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ahejlsbergahejlsberg
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Properly reduce intersections to never in identity relation (microsoft#48111)
* Exclude types that may simplify to other forms * Add regression test
1 parent 04238e6 commit 0271738

5 files changed

Lines changed: 181 additions & 1 deletion

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‎src/compiler/checker.ts‎

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@@ -18104,7 +18104,8 @@ namespace ts {
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return true;
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}
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}
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else {
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else if (!((source.flags | target.flags) & (TypeFlags.UnionOrIntersection | TypeFlags.IndexedAccess | TypeFlags.Conditional | TypeFlags.Substitution))) {
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// We have excluded types that may simplify to other forms, so types must have identical flags
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if (source.flags !== target.flags) return false;
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if (source.flags & TypeFlags.Singleton) return true;
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}

‎tests/baselines/reference/identityRelationNeverTypes.js‎

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//// [identityRelationNeverTypes.ts]
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// Repro from #47996
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type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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declare class State<TContext> {
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_context: TContext;
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_value: string;
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matches<TSV extends string>(stateValue: TSV): this is State<TContext> & { value: TSV };
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}
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function f1(state: State<{ foo: number }>) {
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if (state.matches('a') && state.matches('a.b')) {
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state; // never
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type T1 = Equals<typeof state, never>; // true
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type T2 = Equals<never, never>; // true
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}
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}
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//// [identityRelationNeverTypes.js]
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"use strict";
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// Repro from #47996
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function f1(state) {
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if (state.matches('a') && state.matches('a.b')) {
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state; // never
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}
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}
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//// [identityRelationNeverTypes.d.ts]
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declare type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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declare class State<TContext> {
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_context: TContext;
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_value: string;
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matches<TSV extends string>(stateValue: TSV): this is State<TContext> & {
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value: TSV;
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};
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}
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declare function f1(state: State<{
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foo: number;
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}>): void;

‎tests/baselines/reference/identityRelationNeverTypes.symbols‎

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=== tests/cases/compiler/identityRelationNeverTypes.ts ===
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// Repro from #47996
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type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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>Equals : Symbol(Equals, Decl(identityRelationNeverTypes.ts, 0, 0))
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>A : Symbol(A, Decl(identityRelationNeverTypes.ts, 2, 12))
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>B : Symbol(B, Decl(identityRelationNeverTypes.ts, 2, 14))
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>T : Symbol(T, Decl(identityRelationNeverTypes.ts, 2, 22))
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>T : Symbol(T, Decl(identityRelationNeverTypes.ts, 2, 22))
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>B : Symbol(B, Decl(identityRelationNeverTypes.ts, 2, 14))
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>T : Symbol(T, Decl(identityRelationNeverTypes.ts, 2, 61))
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>T : Symbol(T, Decl(identityRelationNeverTypes.ts, 2, 61))
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>A : Symbol(A, Decl(identityRelationNeverTypes.ts, 2, 12))
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declare class State<TContext> {
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>State : Symbol(State, Decl(identityRelationNeverTypes.ts, 2, 105))
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>TContext : Symbol(TContext, Decl(identityRelationNeverTypes.ts, 4, 20))
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_context: TContext;
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>_context : Symbol(State._context, Decl(identityRelationNeverTypes.ts, 4, 31))
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>TContext : Symbol(TContext, Decl(identityRelationNeverTypes.ts, 4, 20))
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_value: string;
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>_value : Symbol(State._value, Decl(identityRelationNeverTypes.ts, 5, 23))
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matches<TSV extends string>(stateValue: TSV): this is State<TContext> & { value: TSV };
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>matches : Symbol(State.matches, Decl(identityRelationNeverTypes.ts, 6, 19))
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>TSV : Symbol(TSV, Decl(identityRelationNeverTypes.ts, 7, 12))
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>stateValue : Symbol(stateValue, Decl(identityRelationNeverTypes.ts, 7, 32))
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>TSV : Symbol(TSV, Decl(identityRelationNeverTypes.ts, 7, 12))
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>State : Symbol(State, Decl(identityRelationNeverTypes.ts, 2, 105))
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>TContext : Symbol(TContext, Decl(identityRelationNeverTypes.ts, 4, 20))
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>value : Symbol(value, Decl(identityRelationNeverTypes.ts, 7, 77))
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>TSV : Symbol(TSV, Decl(identityRelationNeverTypes.ts, 7, 12))
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}
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function f1(state: State<{ foo: number }>) {
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>f1 : Symbol(f1, Decl(identityRelationNeverTypes.ts, 8, 1))
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>state : Symbol(state, Decl(identityRelationNeverTypes.ts, 10, 12))
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>State : Symbol(State, Decl(identityRelationNeverTypes.ts, 2, 105))
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>foo : Symbol(foo, Decl(identityRelationNeverTypes.ts, 10, 26))
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if (state.matches('a') && state.matches('a.b')) {
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>state.matches : Symbol(State.matches, Decl(identityRelationNeverTypes.ts, 6, 19))
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>state : Symbol(state, Decl(identityRelationNeverTypes.ts, 10, 12))
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>matches : Symbol(State.matches, Decl(identityRelationNeverTypes.ts, 6, 19))
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>state.matches : Symbol(State.matches, Decl(identityRelationNeverTypes.ts, 6, 19))
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>state : Symbol(state, Decl(identityRelationNeverTypes.ts, 10, 12))
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>matches : Symbol(State.matches, Decl(identityRelationNeverTypes.ts, 6, 19))
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state; // never
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>state : Symbol(state, Decl(identityRelationNeverTypes.ts, 10, 12))
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type T1 = Equals<typeof state, never>; // true
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>T1 : Symbol(T1, Decl(identityRelationNeverTypes.ts, 12, 14))
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>Equals : Symbol(Equals, Decl(identityRelationNeverTypes.ts, 0, 0))
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>state : Symbol(state, Decl(identityRelationNeverTypes.ts, 10, 12))
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type T2 = Equals<never, never>; // true
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>T2 : Symbol(T2, Decl(identityRelationNeverTypes.ts, 13, 46))
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>Equals : Symbol(Equals, Decl(identityRelationNeverTypes.ts, 0, 0))
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}
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}
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‎tests/baselines/reference/identityRelationNeverTypes.types‎

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=== tests/cases/compiler/identityRelationNeverTypes.ts ===
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// Repro from #47996
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type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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>Equals : Equals<A, B>
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>true : true
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>false : false
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declare class State<TContext> {
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>State : State<TContext>
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_context: TContext;
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>_context : TContext
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_value: string;
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>_value : string
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matches<TSV extends string>(stateValue: TSV): this is State<TContext> & { value: TSV };
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>matches : <TSV extends string>(stateValue: TSV) => this is State<TContext> & { value: TSV; }
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>stateValue : TSV
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>value : TSV
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}
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function f1(state: State<{ foo: number }>) {
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>f1 : (state: State<{ foo: number;}>) => void
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>state : State<{ foo: number; }>
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>foo : number
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if (state.matches('a') && state.matches('a.b')) {
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>state.matches('a') && state.matches('a.b') : boolean
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>state.matches('a') : boolean
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>state.matches : <TSV extends string>(stateValue: TSV) => this is State<{ foo: number; }> & { value: TSV; }
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>state : State<{ foo: number; }>
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>matches : <TSV extends string>(stateValue: TSV) => this is State<{ foo: number; }> & { value: TSV; }
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>'a' : "a"
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>state.matches('a.b') : boolean
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>state.matches : <TSV extends string>(stateValue: TSV) => this is State<{ foo: number; }> & { value: TSV; }
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>state : State<{ foo: number; }> & { value: "a"; }
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>matches : <TSV extends string>(stateValue: TSV) => this is State<{ foo: number; }> & { value: TSV; }
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>'a.b' : "a.b"
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state; // never
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>state : never
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type T1 = Equals<typeof state, never>; // true
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>T1 : true
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>state : never
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type T2 = Equals<never, never>; // true
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>T2 : true
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}
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}
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‎tests/cases/compiler/identityRelationNeverTypes.ts‎

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// @strict: true
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// @declaration: true
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// Repro from #47996
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type Equals<A, B> = (<T>() => T extends B ? 1 : 0) extends (<T>() => T extends A ? 1 : 0) ? true : false;
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declare class State<TContext> {
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_context: TContext;
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_value: string;
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matches<TSV extends string>(stateValue: TSV): this is State<TContext> & { value: TSV };
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}
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function f1(state: State<{ foo: number }>) {
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if (state.matches('a') && state.matches('a.b')) {
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state; // never
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type T1 = Equals<typeof state, never>; // true
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type T2 = Equals<never, never>; // true
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}
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}

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