ci: add pull request stats comment (#467)

Author: mr-zwets

.cspell.json

@@ -126,6 +126,7 @@
         "numequal",
         "numequalverify",
         "numnotequal",
+        "numstat",
         "NOTEQUAL",
         "op",
         "opcode",

.github/scripts/pr-stats.ts

@@ -0,0 +1,390 @@
+// Breaks a pull request's changed lines down by package and by kind of change (source, tests, docs,
+// dependencies, ...), so reviewers can see at a glance how big a change is and where it lands.
+//
+// Usage: node .github/scripts/pr-stats.ts <base-revision> <head-revision>
+//
+// The script has no dependencies and only reads git history, so it is safe to run against untrusted
+// pull request revisions. Node runs the TypeScript directly (type stripping, Node 22.18+).
+
+import { execFileSync } from 'node:child_process';
+
+type Area = 'compiler' | 'sdk' | 'utils' | 'website' | 'examples' | 'repository';
+type Kind = 'source' | 'tests' | 'docs' | 'dependencies' | 'config' | 'version' | 'generated';
+
+interface FileChange {
+  filePath: string;
+  area: Area;
+  kind: Kind;
+  added: number;
+  removed: number;
+}
+
+interface Churn {
+  added: number;
+  removed: number;
+}
+
+const areaRules: { area: Area; prefix: string }[] = [
+  { area: 'compiler', prefix: 'packages/cashc/' },
+  { area: 'sdk', prefix: 'packages/cashscript/' },
+  { area: 'utils', prefix: 'packages/utils/' },
+  { area: 'website', prefix: 'website/' },
+  { area: 'examples', prefix: 'examples/' },
+];
+
+// Order matters: the first matching rule wins, anything unmatched is source.
+const kindRules: { kind: Kind; matches: (filePath: string) => boolean }[] = [
+  {
+    kind: 'generated',
+    matches: (filePath) => baseName(filePath) === 'yarn.lock' || isGeneratedGrammar(filePath),
+  },
+  { kind: 'dependencies', matches: (filePath) => baseName(filePath) === 'package.json' },
+  { kind: 'tests', matches: (filePath) => filePath.includes('/test/') || filePath.endsWith('.test.ts') },
+  // Agent instructions are tooling configuration rather than documentation for readers, despite being markdown.
+  {
+    kind: 'config',
+    matches: (filePath) => filePath.startsWith('.github/')
+      || baseName(filePath).startsWith('.')
+      || /^(tsconfig.*\.json|vitest\.(config|setup)\.ts|lerna\.json|docusaurus\.config\.ts|sidebars\.ts)$/
+        .test(baseName(filePath))
+      || ['AGENTS.md', 'CLAUDE.md'].includes(baseName(filePath)),
+  },
+  {
+    kind: 'docs',
+    matches: (filePath) => /\.mdx?$/.test(filePath) || /^website\/(docs|static)\//.test(filePath),
+  },
+];
+
+const areaLabels: Record<Area, string> = {
+  compiler: 'Compiler (`cashc`)',
+  sdk: 'SDK (`cashscript`)',
+  utils: 'Utils (`@cashscript/utils`)',
+  website: 'Website',
+  examples: 'Examples',
+  repository: 'Repository',
+};
+
+const kindLabels: Record<Kind, string> = {
+  source: 'Source',
+  tests: 'Tests',
+  docs: 'Docs',
+  dependencies: 'Deps',
+  config: 'Config',
+  version: 'Version',
+  generated: 'Generated',
+};
+
+const areaOrder: Area[] = ['compiler', 'sdk', 'utils', 'website', 'examples', 'repository'];
+const kindOrder: Kind[] = ['source', 'tests', 'docs', 'dependencies', 'config', 'version', 'generated'];
+
+// Version bumps and generated files are left out of the totals: there is nothing in them to review, and a
+// lock file update would otherwise dwarf everything else.
+const excludedFromTotal: Kind[] = ['version', 'generated'];
+
+// Workspace packages are bumped together on every release. Their version lines count as version bumps
+// rather than dependency changes, and are summarised once instead of listed per package.json.
+const workspacePackages = ['cashc', 'cashscript', '@cashscript/utils'];
+const versionConstantPath = 'packages/cashc/src/index.ts';
+
+const releaseNotesPath = 'website/docs/releases/release-notes.md';
+const publishedAreas: Area[] = ['compiler', 'sdk', 'utils'];
+const listedNewFiles = 10;
+
+const [baseRevision, headRevision] = requireRevisions();
+// Diffing against the merge base keeps commits that landed on the base branch after the pull request
+// was opened out of the numbers.
+const mergeBase = git(['merge-base', baseRevision, headRevision]).trim();
+
+const lineCounts = git(['diff', '--numstat', '--no-renames', mergeBase, headRevision]);
+console.log(renderReport(parseLineCounts(lineCounts).flatMap(splitVersionLines)));
+
+function renderReport(changes: FileChange[]): string {
+  if (changes.length === 0) return 'No line changes in this pull request.';
+
+  return [
+    '### Pull request stats',
+    '',
+    ...renderTable(changes),
+    '',
+    ...renderSummary(changes),
+    ...renderVersionBump(changes),
+    ...renderDependencyChanges(changes),
+    ...renderNewFiles(),
+    ...renderReleaseNotesReminder(changes),
+  ].join('\n');
+}
+
+function renderTable(changes: FileChange[]): string[] {
+  const areas = areaOrder.filter((area) => changes.some((change) => change.area === area));
+  const kinds = kindOrder.filter((kind) => changes.some((change) => change.kind === kind));
+  const reviewableChurn = churnOf(reviewable(changes));
+
+  const header = `| | ${kinds.map((kind) => kindLabels[kind]).join(' | ')} | Total | Net | Share |`;
+  const separator = `|---|${kinds.map(() => '---:|').join('')}---:|---:|---:|`;
+  const rows = areas.map((area) => {
+    const inArea = changes.filter((change) => change.area === area);
+    return renderRow(areaLabels[area], inArea, kinds, reviewableChurn);
+  });
+  const totalRow = renderRow('**Total**', changes, kinds, reviewableChurn);
+
+  return [header, separator, ...rows, totalRow];
+}
+
+function renderRow(label: string, changes: FileChange[], kinds: Kind[], reviewableChurn: Churn): string {
+  const cells = kinds.map((kind) => formatChurn(churnOf(changes.filter((change) => change.kind === kind))));
+  const total = churnOf(reviewable(changes));
+  const share = sizeOf(reviewableChurn) === 0 ? '—' : formatPercentage(sizeOf(total) / sizeOf(reviewableChurn));
+  return `| ${label} | ${cells.join(' | ')} | ${formatChurn(total)} | ${formatNet(total)} | ${share} |`;
+}
+
+function renderSummary(changes: FileChange[]): string[] {
+  const reviewableChurn = churnOf(reviewable(changes));
+  const net = sizeOf(reviewableChurn) === 0 ? '' : ` (net ${formatNet(reviewableChurn)})`;
+  const lines = [
+    `Reviewable churn: ${sizeOf(reviewableChurn)} lines${net}, version bumps and generated files excluded.`,
+  ];
+
+  const sourceChurn = sizeOf(churnOf(changes.filter((change) => change.kind === 'source')));
+  const testChurn = sizeOf(churnOf(changes.filter((change) => change.kind === 'tests')));
+  if (sourceChurn > 0) lines.push(`Test lines per line of source: ${(testChurn / sourceChurn).toFixed(2)}.`);
+
+  // Only source files are read line by line, which keeps lock files and fixtures out of the comment share.
+  const addedSourceLines = changes
+    .filter((change) => change.kind === 'source')
+    .flatMap((change) => addedLinesOf(change.filePath))
+    .filter((line) => !isVersionLine(line));
+  const comments = addedSourceLines.filter(isComment).length;
+  const nonBlank = addedSourceLines.filter((line) => line.trim() !== '').length;
+  if (nonBlank > 0) {
+    lines.push(`Comments: ${comments} of ${nonBlank} added source lines, ${formatPercentage(comments / nonBlank)}.`);
+  }
+
+  return lines;
+}
+
+// A release bumps every package.json at once, which reads best as one line rather than one per file.
+function renderVersionBump(changes: FileChange[]): string[] {
+  const bumps = new Map<string, string[]>();
+
+  for (const change of changes.filter((entry) => entry.kind === 'version' && baseName(entry.filePath) === 'package.json')) {
+    const before = packageManifest(fileAt(mergeBase, change.filePath));
+    const after = packageManifest(fileAt(headRevision, change.filePath));
+    if (!before.version || !after.version || before.version === after.version) continue;
+
+    const bump = `${before.version} → ${after.version}`;
+    bumps.set(bump, [...(bumps.get(bump) ?? []), `\`${after.name ?? change.filePath}\``]);
+  }
+
+  return [...bumps].map(([bump, packages]) => `Version bump: ${bump} in ${packages.join(', ')}.`);
+}
+
+// Which packages the pull request brings in or drops, as opposed to how many lines of package.json moved.
+// A new dependency is the part that warrants a look of its own.
+function renderDependencyChanges(changes: FileChange[]): string[] {
+  const lines: string[] = [];
+
+  for (const change of changes.filter((entry) => entry.kind === 'dependencies')) {
+    const before = declaredDependencies(fileAt(mergeBase, change.filePath));
+    const after = declaredDependencies(fileAt(headRevision, change.filePath));
+    const added = Object.entries(after)
+      .filter(([name]) => !(name in before))
+      .map(([name, version]) => `\`${name}@${version}\``);
+    const removed = Object.keys(before).filter((name) => !(name in after)).map((name) => `\`${name}\``);
+    const updated = Object.entries(after)
+      .filter(([name, version]) => name in before && before[name] !== version && !workspacePackages.includes(name))
+      .map(([name, version]) => `\`${name}\` ${before[name]} → ${version}`);
+
+    if (added.length > 0) lines.push(`- \`${change.filePath}\` adds ${added.join(', ')}`);
+    if (removed.length > 0) lines.push(`- \`${change.filePath}\` removes ${removed.join(', ')}`);
+    if (updated.length > 0) lines.push(`- \`${change.filePath}\` updates ${updated.join(', ')}`);
+  }
+
+  return lines.length === 0 ? [] : ['', 'Dependency changes:', ...lines];
+}
+
+// Files added by this pull request say how much of it is new surface rather than edits to code that
+// already had reviewers.
+function renderNewFiles(): string[] {
+  const newFiles = git(['diff', '--name-status', '--no-renames', mergeBase, headRevision])
+    .split('\n')
+    .filter((line) => line.startsWith('A\t'))
+    .map((line) => line.slice(2))
+    .filter((filePath) => kindOf(filePath) !== 'generated');
+  if (newFiles.length === 0) return [];
+
+  const shown = newFiles.slice(0, listedNewFiles).map((filePath) => `- \`${filePath}\``);
+  const hidden = newFiles.length > listedNewFiles ? [`- and ${newFiles.length - listedNewFiles} more`] : [];
+  return ['', `New files: ${newFiles.length}`, ...shown, ...hidden];
+}
+
+// Source changes to a published package usually deserve a line in the release notes.
+function renderReleaseNotesReminder(changes: FileChange[]): string[] {
+  const changesPublishedSource = changes
+    .some((change) => change.kind === 'source' && publishedAreas.includes(change.area));
+  const touchesReleaseNotes = changes.some((change) => change.filePath === releaseNotesPath);
+  if (!changesPublishedSource || touchesReleaseNotes) return [];
+
+  return ['', `Package source changed without an update to \`${releaseNotesPath}\`.`];
+}
+
+function requireRevisions(): [string, string] {
+  const [base, head] = process.argv.slice(2);
+  if (!base || !head) {
+    console.error('Usage: node .github/scripts/pr-stats.ts <base-revision> <head-revision>');
+    process.exit(1);
+  }
+  return [base, head];
+}
+
+// Version lines in files that hold a version are split off from the rest of the file's changes, so a release
+// bump does not read as dependency or source changes.
+function splitVersionLines(change: FileChange): FileChange[] {
+  if (!isVersionedFile(change.filePath)) return [change];
+
+  const changedLines = changedLinesOf(change.filePath);
+  const versionLines = changedLines.filter((line) => isVersionLine(line.slice(1)));
+  const otherLines = changedLines.filter((line) => !isVersionLine(line.slice(1)));
+
+  return [
+    { ...change, kind: 'version' as Kind, ...countLines(versionLines) },
+    { ...change, ...countLines(otherLines) },
+  ].filter((entry) => sizeOf(entry) > 0);
+}
+
+function isVersionedFile(filePath: string): boolean {
+  return ['package.json', 'lerna.json'].includes(baseName(filePath)) || filePath === versionConstantPath;
+}
+
+// A package's own version, a workspace package's version in a dependency list, or the compiler's version constant.
+function isVersionLine(line: string): boolean {
+  const workspaceDependency = workspacePackages.some((name) => line.trim().startsWith(`"${name}":`));
+  return /^\s*"version":/.test(line) || /^export const version = /.test(line) || workspaceDependency;
+}
+
+function countLines(changedLines: string[]): Churn {
+  return {
+    added: changedLines.filter((line) => line.startsWith('+')).length,
+    removed: changedLines.filter((line) => line.startsWith('-')).length,
+  };
+}
+
+// Parses the output of `git diff --numstat`, one "<added>\t<removed>\t<path>" line per file.
+// Binary files report "-" for both counts and are left out.
+function parseLineCounts(lineCounts: string): FileChange[] {
+  return lineCounts
+    .split('\n')
+    .filter((line) => line.trim() !== '')
+    .map((line) => {
+      const [added, removed, filePath] = line.split('\t');
+      return { filePath, area: areaOf(filePath), kind: kindOf(filePath), added: Number(added), removed: Number(removed) };
+    })
+    .filter((change) => Number.isInteger(change.added) && Number.isInteger(change.removed));
+}
+
+function areaOf(filePath: string): Area {
+  return areaRules.find((rule) => filePath.startsWith(rule.prefix))?.area ?? 'repository';
+}
+
+function kindOf(filePath: string): Kind {
+  return kindRules.find((rule) => rule.matches(filePath))?.kind ?? 'source';
+}
+
+// The ANTLR output next to the grammar is regenerated with `yarn antlr`, only the .g4 file is written by hand.
+function isGeneratedGrammar(filePath: string): boolean {
+  return filePath.startsWith('packages/cashc/src/grammar/') && !filePath.endsWith('.g4');
+}
+
+function baseName(filePath: string): string {
+  return filePath.slice(filePath.lastIndexOf('/') + 1);
+}
+
+function reviewable(changes: FileChange[]): FileChange[] {
+  return changes.filter((change) => !excludedFromTotal.includes(change.kind));
+}
+
+function churnOf(changes: FileChange[]): Churn {
+  return {
+    added: changes.reduce((sum, change) => sum + change.added, 0),
+    removed: changes.reduce((sum, change) => sum + change.removed, 0),
+  };
+}
+
+function sizeOf(churn: Churn): number {
+  return churn.added + churn.removed;
+}
+
+function formatChurn(churn: Churn): string {
+  return sizeOf(churn) === 0 ? '' : `+${churn.added} −${churn.removed}`;
+}
+
+function formatNet(churn: Churn): string {
+  const net = churn.added - churn.removed;
+  if (sizeOf(churn) === 0) return '';
+  if (net === 0) return '±0';
+  return net > 0 ? `+${net}` : `−${-net}`;
+}
+
+function formatPercentage(fraction: number): string {
+  if (fraction > 0 && fraction < 0.01) return '<1%';
+  return `${Math.round(fraction * 100)}%`;
+}
+
+// Lines carrying nothing but a comment, in both TypeScript and CashScript: the line form, and the opening,
+// body and closing of the block form, which this codebase writes with a leading asterisk.
+function isComment(line: string): boolean {
+  const trimmed = line.trim();
+  return trimmed.startsWith('//') || trimmed.startsWith('/*') || trimmed.startsWith('*');
+}
+
+function addedLinesOf(filePath: string): string[] {
+  return changedLinesOf(filePath).filter((line) => line.startsWith('+')).map((line) => line.slice(1));
+}
+
+// The added and removed lines of a file, each still carrying its "+" or "-" prefix. Without context lines,
+// everything after the file header is a hunk header or a changed line.
+function changedLinesOf(filePath: string): string[] {
+  const diffLines = git(['diff', '-U0', '--no-renames', mergeBase, headRevision, '--', filePath]).split('\n');
+  const firstHunk = diffLines.findIndex((line) => line.startsWith('@@'));
+  return firstHunk === -1 ? [] : diffLines.slice(firstHunk).filter((line) => /^[+-]/.test(line));
+}
+
+interface PackageManifest {
+  name?: string;
+  version?: string;
+  dependencies?: Record<string, string>;
+  devDependencies?: Record<string, string>;
+  peerDependencies?: Record<string, string>;
+}
+
+function declaredDependencies(content: string): Record<string, string> {
+  const manifest = packageManifest(content);
+  return { ...manifest.dependencies, ...manifest.devDependencies, ...manifest.peerDependencies };
+}
+
+// Returns an empty manifest for a missing or invalid package.json.
+function packageManifest(content: string): PackageManifest {
+  if (content === '') return {};
+  try {
+    return JSON.parse(content) as PackageManifest;
+  } catch {
+    return {};
+  }
+}
+
+function git(args: string[]): string {
+  return execFileSync('git', args, { encoding: 'utf8', maxBuffer: 64 * 1024 * 1024 });
+}
+
+// Returns an empty string when the file does not exist at that revision, which is the case on either side
+// of an addition or a deletion. Git reports that on stderr, which is silenced so it does not read as a failure.
+function fileAt(revision: string, filePath: string): string {
+  try {
+    return execFileSync('git', ['show', `${revision}:${filePath}`], {
+      encoding: 'utf8',
+      maxBuffer: 64 * 1024 * 1024,
+      stdio: ['ignore', 'pipe', 'ignore'],
+    });
+  } catch {
+    return '';
+  }
+}