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🤖 Pick PR #53351 (Fix subtype reduction involving typ...) into release-5.0 (#53422)
Co-authored-by: Anders Hejlsberg <[email protected]>
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‎src/compiler/checker.ts

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@@ -16199,6 +16199,16 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
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i--;
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const source = types[i];
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if (hasEmptyObject || source.flags & TypeFlags.StructuredOrInstantiable) {
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// A type parameter with a union constraint may be a subtype of some union, but not a subtype of the
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// individual constituents of that union. For example, `T extends A | B` is a subtype of `A | B`, but not
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// a subtype of just `A` or just `B`. When we encounter such a type parameter, we therefore check if the
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// type parameter is a subtype of a union of all the other types.
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if (source.flags & TypeFlags.TypeParameter && getBaseConstraintOrType(source).flags & TypeFlags.Union) {
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if (isTypeRelatedTo(source, getUnionType(map(types, t => t === source ? neverType : t)), strictSubtypeRelation)) {
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orderedRemoveItemAt(types, i);
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}
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continue;
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}
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// Find the first property with a unit type, if any. When constituents have a property by the same name
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// but of a different unit type, we can quickly disqualify them from subtype checks. This helps subtype
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// reduction of large discriminated union types.

‎tests/baselines/reference/subtypeReductionUnionConstraints.symbols

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=== tests/cases/compiler/subtypeReductionUnionConstraints.ts ===
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// Repro from #53311
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type FooNode = {
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>FooNode : Symbol(FooNode, Decl(subtypeReductionUnionConstraints.ts, 0, 0))
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kind: 'foo';
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>kind : Symbol(kind, Decl(subtypeReductionUnionConstraints.ts, 2, 16))
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children: Node[];
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>children : Symbol(children, Decl(subtypeReductionUnionConstraints.ts, 3, 16))
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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};
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type BarNode = {
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>BarNode : Symbol(BarNode, Decl(subtypeReductionUnionConstraints.ts, 5, 2))
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kind: 'bar';
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>kind : Symbol(kind, Decl(subtypeReductionUnionConstraints.ts, 7, 16))
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}
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type Node = FooNode | BarNode;
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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>FooNode : Symbol(FooNode, Decl(subtypeReductionUnionConstraints.ts, 0, 0))
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>BarNode : Symbol(BarNode, Decl(subtypeReductionUnionConstraints.ts, 5, 2))
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type Document = {
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>Document : Symbol(Document, Decl(subtypeReductionUnionConstraints.ts, 11, 30))
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kind: 'document';
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>kind : Symbol(kind, Decl(subtypeReductionUnionConstraints.ts, 13, 17))
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children: Node[];
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>children : Symbol(children, Decl(subtypeReductionUnionConstraints.ts, 14, 21))
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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};
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declare function isNode(node: unknown): node is Node;
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>isNode : Symbol(isNode, Decl(subtypeReductionUnionConstraints.ts, 16, 2))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 18, 24))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 18, 24))
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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declare function isBar(node: Node): node is BarNode;
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>isBar : Symbol(isBar, Decl(subtypeReductionUnionConstraints.ts, 18, 53))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 19, 23))
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 19, 23))
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>BarNode : Symbol(BarNode, Decl(subtypeReductionUnionConstraints.ts, 5, 2))
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export function visitNodes<T extends Node>(node: Document | Node, predicate: (testNode: Node) => testNode is T): void {
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>visitNodes : Symbol(visitNodes, Decl(subtypeReductionUnionConstraints.ts, 19, 52))
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>T : Symbol(T, Decl(subtypeReductionUnionConstraints.ts, 21, 27))
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
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>Document : Symbol(Document, Decl(subtypeReductionUnionConstraints.ts, 11, 30))
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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>predicate : Symbol(predicate, Decl(subtypeReductionUnionConstraints.ts, 21, 65))
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>testNode : Symbol(testNode, Decl(subtypeReductionUnionConstraints.ts, 21, 78))
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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>testNode : Symbol(testNode, Decl(subtypeReductionUnionConstraints.ts, 21, 78))
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>T : Symbol(T, Decl(subtypeReductionUnionConstraints.ts, 21, 27))
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isNode(node) && predicate(node);
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>isNode : Symbol(isNode, Decl(subtypeReductionUnionConstraints.ts, 16, 2))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
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>predicate : Symbol(predicate, Decl(subtypeReductionUnionConstraints.ts, 21, 65))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
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if (!isNode(node) || !isBar(node)) {
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>isNode : Symbol(isNode, Decl(subtypeReductionUnionConstraints.ts, 16, 2))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
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>isBar : Symbol(isBar, Decl(subtypeReductionUnionConstraints.ts, 18, 53))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
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const nodes: Node[] = node.children;
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>nodes : Symbol(nodes, Decl(subtypeReductionUnionConstraints.ts, 24, 13))
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>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
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>node.children : Symbol(children, Decl(subtypeReductionUnionConstraints.ts, 3, 16), Decl(subtypeReductionUnionConstraints.ts, 14, 21))
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>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
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>children : Symbol(children, Decl(subtypeReductionUnionConstraints.ts, 3, 16), Decl(subtypeReductionUnionConstraints.ts, 14, 21))
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}
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}
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// Repro from #53311
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type A = { a: string };
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>A : Symbol(A, Decl(subtypeReductionUnionConstraints.ts, 26, 1))
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>a : Symbol(a, Decl(subtypeReductionUnionConstraints.ts, 30, 10))
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type B = { b: string };
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>B : Symbol(B, Decl(subtypeReductionUnionConstraints.ts, 30, 23))
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>b : Symbol(b, Decl(subtypeReductionUnionConstraints.ts, 31, 10))
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function f1<T extends A | B>(t: T, x: A | B) {
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>f1 : Symbol(f1, Decl(subtypeReductionUnionConstraints.ts, 31, 23))
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>T : Symbol(T, Decl(subtypeReductionUnionConstraints.ts, 33, 12))
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>A : Symbol(A, Decl(subtypeReductionUnionConstraints.ts, 26, 1))
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>B : Symbol(B, Decl(subtypeReductionUnionConstraints.ts, 30, 23))
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>t : Symbol(t, Decl(subtypeReductionUnionConstraints.ts, 33, 29))
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>T : Symbol(T, Decl(subtypeReductionUnionConstraints.ts, 33, 12))
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>x : Symbol(x, Decl(subtypeReductionUnionConstraints.ts, 33, 34))
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>A : Symbol(A, Decl(subtypeReductionUnionConstraints.ts, 26, 1))
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>B : Symbol(B, Decl(subtypeReductionUnionConstraints.ts, 30, 23))
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const a = [t, x]; // (A | B)[] by subtype reduction
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>a : Symbol(a, Decl(subtypeReductionUnionConstraints.ts, 34, 9))
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>t : Symbol(t, Decl(subtypeReductionUnionConstraints.ts, 33, 29))
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>x : Symbol(x, Decl(subtypeReductionUnionConstraints.ts, 33, 34))
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}
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‎tests/baselines/reference/subtypeReductionUnionConstraints.types

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=== tests/cases/compiler/subtypeReductionUnionConstraints.ts ===
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// Repro from #53311
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type FooNode = {
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>FooNode : { kind: 'foo'; children: Node[]; }
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kind: 'foo';
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>kind : "foo"
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children: Node[];
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>children : Node[]
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};
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type BarNode = {
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>BarNode : { kind: 'bar'; }
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kind: 'bar';
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>kind : "bar"
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}
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type Node = FooNode | BarNode;
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>Node : FooNode | BarNode
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type Document = {
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>Document : { kind: 'document'; children: Node[]; }
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kind: 'document';
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>kind : "document"
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children: Node[];
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>children : Node[]
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};
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declare function isNode(node: unknown): node is Node;
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>isNode : (node: unknown) => node is Node
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>node : unknown
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declare function isBar(node: Node): node is BarNode;
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>isBar : (node: Node) => node is BarNode
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>node : Node
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export function visitNodes<T extends Node>(node: Document | Node, predicate: (testNode: Node) => testNode is T): void {
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>visitNodes : <T extends Node>(node: Document | Node, predicate: (testNode: Node) => testNode is T) => void
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>node : Node | Document
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>predicate : (testNode: Node) => testNode is T
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>testNode : Node
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isNode(node) && predicate(node);
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>isNode(node) && predicate(node) : boolean
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>isNode(node) : boolean
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>isNode : (node: unknown) => node is Node
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>node : Node | Document
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>predicate(node) : boolean
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>predicate : (testNode: Node) => testNode is T
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>node : Node
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if (!isNode(node) || !isBar(node)) {
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>!isNode(node) || !isBar(node) : boolean
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>!isNode(node) : boolean
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>isNode(node) : boolean
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>isNode : (node: unknown) => node is Node
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>node : Node | Document
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>!isBar(node) : boolean
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>isBar(node) : boolean
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>isBar : (node: Node) => node is BarNode
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>node : Node
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const nodes: Node[] = node.children;
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>nodes : Node[]
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>node.children : Node[]
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>node : FooNode | Document
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>children : Node[]
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}
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}
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// Repro from #53311
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type A = { a: string };
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>A : { a: string; }
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>a : string
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type B = { b: string };
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>B : { b: string; }
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>b : string
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function f1<T extends A | B>(t: T, x: A | B) {
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>f1 : <T extends A | B>(t: T, x: A | B) => void
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>t : T
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>x : A | B
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const a = [t, x]; // (A | B)[] by subtype reduction
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>a : (A | B)[]
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>[t, x] : (A | B)[]
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>t : T
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>x : A | B
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}
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‎tests/cases/compiler/subtypeReductionUnionConstraints.ts

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// @strict: true
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// @noEmit: true
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// Repro from #53311
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type FooNode = {
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kind: 'foo';
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children: Node[];
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};
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type BarNode = {
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kind: 'bar';
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}
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type Node = FooNode | BarNode;
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type Document = {
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kind: 'document';
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children: Node[];
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};
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declare function isNode(node: unknown): node is Node;
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declare function isBar(node: Node): node is BarNode;
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export function visitNodes<T extends Node>(node: Document | Node, predicate: (testNode: Node) => testNode is T): void {
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isNode(node) && predicate(node);
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if (!isNode(node) || !isBar(node)) {
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const nodes: Node[] = node.children;
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}
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}
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// Repro from #53311
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type A = { a: string };
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type B = { b: string };
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function f1<T extends A | B>(t: T, x: A | B) {
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const a = [t, x]; // (A | B)[] by subtype reduction
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}

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