Merge pull request #4217 from github/mario-campos/warn-on-changelog-write

Add `post-comment` Action

.github/actions/post-comment/action.yml

@@ -0,0 +1,41 @@
+name: "Post comment"
+description: "Create or update a sticky PR comment identified by a caller-provided marker."
+inputs:
+  marker:
+    description: >
+      Non-empty plain-text identifier for the comment. Use a unique, stable value
+      for each distinct comment; it is automatically wrapped in a hidden HTML comment.
+    required: true
+  body:
+    description: "Full comment markdown."
+    required: true
+  update-only:
+    description: Do nothing if no comment with the specified marker exists.
+    required: false
+    default: "false"
+  issue-id:
+    description: >
+      The issue or pull request number to post/update the comment on.
+      Defaults to the current pull request if not provided.
+    required: false
+  token:
+    description: "The GitHub token to authenticate with."
+    required: true
+runs:
+  using: composite
+  steps:
+    - name: Post comment
+      shell: bash
+      env:
+        BODY: ${{ inputs.body }}
+        MARKER: ${{ inputs.marker }}
+        UPDATE_ONLY: ${{ case(inputs.update-only == 'true', '--update-only', '') }}
+        GH_TOKEN: ${{ inputs.token }}
+        ISSUE_ID: ${{ inputs.issue-id || github.event.pull_request.number }}
+      run: |
+        npx tsx ./pr-checks/post-comment.ts \
+          --body "$BODY" \
+          --marker "$MARKER" \
+          $UPDATE_ONLY \
+          --issue-id "$ISSUE_ID" \
+          --repository "$GITHUB_REPOSITORY"

.github/actions/prepare-test/action.yml

@@ -36,7 +36,14 @@ runs:
         set -e # Fail this Action if `gh release list` fails.
 
         if [[ "$VERSION" == "nightly" || "$VERSION" == "nightly-latest" ]]; then
-          echo "tools-url=nightly" >> "$GITHUB_OUTPUT"
+          if [[ "$USE_ALL_PLATFORM_BUNDLE" == "true" ]]; then
+            # With `tools: nightly`, the Action downloads the bundle for the runner's platform, so look
+            # up the latest nightly release here to get its all-platform bundle instead.
+            tag=$(gh release list --repo dsp-testing/codeql-cli-nightlies --limit 1 --json tagName --jq '.[0].tagName')
+            echo "tools-url=https://github.com/dsp-testing/codeql-cli-nightlies/releases/download/$tag/codeql-bundle.tar.gz" >> "$GITHUB_OUTPUT"
+          else
+            echo "tools-url=nightly" >> "$GITHUB_OUTPUT"
+          fi
           exit 0
         elif [[ "$VERSION" == "linked" ]]; then
           echo "tools-url=linked" >> "$GITHUB_OUTPUT"

.github/codeql/codeql-config-actions.yml

@@ -1,5 +0,0 @@
-paths-ignore:
-  - lib
-  - tests
-queries:
-  - uses: security-and-quality

.github/workflows/__all-platform-bundle.yml

@@ -92,6 +92,18 @@ jobs:
           # Swift is not supported on Ubuntu so we manually exclude it from the list here
           languages: cpp,csharp,go,java,javascript,python,ruby
           tools: ${{ steps.prepare-test.outputs.tools-url }}
+      - name: Check that the bundle contains tools for all platforms
+        env:
+          CODEQL_PATH: ${{ steps.init.outputs.codeql-path }}
+        run: |
+          # Platform-specific bundles only contain the tools for their own platform.
+          tools_dir="$(dirname "$CODEQL_PATH")/tools"
+          for platform in linux64 osx64 win64; do
+            if [[ ! -d "$tools_dir/$platform" ]]; then
+              echo "::error::Expected an all-platform CodeQL bundle, but '$tools_dir' does not contain a '$platform' directory."
+              exit 1
+            fi
+          done
       - name: Build code
         run: ./build.sh
       - uses: ./../action/analyze

.github/workflows/__linux-arm64.yml

@@ -3,7 +3,7 @@
 #     pr-checks/sync.sh
 # to regenerate this file.
 
-name: PR Check - Runner images
+name: PR Check - Linux Arm64
 env:
   GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
   GO111MODULE: auto
@@ -47,38 +47,16 @@ defaults:
     shell: bash
 concurrency:
   cancel-in-progress: ${{ github.event_name == 'pull_request' || false }}
-  group: runner-images-${{github.ref}}-${{inputs.dotnet-version}}-${{inputs.go-version}}
+  group: linux-arm64-${{github.ref}}-${{inputs.dotnet-version}}-${{inputs.go-version}}
 jobs:
-  runner-images:
+  linux-arm64:
     strategy:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-22.04
-            version: linked
-          - os: ubuntu-22.04-arm
-            version: linked
-          - os: ubuntu-24.04
-            version: linked
           - os: ubuntu-24.04-arm
-            version: linked
-          - os: ubuntu-26.04
-            version: linked
-          - os: ubuntu-26.04-arm
-            version: linked
-          - os: windows-2022
-            version: linked
-          - os: windows-2025
-            version: linked
-          - os: macos-15-large
-            version: linked
-          - os: macos-15-xlarge
-            version: linked
-          - os: macos-26-large
-            version: linked
-          - os: macos-26-xlarge
-            version: linked
-    name: Runner images
+            version: nightly-latest
+    name: Linux Arm64
     if: github.triggering_actor != 'dependabot[bot]'
     permissions:
       contents: read
@@ -124,5 +102,5 @@ jobs:
             echo "Found database for $lang"
           done
     env:
-      LANGUAGES: cpp,csharp,go,java,javascript,python,ruby${{ startsWith(matrix.os, 'macos') && ',swift' || '' }}
+      LANGUAGES: cpp,csharp,go,java,javascript,python,ruby
       CODEQL_ACTION_TEST_MODE: true

.github/workflows/codeql.yml

@@ -19,16 +19,69 @@ env:
   CODEQL_ACTION_TESTING_ENVIRONMENT: codeql-action-pr-checks
 
 jobs:
-  analyze:
+  # Identify the CodeQL tool versions to use in the analysis job.
+  check-codeql-versions:
     if: github.triggering_actor != 'dependabot[bot]'
     runs-on: ubuntu-26.04
+    outputs:
+      versions: ${{ steps.compare.outputs.versions }}
 
+    permissions:
+      contents: read
+      # We currently need `security-events: read` to access feature flags.
+      security-events: read
+
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Set up default CodeQL bundle
+        id: setup-default
+        uses: ./setup-codeql
+      - name: Set up linked CodeQL bundle
+        id: setup-linked
+        uses: ./setup-codeql
+        with:
+          tools: linked
+      - name: Compare default and linked CodeQL bundle versions
+        id: compare
+        env:
+          CODEQL_DEFAULT: ${{ steps.setup-default.outputs.codeql-path }}
+          CODEQL_LINKED: ${{ steps.setup-linked.outputs.codeql-path }}
+        run: |
+          CODEQL_VERSION_DEFAULT="$("$CODEQL_DEFAULT" version --format terse)"
+          CODEQL_VERSION_LINKED="$("$CODEQL_LINKED" version --format terse)"
+          echo "Default CodeQL bundle version is $CODEQL_VERSION_DEFAULT"
+          echo "Linked CodeQL bundle version is $CODEQL_VERSION_LINKED"
+
+          # If we're running on a pull request, run with both bundles, even if `tools: linked` would
+          # be the same as `tools: null`. This allows us to make the job for each of the bundles a
+          # required status check.
+          #
+          # If we're running on push or schedule, then we can skip running with `tools: linked` when it would be
+          # the same as running with `tools: null`.
+          if [[ "$GITHUB_EVENT_NAME" != "pull_request" && "$GITHUB_EVENT_NAME" != "merge_group" && "$CODEQL_VERSION_DEFAULT" == "$CODEQL_VERSION_LINKED" ]]; then
+            VERSIONS_JSON='[null]'
+          else
+            VERSIONS_JSON='[null, "linked"]'
+          fi
+
+          # Output a JSON-encoded list with the distinct versions to test against.
+          echo "Suggested matrix config for analysis job: $VERSIONS_JSON"
+          echo "versions=${VERSIONS_JSON}" >> $GITHUB_OUTPUT
+
+  analyze-javascript:
+    if: github.triggering_actor != 'dependabot[bot]'
+    needs: [check-codeql-versions]
     strategy:
       fail-fast: false
       matrix:
-        language:
-          - actions
-          - javascript
+        os:
+          - ubuntu-22.04
+          - ubuntu-24.04
+          - windows-2022
+          - windows-2025
+          - macos-15-xlarge
+        tools: ${{ fromJson(needs.check-codeql-versions.outputs.versions) }}
+    runs-on: ${{ matrix.os }}
 
     permissions:
       contents: read
@@ -41,15 +94,49 @@ jobs:
         uses: ./init
         id: init
         with:
-          languages: ${{ matrix.language }}
-          build-mode: none
-          config-file: ./.github/codeql/codeql-config-${{ matrix.language }}.yml
+          languages: javascript
+          config-file: ./.github/codeql/codeql-config-javascript.yml
+          tools: ${{ matrix.tools }}
       # confirm steps.init.outputs.codeql-path points to the codeql binary
       - name: Print CodeQL Version
         run: >
           "$CODEQL" version --format=json
         env:
           CODEQL: ${{steps.init.outputs.codeql-path}}
+      - name: Perform CodeQL Analysis
+        uses: ./analyze
+        with:
+          category: "/language:javascript"
+          upload: ${{ (matrix.os == 'ubuntu-24.04' && !matrix.tools && github.event_name != 'merge_group' && 'always' ) || 'never' }}
+
+  analyze-other:
+    if: github.triggering_actor != 'dependabot[bot]'
+    runs-on: ubuntu-26.04
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - language: actions
+
+    permissions:
+      contents: read
+      security-events: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Initialize CodeQL
+        uses: ./init
+        with:
+          languages: ${{ matrix.language }}
+          build-mode: none
+          config: >
+            paths-ignore:
+              - lib
+              - tests
+            queries:
+              - uses: security-and-quality
       - name: Perform CodeQL Analysis
         uses: ./analyze
         with:

.github/workflows/deflake.yml

@@ -31,7 +31,6 @@ on:
       - "PR Check - C/C\\+\\+: autoinstalling dependencies is skipped (macOS)"
       - "PR Check - C/C\\+\\+: disabling autoinstalling dependencies (Linux)"
       - "PR Check - Clean up database cluster directory"
-      - "PR Check - CodeQL Bundle All"
       - "PR Check - Config export"
       - "PR Check - Config input"
       - "PR Check - Custom source root"
@@ -61,7 +60,6 @@ on:
       - "PR Check - Remote config file"
       - "PR Check - Resolve environment"
       - "PR Check - Ruby analysis"
-      - "PR Check - Runner images"
       - "PR Check - Rust analysis"
       - "PR Check - Split workflow"
       - "PR Check - Start proxy"

.github/workflows/test-codeql-bundle-all.yml

@@ -1,62 +0,0 @@
-name: "PR Check - CodeQL Bundle All"
-env:
-  GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-  GO111MODULE: auto
-on:
-  push:
-    branches:
-      - main
-      - releases/v*
-  pull_request:
-  merge_group:
-    types: [checks_requested]
-  schedule:
-    - cron: "0 5 * * *"
-  workflow_dispatch:
-
-concurrency:
-  cancel-in-progress: ${{ github.event_name == 'pull_request' || false }}
-  group: ${{ github.workflow }}-${{ github.ref }}
-
-defaults:
-  run:
-    shell: bash
-jobs:
-  test-codeql-bundle-all:
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - os: ubuntu-26.04
-            version: nightly-latest
-    name: "CodeQL Bundle All"
-    if: github.triggering_actor != 'dependabot[bot]'
-    permissions:
-      contents: read
-      security-events: read
-    timeout-minutes: 45
-    runs-on: ${{ matrix.os }}
-    steps:
-      - name: Check out repository
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-      - name: Prepare test
-        id: prepare-test
-        uses: ./.github/actions/prepare-test
-        with:
-          version: ${{ matrix.version }}
-          use-all-platform-bundle: true
-      - name: Install .NET
-        uses: actions/setup-dotnet@a98b56852c35b8e3190ac28c8c2271da59106c68 # v6.0.0
-        with:
-          dotnet-version: "9.x"
-      - id: init
-        uses: ./../action/init
-        with:
-          # We manually exclude Swift from the languages list here, as it is not supported on Ubuntu
-          languages: cpp,csharp,go,java,javascript,python,ruby
-          tools: ${{ steps.prepare-test.outputs.tools-url }}
-      - name: Build code
-        run: ./build.sh
-      - uses: ./../action/analyze
-    env:
-      CODEQL_ACTION_TEST_MODE: true

pr-checks/api-client.ts

@@ -8,3 +8,14 @@ export function getApiClient(token: string): ApiClient {
   const opts = githubUtils.getOctokitOptions(token);
   return new githubUtils.GitHub(opts);
 }
+
+/** Resolves the GitHub API token to use, from `GH_TOKEN` or `GITHUB_TOKEN`. */
+export function resolveToken(env: NodeJS.ProcessEnv): string {
+  const token = env.GH_TOKEN?.trim() || env.GITHUB_TOKEN?.trim();
+  if (!token) {
+    throw new Error(
+      "Missing authentication token. Set GH_TOKEN or GITHUB_TOKEN.",
+    );
+  }
+  return token;
+}

pr-checks/checks/all-platform-bundle.yml

@@ -17,6 +17,18 @@ steps:
       # Swift is not supported on Ubuntu so we manually exclude it from the list here
       languages: cpp,csharp,go,java,javascript,python,ruby
       tools: ${{ steps.prepare-test.outputs.tools-url }}
+  - name: Check that the bundle contains tools for all platforms
+    env:
+      CODEQL_PATH: ${{ steps.init.outputs.codeql-path }}
+    run: |
+      # Platform-specific bundles only contain the tools for their own platform.
+      tools_dir="$(dirname "$CODEQL_PATH")/tools"
+      for platform in linux64 osx64 win64; do
+        if [[ ! -d "$tools_dir/$platform" ]]; then
+          echo "::error::Expected an all-platform CodeQL bundle, but '$tools_dir' does not contain a '$platform' directory."
+          exit 1
+        fi
+      done
   - name: Build code
     run: ./build.sh
   - uses: ./../action/analyze

pr-checks/checks/linux-arm64.yml

@@ -0,0 +1,35 @@
+name: "Linux Arm64"
+description: "An end-to-end integration test running on a Linux Arm64 runner, checking that the native linux-arm64 CodeQL bundle is downloaded and can analyze interpreted and compiled code"
+operatingSystems:
+  - os: ubuntu
+    runner-image: ubuntu-24.04-arm
+# The native linux-arm64 CodeQL bundle is only available in recent CLI releases, so we restrict this
+# check to `nightly-latest`, which is guaranteed to ship it. Older stable versions do not have an
+# arm64 asset, and `prepare-test` would resolve an x64 bundle URL for them on this runner.
+versions:
+  - nightly-latest
+installGo: true
+installDotNet: true
+# The set of languages CodeQL supports on this platform, excluding Swift (macOS only).
+env:
+  LANGUAGES: cpp,csharp,go,java,javascript,python,ruby
+steps:
+  - uses: ./../action/init
+    with:
+      languages: ${{ env.LANGUAGES }}
+      tools: ${{ steps.prepare-test.outputs.tools-url }}
+  - name: Build code
+    run: ./build.sh
+  - uses: ./../action/analyze
+    with:
+      upload-database: false
+  - name: Assert databases exist
+    run: |
+      cd "$RUNNER_TEMP/codeql_databases"
+      for lang in ${LANGUAGES//,/ }; do
+        if [[ ! -d "$lang" ]]; then
+          echo "Did not find a database for $lang"
+          exit 1
+        fi
+        echo "Found database for $lang"
+      done

pr-checks/checks/runner-images.yml

@@ -1,66 +0,0 @@
-name: "Runner images"
-description: "An end-to-end integration test checking that CodeQL can analyze interpreted and compiled code on the GitHub-hosted runner images"
-# This check runs on each image listed in
-# https://github.com/actions/runner-images#available-images, except for:
-# - `ubuntu-slim`, which is intended for lightweight jobs rather than builds like this one.
-# - `windows-11-arm`, since CodeQL doesn't support Windows on Arm64.
-# - `xcode-27`, a preview image that the `unsupported-macos` check runs on.
-operatingSystems:
-  # The Ubuntu 22.04 images have brownouts from 23 March 2027 and are retired on 17 April 2027, so
-  # remove them before the brownouts start.
-  # See https://github.com/actions/runner-images/issues/14254.
-  - os: ubuntu
-    runner-image: ubuntu-22.04
-  - os: ubuntu
-    runner-image: ubuntu-22.04-arm
-  - os: ubuntu
-    runner-image: ubuntu-24.04
-  - os: ubuntu
-    runner-image: ubuntu-24.04-arm
-  - os: ubuntu
-    runner-image: ubuntu-26.04
-  - os: ubuntu
-    runner-image: ubuntu-26.04-arm
-  - os: windows
-    runner-image: windows-2022
-  - os: windows
-    runner-image: windows-2025
-  # Use larger runners for macOS to keep these jobs off the critical path.
-  - os: macos
-    runner-image: macos-15-large
-  - os: macos
-    runner-image: macos-15-xlarge
-  - os: macos
-    runner-image: macos-26-large
-  - os: macos
-    runner-image: macos-26-xlarge
-# Other PR checks cover the supported CodeQL versions, so this check only tests the linked version.
-# Linux Arm64 bundles are only available for CodeQL 2.27.0 and later, so older stable versions
-# can't run on the Arm64 images.
-versions:
-  - linked
-installGo: true
-installDotNet: true
-# The languages to build and analyze. CodeQL only supports Swift on macOS.
-env:
-  LANGUAGES: "cpp,csharp,go,java,javascript,python,ruby${{ startsWith(matrix.os, 'macos') && ',swift' || '' }}"
-steps:
-  - uses: ./../action/init
-    with:
-      languages: ${{ env.LANGUAGES }}
-      tools: ${{ steps.prepare-test.outputs.tools-url }}
-  - name: Build code
-    run: ./build.sh
-  - uses: ./../action/analyze
-    with:
-      upload-database: false
-  - name: Assert databases exist
-    run: |
-      cd "$RUNNER_TEMP/codeql_databases"
-      for lang in ${LANGUAGES//,/ }; do
-        if [[ ! -d "$lang" ]]; then
-          echo "Did not find a database for $lang"
-          exit 1
-        fi
-        echo "Found database for $lang"
-      done

pr-checks/post-comment.test.ts

@@ -0,0 +1,344 @@
+#!/usr/bin/env npx tsx
+
+/*
+Tests for post-comment.ts.
+*/
+
+import * as assert from "node:assert/strict";
+import { describe, it } from "node:test";
+
+import { type ApiClient, resolveToken } from "./api-client";
+import {
+  findExistingComment,
+  type Options,
+  parseOptions,
+  setComment,
+} from "./post-comment";
+
+/** A baseline set of valid CLI flags, as an array, for use in parseOptions tests. */
+const validFlags = [
+  "--body",
+  "hello",
+  "--marker",
+  "marker",
+  "--issue-id",
+  "42",
+  "--repository",
+  "github/codeql-action",
+];
+
+/** Returns a copy of `validFlags` with the value following `flag` replaced by `value`. */
+function withFlag(flag: string, value: string): string[] {
+  const flags = [...validFlags];
+  const index = flags.indexOf(flag);
+  flags[index + 1] = value;
+  return flags;
+}
+
+/** Returns a copy of `validFlags` with `flag` (and its value) removed entirely. */
+function withoutFlag(flag: string): string[] {
+  const flags = [...validFlags];
+  const index = flags.indexOf(flag);
+  flags.splice(index, 2);
+  return flags;
+}
+
+describe("parseOptions", async () => {
+  await it("parses valid flags", () => {
+    const options = parseOptions(validFlags);
+    assert.deepEqual(options, {
+      body: "hello",
+      marker: "marker",
+      updateOnly: false,
+      issueId: 42,
+      repository: { owner: "github", repo: "codeql-action" },
+    });
+  });
+
+  await it("enables update-only mode when --update-only is supplied", () => {
+    const options = parseOptions([...validFlags, "--update-only"]);
+    assert.equal(options.updateOnly, true);
+  });
+
+  await it("rejects a missing --body", () => {
+    assert.throws(
+      () => parseOptions(withoutFlag("--body")),
+      /Missing required flag --body/,
+    );
+  });
+
+  await it("rejects an empty --body", () => {
+    assert.throws(
+      () => parseOptions(withFlag("--body", "")),
+      /The value for --body cannot be empty/,
+    );
+  });
+
+  await it("rejects a whitespace-only --body", () => {
+    assert.throws(
+      () => parseOptions(withFlag("--body", " \t\n")),
+      /The value for --body cannot be empty/,
+    );
+  });
+
+  await it("rejects a missing --marker", () => {
+    assert.throws(
+      () => parseOptions(withoutFlag("--marker")),
+      /Missing required flag --marker/,
+    );
+  });
+
+  await it("rejects an empty --marker", () => {
+    assert.throws(
+      () => parseOptions(withFlag("--marker", "")),
+      /The value for --marker cannot be empty/,
+    );
+  });
+
+  await it("rejects a whitespace-only --marker", () => {
+    assert.throws(
+      () => parseOptions(withFlag("--marker", " \t\n")),
+      /The value for --marker cannot be empty/,
+    );
+  });
+
+  await it("rejects a missing --repository", () => {
+    assert.throws(
+      () => parseOptions(withoutFlag("--repository")),
+      /Missing required flag --repository/,
+    );
+  });
+
+  await it("rejects an empty --repository", () => {
+    assert.throws(
+      () => parseOptions(withFlag("--repository", "")),
+      /The value for --repository cannot be empty/,
+    );
+  });
+
+  await it("rejects a whitespace-only --repository", () => {
+    assert.throws(
+      () => parseOptions(withFlag("--repository", " \t\n")),
+      /The value for --repository cannot be empty/,
+    );
+  });
+
+  await it("rejects an invalid --repository value", () => {
+    assert.throws(
+      () => parseOptions(withFlag("--repository", "github/codeql/action")),
+      /Invalid --repository value/,
+    );
+  });
+});
+
+describe("resolveToken", async () => {
+  await it("reads the token from GH_TOKEN", () => {
+    assert.equal(
+      resolveToken({ GH_TOKEN: "gh-token", GITHUB_TOKEN: "gha-token" }),
+      "gh-token",
+    );
+  });
+
+  await it("falls back to GITHUB_TOKEN", () => {
+    assert.equal(resolveToken({ GITHUB_TOKEN: "gha-token" }), "gha-token");
+  });
+
+  await it("throws when no token is set", () => {
+    assert.throws(() => resolveToken({}), /Missing authentication token/);
+  });
+});
+
+/** A minimal fake of the subset of `ApiClient` used by post-comment.ts. */
+function fakeClient(existingComments: Array<{ id: number; body?: string }>) {
+  const comments = existingComments.map((comment) => ({ ...comment }));
+  let nextId =
+    comments.reduce((maxId, comment) => Math.max(maxId, comment.id), 0) + 1;
+
+  const client = {
+    paginate: async () => comments,
+    rest: {
+      issues: {
+        listComments: () => {},
+        createComment: async ({ body }: { body: string }) => {
+          comments.push({ id: nextId++, body });
+        },
+        updateComment: async ({
+          comment_id,
+          body,
+        }: {
+          comment_id: number;
+          body: string;
+        }) => {
+          const comment = comments.find(({ id }) => id === comment_id);
+          assert.ok(comment, `Comment ${comment_id} does not exist.`);
+          comment.body = body;
+        },
+      },
+    },
+  };
+
+  return { client: client as unknown as ApiClient, comments };
+}
+
+describe("findExistingComment", async () => {
+  await it("finds the id of the first comment containing the marker", async () => {
+    const { client } = fakeClient([
+      { id: 1, body: "unrelated" },
+      { id: 2, body: "<!-- marker -->\nhello" },
+      { id: 3, body: "<!-- marker -->\nanother" },
+    ]);
+    const id = await findExistingComment(
+      client,
+      { owner: "owner", repo: "repo" },
+      1,
+      "marker",
+    );
+    assert.equal(id, 3);
+  });
+
+  await it("returns undefined when no comment matches", async () => {
+    const { client } = fakeClient([{ id: 1, body: "unrelated" }]);
+    const id = await findExistingComment(
+      client,
+      { owner: "owner", repo: "repo" },
+      1,
+      "marker",
+    );
+    assert.equal(id, undefined);
+  });
+});
+
+/** A baseline set of `Options`, for use in `setComment` tests. */
+const baseOptions: Options = {
+  body: "hello",
+  marker: "marker",
+  updateOnly: false,
+  issueId: 42,
+  repository: { owner: "owner", repo: "repo" },
+};
+
+function assertCommentContent(
+  comment: { body?: string },
+  marker: string,
+  body: string,
+): void {
+  assert.ok(comment.body?.startsWith(`<!-- ${marker} -->`));
+  assert.ok(comment.body?.endsWith(body));
+}
+
+describe("setComment", async () => {
+  await it("does not create a comment in update-only mode when none exists", async () => {
+    const { client, comments } = fakeClient([]);
+
+    await setComment(client, { ...baseOptions, updateOnly: true });
+
+    // Resolution does not introduce a warning that was never posted.
+    assert.deepEqual(comments, []);
+  });
+
+  await it("leaves unrelated comments unchanged in update-only mode", async () => {
+    const originalComments = [{ id: 7, body: "unrelated" }];
+    const { client, comments } = fakeClient(originalComments);
+
+    await setComment(client, { ...baseOptions, updateOnly: true });
+
+    // Unrelated comments neither trigger resolution nor get overwritten.
+    assert.deepEqual(comments, originalComments);
+  });
+
+  await it("uses the supplied marker without affecting other comments", async () => {
+    const marker = "custom-warning";
+    const { client, comments } = fakeClient([
+      { id: 1, body: "<!-- marker -->\nunrelated warning" },
+      { id: 2, body: "<!-- custom-warning -->\nold warning" },
+    ]);
+    const options = parseOptions(withFlag("--marker", marker));
+
+    await setComment(client, options);
+
+    // Only the comment with the supplied marker changes.
+    assert.equal(comments.length, 2);
+    assert.deepEqual(comments[0], {
+      id: 1,
+      body: "<!-- marker -->\nunrelated warning",
+    });
+    assert.equal(comments[1].id, 2);
+    assertCommentContent(comments[1], marker, options.body);
+  });
+
+  await it("creates a new comment with the marker prepended", async () => {
+    const { client, comments } = fakeClient([]);
+    // No comment has the marker before posting.
+    assert.equal(comments.length, 0);
+    assert.ok(
+      !comments.some(({ body }) => body?.startsWith("<!-- marker -->")),
+    );
+
+    await setComment(client, baseOptions);
+
+    // Posting adds exactly one comment with the marker before the body.
+    assert.equal(comments.length, 1);
+    assertCommentContent(comments[0], baseOptions.marker, baseOptions.body);
+  });
+
+  await it("creates a new comment when no existing comment matches", async () => {
+    const originalComments = [
+      { id: 7, body: "unrelated" },
+      { id: 2, body: "another unrelated comment" },
+    ];
+    const { client, comments } = fakeClient(originalComments);
+    // Existing comments do not match the marker.
+    assert.ok(
+      !comments.some(({ body }) => body?.startsWith("<!-- marker -->")),
+    );
+
+    await setComment(client, baseOptions);
+
+    // A new comment is added without changing unrelated comments.
+    assert.equal(comments.length, originalComments.length + 1);
+    assert.deepEqual(
+      comments.slice(0, originalComments.length),
+      originalComments,
+    );
+    const markedComments = comments.filter(({ body }) =>
+      body?.startsWith("<!-- marker -->"),
+    );
+    // Exactly one comment contains the expected marker and body.
+    assert.equal(markedComments.length, 1);
+    assertCommentContent(
+      markedComments[0],
+      baseOptions.marker,
+      baseOptions.body,
+    );
+    // The new comment's ID does not collide with existing IDs.
+    assert.equal(new Set(comments.map(({ id }) => id)).size, comments.length);
+  });
+
+  await it("updates the existing comment when one is found", async () => {
+    const { client, comments } = fakeClient([
+      { id: 7, body: "<!-- marker -->\nold" },
+    ]);
+
+    await setComment(client, baseOptions);
+
+    // Updating preserves the comment's ID without creating a duplicate.
+    assert.equal(comments.length, 1);
+    assert.equal(comments[0].id, 7);
+    assertCommentContent(comments[0], baseOptions.marker, baseOptions.body);
+  });
+
+  await it("replaces a warning with the resolved state using the same marker", async () => {
+    const { client, comments } = fakeClient([
+      { id: 9, body: "<!-- marker -->\nold" },
+    ]);
+    const body =
+      "`CHANGELOG.md` is not modified in this PR. No changelog action is needed.";
+
+    await setComment(client, { ...baseOptions, body, updateOnly: true });
+
+    // The resolved state replaces the warning on the same marked comment.
+    assert.equal(comments.length, 1);
+    assert.equal(comments[0].id, 9);
+    assertCommentContent(comments[0], baseOptions.marker, body);
+  });
+});

pr-checks/post-comment.ts

@@ -0,0 +1,180 @@
+#!/usr/bin/env npx tsx
+
+/*
+Creates or updates a pull-request comment identified by a marker.
+
+The marker is supplied via `--marker` and must be a non-empty plain-text identifier.
+The CLI wraps the marker in a hidden HTML comment, prepends it to `--body`,
+and uses it to find the comment on later runs.
+
+Supply `--update-only` to suppress creation of comment; omit it
+to update or create comments.
+
+Example:
+```sh
+GH_TOKEN=<token> npx tsx ./pr-checks/post-comment.ts \
+  --body "The changelog needs updating." \
+  --marker "my-bot" \
+  --issue-id 123 \
+  --repository github/codeql-action
+```
+*/
+
+import assert from "node:assert/strict";
+import { parseArgs } from "node:util";
+
+import { parseRepositoryNwo, type RepositoryNwo } from "../src/repository";
+
+import { type ApiClient, getApiClient, resolveToken } from "./api-client";
+
+/** Represents the command-line options. */
+export interface Options {
+  /** The full comment body. */
+  body: string;
+  /** Plain-text identifier wrapped in a hidden HTML comment. */
+  marker: string;
+  /** Whether to only update a comment if a matching marker exists. */
+  updateOnly: boolean;
+  /** The issue/pull request number to post/update the comment on. */
+  issueId: number;
+  /** The repository to operate on. */
+  repository: RepositoryNwo;
+}
+
+function hiddenMarker(marker: string): string {
+  return `<!-- ${marker} -->`;
+}
+
+/** Parses CLI arguments supplied by the composite action into `Options`. */
+export function parseOptions(argv?: string[]): Options {
+  const { values } = parseArgs({
+    args: argv,
+    options: {
+      body: { type: "string" },
+      marker: { type: "string" },
+      "update-only": { type: "boolean", default: false },
+      "issue-id": { type: "string" },
+      repository: { type: "string" },
+    },
+    strict: true,
+  });
+
+  assert(values.body !== undefined, "Missing required flag --body.");
+  assert(values.body.trim() !== "", "The value for --body cannot be empty.");
+  assert(values.marker !== undefined, "Missing required flag --marker.");
+  assert(
+    values.marker.trim() !== "",
+    "The value for --marker cannot be empty.",
+  );
+  assert(
+    values.repository !== undefined,
+    "Missing required flag --repository.",
+  );
+  assert(
+    values.repository.trim() !== "",
+    "The value for --repository cannot be empty.",
+  );
+  assert(
+    /^[\w.-]+\/[\w.-]+$/.test(values.repository),
+    "Invalid --repository value.",
+  );
+
+  return {
+    body: values.body,
+    marker: values.marker,
+    updateOnly: values["update-only"],
+    issueId: Number(values["issue-id"]),
+    repository: parseRepositoryNwo(values.repository),
+  };
+}
+
+/**
+ * Finds the first comment on the given issue/pull request whose body starts with `marker`, if any.
+ */
+export async function findExistingComment(
+  client: ApiClient,
+  repository: RepositoryNwo,
+  issueNumber: number,
+  marker: string,
+): Promise<number | undefined> {
+  const formattedMarker = hiddenMarker(marker);
+  const comments = await client.paginate(client.rest.issues.listComments, {
+    ...repository,
+    issue_number: issueNumber,
+    per_page: 100,
+  });
+  const markedComments = comments.filter((comment) =>
+    comment.body?.startsWith(formattedMarker),
+  );
+  if (markedComments.length > 1) {
+    console.warn(
+      `Found ${markedComments.length} comments with marker "${formattedMarker}". ` +
+        "Updating the first one and leaving the others unchanged. " +
+        "Use a unique marker for each distinct managed comment to avoid this situation.",
+    );
+  }
+  return markedComments.at(-1)?.id;
+}
+
+/**
+ * Creates or updates a marked comment using `client` to talk to the GitHub API.
+ */
+export async function setComment(
+  client: ApiClient,
+  options: Options,
+): Promise<void> {
+  const { issueId, marker, repository } = options;
+  const body = `${hiddenMarker(marker)}\n${options.body}`;
+
+  const existingCommentId = await findExistingComment(
+    client,
+    repository,
+    issueId,
+    marker,
+  );
+  if (existingCommentId === undefined) {
+    if (options.updateOnly) {
+      console.info(
+        "No existing comment found; skipping creation because --update-only was specified.",
+      );
+      return;
+    }
+    console.info("No existing comment found; creating a new comment.");
+    await client.rest.issues.createComment({
+      ...repository,
+      issue_number: issueId,
+      body,
+    });
+  } else {
+    console.info(`Updating existing comment ${existingCommentId}.`);
+    await client.rest.issues.updateComment({
+      ...repository,
+      comment_id: existingCommentId,
+      body,
+    });
+  }
+}
+
+async function main(): Promise<number> {
+  const options = parseOptions();
+
+  const token = resolveToken(process.env);
+  const client = getApiClient(token);
+
+  await setComment(client, options);
+
+  return 0;
+}
+
+async function run(): Promise<void> {
+  try {
+    process.exit(await main());
+  } catch (err) {
+    console.error(err instanceof Error ? err.message : String(err));
+    process.exit(1);
+  }
+}
+
+if (import.meta.main) {
+  void run();
+}