automatic semicolon insertion (fixes #1004, #1009). fight me

src/ast/Node.js

@@ -66,6 +66,12 @@ export default class Node {
 		this.eachChild( child => child.initialise( this.scope || scope ) );
 	}
 
+	insertSemicolon ( code ) {
+		if ( code.original[ this.end - 1 ] !== ';' ) {
+			code.insertLeft( this.end, ';' );
+		}
+	}
+
 	locate () {
 		// useful for debugging
 		const location = getLocation( this.module.code, this.start );

src/ast/nodes/ExpressionStatement.js

@@ -1,5 +1,8 @@
 import Statement from './shared/Statement.js';
 
 export default class ExpressionStatement extends Statement {
-
+	render ( code, es ) {
+		super.render( code, es );
+		if ( this.shouldInclude ) this.insertSemicolon( code );
+	}
 }

src/ast/nodes/VariableDeclaration.js

@@ -14,7 +14,7 @@ function getSeparator ( code, start ) {
 	return `;\n${lineStart}`;
 }
 
-const forStatement = /^For(?:Of|In)Statement/;
+const forStatement = /^For(?:Of|In)?Statement/;
 
 export default class VariableDeclaration extends Node {
 	initialise ( scope ) {
@@ -92,9 +92,16 @@ export default class VariableDeclaration extends Node {
 
 		if ( treeshake && empty ) {
 			code.remove( this.leadingCommentStart || this.start, this.next || this.end );
-		} else if ( this.end > c ) {
-			const hasSemicolon = code.original[ this.end - 1 ] === ';';
-			code.overwrite( c, this.end, hasSemicolon ? ';' : '' );
+		} else {
+			// always include a semi-colon (https://github.com/rollup/rollup/pull/1013),
+			// unless it's a var declaration in a loop head
+			const needsSemicolon = !forStatement.test( this.parent.type );
+
+			if ( this.end > c ) {
+				code.overwrite( c, this.end, needsSemicolon ? ';' : '' );
+			} else if ( needsSemicolon  ) {
+				this.insertSemicolon( code );
+			}
 		}
 	}
 }

test/function/adds-semicolons-if-necessary-b/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'adds semi-colons if necessary'
+};

test/function/adds-semicolons-if-necessary-b/foo.js

@@ -0,0 +1 @@
+assert.ok( true )

test/function/adds-semicolons-if-necessary-b/main.js

@@ -0,0 +1,3 @@
+import './foo.js';
+
+(function bar() {})();

test/function/adds-semicolons-if-necessary/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'adds semi-colons if necessary'
+};

test/function/adds-semicolons-if-necessary/foo.js

@@ -0,0 +1,3 @@
+export var foo = function () {
+	return 42;
+}

test/function/adds-semicolons-if-necessary/main.js

@@ -0,0 +1,7 @@
+import { foo } from './foo.js';
+
+(function bar() {
+	assert.ok( true );
+})();
+
+assert.equal( foo(), 42 );