Fix destructuring evaluation order for initializers

Author: rbuckton

src/compiler/transformers/destructuring.ts

@@ -5,6 +5,7 @@ namespace ts {
         level: FlattenLevel;
         downlevelIteration: boolean;
         hoistTempVariables: boolean;
+        hasTransformedPriorElement?: boolean; // indicates whether we've transformed a prior declaration
         emitExpression: (value: Expression) => void;
         emitBindingOrAssignment: (target: BindingOrAssignmentElementTarget, value: Expression, location: TextRange, original: Node | undefined) => void;
         createArrayBindingOrAssignmentPattern: (elements: BindingOrAssignmentElement[]) => ArrayBindingOrAssignmentPattern;
@@ -265,18 +266,27 @@ namespace ts {
         value: Expression | undefined,
         location: TextRange,
         skipInitializer?: boolean) {
+        const bindingTarget = getTargetOfBindingOrAssignmentElement(element)!; // TODO: GH#18217
         if (!skipInitializer) {
             const initializer = visitNode(getInitializerOfBindingOrAssignmentElement(element), flattenContext.visitor, isExpression);
             if (initializer) {
                 // Combine value and initializer
-                value = value ? createDefaultValueCheck(flattenContext, value, initializer, location) : initializer;
+                if (value) {
+                    value = createDefaultValueCheck(flattenContext, value, initializer, location);
+                    // If 'value' is not a simple expression, it could contain side-effecting code that should evaluate before an object or array binding pattern.
+                    if (!isSimpleInlineableExpression(initializer) && isBindingOrAssignmentPattern(bindingTarget)) {
+                        value = ensureIdentifier(flattenContext, value, /*reuseIdentifierExpressions*/ true, location);
+                    }
+                }
+                else {
+                    value = initializer;
+                }
             }
             else if (!value) {
                 // Use 'void 0' in absence of value and initializer
                 value = flattenContext.context.factory.createVoidZero();
             }
         }
-        const bindingTarget = getTargetOfBindingOrAssignmentElement(element)!; // TODO: GH#18217
         if (isObjectBindingOrAssignmentPattern(bindingTarget)) {
             flattenObjectBindingOrAssignmentPattern(flattenContext, element, bindingTarget, value!, location);
         }
@@ -393,7 +403,8 @@ namespace ts {
             if (flattenContext.level >= FlattenLevel.ObjectRest) {
                 // If an array pattern contains an ObjectRest, we must cache the result so that we
                 // can perform the ObjectRest destructuring in a different declaration
-                if (element.transformFlags & TransformFlags.ContainsObjectRestOrSpread) {
+                if (element.transformFlags & TransformFlags.ContainsObjectRestOrSpread || flattenContext.hasTransformedPriorElement && !isSimpleBindingOrAssignmentElement(element)) {
+                    flattenContext.hasTransformedPriorElement = true;
                     const temp = flattenContext.context.factory.createTempVariable(/*recordTempVariable*/ undefined);
                     if (flattenContext.hoistTempVariables) {
                         flattenContext.context.hoistVariableDeclaration(temp);
@@ -428,6 +439,17 @@ namespace ts {
         }
     }
 
+    function isSimpleBindingOrAssignmentElement(element: BindingOrAssignmentElement): boolean {
+        const target = getTargetOfBindingOrAssignmentElement(element);
+        if (!target || isOmittedExpression(target)) return true;
+        const propertyName = tryGetPropertyNameOfBindingOrAssignmentElement(element);
+        if (propertyName && !isPropertyNameLiteral(propertyName)) return false;
+        const initializer = getInitializerOfBindingOrAssignmentElement(element);
+        if (initializer && !isSimpleInlineableExpression(initializer)) return false;
+        if (isBindingOrAssignmentPattern(target)) return every(getElementsOfBindingOrAssignmentPattern(target), isSimpleBindingOrAssignmentElement);
+        return isIdentifier(target);
+    }
+
     /**
      * Creates an expression used to provide a default value if a value is `undefined` at runtime.
      *

src/testRunner/tsconfig.json

@@ -89,6 +89,7 @@
         "unittests/evaluation/asyncArrow.ts",
         "unittests/evaluation/asyncGenerator.ts",
         "unittests/evaluation/awaiter.ts",
+        "unittests/evaluation/destructuring.ts",
         "unittests/evaluation/forAwaitOf.ts",
         "unittests/evaluation/forOf.ts",
         "unittests/evaluation/optionalCall.ts",

src/testRunner/unittests/evaluation/destructuring.ts

@@ -0,0 +1,39 @@
+describe("unittests:: evaluation:: destructuring", () => {
+    // https://github.com/microsoft/TypeScript/issues/39205
+    describe("correct order for array destructuring evaluation and initializers", () => {
+        it("when element is undefined", () => {
+            const result = evaluator.evaluateTypeScript(`
+                export const output: any[] = [];
+                const order = (n: any): any => output.push(n);
+                let [{ [order(1)]: x } = order(0)] = [];
+            `, { target: ts.ScriptTarget.ES5 });
+            assert.deepEqual(result.output, [0, 1]);
+        });
+        it("when element is defined", async () => {
+            const result = evaluator.evaluateTypeScript(`
+                export const output: any[] = [];
+                const order = (n: any): any => output.push(n);
+                let [{ [order(1)]: x } = order(0)] = [{}];
+            `, { target: ts.ScriptTarget.ES5 });
+            assert.deepEqual(result.output, [1]);
+        });
+    });
+    describe("correct order for array destructuring evaluation and initializers with spread", () => {
+        it("ES5", () => {
+            const result = evaluator.evaluateTypeScript(`
+                export const output: any[] = [];
+                const order = (n: any): any => output.push(n);
+                let { [order(0)]: { [order(2)]: z } = order(1), ...w } = {} as any;
+                `, { target: ts.ScriptTarget.ES5 });
+            assert.deepEqual(result.output, [0, 1, 2]);
+        });
+        it("ES2015", () => {
+            const result = evaluator.evaluateTypeScript(`
+                export const output: any[] = [];
+                const order = (n: any): any => output.push(n);
+                let { [order(0)]: { [order(2)]: z } = order(1), ...w } = {} as any;
+                `, { target: ts.ScriptTarget.ES2015 });
+            assert.deepEqual(result.output, [0, 1, 2]);
+        });
+    });
+});

tests/baselines/reference/arrowFunctionExpressions.js

@@ -137,7 +137,7 @@ var p8 = function (_a) {
     var _b = _a.a, a = _b === void 0 ? 1 : _b;
 };
 var p9 = function (_a) {
-    var _b = _a.a, _c = (_b === void 0 ? { b: 1 } : _b).b, b = _c === void 0 ? 1 : _c;
+    var _b = _a.a, _c = _b === void 0 ? { b: 1 } : _b, _d = _c.b, b = _d === void 0 ? 1 : _d;
 };
 var p10 = function (_a) {
     var _b = _a[0], value = _b.value, done = _b.done;

tests/baselines/reference/contextualTypeForInitalizedVariablesFiltersUndefined.js

@@ -12,15 +12,15 @@ function fst({ s } = t) { }
 //// [contextualTypeForInitalizedVariablesFiltersUndefined.js]
 "use strict";
 var fInferred = function (_a) {
-    var _b = (_a === void 0 ? {} : _a).a, a = _b === void 0 ? 0 : _b;
+    var _b = _a === void 0 ? {} : _a, _c = _b.a, a = _c === void 0 ? 0 : _c;
     return a;
 };
 // const fInferred: ({ a }?: { a?: number; }) => number
 var fAnnotated = function (_a) {
-    var _b = (_a === void 0 ? {} : _a).a, a = _b === void 0 ? 0 : _b;
+    var _b = _a === void 0 ? {} : _a, _c = _b.a, a = _c === void 0 ? 0 : _c;
     return a;
 };
 var s = t.s;
 function fst(_a) {
-    var s = (_a === void 0 ? t : _a).s;
+    var _b = _a === void 0 ? t : _a, s = _b.s;
 }

tests/baselines/reference/contextuallyTypedIife.js

@@ -95,11 +95,11 @@ let eleven = (o => o.a(11))({ a: function(n) { return n; } });
     return p;
 })({ p: 15 });
 (function (_a) {
-    var _b = (_a === void 0 ? { r: 18 } : _a).r, r = _b === void 0 ? 17 : _b;
+    var _b = _a === void 0 ? { r: 18 } : _a, _c = _b.r, r = _c === void 0 ? 17 : _c;
     return r;
 })({ r: 19 });
 (function (_a) {
-    var _b = (_a === void 0 ? { u: 23 } : _a).u, u = _b === void 0 ? 22 : _b;
+    var _b = _a === void 0 ? { u: 23 } : _a, _c = _b.u, u = _c === void 0 ? 22 : _c;
     return u;
 })();
 // contextually typed parameters.

tests/baselines/reference/contextuallyTypedIifeStrict.js

@@ -95,11 +95,11 @@ let eleven = (o => o.a(11))({ a: function(n) { return n; } });
     return p;
 })({ p: 15 });
 (function (_a) {
-    var _b = (_a === void 0 ? { r: 18 } : _a).r, r = _b === void 0 ? 17 : _b;
+    var _b = _a === void 0 ? { r: 18 } : _a, _c = _b.r, r = _c === void 0 ? 17 : _c;
     return r;
 })({ r: 19 });
 (function (_a) {
-    var _b = (_a === void 0 ? { u: 23 } : _a).u, u = _b === void 0 ? 22 : _b;
+    var _b = _a === void 0 ? { u: 23 } : _a, _c = _b.u, u = _c === void 0 ? 22 : _c;
     return u;
 })();
 // contextually typed parameters.

tests/baselines/reference/crashInGetTextOfComputedPropertyName.js

@@ -41,7 +41,7 @@ typeof itemOk1; // pass
 var objWithItems = { items: {} };
 var itemOk2 = objWithItems.items[itemId];
 typeof itemOk2; // pass
-var _c = objWithItems, _d = _c.items /*happens when default value is provided*/, _e = itemId, itemWithTSError = (_d === void 0 ? {} /*happens when default value is provided*/ : _d)[_e];
+var _c = objWithItems, _d = _c.items /*happens when default value is provided*/, _e = _d === void 0 ? {} : _d /*happens when default value is provided*/, _f = itemId, itemWithTSError = _e[_f];
 // in order to re-produce the error, uncomment next line:
 typeof itemWithTSError; // :(
 // will result in:

tests/baselines/reference/declarationEmitBindingPatterns.js

@@ -13,7 +13,7 @@ var a;
 function f(_a, _b, _c) {
     _a = a;
     _b = a;
-    var _d = (_c === void 0 ? a : _c).p, _e = _d === void 0 ? a : _d;
+    var _d = _c === void 0 ? a : _c, _e = _d.p, _f = _e === void 0 ? a : _e, _g = _f;
 }
 
 

tests/baselines/reference/declarationEmitDestructuring4.js

@@ -20,7 +20,7 @@ function baz1(_a) {
     _a = [1, 2, 3];
 }
 function baz2(_a) {
-    var _b = (_a === void 0 ? [[1, 2, 3]] : _a)[0];
+    var _b = _a === void 0 ? [[1, 2, 3]] : _a, _c = _b[0];
 }
 function baz3(_a) { }
 function baz4(_a) {