Fixed reported errors for variadic element mismatches (#58708)

src/compiler/checker.ts

@@ -23665,7 +23665,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     const sourceArity = getTypeReferenceArity(source);
                     const targetArity = getTypeReferenceArity(target);
                     const sourceRestFlag = isTupleType(source) ? source.target.combinedFlags & ElementFlags.Rest : ElementFlags.Rest;
-                    const targetRestFlag = target.target.combinedFlags & ElementFlags.Rest;
+                    const targetHasRestElement = !!(target.target.combinedFlags & ElementFlags.Variable);
                     const sourceMinLength = isTupleType(source) ? source.target.minLength : 0;
                     const targetMinLength = target.target.minLength;
                     if (!sourceRestFlag && sourceArity < targetMinLength) {
@@ -23674,13 +23674,13 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                         }
                         return Ternary.False;
                     }
-                    if (!targetRestFlag && targetArity < sourceMinLength) {
+                    if (!targetHasRestElement && targetArity < sourceMinLength) {
                         if (reportErrors) {
                             reportError(Diagnostics.Source_has_0_element_s_but_target_allows_only_1, sourceMinLength, targetArity);
                         }
                         return Ternary.False;
                     }
-                    if (!targetRestFlag && (sourceRestFlag || targetArity < sourceArity)) {
+                    if (!targetHasRestElement && (sourceRestFlag || targetArity < sourceArity)) {
                         if (reportErrors) {
                             if (sourceMinLength < targetMinLength) {
                                 reportError(Diagnostics.Target_requires_0_element_s_but_source_may_have_fewer, targetMinLength);
@@ -23695,7 +23695,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     const targetTypeArguments = getTypeArguments(target);
                     const targetStartCount = getStartElementCount(target.target, ElementFlags.NonRest);
                     const targetEndCount = getEndElementCount(target.target, ElementFlags.NonRest);
-                    const targetHasRestElement = target.target.hasRestElement;
                     let canExcludeDiscriminants = !!excludedProperties;
                     for (let sourcePosition = 0; sourcePosition < sourceArity; sourcePosition++) {
                         const sourceFlags = isTupleType(source) ? source.target.elementFlags[sourcePosition] : ElementFlags.Rest;

tests/baselines/reference/variadicTuples1.errors.txt

@@ -5,9 +5,9 @@ variadicTuples1.ts(62,5): error TS2345: Argument of type '[]' is not assignable
 variadicTuples1.ts(131,9): error TS2344: Type 'V' does not satisfy the constraint 'unknown[]'.
   The type 'readonly unknown[]' is 'readonly' and cannot be assigned to the mutable type 'unknown[]'.
 variadicTuples1.ts(149,5): error TS2322: Type '[string, ...unknown[]]' is not assignable to type '[string, ...T]'.
-  Target requires 2 element(s) but source may have fewer.
+  Source provides no match for variadic element at position 1 in target.
 variadicTuples1.ts(151,5): error TS2322: Type '[string, ...unknown[]]' is not assignable to type '[string, ...U]'.
-  Target requires 2 element(s) but source may have fewer.
+  Source provides no match for variadic element at position 1 in target.
 variadicTuples1.ts(152,5): error TS2322: Type '[string, ...T]' is not assignable to type '[string, ...U]'.
   Type at position 1 in source is not compatible with type at position 1 in target.
     Type 'T' is not assignable to type 'U'.
@@ -22,7 +22,7 @@ variadicTuples1.ts(170,5): error TS2322: Type 'T' is not assignable to type '[..
 variadicTuples1.ts(171,5): error TS4104: The type 'readonly [...T]' is 'readonly' and cannot be assigned to the mutable type '[...T]'.
 variadicTuples1.ts(181,5): error TS2322: Type 'T' is not assignable to type '[...U]'.
   Type 'string[]' is not assignable to type '[...U]'.
-    Target requires 1 element(s) but source may have fewer.
+    Source provides no match for variadic element at position 0 in target.
 variadicTuples1.ts(182,5): error TS2322: Type '[...T]' is not assignable to type '[...U]'.
   Type 'T' is not assignable to type 'U'.
     'T' is assignable to the constraint of type 'U', but 'U' could be instantiated with a different subtype of constraint 'string[]'.
@@ -211,12 +211,12 @@ variadicTuples1.ts(411,7): error TS2322: Type '[boolean, false]' is not assignab
         y = x;  // Error
         ~
 !!! error TS2322: Type '[string, ...unknown[]]' is not assignable to type '[string, ...T]'.
-!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
+!!! error TS2322:   Source provides no match for variadic element at position 1 in target.
         y = z;
         z = x;  // Error
         ~
 !!! error TS2322: Type '[string, ...unknown[]]' is not assignable to type '[string, ...U]'.
-!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
+!!! error TS2322:   Source provides no match for variadic element at position 1 in target.
         z = y;  // Error
         ~
 !!! error TS2322: Type '[string, ...T]' is not assignable to type '[string, ...U]'.
@@ -268,7 +268,7 @@ variadicTuples1.ts(411,7): error TS2322: Type '[boolean, false]' is not assignab
         ~~
 !!! error TS2322: Type 'T' is not assignable to type '[...U]'.
 !!! error TS2322:   Type 'string[]' is not assignable to type '[...U]'.
-!!! error TS2322:     Target requires 1 element(s) but source may have fewer.
+!!! error TS2322:     Source provides no match for variadic element at position 0 in target.
         t2 = t1;  // Error
         ~~
 !!! error TS2322: Type '[...T]' is not assignable to type '[...U]'.

tests/baselines/reference/variadicTuples2.errors.txt

@@ -38,7 +38,7 @@ variadicTuples2.ts(73,8): error TS2345: Argument of type '["abc", "def", true]'
 variadicTuples2.ts(76,5): error TS2322: Type '[number, number]' is not assignable to type '[number, ...T]'.
   Source provides no match for variadic element at position 1 in target.
 variadicTuples2.ts(77,5): error TS2322: Type '[number, ...number[]]' is not assignable to type '[number, ...T]'.
-  Target requires 2 element(s) but source may have fewer.
+  Source provides no match for variadic element at position 1 in target.
 variadicTuples2.ts(78,5): error TS2322: Type '[number, ...T]' is not assignable to type '[number, number]'.
   Type '[number, ...unknown[]]' is not assignable to type '[number, number]'.
     Target requires 2 element(s) but source may have fewer.
@@ -208,7 +208,7 @@ variadicTuples2.ts(139,25): error TS2345: Argument of type '["blah2", 1, 2, 3]'
         x = z;  // Error
         ~
 !!! error TS2322: Type '[number, ...number[]]' is not assignable to type '[number, ...T]'.
-!!! error TS2322:   Target requires 2 element(s) but source may have fewer.
+!!! error TS2322:   Source provides no match for variadic element at position 1 in target.
         y = x;  // Error
         ~
 !!! error TS2322: Type '[number, ...T]' is not assignable to type '[number, number]'.

tests/baselines/reference/variadicTuples3.errors.txt

@@ -0,0 +1,35 @@
+variadicTuples3.ts(5,3): error TS2322: Type 'any[]' is not assignable to type '[...T, ...P]'.
+  Source provides no match for variadic element at position 0 in target.
+variadicTuples3.ts(10,3): error TS2322: Type '[any, any]' is not assignable to type '[...T, ...P]'.
+  Source provides no match for variadic element at position 0 in target.
+variadicTuples3.ts(15,3): error TS2322: Type '[any, any, any]' is not assignable to type '[...T, ...P]'.
+  Source provides no match for variadic element at position 0 in target.
+
+
+==== variadicTuples3.ts (3 errors) ====
+    // https://github.com/microsoft/TypeScript/issues/58697
+    
+    function test1<T extends any[], P extends any[]>(): [...T, ...P] {
+      let x: any[] = [];
+      return x;
+      ~~~~~~
+!!! error TS2322: Type 'any[]' is not assignable to type '[...T, ...P]'.
+!!! error TS2322:   Source provides no match for variadic element at position 0 in target.
+    }
+    
+    function test2<T extends any[], P extends any[]>(): [...T, ...P] {
+      let x: [any, any] = [null, null];
+      return x;
+      ~~~~~~
+!!! error TS2322: Type '[any, any]' is not assignable to type '[...T, ...P]'.
+!!! error TS2322:   Source provides no match for variadic element at position 0 in target.
+    }
+    
+    function test3<T extends any[], P extends any[]>(): [...T, ...P] {
+      let x: [any, any, any] = [null, null, null];
+      return x;
+      ~~~~~~
+!!! error TS2322: Type '[any, any, any]' is not assignable to type '[...T, ...P]'.
+!!! error TS2322:   Source provides no match for variadic element at position 0 in target.
+    }
+    

tests/baselines/reference/variadicTuples3.symbols

@@ -0,0 +1,47 @@
+//// [tests/cases/conformance/types/tuple/variadicTuples3.ts] ////
+
+=== variadicTuples3.ts ===
+// https://github.com/microsoft/TypeScript/issues/58697
+
+function test1<T extends any[], P extends any[]>(): [...T, ...P] {
+>test1 : Symbol(test1, Decl(variadicTuples3.ts, 0, 0))
+>T : Symbol(T, Decl(variadicTuples3.ts, 2, 15))
+>P : Symbol(P, Decl(variadicTuples3.ts, 2, 31))
+>T : Symbol(T, Decl(variadicTuples3.ts, 2, 15))
+>P : Symbol(P, Decl(variadicTuples3.ts, 2, 31))
+
+  let x: any[] = [];
+>x : Symbol(x, Decl(variadicTuples3.ts, 3, 5))
+
+  return x;
+>x : Symbol(x, Decl(variadicTuples3.ts, 3, 5))
+}
+
+function test2<T extends any[], P extends any[]>(): [...T, ...P] {
+>test2 : Symbol(test2, Decl(variadicTuples3.ts, 5, 1))
+>T : Symbol(T, Decl(variadicTuples3.ts, 7, 15))
+>P : Symbol(P, Decl(variadicTuples3.ts, 7, 31))
+>T : Symbol(T, Decl(variadicTuples3.ts, 7, 15))
+>P : Symbol(P, Decl(variadicTuples3.ts, 7, 31))
+
+  let x: [any, any] = [null, null];
+>x : Symbol(x, Decl(variadicTuples3.ts, 8, 5))
+
+  return x;
+>x : Symbol(x, Decl(variadicTuples3.ts, 8, 5))
+}
+
+function test3<T extends any[], P extends any[]>(): [...T, ...P] {
+>test3 : Symbol(test3, Decl(variadicTuples3.ts, 10, 1))
+>T : Symbol(T, Decl(variadicTuples3.ts, 12, 15))
+>P : Symbol(P, Decl(variadicTuples3.ts, 12, 31))
+>T : Symbol(T, Decl(variadicTuples3.ts, 12, 15))
+>P : Symbol(P, Decl(variadicTuples3.ts, 12, 31))
+
+  let x: [any, any, any] = [null, null, null];
+>x : Symbol(x, Decl(variadicTuples3.ts, 13, 5))
+
+  return x;
+>x : Symbol(x, Decl(variadicTuples3.ts, 13, 5))
+}
+

tests/baselines/reference/variadicTuples3.types

@@ -0,0 +1,50 @@
+//// [tests/cases/conformance/types/tuple/variadicTuples3.ts] ////
+
+=== variadicTuples3.ts ===
+// https://github.com/microsoft/TypeScript/issues/58697
+
+function test1<T extends any[], P extends any[]>(): [...T, ...P] {
+>test1 : <T extends any[], P extends any[]>() => [...T, ...P]
+>      : ^ ^^^^^^^^^     ^^ ^^^^^^^^^     ^^^^^^^            
+
+  let x: any[] = [];
+>x : any[]
+>  : ^^^^^
+>[] : never[]
+>   : ^^^^^^^
+
+  return x;
+>x : any[]
+>  : ^^^^^
+}
+
+function test2<T extends any[], P extends any[]>(): [...T, ...P] {
+>test2 : <T extends any[], P extends any[]>() => [...T, ...P]
+>      : ^ ^^^^^^^^^     ^^ ^^^^^^^^^     ^^^^^^^            
+
+  let x: [any, any] = [null, null];
+>x : [any, any]
+>  : ^^^^^^^^^^
+>[null, null] : [null, null]
+>             : ^^^^^^^^^^^^
+
+  return x;
+>x : [any, any]
+>  : ^^^^^^^^^^
+}
+
+function test3<T extends any[], P extends any[]>(): [...T, ...P] {
+>test3 : <T extends any[], P extends any[]>() => [...T, ...P]
+>      : ^ ^^^^^^^^^     ^^ ^^^^^^^^^     ^^^^^^^            
+
+  let x: [any, any, any] = [null, null, null];
+>x : [any, any, any]
+>  : ^^^^^^^^^^^^^^^
+>[null, null, null] : [null, null, null]
+>                   : ^^^^^^^^^^^^^^^^^^
+
+  return x;
+>x : [any, any, any]
+>  : ^^^^^^^^^^^^^^^
+}
+

tests/cases/conformance/types/tuple/variadicTuples3.ts

@@ -0,0 +1,19 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/58697
+
+function test1<T extends any[], P extends any[]>(): [...T, ...P] {
+  let x: any[] = [];
+  return x;
+}
+
+function test2<T extends any[], P extends any[]>(): [...T, ...P] {
+  let x: [any, any] = [null, null];
+  return x;
+}
+
+function test3<T extends any[], P extends any[]>(): [...T, ...P] {
+  let x: [any, any, any] = [null, null, null];
+  return x;
+}