feat(linter): Support --print-config feature of ESLint (#18260)

docs/generated/packages/linter/executors/eslint.json

@@ -128,6 +128,11 @@
         "type": "string",
         "enum": ["off", "warn", "error"],
         "description": "The equivalent of the `--report-unused-disable-directives` flag on the ESLint CLI."
+      },
+      "printConfig": {
+        "type": "string",
+        "description": "The equivalent of the `--print-config` flag on the ESLint CLI.",
+        "x-completion-type": "file"
       }
     },
     "required": ["lintFilePatterns"],

e2e/linter/src/linter.test.ts

@@ -246,6 +246,21 @@ describe('Linter', () => {
           'A project tagged with "validtag" can only depend on libs tagged with "validtag"'
         );
       }, 1000000);
+
+      it('should print the effective configuration for a file specified using --printConfig', () => {
+        const eslint = readJson('.eslintrc.json');
+        eslint.overrides.push({
+          files: ['src/index.ts'],
+          rules: {
+            'specific-rule': 'off',
+          },
+        });
+        updateFile('.eslintrc.json', JSON.stringify(eslint, null, 2));
+        const out = runCLI(`lint ${myapp} --printConfig src/index.ts`, {
+          silenceError: true,
+        });
+        expect(out).toContain('"specific-rule": [');
+      }, 1000000);
     });
 
     describe('workspace boundary rules', () => {

packages/linter/src/executors/eslint/lint.impl.spec.ts

@@ -25,6 +25,9 @@ class MockESLint {
   loadFormatter = mockLoadFormatter;
   isPathIgnored = mockIsPathIgnored;
   lintFiles = mockLintFiles;
+  calculateConfigForFile(file: string) {
+    return { file: file };
+  }
 }
 
 const mockResolveAndInstantiateESLint = jest.fn().mockReturnValue(
@@ -65,6 +68,7 @@ function createValidRunBuilderOptions(
     rulesdir: [],
     resolvePluginsRelativeTo: null,
     reportUnusedDisableDirectives: null,
+    printConfig: null,
     ...additionalOptions,
   };
 }
@@ -619,4 +623,30 @@ Please see https://nx.dev/guides/eslint for full guidance on how to resolve this
     );
     expect(fs.writeFileSync).not.toHaveBeenCalled();
   });
+
+  it('should print the ESLint configuration for a specified file if printConfiguration is specified', async () => {
+    setupMocks();
+    jest.spyOn(console, 'log');
+    const result = await lintExecutor(
+      createValidRunBuilderOptions({
+        lintFilePatterns: [],
+        eslintConfig: './.eslintrc.json',
+        fix: true,
+        cache: true,
+        cacheLocation: 'cacheLocation1',
+        format: 'stylish',
+        force: false,
+        silent: false,
+        ignorePath: null,
+        maxWarnings: null,
+        outputFile: null,
+        quiet: false,
+        reportUnusedDisableDirectives: null,
+        printConfig: 'test-source.ts',
+      }),
+      mockContext
+    );
+    expect(console.log).toHaveBeenCalledWith('{\n "file": "test-source.ts"\n}');
+    expect(result).toEqual({ success: true });
+  });
 });

packages/linter/src/executors/eslint/lint.impl.ts

@@ -39,6 +39,8 @@ export default async function run(
     ? join(options.cacheLocation, projectName)
     : undefined;
 
+  const { printConfig, ...normalizedOptions } = options;
+
   /**
    * Until ESLint v9 is released and the new so called flat config is the default
    * we only want to support it if the user has explicitly opted into it by converting
@@ -49,7 +51,7 @@ export default async function run(
   );
   const { eslint, ESLint } = await resolveAndInstantiateESLint(
     eslintConfigPath,
-    options,
+    normalizedOptions,
     useFlatConfig
   );
 
@@ -63,10 +65,25 @@ export default async function run(
     throw new Error('ESLint must be version 7.6 or higher.');
   }
 
+  if (printConfig) {
+    try {
+      const fileConfig = await eslint.calculateConfigForFile(printConfig);
+      console.log(JSON.stringify(fileConfig, null, ' '));
+      return {
+        success: true,
+      };
+    } catch (err) {
+      console.error(err);
+      return {
+        success: false,
+      };
+    }
+  }
+
   let lintResults: ESLint.LintResult[] = [];
 
   try {
-    lintResults = await eslint.lintFiles(options.lintFilePatterns);
+    lintResults = await eslint.lintFiles(normalizedOptions.lintFilePatterns);
   } catch (err) {
     if (
       err.message.includes(
@@ -98,7 +115,7 @@ Please see https://nx.dev/guides/eslint for full guidance on how to resolve this
   if (lintResults.length === 0) {
     const ignoredPatterns = (
       await Promise.all(
-        options.lintFilePatterns.map(async (pattern) =>
+        normalizedOptions.lintFilePatterns.map(async (pattern) =>
           (await eslint.isPathIgnored(pattern)) ? pattern : null
         )
       )
@@ -121,12 +138,12 @@ Please see https://nx.dev/guides/eslint for full guidance on how to resolve this
   await ESLint.outputFixes(lintResults);
 
   // if quiet, only show errors
-  if (options.quiet) {
+  if (normalizedOptions.quiet) {
     console.debug('Quiet mode enabled - filtering out warnings\n');
     lintResults = ESLint.getErrorResults(lintResults);
   }
 
-  const formatter = await eslint.loadFormatter(options.format);
+  const formatter = await eslint.loadFormatter(normalizedOptions.format);
 
   let totalErrors = 0;
   let totalWarnings = 0;
@@ -140,8 +157,8 @@ Please see https://nx.dev/guides/eslint for full guidance on how to resolve this
 
   const formattedResults = await formatter.format(lintResults);
 
-  if (options.outputFile) {
+  if (normalizedOptions.outputFile) {
-    const pathToOutputFile = join(context.root, options.outputFile);
+    const pathToOutputFile = join(context.root, normalizedOptions.outputFile);
     mkdirSync(dirname(pathToOutputFile), { recursive: true });
     writeFileSync(pathToOutputFile, formattedResults);
   } else {
@@ -162,8 +179,9 @@ Please see https://nx.dev/guides/eslint for full guidance on how to resolve this
 
   return {
     success:
-      options.force ||
+      normalizedOptions.force ||
       (totalErrors === 0 &&
-        (options.maxWarnings === -1 || totalWarnings <= options.maxWarnings)),
+        (normalizedOptions.maxWarnings === -1 ||
+          totalWarnings <= normalizedOptions.maxWarnings)),
   };
 }

packages/linter/src/executors/eslint/schema.d.ts

@@ -20,6 +20,7 @@ export interface Schema extends JsonObject {
   rulesdir: string[];
   resolvePluginsRelativeTo: string | null;
   reportUnusedDisableDirectives: Linter.RuleLevel | null;
+  printConfig?: string | null;
 }
 
 type Formatter =

packages/linter/src/executors/eslint/schema.json

@@ -132,6 +132,11 @@
       "type": "string",
       "enum": ["off", "warn", "error"],
       "description": "The equivalent of the `--report-unused-disable-directives` flag on the ESLint CLI."
+    },
+    "printConfig": {
+      "type": "string",
+      "description": "The equivalent of the `--print-config` flag on the ESLint CLI.",
+      "x-completion-type": "file"
     }
   },
   "required": ["lintFilePatterns"],