Give users helpful feedback if they are detected as using the wrong sourceType.

packages/babel-core/src/transformation/normalize-file.js

@@ -89,6 +89,12 @@ function parser(pluginPasses, options, code) {
     }
     throw new Error("More than one plugin attempted to override parsing.");
   } catch (err) {
+    if (err.code === "BABEL_PARSER_SOURCETYPE_MODULE_REQUIRED") {
+      err.message +=
+        "\nConsider renaming the file to '.mjs', or setting sourceType:module " +
+        "or sourceType:unambiguous in your Babel config for this file.";
+    }
+
     const { loc, missingPlugin } = err;
     if (loc) {
       const codeFrame = codeFrameColumns(

packages/babel-plugin-transform-modules-commonjs/src/index.js

@@ -31,7 +31,10 @@ export default function(api, options) {
 
   const getAssertion = localName => template.expression.ast`
     (function(){
-      throw new Error("The CommonJS '" + "${localName}" + "' variable is not available in ES6 modules.");
+      throw new Error(
+        "The CommonJS '" + "${localName}" + "' variable is not available in ES6 modules." +
+        "Consider setting setting sourceType:script or sourceType:unambiguous in your " +
+        "Babel config for this file.");
     })()
   `;
 

packages/babel-plugin-transform-modules-commonjs/test/fixtures/misc/module-exports/output.js

@@ -3,56 +3,56 @@
 require("foo");
 
 console.log(function () {
-  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }());
 console.log(function () {
-  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }().prop);
 
 exports = function () {
-  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }() + 1;
 
 exports = function () {
-  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }() + 4;
 
 ({
   exports
 } = ({}, function () {
-  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }()));
 [exports] = ([], function () {
-  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }());
 exports = {};
 (function () {
-  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "exports" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 })().prop = "";
 console.log(function () {
-  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }());
 console.log(function () {
-  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }().exports);
 
 module = function () {
-  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }() + 1;
 
 module = function () {
-  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }() + 4;
 
 ({
   module
 } = ({}, function () {
-  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }()));
 [module] = ([], function () {
-  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 }());
 module = {};
 (function () {
-  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules.");
+  throw new Error("The CommonJS '" + "module" + "' variable is not available in ES6 modules." + "Consider setting setting sourceType:script or sourceType:unambiguous in your " + "Babel config for this file.");
 })().prop = "";

packages/babylon/src/parser/expression.js

@@ -949,6 +949,7 @@ export default class ExpressionParser extends LValParser {
       this.raise(
         id.start,
         `import.meta may appear only with 'sourceType: "module"'`,
+        { code: "BABEL_PARSER_SOURCETYPE_MODULE_REQUIRED" },
       );
     }
     return this.parseMetaProperty(node, id, "meta");

packages/babylon/src/parser/location.js

@@ -15,8 +15,10 @@ export default class LocationParser extends CommentsParser {
     message: string,
     {
       missingPluginNames,
+      code,
     }: {
       missingPluginNames?: Array<string>,
+      code?: string,
     } = {},
   ): empty {
     const loc = getLineInfo(this.input, pos);
@@ -30,6 +32,9 @@ export default class LocationParser extends CommentsParser {
     if (missingPluginNames) {
       err.missingPlugin = missingPluginNames;
     }
+    if (code !== undefined) {
+      err.code = code;
+    }
     throw err;
   }
 }

packages/babylon/src/parser/statement.js

@@ -192,6 +192,9 @@ export default class StatementParser extends ExpressionParser {
       this.raise(
         node.start,
         `'import' and 'export' may appear only with 'sourceType: "module"'`,
+        {
+          code: "BABEL_PARSER_SOURCETYPE_MODULE_REQUIRED",
+        },
       );
     }
   }