Merge pull request microsoft#22830 from Microsoft/fixDestructuringWithConstraint

Fix control flow analysis for destructuring with constraint

Author: ahejlsberg

src/compiler/checker.ts

@@ -4082,8 +4082,7 @@ namespace ts {
                     if (strictNullChecks && declaration.flags & NodeFlags.Ambient && isParameterDeclaration(declaration)) {
                         parentType = getNonNullableType(parentType);
                     }
-                    const propType = getTypeOfPropertyOfType(parentType, text);
-                    const declaredType = propType && getConstraintForLocation(propType, declaration.name);
+                    const declaredType = getConstraintForLocation(getTypeOfPropertyOfType(parentType, text), declaration.name);
                     type = declaredType && getFlowTypeOfReference(declaration, declaredType) ||
                         isNumericLiteralName(text) && getIndexTypeOfType(parentType, IndexKind.Number) ||
                         getIndexTypeOfType(parentType, IndexKind.String);
@@ -12382,7 +12381,7 @@ namespace ts {
 
         function getTypeOfDestructuredProperty(type: Type, name: PropertyName) {
             const text = getTextOfPropertyName(name);
-            return getTypeOfPropertyOfType(type, text) ||
+            return getConstraintForLocation(getTypeOfPropertyOfType(type, text), name) ||
                 isNumericLiteralName(text) && getIndexTypeOfType(type, IndexKind.Number) ||
                 getIndexTypeOfType(type, IndexKind.String) ||
                 unknownType;
@@ -13498,7 +13497,7 @@ namespace ts {
             // and the type of the node includes type variables with constraints that are nullable, we fetch the
             // apparent type of the node *before* performing control flow analysis such that narrowings apply to
             // the constraint type.
-            if (isConstraintPosition(node) && forEachType(type, typeHasNullableConstraint)) {
+            if (type && isConstraintPosition(node) && forEachType(type, typeHasNullableConstraint)) {
                 return mapType(getWidenedType(type), getBaseConstraintOrType);
             }
             return type;

tests/baselines/reference/destructuringWithConstraint.js

@@ -0,0 +1,20 @@
+//// [destructuringWithConstraint.ts]
+// Repro from #22823
+
+interface Props {
+    foo?: boolean;
+}
+
+function foo<P extends Props>(props: Readonly<P>) {
+    let { foo = false } = props;
+    if (foo === true) { }
+}
+
+
+//// [destructuringWithConstraint.js]
+"use strict";
+// Repro from #22823
+function foo(props) {
+    var _a = props.foo, foo = _a === void 0 ? false : _a;
+    if (foo === true) { }
+}

tests/baselines/reference/destructuringWithConstraint.symbols

@@ -0,0 +1,26 @@
+=== tests/cases/compiler/destructuringWithConstraint.ts ===
+// Repro from #22823
+
+interface Props {
+>Props : Symbol(Props, Decl(destructuringWithConstraint.ts, 0, 0))
+
+    foo?: boolean;
+>foo : Symbol(Props.foo, Decl(destructuringWithConstraint.ts, 2, 17))
+}
+
+function foo<P extends Props>(props: Readonly<P>) {
+>foo : Symbol(foo, Decl(destructuringWithConstraint.ts, 4, 1))
+>P : Symbol(P, Decl(destructuringWithConstraint.ts, 6, 13))
+>Props : Symbol(Props, Decl(destructuringWithConstraint.ts, 0, 0))
+>props : Symbol(props, Decl(destructuringWithConstraint.ts, 6, 30))
+>Readonly : Symbol(Readonly, Decl(lib.d.ts, --, --))
+>P : Symbol(P, Decl(destructuringWithConstraint.ts, 6, 13))
+
+    let { foo = false } = props;
+>foo : Symbol(foo, Decl(destructuringWithConstraint.ts, 7, 9))
+>props : Symbol(props, Decl(destructuringWithConstraint.ts, 6, 30))
+
+    if (foo === true) { }
+>foo : Symbol(foo, Decl(destructuringWithConstraint.ts, 7, 9))
+}
+

tests/baselines/reference/destructuringWithConstraint.types

@@ -0,0 +1,29 @@
+=== tests/cases/compiler/destructuringWithConstraint.ts ===
+// Repro from #22823
+
+interface Props {
+>Props : Props
+
+    foo?: boolean;
+>foo : boolean | undefined
+}
+
+function foo<P extends Props>(props: Readonly<P>) {
+>foo : <P extends Props>(props: Readonly<P>) => void
+>P : P
+>Props : Props
+>props : Readonly<P>
+>Readonly : Readonly<T>
+>P : P
+
+    let { foo = false } = props;
+>foo : boolean
+>false : false
+>props : Readonly<P>
+
+    if (foo === true) { }
+>foo === true : boolean
+>foo : boolean
+>true : true
+}
+

tests/cases/compiler/destructuringWithConstraint.ts

@@ -0,0 +1,12 @@
+// @strict: true
+
+// Repro from #22823
+
+interface Props {
+    foo?: boolean;
+}
+
+function foo<P extends Props>(props: Readonly<P>) {
+    let { foo = false } = props;
+    if (foo === true) { }
+}