Optimize intersections of unions of unit types

src/compiler/checker.ts

@@ -8319,7 +8319,7 @@ namespace ts {
                     includes & TypeFlags.Undefined ? includes & TypeFlags.NonWideningType ? undefinedType : undefinedWideningType :
                         neverType;
             }
-            return getUnionTypeFromSortedList(typeSet, aliasSymbol, aliasTypeArguments);
+            return getUnionTypeFromSortedList(typeSet, includes & TypeFlags.NotUnit ? 0 : TypeFlags.UnionOfUnitTypes, aliasSymbol, aliasTypeArguments);
         }
 
         function getUnionTypePredicate(signatures: ReadonlyArray<Signature>): TypePredicate {
@@ -8359,7 +8359,7 @@ namespace ts {
         }
 
         // This function assumes the constituent type list is sorted and deduplicated.
-        function getUnionTypeFromSortedList(types: Type[], aliasSymbol?: Symbol, aliasTypeArguments?: Type[]): Type {
+        function getUnionTypeFromSortedList(types: Type[], unionOfUnitTypes: TypeFlags, aliasSymbol?: Symbol, aliasTypeArguments?: Type[]): Type {
             if (types.length === 0) {
                 return neverType;
             }
@@ -8370,7 +8370,7 @@ namespace ts {
             let type = unionTypes.get(id);
             if (!type) {
                 const propagatedFlags = getPropagatingFlagsOfTypes(types, /*excludeKinds*/ TypeFlags.Nullable);
-                type = <UnionType>createType(TypeFlags.Union | propagatedFlags);
+                type = <UnionType>createType(TypeFlags.Union | propagatedFlags | unionOfUnitTypes);
                 unionTypes.set(id, type);
                 type.types = types;
                 /*
@@ -8441,6 +8441,29 @@ namespace ts {
             }
         }
 
+        // When intersecting unions of unit types we can simply intersect based on type identity.
+        // Here we remove all unions of unit types from the given list and replace them with a
+        // a single union containing an intersection of the unit types.
+        function intersectUnionsOfUnitTypes(types: Type[]) {
+            const unionIndex = findIndex(types, t => (t.flags & TypeFlags.UnionOfUnitTypes) !== 0);
+            const unionType = <UnionType>types[unionIndex];
+            let intersection = unionType.types;
+            let i = types.length - 1;
+            while (i > unionIndex) {
+                const t = types[i];
+                if (t.flags & TypeFlags.UnionOfUnitTypes) {
+                    intersection = filter(intersection, u => containsType((<UnionType>t).types, u));
+                    orderedRemoveItemAt(types, i);
+                }
+                i--;
+            }
+            if (intersection === unionType.types) {
+                return false;
+            }
+            types[unionIndex] = getUnionTypeFromSortedList(intersection, unionType.flags & TypeFlags.UnionOfUnitTypes);
+            return true;
+        }
+
         // We normalize combinations of intersection and union types based on the distributive property of the '&'
         // operator. Specifically, because X & (A | B) is equivalent to X & A | X & B, we can transform intersection
         // types with union type constituents into equivalent union types with intersection type constituents and
@@ -8475,6 +8498,12 @@ namespace ts {
                 return typeSet[0];
             }
             if (includes & TypeFlags.Union) {
+                if (includes & TypeFlags.UnionOfUnitTypes && intersectUnionsOfUnitTypes(typeSet)) {
+                    // When the intersection creates a reduced set (which might mean that *all* union types have
+                    // disappeared), we restart the operation to get a new set of combined flags. Once we have
+                    // reduced we'll never reduce again, so this occurs at most once.
+                    return getIntersectionType(typeSet, aliasSymbol, aliasTypeArguments);
+                }
                 // We are attempting to construct a type of the form X & (A | B) & Y. Transform this into a type of
                 // the form X & A & Y | X & B & Y and recursively reduce until no union type constituents remain.
                 const unionIndex = findIndex(typeSet, t => (t.flags & TypeFlags.Union) !== 0);
@@ -13234,7 +13263,7 @@ namespace ts {
             if (type.flags & TypeFlags.Union) {
                 const types = (<UnionType>type).types;
                 const filtered = filter(types, f);
-                return filtered === types ? type : getUnionTypeFromSortedList(filtered);
+                return filtered === types ? type : getUnionTypeFromSortedList(filtered, type.flags & TypeFlags.UnionOfUnitTypes);
             }
             return f(type) ? type : neverType;
         }

src/compiler/types.ts

@@ -3674,6 +3674,8 @@ namespace ts {
         ContainsAnyFunctionType = 1 << 26,  // Type is or contains the anyFunctionType
         NonPrimitive            = 1 << 27,  // intrinsic object type
         /* @internal */
+        UnionOfUnitTypes        = 1 << 28,  // Type is union of unit types
+        /* @internal */
         GenericMappedType       = 1 << 29,  // Flag used by maybeTypeOfKind
 
         /* @internal */
@@ -3711,6 +3713,8 @@ namespace ts {
         Narrowable = Any | StructuredOrInstantiable | StringLike | NumberLike | BooleanLike | ESSymbol | UniqueESSymbol | NonPrimitive,
         NotUnionOrUnit = Any | ESSymbol | Object | NonPrimitive,
         /* @internal */
+        NotUnit = Any | String | Number | Boolean | Enum | ESSymbol | Void | Never | StructuredOrInstantiable,
+        /* @internal */
         RequiresWidening = ContainsWideningType | ContainsObjectLiteral,
         /* @internal */
         PropagatingFlags = ContainsWideningType | ContainsObjectLiteral | ContainsAnyFunctionType,

tests/baselines/reference/intersectionsOfLargeUnions.errors.txt

@@ -0,0 +1,35 @@
+tests/cases/compiler/intersectionsOfLargeUnions.ts(21,15): error TS2536: Type 'T' cannot be used to index type 'HTMLElementTagNameMap'.
+tests/cases/compiler/intersectionsOfLargeUnions.ts(21,15): error TS2536: Type 'P' cannot be used to index type 'HTMLElementTagNameMap[T]'.
+
+
+==== tests/cases/compiler/intersectionsOfLargeUnions.ts (2 errors) ====
+    // Repro from #23977
+
+    export function assertIsElement(node: Node | null): node is Element {
+        let nodeType = node === null ? null : node.nodeType;
+        return nodeType === 1;
+    }
+
+    export function assertNodeTagName<
+        T extends keyof ElementTagNameMap,
+        U extends ElementTagNameMap[T]>(node: Node | null, tagName: T): node is U {
+        if (assertIsElement(node)) {
+            const nodeTagName = node.tagName.toLowerCase();
+             return nodeTagName === tagName;
+        }
+        return false;
+    }
+
+    export function assertNodeProperty<
+        T extends keyof ElementTagNameMap,
+        P extends keyof ElementTagNameMap[T],
+        V extends HTMLElementTagNameMap[T][P]>(node: Node | null, tagName: T, prop: P, value: V) {
+                  ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2536: Type 'T' cannot be used to index type 'HTMLElementTagNameMap'.
+                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2536: Type 'P' cannot be used to index type 'HTMLElementTagNameMap[T]'.
+        if (assertNodeTagName(node, tagName)) {
+            node[prop];
+        }
+    }
+

tests/baselines/reference/intersectionsOfLargeUnions.js

@@ -0,0 +1,51 @@
+//// [intersectionsOfLargeUnions.ts]
+// Repro from #23977
+
+export function assertIsElement(node: Node | null): node is Element {
+    let nodeType = node === null ? null : node.nodeType;
+    return nodeType === 1;
+}
+
+export function assertNodeTagName<
+    T extends keyof ElementTagNameMap,
+    U extends ElementTagNameMap[T]>(node: Node | null, tagName: T): node is U {
+    if (assertIsElement(node)) {
+        const nodeTagName = node.tagName.toLowerCase();
+         return nodeTagName === tagName;
+    }
+    return false;
+}
+
+export function assertNodeProperty<
+    T extends keyof ElementTagNameMap,
+    P extends keyof ElementTagNameMap[T],
+    V extends HTMLElementTagNameMap[T][P]>(node: Node | null, tagName: T, prop: P, value: V) {
+    if (assertNodeTagName(node, tagName)) {
+        node[prop];
+    }
+}
+
+
+//// [intersectionsOfLargeUnions.js]
+"use strict";
+// Repro from #23977
+exports.__esModule = true;
+function assertIsElement(node) {
+    var nodeType = node === null ? null : node.nodeType;
+    return nodeType === 1;
+}
+exports.assertIsElement = assertIsElement;
+function assertNodeTagName(node, tagName) {
+    if (assertIsElement(node)) {
+        var nodeTagName = node.tagName.toLowerCase();
+        return nodeTagName === tagName;
+    }
+    return false;
+}
+exports.assertNodeTagName = assertNodeTagName;
+function assertNodeProperty(node, tagName, prop, value) {
+    if (assertNodeTagName(node, tagName)) {
+        node[prop];
+    }
+}
+exports.assertNodeProperty = assertNodeProperty;

tests/baselines/reference/intersectionsOfLargeUnions.symbols

@@ -0,0 +1,95 @@
+=== tests/cases/compiler/intersectionsOfLargeUnions.ts ===
+// Repro from #23977
+
+export function assertIsElement(node: Node | null): node is Element {
+>assertIsElement : Symbol(assertIsElement, Decl(intersectionsOfLargeUnions.ts, 0, 0))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 2, 32))
+>Node : Symbol(Node, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 2, 32))
+>Element : Symbol(Element, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+
+    let nodeType = node === null ? null : node.nodeType;
+>nodeType : Symbol(nodeType, Decl(intersectionsOfLargeUnions.ts, 3, 7))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 2, 32))
+>node.nodeType : Symbol(Node.nodeType, Decl(lib.d.ts, --, --))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 2, 32))
+>nodeType : Symbol(Node.nodeType, Decl(lib.d.ts, --, --))
+
+    return nodeType === 1;
+>nodeType : Symbol(nodeType, Decl(intersectionsOfLargeUnions.ts, 3, 7))
+}
+
+export function assertNodeTagName<
+>assertNodeTagName : Symbol(assertNodeTagName, Decl(intersectionsOfLargeUnions.ts, 5, 1))
+
+    T extends keyof ElementTagNameMap,
+>T : Symbol(T, Decl(intersectionsOfLargeUnions.ts, 7, 34))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.d.ts, --, --))
+
+    U extends ElementTagNameMap[T]>(node: Node | null, tagName: T): node is U {
+>U : Symbol(U, Decl(intersectionsOfLargeUnions.ts, 8, 38))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(intersectionsOfLargeUnions.ts, 7, 34))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 9, 36))
+>Node : Symbol(Node, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>tagName : Symbol(tagName, Decl(intersectionsOfLargeUnions.ts, 9, 54))
+>T : Symbol(T, Decl(intersectionsOfLargeUnions.ts, 7, 34))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 9, 36))
+>U : Symbol(U, Decl(intersectionsOfLargeUnions.ts, 8, 38))
+
+    if (assertIsElement(node)) {
+>assertIsElement : Symbol(assertIsElement, Decl(intersectionsOfLargeUnions.ts, 0, 0))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 9, 36))
+
+        const nodeTagName = node.tagName.toLowerCase();
+>nodeTagName : Symbol(nodeTagName, Decl(intersectionsOfLargeUnions.ts, 11, 13))
+>node.tagName.toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
+>node.tagName : Symbol(Element.tagName, Decl(lib.d.ts, --, --))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 9, 36))
+>tagName : Symbol(Element.tagName, Decl(lib.d.ts, --, --))
+>toLowerCase : Symbol(String.toLowerCase, Decl(lib.d.ts, --, --))
+
+         return nodeTagName === tagName;
+>nodeTagName : Symbol(nodeTagName, Decl(intersectionsOfLargeUnions.ts, 11, 13))
+>tagName : Symbol(tagName, Decl(intersectionsOfLargeUnions.ts, 9, 54))
+    }
+    return false;
+}
+
+export function assertNodeProperty<
+>assertNodeProperty : Symbol(assertNodeProperty, Decl(intersectionsOfLargeUnions.ts, 15, 1))
+
+    T extends keyof ElementTagNameMap,
+>T : Symbol(T, Decl(intersectionsOfLargeUnions.ts, 17, 35))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.d.ts, --, --))
+
+    P extends keyof ElementTagNameMap[T],
+>P : Symbol(P, Decl(intersectionsOfLargeUnions.ts, 18, 38))
+>ElementTagNameMap : Symbol(ElementTagNameMap, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(intersectionsOfLargeUnions.ts, 17, 35))
+
+    V extends HTMLElementTagNameMap[T][P]>(node: Node | null, tagName: T, prop: P, value: V) {
+>V : Symbol(V, Decl(intersectionsOfLargeUnions.ts, 19, 41))
+>HTMLElementTagNameMap : Symbol(HTMLElementTagNameMap, Decl(lib.d.ts, --, --))
+>T : Symbol(T, Decl(intersectionsOfLargeUnions.ts, 17, 35))
+>P : Symbol(P, Decl(intersectionsOfLargeUnions.ts, 18, 38))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 20, 43))
+>Node : Symbol(Node, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+>tagName : Symbol(tagName, Decl(intersectionsOfLargeUnions.ts, 20, 61))
+>T : Symbol(T, Decl(intersectionsOfLargeUnions.ts, 17, 35))
+>prop : Symbol(prop, Decl(intersectionsOfLargeUnions.ts, 20, 73))
+>P : Symbol(P, Decl(intersectionsOfLargeUnions.ts, 18, 38))
+>value : Symbol(value, Decl(intersectionsOfLargeUnions.ts, 20, 82))
+>V : Symbol(V, Decl(intersectionsOfLargeUnions.ts, 19, 41))
+
+    if (assertNodeTagName(node, tagName)) {
+>assertNodeTagName : Symbol(assertNodeTagName, Decl(intersectionsOfLargeUnions.ts, 5, 1))
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 20, 43))
+>tagName : Symbol(tagName, Decl(intersectionsOfLargeUnions.ts, 20, 61))
+
+        node[prop];
+>node : Symbol(node, Decl(intersectionsOfLargeUnions.ts, 20, 43))
+>prop : Symbol(prop, Decl(intersectionsOfLargeUnions.ts, 20, 73))
+    }
+}
+