Address review comments

Author: henrymercer

.github/workflows/pr-checks.yml

@@ -73,8 +73,8 @@ jobs:
 
   # These checks do not need to be run as part of the same matrix that we use for the `unit-tests`
   # job.
-  pr-checks:
-    name: PR Checks
+  other-checks:
+    name: Other checks
     if: github.triggering_actor != 'dependabot[bot]'
     permissions:
       contents: read
@@ -96,12 +96,15 @@ jobs:
           cache: 'npm'
 
       - name: Install dependencies
+        id: install-deps
         run: npm ci
 
       - name: Verify PR checks up to date
+        if: ${{ !cancelled() && steps.install-deps.outcome == 'success' }}
         run: .github/workflows/script/verify-pr-checks.sh
 
       - name: Run pr-checks tests
+        if: ${{ !cancelled() && steps.install-deps.outcome == 'success' }}
         working-directory: pr-checks
         run: npx tsx --test
 
@@ -117,6 +120,7 @@ jobs:
           echo "node_version=${NODE_VERSION}" >> $GITHUB_OUTPUT
 
       - name: Fetch base commit
+        id: fetch-base
         # Forks and Dependabot PRs don't have permission to write comments, so skip the repo size
         # check in those cases.
         if: >-
@@ -125,29 +129,28 @@ jobs:
           github.event.pull_request.user.login != 'dependabot[bot]'
         env:
           BASE_SHA: ${{ github.event.pull_request.base.sha }}
-        run: git fetch --no-tags --depth=1 origin "$BASE_SHA"
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          # Compare against the merge base so the size delta reflects only the commits actually
+          # added by this PR, ignoring any changes that have landed on the base branch since the
+          # PR branched off.
+          merge_base=$(gh api "repos/$GITHUB_REPOSITORY/compare/$BASE_SHA...$HEAD_SHA" --jq '.merge_base_commit.sha')
+          echo "merge_base=$merge_base" >> "$GITHUB_OUTPUT"
+          git fetch --no-tags --depth=1 origin "$merge_base" "$HEAD_SHA"
 
       - name: Check repo size
-        # Forks and Dependabot PRs don't have permission to write comments, so skip the repo size
-        # check in those cases.
-        if: >-
-          github.event_name == 'pull_request' &&
-          github.event.pull_request.head.repo.full_name == github.repository &&
-          github.event.pull_request.user.login != 'dependabot[bot]'
+        if: steps.fetch-base.outcome == 'success'
         working-directory: pr-checks
         env:
           BASE_REF: ${{ github.event.pull_request.base.ref }}
-          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          BASE_SHA: ${{ steps.fetch-base.outputs.merge_base }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
           RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
         run: npx tsx check-repo-size.ts --output-dir "$RUNNER_TEMP/repo-size"
 
       - name: Upload repo size comment
-        # Forks and Dependabot PRs don't have permission to write comments, so skip the repo size
-        # check in those cases.
-        if: >-
-          github.event_name == 'pull_request' &&
-          github.event.pull_request.head.repo.full_name == github.repository &&
-          github.event.pull_request.user.login != 'dependabot[bot]'
+        if: steps.fetch-base.outcome == 'success'
         uses: actions/upload-artifact@v7
         with:
           name: repo-size-comment
@@ -176,14 +179,14 @@ jobs:
 
   post-repo-size-comment:
     name: Post repo size comment
-    needs: pr-checks
+    needs: other-checks
     # Keep write permissions isolated from the job that checks out and tests PR code. This job only
     # posts the candidate comment body produced by the read-only `pr-checks` job.
     if: >-
       github.event_name == 'pull_request' &&
       github.event.pull_request.head.repo.full_name == github.repository &&
       github.event.pull_request.user.login != 'dependabot[bot]' &&
-      needs.pr-checks.result == 'success'
+      needs.other-checks.result == 'success'
     permissions:
       contents: read
       pull-requests: write
@@ -205,7 +208,6 @@ jobs:
         env:
           COMMENT_MARKER: "<!-- repo-size-diff-bot -->"
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          GITHUB_REPOSITORY: ${{ github.repository }}
           PR_NUMBER: ${{ github.event.pull_request.number }}
         run: |
           significant=$(jq -r '.significant' repo-size-comment/metadata.json)

pr-checks/check-repo-size.test.ts

@@ -25,24 +25,18 @@ import {
 
 describe("formatBytes", async () => {
   const cases: Array<[number, boolean, string]> = [
-    // Unsigned: bytes / KiB / MiB boundaries.
-    [0, false, "0 B"],
-    [1, false, "1 B"],
-    [1023, false, "1023 B"],
+    // Unsigned values, including sub-KiB amounts which round to 0.00.
+    [0, false, "0.00 KiB"],
+    [512, false, "0.50 KiB"],
     [1024, false, "1.00 KiB"],
-    [2048, false, "2.00 KiB"],
-    [1024 * 1024 - 1, false, "1024.00 KiB"],
-    [1024 * 1024, false, "1.00 MiB"],
-    [2.5 * 1024 * 1024, false, "2.50 MiB"],
+    [1024 * 1024, false, "1024.00 KiB"],
+    [2 * 1024 * 1024, false, "2048.00 KiB"],
     // Negative values always use a leading minus.
-    [-512, false, "-512 B"],
-    [-2048, false, "-2.00 KiB"],
-    [-2 * 1024 * 1024, false, "-2.00 MiB"],
+    [-2 * 1024 * 1024, false, "-2048.00 KiB"],
     // signed=true prepends a + to non-negative values.
-    [0, true, "+0 B"],
-    [512, true, "+512 B"],
-    [2048, true, "+2.00 KiB"],
-    [-512, true, "-512 B"],
+    [0, true, "+0.00 KiB"],
+    [2 * 1024 * 1024, true, "+2048.00 KiB"],
+    [-2 * 1024 * 1024, true, "-2048.00 KiB"],
   ];
   for (const [bytes, signed, expected] of cases) {
     await it(`formats ${bytes} (signed=${signed}) as ${expected}`, () => {
@@ -94,8 +88,8 @@ describe("buildCommentBody", async () => {
     });
 
     assert.match(body, new RegExp(`^${escapeRegExp(COMMENT_MARKER)}`));
-    assert.match(body, /Base \(`main`\) \| 1\.91 MiB \(2000000 bytes\)/);
-    assert.match(body, /This PR \| 2\.19 MiB \(2300000 bytes\)/);
+    assert.match(body, /Base \(`main`\) \| 1953\.13 KiB \(2000000 bytes\)/);
+    assert.match(body, /This PR \| 2246\.09 KiB \(2300000 bytes\)/);
     assert.match(
       body,
       /\*\*Delta\*\* \| \*\*\+292\.97 KiB \(\+300000 bytes, \+15\.00%\)\*\*/,
@@ -118,7 +112,7 @@ describe("buildCommentBody", async () => {
 });
 
 describe("readArgs", async () => {
-  await it("defaults the base ref for local runs", () => {
+  await it("defaults the base ref and head commit for local runs", () => {
     const originalEnv = process.env;
     const originalArgv = process.argv;
 
@@ -130,6 +124,7 @@ describe("readArgs", async () => {
 
       assert.equal(args.baseRef, DEFAULT_BASE_REF);
       assert.equal(args.baseCommitish, `origin/${DEFAULT_BASE_REF}`);
+      assert.equal(args.headCommitish, "HEAD");
       assert.equal(args.outputDir, "/tmp/out");
       assert.equal(args.runUrl, undefined);
     } finally {
@@ -138,14 +133,15 @@ describe("readArgs", async () => {
     }
   });
 
-  await it("uses the base SHA when provided by the workflow", () => {
+  await it("uses the base and head SHAs when provided by the workflow", () => {
     const originalEnv = process.env;
     const originalArgv = process.argv;
 
     try {
       process.env = {
         BASE_REF: "main",
         BASE_SHA: "abc123",
+        HEAD_SHA: "def456",
         RUN_URL: "https://example.test/run",
       };
       process.argv = ["node", "check-repo-size.ts", "--output-dir", "/tmp/out"];
@@ -154,6 +150,7 @@ describe("readArgs", async () => {
 
       assert.equal(args.baseRef, "main");
       assert.equal(args.baseCommitish, "abc123");
+      assert.equal(args.headCommitish, "def456");
       assert.equal(args.outputDir, "/tmp/out");
       assert.equal(args.runUrl, "https://example.test/run");
     } finally {

pr-checks/check-repo-size.ts

@@ -14,6 +14,10 @@ import * as fs from "node:fs";
 import * as path from "node:path";
 import { parseArgs } from "node:util";
 
+import { getErrorMessage } from "../src/util";
+
+import { REPO_ROOT } from "./config";
+
 /** Hidden marker used to find the existing sticky comment on a PR. */
 export const COMMENT_MARKER = "<!-- repo-size-diff-bot -->";
 
@@ -62,15 +66,13 @@ export async function measureArchiveSize(
 }
 
 /**
- * Format a byte count into a human-readable string with binary units. If `signed` is true, a
- * leading `+` is prepended for non-negative values so gains and losses are visually distinct.
+ * Format a byte count as KiB. If `signed` is true, a leading `+` is prepended for non-negative
+ * values so gains and losses are visually distinct.
  */
 export function formatBytes(bytes: number, signed = false): string {
   const sign = bytes < 0 ? "-" : signed ? "+" : "";
-  const abs = Math.abs(bytes);
-  if (abs < 1024) return `${sign}${abs} B`;
-  if (abs < 1024 * 1024) return `${sign}${(abs / 1024).toFixed(2)} KiB`;
-  return `${sign}${(abs / 1024 / 1024).toFixed(2)} MiB`;
+  const kib = Math.abs(bytes) / 1024;
+  return `${sign}${kib.toFixed(2)} KiB`;
 }
 
 /** Format a fraction as a signed percentage with 2 decimal places. */
@@ -131,6 +133,8 @@ interface MainArgs {
   baseRef: string;
   /** Base commit-ish to archive. Defaults to `origin/<baseRef>` for local runs. */
   baseCommitish: string;
+  /** Head commit-ish to archive. Defaults to `HEAD` for local runs. */
+  headCommitish: string;
   /** Optional URL of the workflow run, surfaced in the comment footer. */
   runUrl?: string;
   /** Directory where `body.md` and `metadata.json` are written. */
@@ -152,10 +156,12 @@ export function readArgs(): MainArgs {
 
   const baseRef = process.env.BASE_REF ?? DEFAULT_BASE_REF;
   const baseCommitish = process.env.BASE_SHA ?? `origin/${baseRef}`;
+  const headCommitish = process.env.HEAD_SHA ?? "HEAD";
 
   return {
     baseRef,
     baseCommitish,
+    headCommitish,
     runUrl: process.env.RUN_URL,
     outputDir,
   };
@@ -164,16 +170,12 @@ export function readArgs(): MainArgs {
 async function main(): Promise<number> {
   const args = readArgs();
 
-  // The script lives at `<repoRoot>/pr-checks/check-repo-size.ts`, so the repo root is the parent
-  // directory.
-  const repoRoot = path.resolve(__dirname, "..");
-
   console.log(`Measuring base archive size for ${args.baseCommitish}...`);
-  const baseSize = await measureArchiveSize(args.baseCommitish, repoRoot);
+  const baseSize = await measureArchiveSize(args.baseCommitish, REPO_ROOT);
   console.log(`  ${baseSize} bytes`);
 
-  console.log("Measuring PR archive size for HEAD...");
-  const prSize = await measureArchiveSize("HEAD", repoRoot);
+  console.log(`Measuring PR archive size for ${args.headCommitish}...`);
+  const prSize = await measureArchiveSize(args.headCommitish, REPO_ROOT);
   console.log(`  ${prSize} bytes`);
 
   const delta = prSize - baseSize;
@@ -209,13 +211,15 @@ async function main(): Promise<number> {
   return 0;
 }
 
+async function run(): Promise<void> {
+  try {
+    process.exit(await main());
+  } catch (err) {
+    console.error(getErrorMessage(err));
+    process.exit(1);
+  }
+}
+
 if (require.main === module) {
-  void (async () => {
-    try {
-      process.exit(await main());
-    } catch (err) {
-      console.error(err instanceof Error ? err.message : String(err));
-      process.exit(1);
-    }
-  })();
+  void run();
 }

pr-checks/config.ts

@@ -6,14 +6,17 @@ export const OLDEST_SUPPORTED_MAJOR_VERSION = 3;
 /** The `pr-checks` directory. */
 export const PR_CHECKS_DIR = __dirname;
 
+/** The repository root. */
+export const REPO_ROOT = path.join(PR_CHECKS_DIR, "..");
+
 /** The path of the file configuring which checks shouldn't be required. */
 export const PR_CHECK_EXCLUDED_FILE = path.join(PR_CHECKS_DIR, "excluded.yml");
 
 /** The path to the esbuild metadata file. */
-export const BUNDLE_METADATA_FILE = path.join(PR_CHECKS_DIR, "..", "meta.json");
+export const BUNDLE_METADATA_FILE = path.join(REPO_ROOT, "meta.json");
 
 /** The `src` directory. */
-const SOURCE_ROOT = path.join(PR_CHECKS_DIR, "..", "src");
+const SOURCE_ROOT = path.join(REPO_ROOT, "src");
 
 /** The path to the built-in languages file. */
 export const BUILTIN_LANGUAGES_FILE = path.join(