Update control flow for correct destructuring evaluation order

src/compiler/binder.ts

@@ -218,6 +218,9 @@ namespace ts {
         // or if compiler options contain alwaysStrict.
         let inStrictMode: boolean;
 
+        // If we are binding an assignment pattern, we will bind certain expressions differently.
+        let inAssignmentPattern = false;
+
         let symbolCount = 0;
 
         let Symbol: new (flags: SymbolFlags, name: __String) => Symbol;
@@ -275,6 +278,7 @@ namespace ts {
             currentExceptionTarget = undefined;
             activeLabelList = undefined;
             hasExplicitReturn = false;
+            inAssignmentPattern = false;
             emitFlags = NodeFlags.None;
         }
 
@@ -733,9 +737,14 @@ namespace ts {
         }
 
         function bindChildren(node: Node): void {
+            const saveInAssignmentPattern = inAssignmentPattern;
+            // Most nodes aren't valid in an assignment pattern, so we clear the value here
+            // and set it before we descend into nodes that could actually be part of an assignment pattern.
+            inAssignmentPattern = false;
             if (checkUnreachable(node)) {
                 bindEachChild(node);
                 bindJSDoc(node);
+                inAssignmentPattern = saveInAssignmentPattern;
                 return;
             }
             if (node.kind >= SyntaxKind.FirstStatement && node.kind <= SyntaxKind.LastStatement && !options.allowUnreachableCode) {
@@ -791,6 +800,13 @@ namespace ts {
                     bindPostfixUnaryExpressionFlow(<PostfixUnaryExpression>node);
                     break;
                 case SyntaxKind.BinaryExpression:
+                    if (isDestructuringAssignment(node)) {
+                        // Carry over whether we are in an assignment pattern to
+                        // binary expressions that could actually be an initializer
+                        inAssignmentPattern = saveInAssignmentPattern;
+                        bindDestructuringAssignmentFlow(node);
+                        return;
+                    }
                     bindBinaryExpressionFlow(<BinaryExpression>node);
                     break;
                 case SyntaxKind.DeleteExpression:
@@ -827,11 +843,23 @@ namespace ts {
                 case SyntaxKind.ModuleBlock:
                     bindEachFunctionsFirst((node as Block).statements);
                     break;
+                case SyntaxKind.BindingElement:
+                    bindBindingElementFlow(<BindingElement>node);
+                    break;
+                case SyntaxKind.ObjectLiteralExpression:
+                case SyntaxKind.ArrayLiteralExpression:
+                case SyntaxKind.PropertyAssignment:
+                case SyntaxKind.SpreadElement:
+                    // Carry over whether we are in an assignment pattern of Object and Array literals
+                    // as well as their children that are valid assignment targets.
+                    inAssignmentPattern = saveInAssignmentPattern;
+                    // falls through
                 default:
                     bindEachChild(node);
                     break;
             }
             bindJSDoc(node);
+            inAssignmentPattern = saveInAssignmentPattern;
         }
 
         function isNarrowingExpression(expr: Expression): boolean {
@@ -1449,6 +1477,24 @@ namespace ts {
             }
         }
 
+        function bindDestructuringAssignmentFlow(node: DestructuringAssignment) {
+            if (inAssignmentPattern) {
+                inAssignmentPattern = false;
+                bind(node.operatorToken);
+                bind(node.right);
+                inAssignmentPattern = true;
+                bind(node.left);
+            }
+            else {
+                inAssignmentPattern = true;
+                bind(node.left);
+                inAssignmentPattern = false;
+                bind(node.operatorToken);
+                bind(node.right);
+            }
+            bindAssignmentTargetFlow(node.left);
+        }
+
         const enum BindBinaryExpressionFlowState {
             BindThenBindChildren,
             MaybeBindLeft,
@@ -1617,6 +1663,25 @@ namespace ts {
             }
         }
 
+        function bindBindingElementFlow(node: BindingElement) {
+            if (isBindingPattern(node.name)) {
+                // When evaluating a binding pattern, the initializer is evaluated before the binding pattern, per:
+                // - https://tc39.es/ecma262/#sec-destructuring-binding-patterns-runtime-semantics-iteratorbindinginitialization
+                //   - `BindingElement: BindingPattern Initializer?`
+                // - https://tc39.es/ecma262/#sec-runtime-semantics-keyedbindinginitialization
+                //   - `BindingElement: BindingPattern Initializer?`
+                bindEach(node.decorators);
+                bindEach(node.modifiers);
+                bind(node.dotDotDotToken);
+                bind(node.propertyName);
+                bind(node.initializer);
+                bind(node.name);
+            }
+            else {
+                bindEachChild(node);
+            }
+        }
+
         function bindJSDocTypeAlias(node: JSDocTypedefTag | JSDocCallbackTag | JSDocEnumTag) {
             setParent(node.tagName, node);
             if (node.kind !== SyntaxKind.JSDocEnumTag && node.fullName) {

tests/baselines/reference/controlFlowAssignmentPatternOrder.symbols

@@ -0,0 +1,70 @@
+=== tests/cases/conformance/controlFlow/controlFlowAssignmentPatternOrder.ts ===
+// https://github.com/microsoft/TypeScript/pull/41094#issuecomment-716044363
+{
+    let a: 0 | 1 = 0;
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 2, 7))
+
+    let b: 0 | 1 | 9;
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 3, 7))
+
+    [{ [(a = 1)]: b } = [9, a] as const] = [];
+>[(a = 1)] : Symbol([(a = 1)], Decl(controlFlowAssignmentPatternOrder.ts, 4, 6))
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 2, 7))
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 3, 7))
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 2, 7))
+
+    const bb: 0 = b;
+>bb : Symbol(bb, Decl(controlFlowAssignmentPatternOrder.ts, 5, 9))
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 3, 7))
+}
+{
+    let a: 0 | 1 = 1;
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 8, 7))
+
+    let b: 0 | 1 | 9;
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 9, 7))
+
+    [{ [a]: b } = [9, a = 0] as const] = [];
+>[a] : Symbol([a], Decl(controlFlowAssignmentPatternOrder.ts, 10, 6))
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 8, 7))
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 9, 7))
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 8, 7))
+
+    const bb: 9 = b;
+>bb : Symbol(bb, Decl(controlFlowAssignmentPatternOrder.ts, 11, 9))
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 9, 7))
+}
+{
+    let a: 0 | 1 = 0;
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 14, 7))
+
+    let b: 0 | 1 | 8 | 9;
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 15, 7))
+
+    [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
+>[(a = 1)] : Symbol([(a = 1)], Decl(controlFlowAssignmentPatternOrder.ts, 16, 6))
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 14, 7))
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 15, 7))
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 14, 7))
+
+    const bb: 0 | 8 = b;
+>bb : Symbol(bb, Decl(controlFlowAssignmentPatternOrder.ts, 17, 9))
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 15, 7))
+}
+{
+    let a: 0 | 1 = 1;
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 20, 7))
+
+    let b: 0 | 1 | 8 | 9;
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 21, 7))
+
+    [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+>[a] : Symbol([a], Decl(controlFlowAssignmentPatternOrder.ts, 22, 6))
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 20, 7))
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 21, 7))
+>a : Symbol(a, Decl(controlFlowAssignmentPatternOrder.ts, 20, 7))
+
+    const bb: 0 | 8 = b;
+>bb : Symbol(bb, Decl(controlFlowAssignmentPatternOrder.ts, 23, 9))
+>b : Symbol(b, Decl(controlFlowAssignmentPatternOrder.ts, 21, 7))
+}

tests/baselines/reference/controlFlowAssignmentPatternOrder.types

@@ -0,0 +1,124 @@
+=== tests/cases/conformance/controlFlow/controlFlowAssignmentPatternOrder.ts ===
+// https://github.com/microsoft/TypeScript/pull/41094#issuecomment-716044363
+{
+    let a: 0 | 1 = 0;
+>a : 0 | 1
+>0 : 0
+
+    let b: 0 | 1 | 9;
+>b : 0 | 1 | 9
+
+    [{ [(a = 1)]: b } = [9, a] as const] = [];
+>[{ [(a = 1)]: b } = [9, a] as const] = [] : []
+>[{ [(a = 1)]: b } = [9, a] as const] : [readonly [9, 0]]
+>{ [(a = 1)]: b } = [9, a] as const : readonly [9, 0]
+>{ [(a = 1)]: b } : { 1: 0 | 1 | 9; }
+>[(a = 1)] : 0 | 1 | 9
+>(a = 1) : 1
+>a = 1 : 1
+>a : 0 | 1
+>1 : 1
+>b : 0 | 1 | 9
+>[9, a] as const : readonly [9, 0]
+>[9, a] : readonly [9, 0]
+>9 : 9
+>a : 0
+>[] : []
+
+    const bb: 0 = b;
+>bb : 0
+>b : 0
+}
+{
+    let a: 0 | 1 = 1;
+>a : 0 | 1
+>1 : 1
+
+    let b: 0 | 1 | 9;
+>b : 0 | 1 | 9
+
+    [{ [a]: b } = [9, a = 0] as const] = [];
+>[{ [a]: b } = [9, a = 0] as const] = [] : []
+>[{ [a]: b } = [9, a = 0] as const] : [readonly [9, 0]]
+>{ [a]: b } = [9, a = 0] as const : readonly [9, 0]
+>{ [a]: b } : { 0: 0 | 1 | 9; }
+>[a] : 0 | 1 | 9
+>a : 0
+>b : 0 | 1 | 9
+>[9, a = 0] as const : readonly [9, 0]
+>[9, a = 0] : readonly [9, 0]
+>9 : 9
+>a = 0 : 0
+>a : 0 | 1
+>0 : 0
+>[] : []
+
+    const bb: 9 = b;
+>bb : 9
+>b : 9
+}
+{
+    let a: 0 | 1 = 0;
+>a : 0 | 1
+>0 : 0
+
+    let b: 0 | 1 | 8 | 9;
+>b : 0 | 1 | 9 | 8
+
+    [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
+>[{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const] : [readonly [9, 8]]
+>[{ [(a = 1)]: b } = [9, a] as const] : [readonly [9, 0]]
+>{ [(a = 1)]: b } = [9, a] as const : readonly [9, 0]
+>{ [(a = 1)]: b } : { 1: 0 | 1 | 9 | 8; }
+>[(a = 1)] : 0 | 1 | 9 | 8
+>(a = 1) : 1
+>a = 1 : 1
+>a : 0 | 1
+>1 : 1
+>b : 0 | 1 | 9 | 8
+>[9, a] as const : readonly [9, 0]
+>[9, a] : readonly [9, 0]
+>9 : 9
+>a : 0
+>[[9, 8] as const] : [readonly [9, 8]]
+>[9, 8] as const : readonly [9, 8]
+>[9, 8] : readonly [9, 8]
+>9 : 9
+>8 : 8
+
+    const bb: 0 | 8 = b;
+>bb : 0 | 8
+>b : 0 | 8
+}
+{
+    let a: 0 | 1 = 1;
+>a : 0 | 1
+>1 : 1
+
+    let b: 0 | 1 | 8 | 9;
+>b : 0 | 1 | 9 | 8
+
+    [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+>[{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const] : [readonly [8, 9]]
+>[{ [a]: b } = [a = 0, 9] as const] : [readonly [0, 9]]
+>{ [a]: b } = [a = 0, 9] as const : readonly [0, 9]
+>{ [a]: b } : { 0: 0 | 1 | 9 | 8; }
+>[a] : 0 | 1 | 9 | 8
+>a : 0
+>b : 0 | 1 | 9 | 8
+>[a = 0, 9] as const : readonly [0, 9]
+>[a = 0, 9] : readonly [0, 9]
+>a = 0 : 0
+>a : 0 | 1
+>0 : 0
+>9 : 9
+>[[8, 9] as const] : [readonly [8, 9]]
+>[8, 9] as const : readonly [8, 9]
+>[8, 9] : readonly [8, 9]
+>8 : 8
+>9 : 9
+
+    const bb: 0 | 8 = b;
+>bb : 0 | 8
+>b : 0 | 8
+}

tests/baselines/reference/controlFlowBindingPatternOrder.symbols

@@ -0,0 +1,54 @@
+=== tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts ===
+// https://github.com/microsoft/TypeScript/pull/41094#issuecomment-716044363
+{
+    let a: 0 | 1 = 0;
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 2, 7))
+
+    const [{ [(a = 1)]: b } = [9, a] as const] = [];
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 2, 7))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 3, 12))
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 2, 7))
+
+    const bb: 0 = b;
+>bb : Symbol(bb, Decl(controlFlowBindingPatternOrder.ts, 4, 9))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 3, 12))
+}
+{
+    let a: 0 | 1 = 1;
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 7, 7))
+
+    const [{ [a]: b } = [9, a = 0] as const] = [];
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 7, 7))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 8, 12))
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 7, 7))
+
+    const bb: 9 = b;
+>bb : Symbol(bb, Decl(controlFlowBindingPatternOrder.ts, 9, 9))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 8, 12))
+}
+{
+    let a: 0 | 1 = 0;
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 12, 7))
+
+    const [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 12, 7))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 13, 12))
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 12, 7))
+
+    const bb: 0 | 8 = b;
+>bb : Symbol(bb, Decl(controlFlowBindingPatternOrder.ts, 14, 9))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 13, 12))
+}
+{
+    let a: 0 | 1 = 1;
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 17, 7))
+
+    const [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 17, 7))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 18, 12))
+>a : Symbol(a, Decl(controlFlowBindingPatternOrder.ts, 17, 7))
+
+    const bb: 0 | 8 = b;
+>bb : Symbol(bb, Decl(controlFlowBindingPatternOrder.ts, 19, 9))
+>b : Symbol(b, Decl(controlFlowBindingPatternOrder.ts, 18, 12))
+}

tests/baselines/reference/controlFlowBindingPatternOrder.types

@@ -0,0 +1,92 @@
+=== tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts ===
+// https://github.com/microsoft/TypeScript/pull/41094#issuecomment-716044363
+{
+    let a: 0 | 1 = 0;
+>a : 0 | 1
+>0 : 0
+
+    const [{ [(a = 1)]: b } = [9, a] as const] = [];
+>(a = 1) : 1
+>a = 1 : 1
+>a : 0 | 1
+>1 : 1
+>b : 0
+>[9, a] as const : readonly [9, 0]
+>[9, a] : readonly [9, 0]
+>9 : 9
+>a : 0
+>[] : []
+
+    const bb: 0 = b;
+>bb : 0
+>b : 0
+}
+{
+    let a: 0 | 1 = 1;
+>a : 0 | 1
+>1 : 1
+
+    const [{ [a]: b } = [9, a = 0] as const] = [];
+>a : 0
+>b : 9
+>[9, a = 0] as const : readonly [9, 0]
+>[9, a = 0] : readonly [9, 0]
+>9 : 9
+>a = 0 : 0
+>a : 0 | 1
+>0 : 0
+>[] : []
+
+    const bb: 9 = b;
+>bb : 9
+>b : 9
+}
+{
+    let a: 0 | 1 = 0;
+>a : 0 | 1
+>0 : 0
+
+    const [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
+>(a = 1) : 1
+>a = 1 : 1
+>a : 0 | 1
+>1 : 1
+>b : 0 | 8
+>[9, a] as const : readonly [9, 0]
+>[9, a] : readonly [9, 0]
+>9 : 9
+>a : 0
+>[[9, 8] as const] : [readonly [9, 8]]
+>[9, 8] as const : readonly [9, 8]
+>[9, 8] : readonly [9, 8]
+>9 : 9
+>8 : 8
+
+    const bb: 0 | 8 = b;
+>bb : 0 | 8
+>b : 0 | 8
+}
+{
+    let a: 0 | 1 = 1;
+>a : 0 | 1
+>1 : 1
+
+    const [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+>a : 0
+>b : 0 | 8
+>[a = 0, 9] as const : readonly [0, 9]
+>[a = 0, 9] : readonly [0, 9]
+>a = 0 : 0
+>a : 0 | 1
+>0 : 0
+>9 : 9
+>[[8, 9] as const] : [readonly [8, 9]]
+>[8, 9] as const : readonly [8, 9]
+>[8, 9] : readonly [8, 9]
+>8 : 8
+>9 : 9
+
+    const bb: 0 | 8 = b;
+>bb : 0 | 8
+>b : 0 | 8
+}

tests/cases/conformance/controlFlow/controlFlowAssignmentPatternOrder.ts

@@ -0,0 +1,28 @@
+// @target: esnext
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/pull/41094#issuecomment-716044363
+{
+    let a: 0 | 1 = 0;
+    let b: 0 | 1 | 9;
+    [{ [(a = 1)]: b } = [9, a] as const] = [];
+    const bb: 0 = b;
+}
+{
+    let a: 0 | 1 = 1;
+    let b: 0 | 1 | 9;
+    [{ [a]: b } = [9, a = 0] as const] = [];
+    const bb: 9 = b;
+}
+{
+    let a: 0 | 1 = 0;
+    let b: 0 | 1 | 8 | 9;
+    [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
+    const bb: 0 | 8 = b;
+}
+{
+    let a: 0 | 1 = 1;
+    let b: 0 | 1 | 8 | 9;
+    [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+    const bb: 0 | 8 = b;
+}

tests/cases/conformance/controlFlow/controlFlowBindingPatternOrder.ts

@@ -0,0 +1,24 @@
+// @target: esnext
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/pull/41094#issuecomment-716044363
+{
+    let a: 0 | 1 = 0;
+    const [{ [(a = 1)]: b } = [9, a] as const] = [];
+    const bb: 0 = b;
+}
+{
+    let a: 0 | 1 = 1;
+    const [{ [a]: b } = [9, a = 0] as const] = [];
+    const bb: 9 = b;
+}
+{
+    let a: 0 | 1 = 0;
+    const [{ [(a = 1)]: b } = [9, a] as const] = [[9, 8] as const];
+    const bb: 0 | 8 = b;
+}
+{
+    let a: 0 | 1 = 1;
+    const [{ [a]: b } = [a = 0, 9] as const] = [[8, 9] as const];
+    const bb: 0 | 8 = b;
+}