Remove unnecessary check for misaligned complex rest parameters (#47934)

* Remove unnecessary check for misaligned complex rest parameters

* Add tests

Author: ahejlsberg

src/compiler/checker.ts

@@ -17671,10 +17671,6 @@ namespace ts {
             if (sourceRestType || targetRestType) {
                 void instantiateType(sourceRestType || targetRestType, reportUnreliableMarkers);
             }
-            if (sourceRestType && targetRestType && sourceCount !== targetCount) {
-                // We're not able to relate misaligned complex rest parameters
-                return Ternary.False;
-            }
 
             const kind = target.declaration ? target.declaration.kind : SyntaxKind.Unknown;
             const strictVariance = !(checkMode & SignatureCheckMode.Callback) && strictFunctionTypes && kind !== SyntaxKind.MethodDeclaration &&

tests/baselines/reference/genericRestParameters3.errors.txt

@@ -4,7 +4,6 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(17,11): error TS234
 tests/cases/conformance/types/rest/genericRestParameters3.ts(18,1): error TS2345: Argument of type '[]' is not assignable to parameter of type '[string] | [number, boolean]'.
   Type '[]' is not assignable to type '[number, boolean]'.
     Source has 0 element(s) but target requires 2.
-tests/cases/conformance/types/rest/genericRestParameters3.ts(22,1): error TS2322: Type '(x: string, ...args: [string] | [number, boolean]) => void' is not assignable to type '(...args: [string, string] | [string, number, boolean]) => void'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(23,1): error TS2322: Type '(x: string, y: string) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
   Types of parameters 'y' and 'args' are incompatible.
     Type '[string] | [number, boolean]' is not assignable to type '[y: string]'.
@@ -15,7 +14,6 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(24,1): error TS2322
     Type '[string] | [number, boolean]' is not assignable to type '[y: number, z: boolean]'.
       Type '[string]' is not assignable to type '[y: number, z: boolean]'.
         Source has 1 element(s) but target requires 2.
-tests/cases/conformance/types/rest/genericRestParameters3.ts(25,1): error TS2322: Type '(...args: [string, string] | [string, number, boolean]) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(35,1): error TS2554: Expected 1 arguments, but got 0.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(36,21): error TS2345: Argument of type 'number' is not assignable to parameter of type '(...args: CoolArray<any>) => void'.
 tests/cases/conformance/types/rest/genericRestParameters3.ts(37,21): error TS2345: Argument of type '<T extends any[]>(cb: (...args: T) => void) => void' is not assignable to parameter of type '(...args: CoolArray<any>) => void'.
@@ -36,7 +34,7 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345
     Source has 1 element(s) but target requires 2.
 
 
-==== tests/cases/conformance/types/rest/genericRestParameters3.ts (15 errors) ====
+==== tests/cases/conformance/types/rest/genericRestParameters3.ts (13 errors) ====
     declare let f1: (x: string, ...args: [string] | [number, boolean]) => void;
     declare let f2: (x: string, y: string) => void;
     declare let f3: (x: string, y: number, z: boolean) => void;
@@ -66,9 +64,7 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345
 
     f2 = f1;
     f3 = f1;
-    f4 = f1;  // Error, misaligned complex rest types
-    ~~
-!!! error TS2322: Type '(x: string, ...args: [string] | [number, boolean]) => void' is not assignable to type '(...args: [string, string] | [string, number, boolean]) => void'.
+    f4 = f1;
     f1 = f2;  // Error
     ~~
 !!! error TS2322: Type '(x: string, y: string) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
@@ -83,9 +79,7 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345
 !!! error TS2322:     Type '[string] | [number, boolean]' is not assignable to type '[y: number, z: boolean]'.
 !!! error TS2322:       Type '[string]' is not assignable to type '[y: number, z: boolean]'.
 !!! error TS2322:         Source has 1 element(s) but target requires 2.
-    f1 = f4;  // Error, misaligned complex rest types
-    ~~
-!!! error TS2322: Type '(...args: [string, string] | [string, number, boolean]) => void' is not assignable to type '(x: string, ...args: [string] | [number, boolean]) => void'.
+    f1 = f4;
 
     // Repro from #26110
 
@@ -159,4 +153,23 @@ tests/cases/conformance/types/rest/genericRestParameters3.ts(59,5): error TS2345
     declare function foo2(...args: string[] | number[]): void;
     let x2: ReadonlyArray<string> = ["hello"];
     foo2(...x2);
+    
+    // Repros from #47754
+    
+    type RestParams = [y: string] | [y: number];
+    
+    type Signature = (x: string, ...rest: RestParams) => void;
+    
+    type MergedParams = Parameters<Signature>;  // [x: string, y: string] | [x: string, y: number]
+    
+    declare let ff1: (...rest: [string, string] | [string, number]) => void;
+    declare let ff2: (x: string, ...rest: [string] | [number]) => void;
+    
+    ff1 = ff2;
+    ff2 = ff1;
+    
+    function ff3<A extends unknown[]>(s1: (...args: [x: string, ...rest: A | [number]]) => void, s2: (x: string, ...rest: A | [number]) => void) {
+        s1 = s2;
+        s2 = s1;
+    }
 

tests/baselines/reference/genericRestParameters3.js

@@ -20,10 +20,10 @@ f1("foo");  // Error
 
 f2 = f1;
 f3 = f1;
-f4 = f1;  // Error, misaligned complex rest types
+f4 = f1;
 f1 = f2;  // Error
 f1 = f3;  // Error
-f1 = f4;  // Error, misaligned complex rest types
+f1 = f4;
 
 // Repro from #26110
 
@@ -64,6 +64,25 @@ hmm("what"); // no error?  A = [] | [number, string] ?
 declare function foo2(...args: string[] | number[]): void;
 let x2: ReadonlyArray<string> = ["hello"];
 foo2(...x2);
+
+// Repros from #47754
+
+type RestParams = [y: string] | [y: number];
+
+type Signature = (x: string, ...rest: RestParams) => void;
+
+type MergedParams = Parameters<Signature>;  // [x: string, y: string] | [x: string, y: number]
+
+declare let ff1: (...rest: [string, string] | [string, number]) => void;
+declare let ff2: (x: string, ...rest: [string] | [number]) => void;
+
+ff1 = ff2;
+ff2 = ff1;
+
+function ff3<A extends unknown[]>(s1: (...args: [x: string, ...rest: A | [number]]) => void, s2: (x: string, ...rest: A | [number]) => void) {
+    s1 = s2;
+    s2 = s1;
+}
 
 
 //// [genericRestParameters3.js]
@@ -87,10 +106,10 @@ f1("foo", 10); // Error
 f1("foo"); // Error
 f2 = f1;
 f3 = f1;
-f4 = f1; // Error, misaligned complex rest types
+f4 = f1;
 f1 = f2; // Error
 f1 = f3; // Error
-f1 = f4; // Error, misaligned complex rest types
+f1 = f4;
 foo(); // Error
 foo(100); // Error
 foo(foo); // Error
@@ -112,6 +131,12 @@ hmm(1, "s"); // okay, A = [1, "s"]
 hmm("what"); // no error?  A = [] | [number, string] ?
 var x2 = ["hello"];
 foo2.apply(void 0, x2);
+ff1 = ff2;
+ff2 = ff1;
+function ff3(s1, s2) {
+    s1 = s2;
+    s2 = s1;
+}
 
 
 //// [genericRestParameters3.d.ts]
@@ -135,3 +160,9 @@ declare const ca: CoolArray<number>;
 declare function hmm<A extends [] | [number, string]>(...args: A): void;
 declare function foo2(...args: string[] | number[]): void;
 declare let x2: ReadonlyArray<string>;
+declare type RestParams = [y: string] | [y: number];
+declare type Signature = (x: string, ...rest: RestParams) => void;
+declare type MergedParams = Parameters<Signature>;
+declare let ff1: (...rest: [string, string] | [string, number]) => void;
+declare let ff2: (x: string, ...rest: [string] | [number]) => void;
+declare function ff3<A extends unknown[]>(s1: (...args: [x: string, ...rest: A | [number]]) => void, s2: (x: string, ...rest: A | [number]) => void): void;

tests/baselines/reference/genericRestParameters3.symbols

@@ -67,7 +67,7 @@ f3 = f1;
 >f3 : Symbol(f3, Decl(genericRestParameters3.ts, 2, 11))
 >f1 : Symbol(f1, Decl(genericRestParameters3.ts, 0, 11))
 
-f4 = f1;  // Error, misaligned complex rest types
+f4 = f1;
 >f4 : Symbol(f4, Decl(genericRestParameters3.ts, 3, 11))
 >f1 : Symbol(f1, Decl(genericRestParameters3.ts, 0, 11))
 
@@ -79,7 +79,7 @@ f1 = f3;  // Error
 >f1 : Symbol(f1, Decl(genericRestParameters3.ts, 0, 11))
 >f3 : Symbol(f3, Decl(genericRestParameters3.ts, 2, 11))
 
-f1 = f4;  // Error, misaligned complex rest types
+f1 = f4;
 >f1 : Symbol(f1, Decl(genericRestParameters3.ts, 0, 11))
 >f4 : Symbol(f4, Decl(genericRestParameters3.ts, 3, 11))
 
@@ -190,3 +190,56 @@ foo2(...x2);
 >foo2 : Symbol(foo2, Decl(genericRestParameters3.ts, 58, 12))
 >x2 : Symbol(x2, Decl(genericRestParameters3.ts, 63, 3))
 
+// Repros from #47754
+
+type RestParams = [y: string] | [y: number];
+>RestParams : Symbol(RestParams, Decl(genericRestParameters3.ts, 64, 12))
+
+type Signature = (x: string, ...rest: RestParams) => void;
+>Signature : Symbol(Signature, Decl(genericRestParameters3.ts, 68, 44))
+>x : Symbol(x, Decl(genericRestParameters3.ts, 70, 18))
+>rest : Symbol(rest, Decl(genericRestParameters3.ts, 70, 28))
+>RestParams : Symbol(RestParams, Decl(genericRestParameters3.ts, 64, 12))
+
+type MergedParams = Parameters<Signature>;  // [x: string, y: string] | [x: string, y: number]
+>MergedParams : Symbol(MergedParams, Decl(genericRestParameters3.ts, 70, 58))
+>Parameters : Symbol(Parameters, Decl(lib.es5.d.ts, --, --))
+>Signature : Symbol(Signature, Decl(genericRestParameters3.ts, 68, 44))
+
+declare let ff1: (...rest: [string, string] | [string, number]) => void;
+>ff1 : Symbol(ff1, Decl(genericRestParameters3.ts, 74, 11))
+>rest : Symbol(rest, Decl(genericRestParameters3.ts, 74, 18))
+
+declare let ff2: (x: string, ...rest: [string] | [number]) => void;
+>ff2 : Symbol(ff2, Decl(genericRestParameters3.ts, 75, 11))
+>x : Symbol(x, Decl(genericRestParameters3.ts, 75, 18))
+>rest : Symbol(rest, Decl(genericRestParameters3.ts, 75, 28))
+
+ff1 = ff2;
+>ff1 : Symbol(ff1, Decl(genericRestParameters3.ts, 74, 11))
+>ff2 : Symbol(ff2, Decl(genericRestParameters3.ts, 75, 11))
+
+ff2 = ff1;
+>ff2 : Symbol(ff2, Decl(genericRestParameters3.ts, 75, 11))
+>ff1 : Symbol(ff1, Decl(genericRestParameters3.ts, 74, 11))
+
+function ff3<A extends unknown[]>(s1: (...args: [x: string, ...rest: A | [number]]) => void, s2: (x: string, ...rest: A | [number]) => void) {
+>ff3 : Symbol(ff3, Decl(genericRestParameters3.ts, 78, 10))
+>A : Symbol(A, Decl(genericRestParameters3.ts, 80, 13))
+>s1 : Symbol(s1, Decl(genericRestParameters3.ts, 80, 34))
+>args : Symbol(args, Decl(genericRestParameters3.ts, 80, 39))
+>A : Symbol(A, Decl(genericRestParameters3.ts, 80, 13))
+>s2 : Symbol(s2, Decl(genericRestParameters3.ts, 80, 92))
+>x : Symbol(x, Decl(genericRestParameters3.ts, 80, 98))
+>rest : Symbol(rest, Decl(genericRestParameters3.ts, 80, 108))
+>A : Symbol(A, Decl(genericRestParameters3.ts, 80, 13))
+
+    s1 = s2;
+>s1 : Symbol(s1, Decl(genericRestParameters3.ts, 80, 34))
+>s2 : Symbol(s2, Decl(genericRestParameters3.ts, 80, 92))
+
+    s2 = s1;
+>s2 : Symbol(s2, Decl(genericRestParameters3.ts, 80, 92))
+>s1 : Symbol(s1, Decl(genericRestParameters3.ts, 80, 34))
+}
+

tests/baselines/reference/genericRestParameters3.types

@@ -93,7 +93,7 @@ f3 = f1;
 >f3 : (x: string, y: number, z: boolean) => void
 >f1 : (x: string, ...args: [string] | [number, boolean]) => void
 
-f4 = f1;  // Error, misaligned complex rest types
+f4 = f1;
 >f4 = f1 : (x: string, ...args: [string] | [number, boolean]) => void
 >f4 : (...args: [string, string] | [string, number, boolean]) => void
 >f1 : (x: string, ...args: [string] | [number, boolean]) => void
@@ -108,7 +108,7 @@ f1 = f3;  // Error
 >f1 : (x: string, ...args: [string] | [number, boolean]) => void
 >f3 : (x: string, y: number, z: boolean) => void
 
-f1 = f4;  // Error, misaligned complex rest types
+f1 = f4;
 >f1 = f4 : (...args: [string, string] | [string, number, boolean]) => void
 >f1 : (x: string, ...args: [string] | [number, boolean]) => void
 >f4 : (...args: [string, string] | [string, number, boolean]) => void
@@ -227,3 +227,54 @@ foo2(...x2);
 >...x2 : string
 >x2 : readonly string[]
 
+// Repros from #47754
+
+type RestParams = [y: string] | [y: number];
+>RestParams : RestParams
+
+type Signature = (x: string, ...rest: RestParams) => void;
+>Signature : Signature
+>x : string
+>rest : RestParams
+
+type MergedParams = Parameters<Signature>;  // [x: string, y: string] | [x: string, y: number]
+>MergedParams : [x: string, y: string] | [x: string, y: number]
+
+declare let ff1: (...rest: [string, string] | [string, number]) => void;
+>ff1 : (...rest: [string, string] | [string, number]) => void
+>rest : [string, string] | [string, number]
+
+declare let ff2: (x: string, ...rest: [string] | [number]) => void;
+>ff2 : (x: string, ...rest: [string] | [number]) => void
+>x : string
+>rest : [string] | [number]
+
+ff1 = ff2;
+>ff1 = ff2 : (x: string, ...rest: [string] | [number]) => void
+>ff1 : (...rest: [string, string] | [string, number]) => void
+>ff2 : (x: string, ...rest: [string] | [number]) => void
+
+ff2 = ff1;
+>ff2 = ff1 : (...rest: [string, string] | [string, number]) => void
+>ff2 : (x: string, ...rest: [string] | [number]) => void
+>ff1 : (...rest: [string, string] | [string, number]) => void
+
+function ff3<A extends unknown[]>(s1: (...args: [x: string, ...rest: A | [number]]) => void, s2: (x: string, ...rest: A | [number]) => void) {
+>ff3 : <A extends unknown[]>(s1: (...args: [x: string, ...rest: A | [number]]) => void, s2: (x: string, ...rest: A | [number]) => void) => void
+>s1 : (...args: [x: string, ...rest: A | [number]]) => void
+>args : [string, number] | [x: string, ...rest: A]
+>s2 : (x: string, ...rest: A | [number]) => void
+>x : string
+>rest : [number] | A
+
+    s1 = s2;
+>s1 = s2 : (x: string, ...rest: [number] | A) => void
+>s1 : (...args: [string, number] | [x: string, ...rest: A]) => void
+>s2 : (x: string, ...rest: [number] | A) => void
+
+    s2 = s1;
+>s2 = s1 : (...args: [string, number] | [x: string, ...rest: A]) => void
+>s2 : (x: string, ...rest: [number] | A) => void
+>s1 : (...args: [string, number] | [x: string, ...rest: A]) => void
+}
+

tests/cases/conformance/types/rest/genericRestParameters3.ts

@@ -22,10 +22,10 @@ f1("foo");  // Error
 
 f2 = f1;
 f3 = f1;
-f4 = f1;  // Error, misaligned complex rest types
+f4 = f1;
 f1 = f2;  // Error
 f1 = f3;  // Error
-f1 = f4;  // Error, misaligned complex rest types
+f1 = f4;
 
 // Repro from #26110
 
@@ -66,3 +66,22 @@ hmm("what"); // no error?  A = [] | [number, string] ?
 declare function foo2(...args: string[] | number[]): void;
 let x2: ReadonlyArray<string> = ["hello"];
 foo2(...x2);
+
+// Repros from #47754
+
+type RestParams = [y: string] | [y: number];
+
+type Signature = (x: string, ...rest: RestParams) => void;
+
+type MergedParams = Parameters<Signature>;  // [x: string, y: string] | [x: string, y: number]
+
+declare let ff1: (...rest: [string, string] | [string, number]) => void;
+declare let ff2: (x: string, ...rest: [string] | [number]) => void;
+
+ff1 = ff2;
+ff2 = ff1;
+
+function ff3<A extends unknown[]>(s1: (...args: [x: string, ...rest: A | [number]]) => void, s2: (x: string, ...rest: A | [number]) => void) {
+    s1 = s2;
+    s2 = s1;
+}