🤖 Pick PR #53351 (Fix subtype reduction involving typ...) into release-5.0 (#53422)

Co-authored-by: Anders Hejlsberg <andersh@microsoft.com>

src/compiler/checker.ts

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

tests/baselines/reference/subtypeReductionUnionConstraints.symbols

@@ -0,0 +1,113 @@
+=== tests/cases/compiler/subtypeReductionUnionConstraints.ts ===
+// Repro from #53311
+
+type FooNode = {
+>FooNode : Symbol(FooNode, Decl(subtypeReductionUnionConstraints.ts, 0, 0))
+
+    kind: 'foo';
+>kind : Symbol(kind, Decl(subtypeReductionUnionConstraints.ts, 2, 16))
+
+    children: Node[];
+>children : Symbol(children, Decl(subtypeReductionUnionConstraints.ts, 3, 16))
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+
+};
+
+type BarNode = {
+>BarNode : Symbol(BarNode, Decl(subtypeReductionUnionConstraints.ts, 5, 2))
+
+    kind: 'bar';
+>kind : Symbol(kind, Decl(subtypeReductionUnionConstraints.ts, 7, 16))
+}
+
+type Node = FooNode | BarNode;
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+>FooNode : Symbol(FooNode, Decl(subtypeReductionUnionConstraints.ts, 0, 0))
+>BarNode : Symbol(BarNode, Decl(subtypeReductionUnionConstraints.ts, 5, 2))
+
+type Document = {
+>Document : Symbol(Document, Decl(subtypeReductionUnionConstraints.ts, 11, 30))
+
+    kind: 'document';
+>kind : Symbol(kind, Decl(subtypeReductionUnionConstraints.ts, 13, 17))
+
+    children: Node[];
+>children : Symbol(children, Decl(subtypeReductionUnionConstraints.ts, 14, 21))
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+
+};
+
+declare function isNode(node: unknown): node is Node;
+>isNode : Symbol(isNode, Decl(subtypeReductionUnionConstraints.ts, 16, 2))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 18, 24))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 18, 24))
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+
+declare function isBar(node: Node): node is BarNode;
+>isBar : Symbol(isBar, Decl(subtypeReductionUnionConstraints.ts, 18, 53))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 19, 23))
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 19, 23))
+>BarNode : Symbol(BarNode, Decl(subtypeReductionUnionConstraints.ts, 5, 2))
+
+export function visitNodes<T extends Node>(node: Document | Node, predicate: (testNode: Node) => testNode is T): void {
+>visitNodes : Symbol(visitNodes, Decl(subtypeReductionUnionConstraints.ts, 19, 52))
+>T : Symbol(T, Decl(subtypeReductionUnionConstraints.ts, 21, 27))
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
+>Document : Symbol(Document, Decl(subtypeReductionUnionConstraints.ts, 11, 30))
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+>predicate : Symbol(predicate, Decl(subtypeReductionUnionConstraints.ts, 21, 65))
+>testNode : Symbol(testNode, Decl(subtypeReductionUnionConstraints.ts, 21, 78))
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+>testNode : Symbol(testNode, Decl(subtypeReductionUnionConstraints.ts, 21, 78))
+>T : Symbol(T, Decl(subtypeReductionUnionConstraints.ts, 21, 27))
+
+    isNode(node) && predicate(node);
+>isNode : Symbol(isNode, Decl(subtypeReductionUnionConstraints.ts, 16, 2))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
+>predicate : Symbol(predicate, Decl(subtypeReductionUnionConstraints.ts, 21, 65))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
+
+    if (!isNode(node) || !isBar(node)) {
+>isNode : Symbol(isNode, Decl(subtypeReductionUnionConstraints.ts, 16, 2))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
+>isBar : Symbol(isBar, Decl(subtypeReductionUnionConstraints.ts, 18, 53))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
+
+        const nodes: Node[] = node.children;
+>nodes : Symbol(nodes, Decl(subtypeReductionUnionConstraints.ts, 24, 13))
+>Node : Symbol(Node, Decl(subtypeReductionUnionConstraints.ts, 9, 1))
+>node.children : Symbol(children, Decl(subtypeReductionUnionConstraints.ts, 3, 16), Decl(subtypeReductionUnionConstraints.ts, 14, 21))
+>node : Symbol(node, Decl(subtypeReductionUnionConstraints.ts, 21, 43))
+>children : Symbol(children, Decl(subtypeReductionUnionConstraints.ts, 3, 16), Decl(subtypeReductionUnionConstraints.ts, 14, 21))
+    }
+}
+
+// Repro from #53311
+
+type A = { a: string };
+>A : Symbol(A, Decl(subtypeReductionUnionConstraints.ts, 26, 1))
+>a : Symbol(a, Decl(subtypeReductionUnionConstraints.ts, 30, 10))
+
+type B = { b: string };
+>B : Symbol(B, Decl(subtypeReductionUnionConstraints.ts, 30, 23))
+>b : Symbol(b, Decl(subtypeReductionUnionConstraints.ts, 31, 10))
+
+function f1<T extends A | B>(t: T, x: A | B) {
+>f1 : Symbol(f1, Decl(subtypeReductionUnionConstraints.ts, 31, 23))
+>T : Symbol(T, Decl(subtypeReductionUnionConstraints.ts, 33, 12))
+>A : Symbol(A, Decl(subtypeReductionUnionConstraints.ts, 26, 1))
+>B : Symbol(B, Decl(subtypeReductionUnionConstraints.ts, 30, 23))
+>t : Symbol(t, Decl(subtypeReductionUnionConstraints.ts, 33, 29))
+>T : Symbol(T, Decl(subtypeReductionUnionConstraints.ts, 33, 12))
+>x : Symbol(x, Decl(subtypeReductionUnionConstraints.ts, 33, 34))
+>A : Symbol(A, Decl(subtypeReductionUnionConstraints.ts, 26, 1))
+>B : Symbol(B, Decl(subtypeReductionUnionConstraints.ts, 30, 23))
+
+    const a = [t, x];  // (A | B)[] by subtype reduction
+>a : Symbol(a, Decl(subtypeReductionUnionConstraints.ts, 34, 9))
+>t : Symbol(t, Decl(subtypeReductionUnionConstraints.ts, 33, 29))
+>x : Symbol(x, Decl(subtypeReductionUnionConstraints.ts, 33, 34))
+}
+

tests/baselines/reference/subtypeReductionUnionConstraints.types

@@ -0,0 +1,99 @@
+=== tests/cases/compiler/subtypeReductionUnionConstraints.ts ===
+// Repro from #53311
+
+type FooNode = {
+>FooNode : { kind: 'foo'; children: Node[]; }
+
+    kind: 'foo';
+>kind : "foo"
+
+    children: Node[];
+>children : Node[]
+
+};
+
+type BarNode = {
+>BarNode : { kind: 'bar'; }
+
+    kind: 'bar';
+>kind : "bar"
+}
+
+type Node = FooNode | BarNode;
+>Node : FooNode | BarNode
+
+type Document = {
+>Document : { kind: 'document'; children: Node[]; }
+
+    kind: 'document';
+>kind : "document"
+
+    children: Node[];
+>children : Node[]
+
+};
+
+declare function isNode(node: unknown): node is Node;
+>isNode : (node: unknown) => node is Node
+>node : unknown
+
+declare function isBar(node: Node): node is BarNode;
+>isBar : (node: Node) => node is BarNode
+>node : Node
+
+export function visitNodes<T extends Node>(node: Document | Node, predicate: (testNode: Node) => testNode is T): void {
+>visitNodes : <T extends Node>(node: Document | Node, predicate: (testNode: Node) => testNode is T) => void
+>node : Node | Document
+>predicate : (testNode: Node) => testNode is T
+>testNode : Node
+
+    isNode(node) && predicate(node);
+>isNode(node) && predicate(node) : boolean
+>isNode(node) : boolean
+>isNode : (node: unknown) => node is Node
+>node : Node | Document
+>predicate(node) : boolean
+>predicate : (testNode: Node) => testNode is T
+>node : Node
+
+    if (!isNode(node) || !isBar(node)) {
+>!isNode(node) || !isBar(node) : boolean
+>!isNode(node) : boolean
+>isNode(node) : boolean
+>isNode : (node: unknown) => node is Node
+>node : Node | Document
+>!isBar(node) : boolean
+>isBar(node) : boolean
+>isBar : (node: Node) => node is BarNode
+>node : Node
+
+        const nodes: Node[] = node.children;
+>nodes : Node[]
+>node.children : Node[]
+>node : FooNode | Document
+>children : Node[]
+    }
+}
+
+// Repro from #53311
+
+type A = { a: string };
+>A : { a: string; }
+>a : string
+
+type B = { b: string };
+>B : { b: string; }
+>b : string
+
+function f1<T extends A | B>(t: T, x: A | B) {
+>f1 : <T extends A | B>(t: T, x: A | B) => void
+>t : T
+>x : A | B
+
+    const a = [t, x];  // (A | B)[] by subtype reduction
+>a : (A | B)[]
+>[t, x] : (A | B)[]
+>t : T
+>x : A | B
+}
+

tests/cases/compiler/subtypeReductionUnionConstraints.ts

@@ -0,0 +1,39 @@
+// @strict: true
+// @noEmit: true
+
+// Repro from #53311
+
+type FooNode = {
+    kind: 'foo';
+    children: Node[];
+};
+
+type BarNode = {
+    kind: 'bar';
+}
+
+type Node = FooNode | BarNode;
+
+type Document = {
+    kind: 'document';
+    children: Node[];
+};
+
+declare function isNode(node: unknown): node is Node;
+declare function isBar(node: Node): node is BarNode;
+
+export function visitNodes<T extends Node>(node: Document | Node, predicate: (testNode: Node) => testNode is T): void {
+    isNode(node) && predicate(node);
+    if (!isNode(node) || !isBar(node)) {
+        const nodes: Node[] = node.children;
+    }
+}
+
+// Repro from #53311
+
+type A = { a: string };
+type B = { b: string };
+
+function f1<T extends A | B>(t: T, x: A | B) {
+    const a = [t, x];  // (A | B)[] by subtype reduction
+}