fix: [rush] Parse pnpm-config.json with JsonSyntax.JsonWithComments (#5820)

Co-authored-by: Bart van den Ende <bartvandenende-wm@users.noreply.github.com>

Author: bartvandenende-wm

common/changes/@microsoft/rush/fix-pnpm-config-jsonc_2026-06-06-09-15.json

@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "comment": "Fix a regression where Rush change-detection treated any `pnpm-config.json` containing comments as unparseable, causing every project to be flagged as impacted.",
+      "type": "patch",
+      "packageName": "@microsoft/rush"
+    }
+  ],
+  "packageName": "@microsoft/rush",
+  "email": "bartvandenende-wm@users.noreply.github.com"
+}

libraries/rush-lib/src/logic/ProjectChangeAnalyzer.ts

@@ -6,7 +6,7 @@ import * as path from 'node:path';
 import ignore, { type Ignore } from 'ignore';
 
 import type { IReadonlyLookupByPath, LookupByPath, IPrefixMatch } from '@rushstack/lookup-by-path';
-import { Path, FileSystem, Async, AlreadyReportedError, Sort } from '@rushstack/node-core-library';
+import { Path, FileSystem, Async, AlreadyReportedError, Sort, JsonFile } from '@rushstack/node-core-library';
 import {
   getRepoChanges,
   getRepoRoot,
@@ -545,16 +545,16 @@ export class ProjectChangeAnalyzer {
         blobSpec: `${mergeCommit}:${pnpmConfigRelativePath}`,
         repositoryRoot: repoRoot
       });
-      const oldPnpmConfig: IPnpmOptionsJson = JSON.parse(oldPnpmConfigText);
+      const oldPnpmConfig: IPnpmOptionsJson = JsonFile.parseString(oldPnpmConfigText);
       oldCatalogs = oldPnpmConfig.globalCatalogs ?? {};
     } catch {
       // Old file didn't exist or was unparseable — treat all packages in all current catalogs as changed
       if (rushConfiguration.subspacesFeatureEnabled) {
-        terminal.writeLine(
+        terminal.writeWarningLine(
           `"${subspace.subspaceName}" subspace pnpm-config.json was created or unparseable. Assuming all projects are affected.`
         );
       } else {
-        terminal.writeLine(
+        terminal.writeWarningLine(
           `pnpm-config.json was created or unparseable. Assuming all projects are affected.`
         );
       }
@@ -608,8 +608,7 @@ export class ProjectChangeAnalyzer {
       // Check each project in the subspace to see if it depends on a changed catalog package
       const subspaceProjects: RushConfigurationProject[] = subspace.getProjects();
       subspaceProjects.forEach((project) => {
-        const { dependencies, devDependencies, optionalDependencies, peerDependencies } =
-          project.packageJson;
+        const { dependencies, devDependencies, optionalDependencies, peerDependencies } = project.packageJson;
         const allDependencies: Set<[string, string]> = new Set(
           [dependencies, devDependencies, optionalDependencies, peerDependencies].flatMap((deps) =>
             Object.entries(deps ?? {})

libraries/rush-lib/src/logic/test/ProjectChangeAnalyzer.test.ts

@@ -842,6 +842,35 @@ describe(ProjectChangeAnalyzer.name, () => {
         // 'c' has no catalog deps
         expect(changedProjects.has(rushConfiguration.getProjectByName('c')!)).toBe(false);
       });
+
+      it('parses pnpm-config.json blobs containing comments (regression #5813)', async () => {
+        const rushConfiguration: RushConfiguration = getCatalogRushConfiguration();
+        mockPnpmConfigChanged();
+        mockGetBlobContentAsync.mockImplementation(() => {
+          return Promise.resolve(
+            `// banner comment from rush init template\n` +
+              `/* block comment */\n` +
+              JSON.stringify({
+                globalCatalogs: {
+                  default: { react: '^18.0.0', semver: '^7.5.4' },
+                  tools: { typescript: '~5.3.0', eslint: '^8.50.0' }
+                }
+              })
+          );
+        });
+
+        const projectChangeAnalyzer: ProjectChangeAnalyzer = new ProjectChangeAnalyzer(rushConfiguration);
+        const terminal: Terminal = new Terminal(new StringBufferTerminalProvider(true));
+
+        const changedProjects = await projectChangeAnalyzer.getChangedProjectsAsync({
+          enableFiltering: false,
+          includeExternalDependencies: false,
+          targetBranchName: 'main',
+          terminal
+        });
+
+        expect(changedProjects.size).toBe(0);
+      });
     });
 
     describe('subspace catalog change detection', () => {