feat(experimental-utils): expose our RuleTester extension

There are a few things we've built in (like automatically adding a filename) that others might find value in.
Plus I want to use it in the internal plugin.

packages/eslint-plugin-internal/tests/RuleTester.ts

@@ -1,22 +1,10 @@
-import { TSESLint, ESLintUtils } from '@typescript-eslint/experimental-utils';
+import { ESLintUtils } from '@typescript-eslint/experimental-utils';
+import path from 'path';
 
-const { batchedSingleLineTests } = ESLintUtils;
-
-const parser = '@typescript-eslint/parser';
-
-type RuleTesterConfig = Omit<TSESLint.RuleTesterConfig, 'parser'> & {
-  parser: typeof parser;
-};
-class RuleTester extends TSESLint.RuleTester {
-  // as of eslint 6 you have to provide an absolute path to the parser
-  // but that's not as clean to type, this saves us trying to manually enforce
-  // that contributors require.resolve everything
-  constructor(options: RuleTesterConfig) {
-    super({
-      ...options,
-      parser: require.resolve(options.parser),
-    });
-  }
+function getFixturesRootDir(): string {
+  return path.join(__dirname, 'fixtures');
 }
 
-export { RuleTester, batchedSingleLineTests };
+const { batchedSingleLineTests, RuleTester } = ESLintUtils;
+
+export { RuleTester, batchedSingleLineTests, getFixturesRootDir };

packages/eslint-plugin/tests/RuleTester.ts

@@ -1,104 +1,10 @@
-import { TSESLint, ESLintUtils } from '@typescript-eslint/experimental-utils';
-import { clearCaches } from '@typescript-eslint/parser';
+import { ESLintUtils } from '@typescript-eslint/experimental-utils';
 import * as path from 'path';
 
-const parser = '@typescript-eslint/parser';
-
-type RuleTesterConfig = Omit<TSESLint.RuleTesterConfig, 'parser'> & {
-  parser: typeof parser;
-};
-class RuleTester extends TSESLint.RuleTester {
-  // as of eslint 6 you have to provide an absolute path to the parser
-  // but that's not as clean to type, this saves us trying to manually enforce
-  // that contributors require.resolve everything
-  constructor(private readonly options: RuleTesterConfig) {
-    super({
-      ...options,
-      parser: require.resolve(options.parser),
-    });
-  }
-  private getFilename(options?: TSESLint.ParserOptions): string {
-    if (options) {
-      const filename = `file.ts${
-        options.ecmaFeatures && options.ecmaFeatures.jsx ? 'x' : ''
-      }`;
-      if (options.project) {
-        return path.join(getFixturesRootDir(), filename);
-      }
-
-      return filename;
-    } else if (this.options.parserOptions) {
-      return this.getFilename(this.options.parserOptions);
-    }
-
-    return 'file.ts';
-  }
-
-  // as of eslint 6 you have to provide an absolute path to the parser
-  // If you don't do that at the test level, the test will fail somewhat cryptically...
-  // This is a lot more explicit
-  run<TMessageIds extends string, TOptions extends Readonly<unknown[]>>(
-    name: string,
-    rule: TSESLint.RuleModule<TMessageIds, TOptions>,
-    tests: TSESLint.RunTests<TMessageIds, TOptions>,
-  ): void {
-    const errorMessage = `Do not set the parser at the test level unless you want to use a parser other than ${parser}`;
-
-    // standardize the valid tests as objects
-    tests.valid = tests.valid.map(test => {
-      if (typeof test === 'string') {
-        return {
-          code: test,
-        };
-      }
-      return test;
-    });
-
-    tests.valid.forEach(test => {
-      if (typeof test !== 'string') {
-        if (test.parser === parser) {
-          throw new Error(errorMessage);
-        }
-        if (!test.filename) {
-          test.filename = this.getFilename(test.parserOptions);
-        }
-      }
-    });
-    tests.invalid.forEach(test => {
-      if (test.parser === parser) {
-        throw new Error(errorMessage);
-      }
-      if (!test.filename) {
-        test.filename = this.getFilename(test.parserOptions);
-      }
-    });
-
-    super.run(name, rule, tests);
-  }
-}
-
 function getFixturesRootDir(): string {
-  return path.join(process.cwd(), 'tests/fixtures/');
+  return path.join(__dirname, 'fixtures');
 }
 
-const { batchedSingleLineTests } = ESLintUtils;
-
-// make sure that the parser doesn't hold onto file handles between tests
-// on linux (i.e. our CI env), there can be very a limited number of watch handles available
-afterAll(() => {
-  clearCaches();
-});
-
-/**
- * Simple no-op tag to mark code samples as "should not format with prettier"
- *   for the internal/plugin-test-formatting lint rule
- */
-function noFormat(strings: TemplateStringsArray, ...keys: string[]): string {
-  const lastIndex = strings.length - 1;
-  return (
-    strings.slice(0, lastIndex).reduce((p, s, i) => p + s + keys[i], '') +
-    strings[lastIndex]
-  );
-}
+const { batchedSingleLineTests, RuleTester, noFormat } = ESLintUtils;
 
 export { batchedSingleLineTests, getFixturesRootDir, noFormat, RuleTester };

packages/experimental-utils/src/eslint-utils/RuleTester.ts

@@ -0,0 +1,109 @@
+import * as TSESLint from '../ts-eslint';
+import * as path from 'path';
+
+const parser = '@typescript-eslint/parser';
+
+type RuleTesterConfig = Omit<TSESLint.RuleTesterConfig, 'parser'> & {
+  parser: typeof parser;
+};
+
+class RuleTester extends TSESLint.RuleTester {
+  // as of eslint 6 you have to provide an absolute path to the parser
+  // but that's not as clean to type, this saves us trying to manually enforce
+  // that contributors require.resolve everything
+  constructor(private readonly options: RuleTesterConfig) {
+    super({
+      ...options,
+      parser: require.resolve(options.parser),
+    });
+
+    // make sure that the parser doesn't hold onto file handles between tests
+    // on linux (i.e. our CI env), there can be very a limited number of watch handles available
+    afterAll(() => {
+      try {
+        // instead of creating a hard dependency, just use a soft require
+        // a bit weird, but if they're using this tooling, it'll be installed
+        require(parser).clearCaches();
+      } catch {
+        // ignored
+      }
+    });
+  }
+  private getFilename(options?: TSESLint.ParserOptions): string {
+    if (options) {
+      const filename = `file.ts${
+        options.ecmaFeatures && options.ecmaFeatures.jsx ? 'x' : ''
+      }`;
+      if (options.project) {
+        return path.join(
+          options.tsconfigRootDir != null
+            ? options.tsconfigRootDir
+            : process.cwd(),
+          filename,
+        );
+      }
+
+      return filename;
+    } else if (this.options.parserOptions) {
+      return this.getFilename(this.options.parserOptions);
+    }
+
+    return 'file.ts';
+  }
+
+  // as of eslint 6 you have to provide an absolute path to the parser
+  // If you don't do that at the test level, the test will fail somewhat cryptically...
+  // This is a lot more explicit
+  run<TMessageIds extends string, TOptions extends Readonly<unknown[]>>(
+    name: string,
+    rule: TSESLint.RuleModule<TMessageIds, TOptions>,
+    tests: TSESLint.RunTests<TMessageIds, TOptions>,
+  ): void {
+    const errorMessage = `Do not set the parser at the test level unless you want to use a parser other than ${parser}`;
+
+    // standardize the valid tests as objects
+    tests.valid = tests.valid.map(test => {
+      if (typeof test === 'string') {
+        return {
+          code: test,
+        };
+      }
+      return test;
+    });
+
+    tests.valid.forEach(test => {
+      if (typeof test !== 'string') {
+        if (test.parser === parser) {
+          throw new Error(errorMessage);
+        }
+        if (!test.filename) {
+          test.filename = this.getFilename(test.parserOptions);
+        }
+      }
+    });
+    tests.invalid.forEach(test => {
+      if (test.parser === parser) {
+        throw new Error(errorMessage);
+      }
+      if (!test.filename) {
+        test.filename = this.getFilename(test.parserOptions);
+      }
+    });
+
+    super.run(name, rule, tests);
+  }
+}
+
+/**
+ * Simple no-op tag to mark code samples as "should not format with prettier"
+ *   for the internal/plugin-test-formatting lint rule
+ */
+function noFormat(strings: TemplateStringsArray, ...keys: string[]): string {
+  const lastIndex = strings.length - 1;
+  return (
+    strings.slice(0, lastIndex).reduce((p, s, i) => p + s + keys[i], '') +
+    strings[lastIndex]
+  );
+}
+
+export { noFormat, RuleTester };

packages/experimental-utils/src/eslint-utils/index.ts

@@ -2,4 +2,5 @@ export * from './applyDefault';
 export * from './batchedSingleLineTests';
 export * from './getParserServices';
 export * from './RuleCreator';
+export * from './RuleTester';
 export * from './deepMerge';