collect telemetry for ESLint rules (#34564)

This commit adds functionality to track usage of `@next/next/*` ESLint rules and their severity levels.

## Bug

- [ ] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Documentation added
- [x] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

packages/next/lib/eslint/runLintCheck.ts

@@ -25,6 +25,14 @@ type Config = {
   rules: { [key: string]: Array<number | string> }
 }
 
+// 0 is off, 1 is warn, 2 is error. See https://eslint.org/docs/user-guide/configuring/rules#configuring-rules
+const VALID_SEVERITY = ['off', 'warn', 'error'] as const
+type Severity = typeof VALID_SEVERITY[number]
+
+function isValidSeverity(severity: string): severity is Severity {
+  return VALID_SEVERITY.includes(severity as Severity)
+}
+
 const requiredPackages = [
   { file: 'eslint', pkg: 'eslint' },
   { file: 'eslint-config-next', pkg: 'eslint-config-next' },
@@ -126,6 +134,7 @@ async function lint(
     let eslint = new ESLint(options)
 
     let nextEslintPluginIsEnabled = false
+    const nextRulesEnabled = new Map<string, Severity>()
     const pagesDirRules = ['@next/next/no-html-link-for-pages']
 
     for (const configFile of [eslintrcFile, pkgJsonPath]) {
@@ -137,6 +146,23 @@ async function lint(
 
       if (completeConfig.plugins?.includes('@next/next')) {
         nextEslintPluginIsEnabled = true
+        for (const [name, [severity]] of Object.entries(completeConfig.rules)) {
+          if (!name.startsWith('@next/next/')) {
+            continue
+          }
+          if (
+            typeof severity === 'number' &&
+            severity >= 0 &&
+            severity < VALID_SEVERITY.length
+          ) {
+            nextRulesEnabled.set(name, VALID_SEVERITY[severity])
+          } else if (
+            typeof severity === 'string' &&
+            isValidSeverity(severity)
+          ) {
+            nextRulesEnabled.set(name, severity)
+          }
+        }
         break
       }
     }
@@ -210,6 +236,7 @@ async function lint(
         nextEslintPluginErrorsCount: formattedResult.totalNextPluginErrorCount,
         nextEslintPluginWarningsCount:
           formattedResult.totalNextPluginWarningCount,
+        nextRulesEnabled: Object.fromEntries(nextRulesEnabled),
       },
     }
   } catch (err) {

packages/next/telemetry/events/build.ts

@@ -34,6 +34,9 @@ export type EventLintCheckCompleted = {
   nextEslintPluginVersion?: string | null
   nextEslintPluginErrorsCount?: number
   nextEslintPluginWarningsCount?: number
+  nextRulesEnabled: {
+    [ruleName: `@next/next/${string}`]: 'off' | 'warn' | 'error'
+  }
 }
 
 export function eventLintCheckCompleted(event: EventLintCheckCompleted): {

test/integration/telemetry/test/index.test.js

@@ -529,7 +529,7 @@ describe('Telemetry CLI', () => {
     })
     await fs.remove(path.join(appDir, '.eslintrc'))
 
-    const event1 = /NEXT_LINT_CHECK_COMPLETED[\s\S]+?{([\s\S]+?)}/
+    const event1 = /NEXT_LINT_CHECK_COMPLETED[\s\S]+?{([\s\S}]+?)^}/m
       .exec(stderr)
       .pop()
 
@@ -541,6 +541,8 @@ describe('Telemetry CLI', () => {
     expect(event1).toMatch(/"nextEslintPluginVersion": ".*?\..*?\..*?"/)
     expect(event1).toMatch(/"nextEslintPluginErrorsCount": \d{1,}/)
     expect(event1).toMatch(/"nextEslintPluginWarningsCount": \d{1,}/)
+    expect(event1).toMatch(`"nextRulesEnabled": {`)
+    expect(event1).toMatch(/"@next\/next\/.+?": "(off|warn|error)"/)
 
     const event2 = /NEXT_BUILD_FEATURE_USAGE[\s\S]+?{([\s\S]+?)}/
       .exec(stderr)
@@ -594,7 +596,7 @@ describe('Telemetry CLI', () => {
     })
     await fs.remove(path.join(appDir, '.eslintrc'))
 
-    const event1 = /NEXT_LINT_CHECK_COMPLETED[\s\S]+?{([\s\S]+?)}/
+    const event1 = /NEXT_LINT_CHECK_COMPLETED[\s\S]+?{([\s\S]+?)^}/m
       .exec(stderr)
       .pop()
 
@@ -606,6 +608,8 @@ describe('Telemetry CLI', () => {
     expect(event1).toMatch(/"nextEslintPluginVersion": ".*?\..*?\..*?"/)
     expect(event1).toMatch(/"nextEslintPluginErrorsCount": \d{1,}/)
     expect(event1).toMatch(/"nextEslintPluginWarningsCount": \d{1,}/)
+    expect(event1).toMatch(`"nextRulesEnabled": {`)
+    expect(event1).toMatch(/"@next\/next\/.+?": "(off|warn|error)"/)
   })
 
   it('emits telemery for usage of image, script & dynamic', async () => {