Always create a temporary for iterated expressions in a for-of loop

src/compiler/emitter.ts

@@ -3614,10 +3614,12 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, Promi
                 //
                 //     for (let v of arr) { }
                 //
-                // we don't want to emit a temporary variable for the RHS, just use it directly.
-                let rhsIsIdentifier = node.expression.kind === SyntaxKind.Identifier;
+                // we can't reuse 'arr' because it might be modified within the body of the loop.
                 let counter = createTempVariable(TempFlags._i);
-                let rhsReference = rhsIsIdentifier ? <Identifier>node.expression : createTempVariable(TempFlags.Auto);
+                let rhsReference = createSynthesizedNode(SyntaxKind.Identifier) as Identifier;
+                rhsReference.text = node.expression.kind === SyntaxKind.Identifier ?
+                    makeUniqueName((<Identifier>node.expression).text) :
+                    makeTempVariableName(TempFlags.Auto);
 
                 // This is the let keyword for the counter and rhsReference. The let keyword for
                 // the LHS will be emitted inside the body.
@@ -3629,15 +3631,13 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, Promi
                 write(" = 0");
                 emitEnd(node.expression);
 
-                if (!rhsIsIdentifier) {
-                    // , _a = expr
-                    write(", ");
-                    emitStart(node.expression);
-                    emitNodeWithoutSourceMap(rhsReference);
-                    write(" = ");
-                    emitNodeWithoutSourceMap(node.expression);
-                    emitEnd(node.expression);
-                }
+                // , _a = expr
+                write(", ");
+                emitStart(node.expression);
+                emitNodeWithoutSourceMap(rhsReference);
+                write(" = ");
+                emitNodeWithoutSourceMap(node.expression);
+                emitEnd(node.expression);
 
                 write("; ");
 

tests/baselines/reference/ES3For-ofTypeCheck4.js

@@ -4,6 +4,6 @@ for (const v of union) { }
 
 //// [ES3For-ofTypeCheck4.js]
 var union;
-for (var _i = 0; _i < union.length; _i++) {
-    var v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    var v = union_1[_i];
 }

tests/baselines/reference/ES3For-ofTypeCheck6.js

@@ -4,6 +4,6 @@ for (var v of union) { }
 
 //// [ES3For-ofTypeCheck6.js]
 var union;
-for (var _i = 0; _i < union.length; _i++) {
-    var v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    var v = union_1[_i];
 }

tests/baselines/reference/ES5For-of24.js

@@ -6,7 +6,7 @@ for (var v of a) {
 
 //// [ES5For-of24.js]
 var a = [1, 2, 3];
-for (var _i = 0; _i < a.length; _i++) {
-    var v = a[_i];
-    var a_1 = 0;
+for (var _i = 0, a_1 = a; _i < a_1.length; _i++) {
+    var v = a_1[_i];
+    var a_2 = 0;
 }

tests/baselines/reference/ES5For-of25.sourcemap.txt

@@ -21,7 +21,7 @@ sourceFile:ES5For-of25.ts
 10>               ^
 11>                ^
 12>                 ^
-13>                  ^^^^^^^^^^^^^^^^^^^^^^->
+13>                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^->
 1 >
 2 >var 
 3 >    a
@@ -47,58 +47,58 @@ sourceFile:ES5For-of25.ts
 11>Emitted(1, 18) Source(1, 18) + SourceIndex(0)
 12>Emitted(1, 19) Source(1, 19) + SourceIndex(0)
 ---
->>>for (var _i = 0; _i < a.length; _i++) {
+>>>for (var _i = 0, a_1 = a; _i < a_1.length; _i++) {
 1->
 2 >^^^
 3 >   ^
 4 >    ^
 5 >     ^^^^^^^^^^
 6 >               ^^
-7 >                 ^^^^^^^^^^^^^
-8 >                              ^^
-9 >                                ^^^^
-10>                                    ^
+7 >                 ^^^^^^^
+8 >                        ^^
+9 >                          ^^^^^^^^^^^^^^^
+10>                                         ^^
+11>                                           ^^^^
+12>                                               ^
 1->
   >
 2 >for
 3 >    
 4 >    (var v of 
 5 >     a
 6 >               
-7 >                 var v
-8 >                              
-9 >                                var v of a
-10>                                    )
+7 >                 a
+8 >                        
+9 >                          var v
+10>                                         
+11>                                           var v of a
+12>                                               )
 1->Emitted(2, 1) Source(2, 1) + SourceIndex(0)
 2 >Emitted(2, 4) Source(2, 4) + SourceIndex(0)
 3 >Emitted(2, 5) Source(2, 5) + SourceIndex(0)
 4 >Emitted(2, 6) Source(2, 15) + SourceIndex(0)
 5 >Emitted(2, 16) Source(2, 16) + SourceIndex(0)
-6 >Emitted(2, 18) Source(2, 6) + SourceIndex(0)
-7 >Emitted(2, 31) Source(2, 11) + SourceIndex(0)
-8 >Emitted(2, 33) Source(2, 6) + SourceIndex(0)
-9 >Emitted(2, 37) Source(2, 16) + SourceIndex(0)
-10>Emitted(2, 38) Source(2, 17) + SourceIndex(0)
+6 >Emitted(2, 18) Source(2, 15) + SourceIndex(0)
+7 >Emitted(2, 25) Source(2, 16) + SourceIndex(0)
+8 >Emitted(2, 27) Source(2, 6) + SourceIndex(0)
+9 >Emitted(2, 42) Source(2, 11) + SourceIndex(0)
+10>Emitted(2, 44) Source(2, 6) + SourceIndex(0)
+11>Emitted(2, 48) Source(2, 16) + SourceIndex(0)
+12>Emitted(2, 49) Source(2, 17) + SourceIndex(0)
 ---
->>>    var v = a[_i];
+>>>    var v = a_1[_i];
 1 >^^^^
 2 >    ^^^^
 3 >        ^
-4 >         ^^^
-5 >            ^
-6 >             ^^^^
+4 >         ^^^^^^^^^^
 1 >
 2 >    var 
 3 >        v
-4 >          of 
-5 >            a
-6 >             
+4 >         
 1 >Emitted(3, 5) Source(2, 6) + SourceIndex(0)
 2 >Emitted(3, 9) Source(2, 10) + SourceIndex(0)
 3 >Emitted(3, 10) Source(2, 11) + SourceIndex(0)
-4 >Emitted(3, 13) Source(2, 15) + SourceIndex(0)
-5 >Emitted(3, 14) Source(2, 16) + SourceIndex(0)
-6 >Emitted(3, 18) Source(2, 11) + SourceIndex(0)
+4 >Emitted(3, 20) Source(2, 11) + SourceIndex(0)
 ---
 >>>    v;
 1 >^^^^

tests/baselines/reference/ES5For-of30.js

@@ -9,8 +9,8 @@ for ([a = 1, b = ""] of tuple) {
 //// [ES5For-of30.js]
 var a, b;
 var tuple = [2, "3"];
-for (var _i = 0; _i < tuple.length; _i++) {
-    _a = tuple[_i], _b = _a[0], a = _b === void 0 ? 1 : _b, _c = _a[1], b = _c === void 0 ? "" : _c;
+for (var _i = 0, tuple_1 = tuple; _i < tuple_1.length; _i++) {
+    _a = tuple_1[_i], _b = _a[0], a = _b === void 0 ? 1 : _b, _c = _a[1], b = _c === void 0 ? "" : _c;
     a;
     b;
 }

tests/baselines/reference/ES5For-ofTypeCheck11.js

@@ -6,6 +6,6 @@ for (v of union) { }
 //// [ES5For-ofTypeCheck11.js]
 var union;
 var v;
-for (var _i = 0; _i < union.length; _i++) {
-    v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    v = union_1[_i];
 }

tests/baselines/reference/ES5For-ofTypeCheck3.js

@@ -4,6 +4,6 @@ for (var v of tuple) { }
 
 //// [ES5For-ofTypeCheck3.js]
 var tuple = ["", 0];
-for (var _i = 0; _i < tuple.length; _i++) {
-    var v = tuple[_i];
+for (var _i = 0, tuple_1 = tuple; _i < tuple_1.length; _i++) {
+    var v = tuple_1[_i];
 }

tests/baselines/reference/ES5For-ofTypeCheck4.js

@@ -4,6 +4,6 @@ for (const v of union) { }
 
 //// [ES5For-ofTypeCheck4.js]
 var union;
-for (var _i = 0; _i < union.length; _i++) {
-    var v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    var v = union_1[_i];
 }

tests/baselines/reference/ES5For-ofTypeCheck5.js

@@ -4,6 +4,6 @@ for (var v of union) { }
 
 //// [ES5For-ofTypeCheck5.js]
 var union;
-for (var _i = 0; _i < union.length; _i++) {
-    var v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    var v = union_1[_i];
 }

tests/baselines/reference/ES5For-ofTypeCheck6.js

@@ -4,6 +4,6 @@ for (var v of union) { }
 
 //// [ES5For-ofTypeCheck6.js]
 var union;
-for (var _i = 0; _i < union.length; _i++) {
-    var v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    var v = union_1[_i];
 }

tests/baselines/reference/ES5For-ofTypeCheck7.js

@@ -4,6 +4,6 @@ for (var v of union) { }
 
 //// [ES5For-ofTypeCheck7.js]
 var union;
-for (var _i = 0; _i < union.length; _i++) {
-    var v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    var v = union_1[_i];
 }

tests/baselines/reference/ES5For-ofTypeCheck8.js

@@ -6,6 +6,6 @@ for (v of union) { }
 //// [ES5For-ofTypeCheck8.js]
 var union;
 var v;
-for (var _i = 0; _i < union.length; _i++) {
-    v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    v = union_1[_i];
 }

tests/baselines/reference/ES5For-ofTypeCheck9.js

@@ -4,6 +4,6 @@ for (let v of union) { }
 
 //// [ES5For-ofTypeCheck9.js]
 var union;
-for (var _i = 0; _i < union.length; _i++) {
-    var v = union[_i];
+for (var _i = 0, union_1 = union; _i < union_1.length; _i++) {
+    var v = union_1[_i];
 }

tests/baselines/reference/ES5for-of32.js

@@ -0,0 +1,23 @@
+//// [ES5for-of32.ts]
+
+var array = [1,2,3];
+var sum = 0;
+
+for (let num of array) {
+    if (sum === 0) {
+        array = [4,5,6]
+    }
+
+    sum += num;
+}
+
+//// [ES5for-of32.js]
+var array = [1, 2, 3];
+var sum = 0;
+for (var _i = 0, array_1 = array; _i < array_1.length; _i++) {
+    var num = array_1[_i];
+    if (sum === 0) {
+        array = [4, 5, 6];
+    }
+    sum += num;
+}

tests/baselines/reference/ES5for-of32.symbols

@@ -0,0 +1,23 @@
+=== tests/cases/conformance/statements/for-ofStatements/ES5for-of32.ts ===
+
+var array = [1,2,3];
+>array : Symbol(array, Decl(ES5for-of32.ts, 1, 3))
+
+var sum = 0;
+>sum : Symbol(sum, Decl(ES5for-of32.ts, 2, 3))
+
+for (let num of array) {
+>num : Symbol(num, Decl(ES5for-of32.ts, 4, 8))
+>array : Symbol(array, Decl(ES5for-of32.ts, 1, 3))
+
+    if (sum === 0) {
+>sum : Symbol(sum, Decl(ES5for-of32.ts, 2, 3))
+
+        array = [4,5,6]
+>array : Symbol(array, Decl(ES5for-of32.ts, 1, 3))
+    }
+
+    sum += num;
+>sum : Symbol(sum, Decl(ES5for-of32.ts, 2, 3))
+>num : Symbol(num, Decl(ES5for-of32.ts, 4, 8))
+}

tests/baselines/reference/ES5for-of32.types

@@ -0,0 +1,36 @@
+=== tests/cases/conformance/statements/for-ofStatements/ES5for-of32.ts ===
+
+var array = [1,2,3];
+>array : number[]
+>[1,2,3] : number[]
+>1 : number
+>2 : number
+>3 : number
+
+var sum = 0;
+>sum : number
+>0 : number
+
+for (let num of array) {
+>num : number
+>array : number[]
+
+    if (sum === 0) {
+>sum === 0 : boolean
+>sum : number
+>0 : number
+
+        array = [4,5,6]
+>array = [4,5,6] : number[]
+>array : number[]
+>[4,5,6] : number[]
+>4 : number
+>5 : number
+>6 : number
+    }
+
+    sum += num;
+>sum += num : number
+>sum : number
+>num : number
+}

tests/baselines/reference/argumentsObjectIterator01_ES5.js

@@ -11,8 +11,8 @@ function doubleAndReturnAsArray(x: number, y: number, z: number): [number, numbe
 //// [argumentsObjectIterator01_ES5.js]
 function doubleAndReturnAsArray(x, y, z) {
     var result = [];
-    for (var _i = 0; _i < arguments.length; _i++) {
-        var arg = arguments[_i];
+    for (var _i = 0, arguments_1 = arguments; _i < arguments_1.length; _i++) {
+        var arg = arguments_1[_i];
         result.push(arg + arg);
     }
     return result;

tests/baselines/reference/emptyVariableDeclarationBindingPatterns01_ES5.js

@@ -80,22 +80,22 @@
 })();
 (function () {
     var ns = [];
-    for (var _i = 0; _i < ns.length; _i++) {
-        var _a = ns[_i];
+    for (var _i = 0, ns_1 = ns; _i < ns_1.length; _i++) {
+        var _a = ns_1[_i];
     }
-    for (var _b = 0; _b < ns.length; _b++) {
-        var _c = ns[_b];
+    for (var _b = 0, ns_2 = ns; _b < ns_2.length; _b++) {
+        var _c = ns_2[_b];
     }
-    for (var _d = 0; _d < ns.length; _d++) {
-        var _e = ns[_d];
+    for (var _d = 0, ns_3 = ns; _d < ns_3.length; _d++) {
+        var _e = ns_3[_d];
     }
-    for (var _f = 0; _f < ns.length; _f++) {
-        var _g = ns[_f];
+    for (var _f = 0, ns_4 = ns; _f < ns_4.length; _f++) {
+        var _g = ns_4[_f];
     }
-    for (var _h = 0; _h < ns.length; _h++) {
-        var _j = ns[_h];
+    for (var _h = 0, ns_5 = ns; _h < ns_5.length; _h++) {
+        var _j = ns_5[_h];
     }
-    for (var _k = 0; _k < ns.length; _k++) {
-        var _l = ns[_k];
+    for (var _k = 0, ns_6 = ns; _k < ns_6.length; _k++) {
+        var _l = ns_6[_k];
     }
 })();

tests/baselines/reference/parserES5ForOfStatement10.js

@@ -3,6 +3,6 @@ for (const v of X) {
 }
 
 //// [parserES5ForOfStatement10.js]
-for (var _i = 0; _i < X.length; _i++) {
-    var v = X[_i];
+for (var _i = 0, X_1 = X; _i < X_1.length; _i++) {
+    var v = X_1[_i];
 }