RFC: Do not set a default ecmaVersion or sourceType

README.md

@@ -66,6 +66,10 @@ $ npm install [email protected] babel-eslint@6 --save-dev
 ```json
 {
   "parser": "babel-eslint",
+  "parserOptions": {
+    "ecmaVersion": 8,
+    "sourceType": "module"
+  },
   "rules": {
     "strict": 0
   }
@@ -76,19 +80,42 @@ Check out the [ESLint docs](http://eslint.org/docs/rules/) for all possible rule
 
 ### Configuration
 
-`sourceType` can be set to `'module'`(default) or `'script'` if your code isn't using ECMAScript modules.
-`allowImportExportEverywhere` can be set to true to allow import and export declarations to appear anywhere a statement is allowed if your build environment supports that. By default, import and export declarations can only appear at a program's top level.
-`codeFrame` can be set to false to disable the code frame in the reporter. This is useful since some eslint formatters don't play well with it.
+* `sourceType`, `ecmaVersion`, `ecmaFeatures.globalReturn` and `ecmaFeatures.impliedStrict` should be set in accordance with http://eslint.org/docs/user-guide/configuring#specifying-parser-options.
+  - `ecmaVersion` is disregarded by `babel-eslint`, however, some ESlint rules depend on this value being set correctly.
+  - If `sourceType` is not set to `"module"`, then using `import`/`export` will error.
+* `allowImportExportEverywhere` (default `false`) can be set to `true` to allow import and export declarations to appear anywhere a statement is allowed if your build environment supports that. By default, import and export declarations can only appear at a program's top level.
+* `allowSuperOutsideMethod` (default `true`) can be set to `false` to disallow use of `super` outside of methods. **Note:** Babel's default is `false`.
+* `codeFrame` can be set to false to disable the code frame in the reporter. This is useful since some ESlint formatters don't play well with it.
 
-**.eslintrc**
+#### `.eslintrc`
+
+**Recommended:**
+
+```json
+{
+  "parser": "babel-eslint",
+  "parserOptions": {
+    "ecmaVersion": 8,
+    "sourceType": "module"
+  }
+}
+```
+
+**Defaults:**
 
 ```json
 {
   "parser": "babel-eslint",
   "parserOptions": {
-    "sourceType": "module",
+    "ecmaVersion": 5,
+    "sourceType": "script",
+    "ecmaFeatures": {
+      "globalReturn": false,
+      "impliedStrict": false
+    },
     "allowImportExportEverywhere": false,
-    "codeFrame": false
+    "allowSuperOutsideMethod": true,
+    "codeFrame": true
   }
 }
 ```

index.js

@@ -8,7 +8,6 @@ var traverse        = require("babel-traverse").default;
 var codeFrame       = require("babel-code-frame");
 
 var hasPatched = false;
-var eslintOptions = {};
 
 function createModule(filename) {
   var mod = new Module(filename);
@@ -49,12 +48,6 @@ function monkeypatch() {
   var escope  = require(escopeLoc);
   var analyze = escope.analyze;
   escope.analyze = function (ast, opts) {
-    opts.ecmaVersion = eslintOptions.ecmaVersion;
-    opts.sourceType = eslintOptions.sourceType;
-    if (eslintOptions.globalReturn !== undefined) {
-      opts.nodejsScope = eslintOptions.globalReturn;
-    }
-
     var results = analyze.call(this, ast, opts);
     return results;
   };
@@ -358,33 +351,23 @@ function monkeypatch() {
 }
 
 exports.parse = function (code, options) {
-  options = options || {};
-  eslintOptions.ecmaVersion = options.ecmaVersion = options.ecmaVersion || 6;
-  eslintOptions.sourceType = options.sourceType = options.sourceType || "module";
-  eslintOptions.allowImportExportEverywhere = options.allowImportExportEverywhere = options.allowImportExportEverywhere || false;
-  if (options.sourceType === "module") {
-    eslintOptions.globalReturn = false;
-  } else {
-    delete eslintOptions.globalReturn;
-  }
-
   try {
     monkeypatch();
   } catch (err) {
     console.error(err.stack);
     process.exit(1);
   }
-
-  return exports.parseNoPatch(code, options);
+  return exports.parseNoPatch(code, options || {});
 };
 
 exports.parseNoPatch = function (code, options) {
+  // Some ESlint APIs (like `getScope()`) and some rules change behavior based
+  // on the values of "ecmaVersion", "sourceType", "globalReturn" and
+  // "impliedStrict" as specified in "parserOptions". For this reason, no
+  // defaults are set that differ from ESlint's own defaults.
   var opts = {
-    codeFrame: options.hasOwnProperty("codeFrame") ? options.codeFrame : true,
+    codeFrame: "codeFrame" in options ? options.codeFrame : true,
     sourceType: options.sourceType,
-    allowImportExportEverywhere: options.allowImportExportEverywhere, // consistent with espree
-    allowReturnOutsideFunction: true,
-    allowSuperOutsideMethod: true,
     plugins: [
       "flow",
       "jsx",
@@ -401,7 +384,19 @@ exports.parseNoPatch = function (code, options) {
       "objectRestSpread",
       "trailingFunctionCommas",
       "dynamicImport"
-    ]
+    ],
+    // espree configurable via "parserOptions":
+    allowReturnOutsideFunction:
+      options.ecmaFeatures &&
+      options.ecmaFeatures.globalReturn || false,
+    strictMode:
+      options.ecmaFeatures &&
+      options.ecmaFeatures.impliedStrict || false,
+    // defaults consistent with espree behavior:
+    allowImportExportEverywhere:
+      options.allowImportExportEverywhere || false,
+    allowSuperOutsideMethod: "allowSuperOutsideMethod" in options ?
+      options.allowSuperOutsideMethod : true,
   };
 
   var ast;

test/babel-eslint.js

@@ -40,8 +40,8 @@ function lookup(obj, keypath, backwardsDepth) {
   .reduce((base, segment) => { return base && base[segment], obj; });
 }
 
-function parseAndAssertSame(code) {
-  var esAST = espree.parse(code, {
+function parseAndAssertSame(code, captureParseErrors) {
+  var options = {
     ecmaFeatures: {
         // enable JSX parsing
       jsx: true,
@@ -59,8 +59,27 @@ function parseAndAssertSame(code) {
     attachComment: true,
     ecmaVersion: 8,
     sourceType: "module"
-  });
-  var babylonAST = babelEslint.parse(code);
+  };
+  var errors = { espree: null, babylon: null };
+  try {
+    var esAST = espree.parse(code, options);
+    errors.espree = false;
+  } catch (err) {
+    errors.espree = err;
+  }
+  try {
+    var babylonAST = babelEslint.parse(code, options);
+    errors.babylon = false;
+  } catch (err) {
+    errors.babylon = err;
+  }
+  if (captureParseErrors) {
+    return errors;
+  } else if (errors.espree) {
+    throw errors.espree;
+  } else if (errors.babylon) {
+    throw errors.babylon;
+  }
   try {
     assertImplementsAST(esAST, babylonAST);
   } catch (err) {
@@ -416,10 +435,18 @@ describe("babylon-to-esprima", () => {
       );
     });
 
-    it("do not allow import export everywhere", () => {
+    it("do not allow import export everywhere (espree)", () => {
+      assert.throws(() => {
+        var errors = parseAndAssertSame("function F() { import a from \"a\"; }", true);
+        throw errors.espree;
+      }, /'import' and 'export' may only appear at the top level/);
+    });
+
+    it("do not allow import export everywhere (babylon)", () => {
       assert.throws(() => {
-        parseAndAssertSame("function F() { import a from \"a\"; }");
-      }, /SyntaxError: 'import' and 'export' may only appear at the top level/);
+        var errors = parseAndAssertSame("function F() { import a from \"a\"; }", true);
+        throw errors.babylon;
+      }, /'import' and 'export' may only appear at the top level/);
     });
 
     it("return outside function", () => {

test/non-regression.js

@@ -18,7 +18,7 @@ function verifyAndAssertMessages(code, rules, expectedMessages, sourceType, over
         experimentalObjectRestSpread: true,
         globalReturn: true
       },
-      sourceType
+      sourceType: sourceType || "module"
     }
   };
 
@@ -1566,7 +1566,7 @@ describe("verify", () => {
     verifyAndAssertMessages(
       "var leakedGlobal = 1;",
       { "no-implicit-globals": 1 },
-      [],
+      [ "1:5 Implicit global variable, assign as global property instead. no-implicit-globals" ],
       null,
       {
         env: {},
@@ -1575,23 +1575,6 @@ describe("verify", () => {
     );
   });
 
-  it("allowImportExportEverywhere option (#327)", () => {
-    verifyAndAssertMessages(
-      unpad(`
-        if (true) { import Foo from 'foo'; }
-        function foo() { import Bar from 'bar'; }
-        switch (a) { case 1: import FooBar from 'foobar'; }
-      `),
-      {},
-      [],
-      "module",
-      {
-        env: {},
-        parserOptions: { ecmaVersion: 6, sourceType: "module", allowImportExportEverywhere: true }
-      }
-    );
-  });
-
   it("with does not crash parsing in script mode (strict off) #171", () => {
     verifyAndAssertMessages(
       "with (arguments) { length; }",