Emit parens around type-asserted binary operators

RyanCavanaugh · RyanCavanaugh · commit 124305d00780 · 2016-07-15T15:56:22.000-07:00
Fixes microsoft#9766
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
@@ -2553,7 +2553,7 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
                             operand = (<TypeAssertion | NonNullExpression>operand).expression;
                         }
 
-                        // We have an expression of the form: (<Type>SubExpr)
+                        // We have an expression of the form: (<Type>SubExpr) or (SubExpr as Type)
                         // Emitting this as (SubExpr) is really not desirable. We would like to emit the subexpr as is.
                         // Omitting the parentheses, however, could cause change in the semantics of the generated
                         // code if the casted expression has a lower precedence than the rest of the expression, e.g.:
@@ -2567,6 +2567,7 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
                             operand.kind !== SyntaxKind.DeleteExpression &&
                             operand.kind !== SyntaxKind.PostfixUnaryExpression &&
                             operand.kind !== SyntaxKind.NewExpression &&
+                            !(operand.kind === SyntaxKind.BinaryExpression && node.expression.kind === SyntaxKind.AsExpression) &&
                             !(operand.kind === SyntaxKind.CallExpression && node.parent.kind === SyntaxKind.NewExpression) &&
                             !(operand.kind === SyntaxKind.FunctionExpression && node.parent.kind === SyntaxKind.CallExpression) &&
                             !(operand.kind === SyntaxKind.NumericLiteral && node.parent.kind === SyntaxKind.PropertyAccessExpression)) {
diff --git a/tests/baselines/reference/asOpEmitParens.js b/tests/baselines/reference/asOpEmitParens.js
@@ -0,0 +1,19 @@
+//// [asOpEmitParens.ts]
+declare var x;
+// Must emit as (x + 1) * 3
+(x + 1 as number) * 3;
+
+// Should still emit as x.y
+(x as any).y;
+
+// Emit as new (x())
+new (x() as any);
+
+
+//// [asOpEmitParens.js]
+// Must emit as (x + 1) * 3
+(x + 1) * 3;
+// Should still emit as x.y
+x.y;
+// Emit as new (x())
+new (x());
diff --git a/tests/baselines/reference/asOpEmitParens.symbols b/tests/baselines/reference/asOpEmitParens.symbols
@@ -0,0 +1,16 @@
+=== tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts ===
+declare var x;
+>x : Symbol(x, Decl(asOpEmitParens.ts, 0, 11))
+
+// Must emit as (x + 1) * 3
+(x + 1 as number) * 3;
+>x : Symbol(x, Decl(asOpEmitParens.ts, 0, 11))
+
+// Should still emit as x.y
+(x as any).y;
+>x : Symbol(x, Decl(asOpEmitParens.ts, 0, 11))
+
+// Emit as new (x())
+new (x() as any);
+>x : Symbol(x, Decl(asOpEmitParens.ts, 0, 11))
+
diff --git a/tests/baselines/reference/asOpEmitParens.types b/tests/baselines/reference/asOpEmitParens.types
@@ -0,0 +1,30 @@
+=== tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts ===
+declare var x;
+>x : any
+
+// Must emit as (x + 1) * 3
+(x + 1 as number) * 3;
+>(x + 1 as number) * 3 : number
+>(x + 1 as number) : number
+>x + 1 as number : number
+>x + 1 : any
+>x : any
+>1 : number
+>3 : number
+
+// Should still emit as x.y
+(x as any).y;
+>(x as any).y : any
+>(x as any) : any
+>x as any : any
+>x : any
+>y : any
+
+// Emit as new (x())
+new (x() as any);
+>new (x() as any) : any
+>(x() as any) : any
+>x() as any : any
+>x() : any
+>x : any
+
diff --git a/tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts b/tests/cases/conformance/expressions/asOperator/asOpEmitParens.ts
@@ -0,0 +1,9 @@
+declare var x;
+// Must emit as (x + 1) * 3
+(x + 1 as number) * 3;
+
+// Should still emit as x.y
+(x as any).y;
+
+// Emit as new (x())
+new (x() as any);
