level — space (same in both), + (new only), - (old only)
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* 2nd (inner): original diff level — space (context), + (added), - (removed)
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*
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* stripping the inner prefix produces a standard unified-diff-like output where
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* +/- means "changed between PR versions" rather than "changed vs base branch".
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*
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* uses a streaming approach: a ring buffer of before-context lines is flushed when
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* a change is hit, then afterCount lines of after-context are emitted directly.
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* nearest preceding ## / @@ headers are force-included when outside the context window.
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*/
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export function postProcessRangeDiff(raw: string, contextLines = 3): string | null {
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if (!raw.trim()) return null;
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if (/^\d+:\s+\w+\s+=\s+\d+:/m.test(raw)) return null;
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type Line = { prefix: string; from: number; to: number; seq: number };
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const beforeBuf: Line[] = [];
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let lastFileHdr: Line | null = null;
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let lastHunkHdr: Line | null = null;
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let fileHdrEmitted = true;
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let hunkHdrEmitted = true;
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let out = "";
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let afterRemaining = 0;
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let lastEmittedSeq = -2;
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let seq = 0;
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let hasChanges = false;
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function emit(line: Line) {
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if (lastEmittedSeq >= 0 && line.seq > lastEmittedSeq + 1) out += (out ? "\n" : "") + "...";
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out += (out ? "\n" : "") + line.prefix + raw.slice(line.from, line.to);
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lastEmittedSeq = line.seq;
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if (lastFileHdr?.seq === line.seq) fileHdrEmitted = true;
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if (lastHunkHdr?.seq === line.seq) hunkHdrEmitted = true;
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}
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function flushBefore() {
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if (lastFileHdr && !fileHdrEmitted) emit(lastFileHdr);
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if (lastHunkHdr && !hunkHdrEmitted) emit(lastHunkHdr);
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for (const line of beforeBuf) {
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if (line.seq > lastEmittedSeq) emit(line);
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}
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beforeBuf.length = 0;
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}
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let cursor = 0;
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while (cursor < raw.length) {
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const eol = raw.indexOf("\n", cursor);
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const lineEnd = eol === -1 ? raw.length : eol;
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if (raw.charCodeAt(cursor) >= 48 && raw.charCodeAt(cursor) <= 57) {
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cursor = lineEnd + 1;
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continue;
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}
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if (lineEnd - cursor >= 5 && raw.startsWith(" ", cursor)) {
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const prefix = raw[cursor + 4];
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if (isDiffPrefix(prefix)) {
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const contentPos = cursor + 5;
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const isOuterChange = prefix !== " ";
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let line: Line;
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let isChange = false;
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if (contentPos >= lineEnd) {
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line = { prefix, from: lineEnd, to: lineEnd, seq };
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} else if (isDiffPrefix(raw[contentPos])) {
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isChange = isOuterChange;
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line = { prefix, from: contentPos + 1, to: lineEnd, seq };
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} else {
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line = { prefix, from: contentPos, to: lineEnd, seq };
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if (
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raw.startsWith("## ", contentPos) &&
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!raw.startsWith("## Commit message", contentPos)
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) {
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lastFileHdr = line;
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fileHdrEmitted = false;
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lastHunkHdr = null;
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hunkHdrEmitted = true;
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} else if (
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raw.startsWith("@@", contentPos) &&
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!raw.startsWith("@@ Metadata", contentPos)
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) {
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lastHunkHdr = line;
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hunkHdrEmitted = false;
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}
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}
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if (isChange) {
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hasChanges = true;
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flushBefore();
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emit(line);
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afterRemaining = contextLines;
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} else if (afterRemaining > 0) {
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emit(line);
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afterRemaining--;
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} else {
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if (beforeBuf.length >= contextLines) beforeBuf.shift();
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beforeBuf.push(line);
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}
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seq++;
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}
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}
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cursor = lineEnd + 1;
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}
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return hasChanges ? out : null;
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}
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