Made Scope.reference stricter. Helps to catch undefined/missing exports.

src/Module.js

@@ -50,6 +50,18 @@ class Id {
 	}
 }
 
+class LateBoundIdPlaceholder {
+	constructor ( module, name ) {
+		this.module = module;
+		this.name = name;
+		this.placeholder = true;
+	}
+
+	mark () {
+		throw new Error(`The imported name "${this.name}" is never exported by "${this.module.id}".`);
+	}
+}
+
 export default class Module {
 	constructor ({ id, source, ast, bundle }) {
 		this.source = source;
@@ -103,6 +115,7 @@ export default class Module {
 			}
 
 			// throw new Error( `The name "${name}" is never exported (from ${this.id})!` );
+			this.exports.define( name, new LateBoundIdPlaceholder( this, name ) );
 			return reference.call( this.exports, name );
 		};
 

src/Scope.js

@@ -81,6 +81,7 @@ export default class Scope {
 		});
 
 		this.ids.filter( isntReference ).forEach( id => {
+			// TODO: can this be removed?
 			if ( typeof id === 'string' ) {
 				throw new Error( `Required name "${id}" is undefined!` );
 			}
@@ -153,7 +154,11 @@ export default class Scope {
 
 	// Get a reference to the identifier `name` in this scope.
 	reference ( name ) {
-		return new Reference( this, this.index( name ) );
+		if ( !( name in this.names ) ) {
+			throw new Error( `Cannot reference undefined identifier "${name}"` );
+		}
+
+		return new Reference( this, this.names[ name ] );
 	}
 
 	// Return the used names of the scope.

test/function/import-of-unexported-fails/_config.js

@@ -0,0 +1,10 @@
+var assert = require( 'assert' );
+
+module.exports = {
+	description: 'marking an imported, but unexported, identifier should throw',
+
+	error: function ( err ) {
+		assert.equal( err.message.slice( 0, 50 ), 'The imported name "default" is never exported by "' );
+		assert.equal( err.message.slice( -10 ), 'empty.js".' );
+	}
+};

test/function/import-of-unexported-fails/main.js

@@ -0,0 +1,3 @@
+import a from './empty.js';
+
+a();

test/testScope.js

@@ -93,7 +93,7 @@ describe( 'Scope', function () {
 		});
 	});
 
-	it( 'dedupes-external-imports', function () {
+	it( 'cannot reference undefined names', function () {
 		var real = new Scope();
 
 		var external = real.virtual(),
@@ -104,17 +104,11 @@ describe( 'Scope', function () {
 
 		locals.bind( 'Comp', external.reference( 'Component' ) );
 
+		assert.throws( function () {
 			exports.bind( 'default', locals.reference( 'Foo' ) );
-
+		}, 'Cannot reference undefined identifier "Foo"' );
-		try {
-			real.deconflict();
-			assert.ok( false, 'Scope.deconflict should throw with "Foo" undefined' );
-		} catch ( ignore ) {
-			// as expected
-		}
 
 		locals.define( 'Foo' );
-
+		exports.bind( 'default', locals.reference( 'Foo' ) );
-		real.deconflict();
 	});
 });