Fix destructuring assignment when assignment target is RHS

src/compiler/transformers/destructuring.ts

@@ -70,7 +70,13 @@ namespace ts {
 
         if (value) {
             value = visitNode(value, visitor, isExpression);
-            if (needsValue) {
+
+            if (isIdentifier(value) && bindingOrAssignmentElementAssignsToName(node, value.escapedText)) {
+                // If the right-hand value of the assignment is also an assignment target then
+                // we need to cache the right-hand value.
+                value = ensureIdentifier(flattenContext, value, /*reuseIdentifierExpressions*/ false, location);
+            }
+            else if (needsValue) {
                 // If the right-hand value of the destructuring assignment needs to be preserved (as
                 // is the case when the destructuring assignment is part of a larger expression),
                 // then we need to cache the right-hand value.
@@ -123,6 +129,27 @@ namespace ts {
         }
     }
 
+    function bindingOrAssignmentElementAssignsToName(element: BindingOrAssignmentElement, escapedName: __String): boolean {
+        const target = getTargetOfBindingOrAssignmentElement(element);
+        if (isBindingOrAssignmentPattern(target)) {
+            return bindingOrAssignmentPatternAssignsToName(target, escapedName);
+        }
+        else if (isIdentifier(target)) {
+            return target.escapedText === escapedName;
+        }
+        return false;
+    }
+
+    function bindingOrAssignmentPatternAssignsToName(pattern: BindingOrAssignmentPattern, escapedName: __String): boolean {
+        const elements = getElementsOfBindingOrAssignmentPattern(pattern);
+        for (const element of elements) {
+            if (bindingOrAssignmentElementAssignsToName(element, escapedName)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     /**
      * Flattens a VariableDeclaration or ParameterDeclaration to one or more variable declarations.
      *
@@ -157,6 +184,17 @@ namespace ts {
             createArrayBindingOrAssignmentElement: makeBindingElement,
             visitor
         };
+
+        if (isVariableDeclaration(node)) {
+            let initializer = getInitializerOfBindingOrAssignmentElement(node);
+            if (initializer && isIdentifier(initializer) && bindingOrAssignmentElementAssignsToName(node, initializer.escapedText)) {
+                // If the right-hand value of the assignment is also an assignment target then
+                // we need to cache the right-hand value.
+                initializer = ensureIdentifier(flattenContext, initializer, /*reuseIdentifierExpressions*/ false, initializer);
+                node = updateVariableDeclaration(node, node.name, node.type, initializer);
+            }
+        }
+
         flattenBindingOrAssignmentElement(flattenContext, node, rval, node, skipInitializer);
         if (pendingExpressions) {
             const temp = createTempVariable(/*recordTempVariable*/ undefined);

src/compiler/types.ts

@@ -1467,7 +1467,7 @@ namespace ts {
         | SpreadAssignment // AssignmentRestProperty
         ;
 
-    export type BindingOrAssignmentElementTarget = BindingOrAssignmentPattern | Expression;
+    export type BindingOrAssignmentElementTarget = BindingOrAssignmentPattern | Identifier | PropertyAccessExpression | ElementAccessExpression | OmittedExpression;
 
     export type ObjectBindingOrAssignmentPattern
         = ObjectBindingPattern

tests/baselines/reference/api/typescript.d.ts

@@ -877,7 +877,7 @@ declare namespace ts {
     type DestructuringAssignment = ObjectDestructuringAssignment | ArrayDestructuringAssignment;
     type BindingOrAssignmentElement = VariableDeclaration | ParameterDeclaration | BindingElement | PropertyAssignment | ShorthandPropertyAssignment | SpreadAssignment | OmittedExpression | SpreadElement | ArrayLiteralExpression | ObjectLiteralExpression | AssignmentExpression<EqualsToken> | Identifier | PropertyAccessExpression | ElementAccessExpression;
     type BindingOrAssignmentElementRestIndicator = DotDotDotToken | SpreadElement | SpreadAssignment;
-    type BindingOrAssignmentElementTarget = BindingOrAssignmentPattern | Expression;
+    type BindingOrAssignmentElementTarget = BindingOrAssignmentPattern | Identifier | PropertyAccessExpression | ElementAccessExpression | OmittedExpression;
     type ObjectBindingOrAssignmentPattern = ObjectBindingPattern | ObjectLiteralExpression;
     type ArrayBindingOrAssignmentPattern = ArrayBindingPattern | ArrayLiteralExpression;
     type AssignmentPattern = ObjectLiteralExpression | ArrayLiteralExpression;

tests/baselines/reference/destructuringReassignsRightHandSide.js

@@ -0,0 +1,18 @@
+//// [destructuringReassignsRightHandSide.ts]
+var foo: any = { foo: 1, bar: 2 };
+var bar: any;
+
+// reassignment in destructuring pattern
+({ foo, bar } = foo);
+
+// reassignment in subsequent var
+var { foo, baz } = foo;
+
+//// [destructuringReassignsRightHandSide.js]
+var foo = { foo: 1, bar: 2 };
+var bar;
+// reassignment in destructuring pattern
+(_a = foo, foo = _a.foo, bar = _a.bar);
+// reassignment in subsequent var
+var _b = foo, foo = _b.foo, baz = _b.baz;
+var _a;

tests/baselines/reference/destructuringReassignsRightHandSide.symbols

@@ -0,0 +1,21 @@
+=== tests/cases/conformance/es6/destructuring/destructuringReassignsRightHandSide.ts ===
+var foo: any = { foo: 1, bar: 2 };
+>foo : Symbol(foo, Decl(destructuringReassignsRightHandSide.ts, 0, 3), Decl(destructuringReassignsRightHandSide.ts, 7, 5))
+>foo : Symbol(foo, Decl(destructuringReassignsRightHandSide.ts, 0, 16))
+>bar : Symbol(bar, Decl(destructuringReassignsRightHandSide.ts, 0, 24))
+
+var bar: any;
+>bar : Symbol(bar, Decl(destructuringReassignsRightHandSide.ts, 1, 3))
+
+// reassignment in destructuring pattern
+({ foo, bar } = foo);
+>foo : Symbol(foo, Decl(destructuringReassignsRightHandSide.ts, 4, 2))
+>bar : Symbol(bar, Decl(destructuringReassignsRightHandSide.ts, 4, 7))
+>foo : Symbol(foo, Decl(destructuringReassignsRightHandSide.ts, 0, 3), Decl(destructuringReassignsRightHandSide.ts, 7, 5))
+
+// reassignment in subsequent var
+var { foo, baz } = foo;
+>foo : Symbol(foo, Decl(destructuringReassignsRightHandSide.ts, 0, 3), Decl(destructuringReassignsRightHandSide.ts, 7, 5))
+>baz : Symbol(baz, Decl(destructuringReassignsRightHandSide.ts, 7, 10))
+>foo : Symbol(foo, Decl(destructuringReassignsRightHandSide.ts, 0, 3), Decl(destructuringReassignsRightHandSide.ts, 7, 5))
+

tests/baselines/reference/destructuringReassignsRightHandSide.types

@@ -0,0 +1,27 @@
+=== tests/cases/conformance/es6/destructuring/destructuringReassignsRightHandSide.ts ===
+var foo: any = { foo: 1, bar: 2 };
+>foo : any
+>{ foo: 1, bar: 2 } : { foo: number; bar: number; }
+>foo : number
+>1 : 1
+>bar : number
+>2 : 2
+
+var bar: any;
+>bar : any
+
+// reassignment in destructuring pattern
+({ foo, bar } = foo);
+>({ foo, bar } = foo) : any
+>{ foo, bar } = foo : any
+>{ foo, bar } : { foo: any; bar: any; }
+>foo : any
+>bar : any
+>foo : any
+
+// reassignment in subsequent var
+var { foo, baz } = foo;
+>foo : any
+>baz : any
+>foo : any
+

tests/baselines/reference/objectRest.js

@@ -85,10 +85,10 @@ var i = removable;
 var { removed } = i, removableRest2 = __rest(i, ["removed"]);
 let computed = 'b';
 let computed2 = 'a';
-var _g = computed, stillNotGreat = o[_g], _h = computed2, soSo = o[_h], o = __rest(o, [typeof _g === "symbol" ? _g : _g + "", typeof _h === "symbol" ? _h : _h + ""]);
-(_j = computed, stillNotGreat = o[_j], _k = computed2, soSo = o[_k], o = __rest(o, [typeof _j === "symbol" ? _j : _j + "", typeof _k === "symbol" ? _k : _k + ""]));
+var _g = o, _h = computed, stillNotGreat = _g[_h], _j = computed2, soSo = _g[_j], o = __rest(_g, [typeof _h === "symbol" ? _h : _h + "", typeof _j === "symbol" ? _j : _j + ""]);
+(_k = o, _l = computed, stillNotGreat = _k[_l], _m = computed2, soSo = _k[_m], o = __rest(_k, [typeof _l === "symbol" ? _l : _l + "", typeof _m === "symbol" ? _m : _m + ""]));
 var noContextualType = (_a) => {
     var { aNumber = 12 } = _a, notEmptyObject = __rest(_a, ["aNumber"]);
     return aNumber + notEmptyObject.anythingGoes;
 };
-var _d, _f, _j, _k;
+var _d, _f, _k, _l, _m;

tests/cases/conformance/es6/destructuring/destructuringReassignsRightHandSide.ts

@@ -0,0 +1,9 @@
+// @target: es5
+var foo: any = { foo: 1, bar: 2 };
+var bar: any;
+
+// reassignment in destructuring pattern
+({ foo, bar } = foo);
+
+// reassignment in subsequent var
+var { foo, baz } = foo;