Fix #973

src/ast/nodes/IfStatement.js

@@ -1,6 +1,16 @@
 import Statement from './shared/Statement.js';
 import { UNKNOWN } from '../values.js';
 
+// Statement types which may contain if-statements as direct children.
+const statementsWithIfStatements = new Set([
+	'DoWhileStatement',
+	'ForInStatement',
+	'ForOfStatement',
+	'ForStatement',
+	'IfStatement',
+	'WhileStatement'
+]);
+
 // TODO DRY this out
 export default class IfStatement extends Statement {
 	initialise ( scope ) {
@@ -14,7 +24,9 @@ export default class IfStatement extends Statement {
 			else if ( this.testValue ) {
 				this.consequent.initialise( scope );
 				this.alternate = null;
-			} else {
+			}
+
+			else {
 				if ( this.alternate ) this.alternate.initialise( scope );
 				this.consequent = null;
 			}
@@ -41,9 +53,18 @@ export default class IfStatement extends Statement {
 					code.remove( this.start, this.consequent.start );
 					code.remove( this.consequent.end, this.end );
 					this.consequent.render( code, es );
-				} else {
+				}
+
+				else {
 					code.remove( this.start, this.alternate ? this.alternate.start : this.next || this.end );
-					if ( this.alternate ) this.alternate.render( code, es );
+
+					if ( this.alternate ) {
+						this.alternate.render( code, es );
+					}
+
+					else if ( statementsWithIfStatements.has( this.parent.type ) ) {
+						code.insertRight( this.start, '{}' );
+					}
 				}
 			}
 		}

test/function/if-statement-with-false-condition/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'if statements with false condition do not break render (#973)'
+};

test/function/if-statement-with-false-condition/main.js

@@ -0,0 +1,47 @@
+export function whileIf(x) {
+	while (x)
+		if (false)
+			// replaced with {}
+			x = 0;
+}
+
+export function whileBlockIf(x) {
+	while (x) {
+		if (false)
+			// removed
+			x = 0;
+	}
+}
+
+export function ifWhile(x) {
+	if (x)
+		while (false)
+			// not optimized
+			x = 0;
+}
+
+export function ifFalseElse(x) {
+	if (false) {
+		// removed
+	} else {
+		// kept
+	}
+}
+
+export function elseIfFalse(x) {
+	if (x) {
+		// kept
+	} else if (false) {
+		// replaced with {}
+	}
+}
+
+export function elseIfFalseElse(x) {
+	if (x) {
+		// kept
+	} else if (false) {
+		// removed
+	} else {
+		// kept
+	}
+}