fix: enable copilot-local ESLint rules in PR CI

[benvillalobos]

🤖 AI Assisted PR

Problem

The Copilot ESLint plugin (.eslintplugin/) has two bugs that prevent copilot-local/* rules from running in PR CI:

Bug 1 — Plugin fails to load. index.ts uses import * as glob from 'glob' + glob.sync(). In the root ESLint's ESM context, the namespace import on CJS glob v5 gives { default: [function] } — no sync property. The plugin silently fails to load, registering zero rules.

Bug 2 — Rule checks absolute paths. no-unlayered-files.ts splits context.filename (an absolute path) and checks if ANY segment matches a layer name. Since vscode is both a valid layer name AND the repo checkout directory, every file's path matches → the rule never fires.

Impact

Since the root ESLint integration was added on April 28 (371c4a0a73c), no copilot-local/* rules have executed in PR CI. This includes no-unlayered-files, no-test-imports, no-runtime-import, and 8+ other custom rules.

On May 7, PR #314783 added a test file to the wrong folder. PR CI passed (copilot rules were dead). The ADO build caught it post-merge, causing 6 consecutive build failures across all platforms (~55 cascading task failures, 2-hour recovery window).

Data: Download Copilot VSIX is the #1 root-cause task in the 14-day OData dataset (81 of 479 root-cause failures). 68% of those were caused by Copilot Lint failures that escaped PR CI.

Fix

Two changes in extensions/copilot/.eslintplugin/:

1. index.ts — Replace glob.sync with fs.readdirSync

The glob package (v5, CJS) doesn't export sync as an ESM named export. fs.readdirSync is a Node.js built-in — zero external dependency, works in both CJS and ESM.

2. no-unlayered-files.ts — Use relative path

Strip the absolute path to be relative to extensions/copilot/ before checking for layer folders. This prevents the repo directory name (vscode) from being matched as a valid layer.

Verification

Local

# Create a misplaced file (same pattern as the May 7 incident)
echo "export const x = 1;" > extensions/copilot/src/platform/chat/test/repro.ts

# Before fix: no copilot-local warnings (plugin broken + path bug)
node build/eslint.ts  # → only header/semi errors, no copilot-local rules

# After fix: copilot-local/no-unlayered-files fires
node build/eslint.ts  # → "File should be inside a 'common, vscode, node...' folder"

Verified locally: bad files caught ✅, correctly layered files pass ✅, no regressions on existing codebase ✅

CI verification PRs (now closed)

PR	Fix?	Bad file?	CI result	ADO result
#316122 (closed)	✅ First fix only	✅	Passed — rule path bug prevented detection	N/A
#316123 (closed)	❌	✅	✅ Passed (the bug — CI doesn't catch it)	❌ Failed (build 438627) — 23 failed tasks, Copilot Lint caught it

PR #316123 + ADO build 438627 prove the current state: CI passes what ADO fails on. This PR closes that gap.

Root cause chain

1. Copilot extension migrated into vscode repo (~March 2026)
2. April 28: root eslint.config.js integrated Copilot ESLint plugin (371c4a0a73c)
3. Plugin's import * as glob doesn't work in ESM → plugin silently fails to load (Bug 1)
4. Even if loaded, no-unlayered-files checks absolute paths containing vscode dir → never fires (Bug 2)
5. May 7: misplaced file escapes CI → ADO Lint catches it post-merge → 6 builds fail → ~55 cascade task failures
6. May 8: PR Run copilot extension lint in PR CI #315368 added npm run lint step to Copilot CI jobs — but both bugs persist, so the step is ineffective

References

• ADO build failure (control): Build 438627 — Copilot Lint fails, 23 tasks cascade
• Original incident: PR Add support for per-turn ubb info #314783 (May 7) → builds 436972–436990
• CI lint step added: PR Run copilot extension lint in PR CI #315368 (May 8)
• Root ESLint integration: commit 371c4a0a73c (April 28)
• ESM/CJS interop proof: import * as glob from 'glob' → glob.sync is undefined (glob v5 is CJS, namespace import gives { default } only)

[Copilot]

Pull request overview

This PR fixes the Copilot local ESLint plugin’s rule discovery so that copilot-local/* rules actually load and run under the repo’s ESM-based ESLint configuration, restoring enforcement in PR CI.

Changes:

• Replace glob.sync('*.ts', …) with fs.readdirSync(…) to enumerate rule files without relying on CJS glob interop.
• Keep the existing filtering to exclude index.ts and utils.ts, and dynamically import each rule module.

Show a summary per file

File	Description
extensions/copilot/.eslintplugin/index.ts	Switches rule-file enumeration from glob.sync to fs.readdirSync to avoid ESM/CJS interop issues and ensure copilot-local/* rules load in ESLint.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0