Improve binding element type inference

src/compiler/checker.ts

@@ -9491,8 +9491,33 @@ namespace ts {
                 // The type implied by a binding pattern is independent of context, so we check the initializer with no
                 // contextual type or, if the element itself is a binding pattern, with the type implied by that binding
                 // pattern.
-                const contextualType = isBindingPattern(element.name) ? getTypeFromBindingPattern(element.name, /*includePatternInType*/ true, /*reportErrors*/ false) : unknownType;
-                return addOptionality(widenTypeInferredFromInitializer(element, checkDeclarationInitializer(element, CheckMode.Normal, contextualType)));
+                if (isBindingPattern(element.name)) {
+                    const contextualType = getTypeFromBindingPattern(element.name, /*includePatternInType*/ true, /*reportErrors*/ false);
+                    return addOptionality(widenTypeInferredFromInitializer(element, checkDeclarationInitializer(element, CheckMode.Normal, contextualType)));
+                }
+
+                // (#49989)
+                // In cases where the intitializer is an identifier referencing a sibling symbol (i.e., one that is
+                // defined in the same declaration) a false circular relationship will be concluded. For example, take
+                // the declarations below:
+                //
+                //   const [a, b = a] = [1];
+                //   const {a, b = a} = {a: 1};
+                //
+                // Here, when the `element` is the second binding element (i.e., `b = a`) the initializer is `a` which
+                // itself is defined within the same binding pattern.
+                //
+                // So, we check the initializer expression for any references to sibling symbols and if any, then we'd
+                // conclude the binding element type as `unknownType` and thus skip further circulations in type
+                // checking.
+                const siblings = mapDefined(element.parent.elements, x => x !== element && isBindingElement(x) && isIdentifier(x.name) ? x : undefined);
+                const checkIsSiblingInvolved = (node: Node) => {
+                    const declaration = isIdentifier(node) && getReferencedValueDeclaration(node);
+                    return declaration && isBindingElement(declaration) && siblings.includes(declaration);
+                };
+                const isSiblingElementInvolded = checkIsSiblingInvolved(element.initializer) || forEachChildRecursively(element.initializer, checkIsSiblingInvolved);
+                return isSiblingElementInvolded ? anyType
+                    : addOptionality(widenTypeInferredFromInitializer(element, checkDeclarationInitializer(element, CheckMode.Normal, unknownType)));
             }
             if (isBindingPattern(element.name)) {
                 return getTypeFromBindingPattern(element.name, includePatternInType, reportErrors);

tests/baselines/reference/dependentDestructuredVariables.errors.txt

@@ -1,8 +1,7 @@
-tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts(314,5): error TS7022: 'value1' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
 tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts(314,5): error TS7031: Binding element 'value1' implicitly has an 'any' type.
 
 
-==== tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts (2 errors) ====
+==== tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts (1 errors) ====
     type Action =
         | { kind: 'A', payload: number }
         | { kind: 'B', payload: string };
@@ -318,8 +317,6 @@ tests/cases/conformance/controlFlow/dependentDestructuredVariables.ts(314,5): er
     function foo({
         value1,
         ~~~~~~
-!!! error TS7022: 'value1' implicitly has type 'any' because it does not have a type annotation and is referenced directly or indirectly in its own initializer.
-        ~~~~~~
 !!! error TS7031: Binding element 'value1' implicitly has an 'any' type.
         test1 = value1.test1,
         test2 = value1.test2,

tests/baselines/reference/destructuringArrayBindingPatternAndAssignment3.types

@@ -1,28 +1,28 @@
 === tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment3.ts ===
 const [a, b = a] = [1]; // ok
->a : any
->b : any
->a : any
+>a : number
+>b : number
+>a : number
 >[1] : [number]
 >1 : 1
 
 const [c, d = c, e = e] = [1]; // error for e = e
->c : any
->d : any
->c : any
+>c : number
+>d : number
+>c : number
 >e : any
 >e : any
 >[1] : [number]
 >1 : 1
 
 const [f, g = f, h = i, i = f] = [1]; // error for h = i
->f : any
->g : any
->f : any
->h : any
->i : any
->i : any
->f : any
+>f : number
+>g : number
+>f : number
+>h : number
+>i : number
+>i : number
+>f : number
 >[1] : [number]
 >1 : 1
 

tests/baselines/reference/destructuringArrayBindingPatternAndAssignment5.js

@@ -0,0 +1,48 @@
+//// [destructuringArrayBindingPatternAndAssignment5.ts]
+// To be inferred as `number`
+function f1() {
+    const [a1, b1 = a1] = [1];
+    const [a2, b2 = 1 + a2] = [1];
+    const [a3, b3 = (() => 1 + a3)()] = [1];
+    const [a4, b4 = (() => (() => 1 + a4)() + 1)()] = [1];
+}
+
+// To be inferred as `string`
+function f2() {
+    const [a1, b1 = a1] = ['hi'];
+    const [a2, b2 = [a2, '!'].join()] = ['hi'];
+    const [a3, b3 = (() => [a3, '!'].join())()] = ['hi'];
+    const [a4, b4 = (() => (() => [a4, '!'].join())() + '!')()] = ['hi'];
+}
+
+// To be inferred as `string | number`
+function f3() {
+    const [a1, b1 = a1] = ['hi', 1];
+    const [a2, b2 = [a2, '!'].join()] = ['hi', 1];
+    const [a3, b3 = (() => [a3, '!'].join())()] = ['hi', 1];
+    const [a4, b4 = (() => (() => [a4, '!'].join())() + '!')()] = ['hi', 1];
+}
+
+
+//// [destructuringArrayBindingPatternAndAssignment5.js]
+// To be inferred as `number`
+function f1() {
+    var _a = [1], a1 = _a[0], _b = _a[1], b1 = _b === void 0 ? a1 : _b;
+    var _c = [1], a2 = _c[0], _d = _c[1], b2 = _d === void 0 ? 1 + a2 : _d;
+    var _e = [1], a3 = _e[0], _f = _e[1], b3 = _f === void 0 ? (function () { return 1 + a3; })() : _f;
+    var _g = [1], a4 = _g[0], _h = _g[1], b4 = _h === void 0 ? (function () { return (function () { return 1 + a4; })() + 1; })() : _h;
+}
+// To be inferred as `string`
+function f2() {
+    var _a = ['hi'], a1 = _a[0], _b = _a[1], b1 = _b === void 0 ? a1 : _b;
+    var _c = ['hi'], a2 = _c[0], _d = _c[1], b2 = _d === void 0 ? [a2, '!'].join() : _d;
+    var _e = ['hi'], a3 = _e[0], _f = _e[1], b3 = _f === void 0 ? (function () { return [a3, '!'].join(); })() : _f;
+    var _g = ['hi'], a4 = _g[0], _h = _g[1], b4 = _h === void 0 ? (function () { return (function () { return [a4, '!'].join(); })() + '!'; })() : _h;
+}
+// To be inferred as `string | number`
+function f3() {
+    var _a = ['hi', 1], a1 = _a[0], _b = _a[1], b1 = _b === void 0 ? a1 : _b;
+    var _c = ['hi', 1], a2 = _c[0], _d = _c[1], b2 = _d === void 0 ? [a2, '!'].join() : _d;
+    var _e = ['hi', 1], a3 = _e[0], _f = _e[1], b3 = _f === void 0 ? (function () { return [a3, '!'].join(); })() : _f;
+    var _g = ['hi', 1], a4 = _g[0], _h = _g[1], b4 = _h === void 0 ? (function () { return (function () { return [a4, '!'].join(); })() + '!'; })() : _h;
+}

tests/baselines/reference/destructuringArrayBindingPatternAndAssignment5.symbols

@@ -0,0 +1,88 @@
+=== tests/cases/conformance/es6/destructuring/destructuringArrayBindingPatternAndAssignment5.ts ===
+// To be inferred as `number`
+function f1() {
+>f1 : Symbol(f1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 0, 0))
+
+    const [a1, b1 = a1] = [1];
+>a1 : Symbol(a1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 2, 11))
+>b1 : Symbol(b1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 2, 14))
+>a1 : Symbol(a1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 2, 11))
+
+    const [a2, b2 = 1 + a2] = [1];
+>a2 : Symbol(a2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 3, 11))
+>b2 : Symbol(b2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 3, 14))
+>a2 : Symbol(a2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 3, 11))
+
+    const [a3, b3 = (() => 1 + a3)()] = [1];
+>a3 : Symbol(a3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 4, 11))
+>b3 : Symbol(b3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 4, 14))
+>a3 : Symbol(a3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 4, 11))
+
+    const [a4, b4 = (() => (() => 1 + a4)() + 1)()] = [1];
+>a4 : Symbol(a4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 5, 11))
+>b4 : Symbol(b4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 5, 14))
+>a4 : Symbol(a4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 5, 11))
+}
+
+// To be inferred as `string`
+function f2() {
+>f2 : Symbol(f2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 6, 1))
+
+    const [a1, b1 = a1] = ['hi'];
+>a1 : Symbol(a1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 10, 11))
+>b1 : Symbol(b1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 10, 14))
+>a1 : Symbol(a1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 10, 11))
+
+    const [a2, b2 = [a2, '!'].join()] = ['hi'];
+>a2 : Symbol(a2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 11, 11))
+>b2 : Symbol(b2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 11, 14))
+>[a2, '!'].join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+>a2 : Symbol(a2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 11, 11))
+>join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+
+    const [a3, b3 = (() => [a3, '!'].join())()] = ['hi'];
+>a3 : Symbol(a3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 12, 11))
+>b3 : Symbol(b3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 12, 14))
+>[a3, '!'].join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+>a3 : Symbol(a3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 12, 11))
+>join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+
+    const [a4, b4 = (() => (() => [a4, '!'].join())() + '!')()] = ['hi'];
+>a4 : Symbol(a4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 13, 11))
+>b4 : Symbol(b4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 13, 14))
+>[a4, '!'].join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+>a4 : Symbol(a4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 13, 11))
+>join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+}
+
+// To be inferred as `string | number`
+function f3() {
+>f3 : Symbol(f3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 14, 1))
+
+    const [a1, b1 = a1] = ['hi', 1];
+>a1 : Symbol(a1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 18, 11))
+>b1 : Symbol(b1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 18, 14))
+>a1 : Symbol(a1, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 18, 11))
+
+    const [a2, b2 = [a2, '!'].join()] = ['hi', 1];
+>a2 : Symbol(a2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 19, 11))
+>b2 : Symbol(b2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 19, 14))
+>[a2, '!'].join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+>a2 : Symbol(a2, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 19, 11))
+>join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+
+    const [a3, b3 = (() => [a3, '!'].join())()] = ['hi', 1];
+>a3 : Symbol(a3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 20, 11))
+>b3 : Symbol(b3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 20, 14))
+>[a3, '!'].join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+>a3 : Symbol(a3, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 20, 11))
+>join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+
+    const [a4, b4 = (() => (() => [a4, '!'].join())() + '!')()] = ['hi', 1];
+>a4 : Symbol(a4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 21, 11))
+>b4 : Symbol(b4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 21, 14))
+>[a4, '!'].join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+>a4 : Symbol(a4, Decl(destructuringArrayBindingPatternAndAssignment5.ts, 21, 11))
+>join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
+}
+