Merge pull request #465 from rollup/skip-dead-conditional-expression-branches

Skip dead branches of a conditional expression.

src/Module.js

@@ -300,7 +300,7 @@ export default class Module {
 		}
 
 		walk( ast, {
-			enter: node => {
+			enter: (node, parent, prop) => {
 				// eliminate dead branches early
 				if ( node.type === 'IfStatement' ) {
 					if ( isFalsy( node.test ) ) {
@@ -310,6 +310,15 @@ export default class Module {
 						this.magicString.overwrite( node.alternate.start, node.alternate.end, '{}' );
 						node.alternate = emptyBlockStatement( node.alternate.start, node.alternate.end );
 					}
+				} else if ( node.type === 'ConditionalExpression' ) {
+					if ( isFalsy( node.test ) ) {
+						this.magicString.remove( node.start, node.alternate.start );
+						parent[prop] = node.alternate;
+					} else if ( isTruthy( node.test ) ) {
+						this.magicString.remove( node.start, node.consequent.start );
+						this.magicString.remove( node.consequent.end, node.end );
+						parent[prop] = node.consequent;
+					}
 				}
 
 				this.magicString.addSourcemapLocation( node.start );

test/function/skips-dead-branches-f/_config.js

@@ -1,7 +1,7 @@
 var assert = require( 'assert' );
 
 module.exports = {
-	description: 'skips a dead branch (g)',
+	description: 'skips a dead branch (f)',
 	code: function ( code ) {
 		assert.equal( code.indexOf( 'obj.foo = function' ), -1, code );
 	}

test/function/skips-dead-branches-g/_config.js

@@ -0,0 +1,9 @@
+var assert = require( 'assert' );
+
+module.exports = {
+  description: 'skips a dead conditional expression branch (g)',
+  code: function ( code ) {
+    assert.ok( code.indexOf( 'var c = a;' ) >= 0, code );
+    assert.ok( code.indexOf( 'var d = b;' ) >= 0, code );
+  }
+};

test/function/skips-dead-branches-g/main.js

@@ -0,0 +1,6 @@
+var a = 0;
+var b = 1;
+var c = true ? a : b;
+var d = false ? a : b;
+
+console.log( c + d );