More explicit error message for function signature length mismatches

src/compiler/checker.ts

@@ -19805,6 +19805,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         const sourceHasMoreParameters = !hasEffectiveRestParameter(target) &&
             (checkMode & SignatureCheckMode.StrictArity ? hasEffectiveRestParameter(source) || getParameterCount(source) > targetCount : getMinArgumentCount(source) > targetCount);
         if (sourceHasMoreParameters) {
+            if (reportErrors && !(checkMode & SignatureCheckMode.StrictArity)) {
+                // the second condition should be redundant, because there is no error reporting when comparing signatures by strict arity
+                // since it is only done for subtype reduction
+                errorReporter!(Diagnostics.Target_signature_provides_too_few_arguments_Expected_0_or_more_but_got_1, getMinArgumentCount(source), targetCount);
+            }
             return Ternary.False;
         }
 

src/compiler/diagnosticMessages.json

@@ -3619,6 +3619,10 @@
         "category": "Error",
         "code": 2848
     },
+    "Target signature provides too few arguments. Expected {0} or more, but got {1}.": {
+        "category": "Error",
+        "code": 2849
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

tests/baselines/reference/addMoreOverloadsToBaseSignature.errors.txt

@@ -1,6 +1,7 @@
 tests/cases/compiler/addMoreOverloadsToBaseSignature.ts(5,11): error TS2430: Interface 'Bar' incorrectly extends interface 'Foo'.
   Types of property 'f' are incompatible.
     Type '(key: string) => string' is not assignable to type '() => string'.
+      Target signature provides too few arguments. Expected 1 or more, but got 0.
 
 
 ==== tests/cases/compiler/addMoreOverloadsToBaseSignature.ts (1 errors) ====
@@ -13,6 +14,7 @@ tests/cases/compiler/addMoreOverloadsToBaseSignature.ts(5,11): error TS2430: Int
 !!! error TS2430: Interface 'Bar' incorrectly extends interface 'Foo'.
 !!! error TS2430:   Types of property 'f' are incompatible.
 !!! error TS2430:     Type '(key: string) => string' is not assignable to type '() => string'.
+!!! error TS2430:       Target signature provides too few arguments. Expected 1 or more, but got 0.
         f(key: string): string;
     }
 

tests/baselines/reference/arrowFunctionErrorSpan.errors.txt

@@ -8,6 +8,7 @@ tests/cases/compiler/arrowFunctionErrorSpan.ts(17,3): error TS2345: Argument of
   Type 'void' is not assignable to type 'number'.
 tests/cases/compiler/arrowFunctionErrorSpan.ts(18,5): error TS1200: Line terminator not permitted before arrow.
 tests/cases/compiler/arrowFunctionErrorSpan.ts(21,3): error TS2345: Argument of type '(a: any, b: any, c: any, d: any) => void' is not assignable to parameter of type '() => number'.
+  Target signature provides too few arguments. Expected 4 or more, but got 0.
 tests/cases/compiler/arrowFunctionErrorSpan.ts(28,7): error TS2345: Argument of type '() => void' is not assignable to parameter of type '() => number'.
   Type 'void' is not assignable to type 'number'.
 tests/cases/compiler/arrowFunctionErrorSpan.ts(32,7): error TS2345: Argument of type '() => void' is not assignable to parameter of type '() => number'.
@@ -17,6 +18,7 @@ tests/cases/compiler/arrowFunctionErrorSpan.ts(36,7): error TS2345: Argument of
 tests/cases/compiler/arrowFunctionErrorSpan.ts(43,5): error TS2345: Argument of type '() => void' is not assignable to parameter of type '() => number'.
   Type 'void' is not assignable to type 'number'.
 tests/cases/compiler/arrowFunctionErrorSpan.ts(52,3): error TS2345: Argument of type '(_: any) => number' is not assignable to parameter of type '() => number'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 
 
 ==== tests/cases/compiler/arrowFunctionErrorSpan.ts (11 errors) ====
@@ -64,6 +66,7 @@ tests/cases/compiler/arrowFunctionErrorSpan.ts(52,3): error TS2345: Argument of
         d) => { });
     ~~~~~~~~~~~~~
 !!! error TS2345: Argument of type '(a: any, b: any, c: any, d: any) => void' is not assignable to parameter of type '() => number'.
+!!! error TS2345:   Target signature provides too few arguments. Expected 4 or more, but got 0.
 
     // single line with a comment
     f(/*
@@ -108,4 +111,5 @@ tests/cases/compiler/arrowFunctionErrorSpan.ts(52,3): error TS2345: Argument of
         2);
     ~~~~~
 !!! error TS2345: Argument of type '(_: any) => number' is not assignable to parameter of type '() => number'.
+!!! error TS2345:   Target signature provides too few arguments. Expected 1 or more, but got 0.
 

tests/baselines/reference/assignmentCompatWithCallSignaturesWithOptionalParameters.errors.txt

@@ -1,10 +1,17 @@
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignaturesWithOptionalParameters.ts(16,5): error TS2322: Type '(x: number) => number' is not assignable to type '() => number'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignaturesWithOptionalParameters.ts(19,5): error TS2322: Type '(x: number) => number' is not assignable to type '() => number'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignaturesWithOptionalParameters.ts(20,5): error TS2322: Type '(x: number, y?: number) => number' is not assignable to type '() => number'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignaturesWithOptionalParameters.ts(22,5): error TS2322: Type '(x: number, y: number) => number' is not assignable to type '() => number'.
+  Target signature provides too few arguments. Expected 2 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignaturesWithOptionalParameters.ts(33,5): error TS2322: Type '(x: number, y: number) => number' is not assignable to type '(x?: number) => number'.
+  Target signature provides too few arguments. Expected 2 or more, but got 1.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignaturesWithOptionalParameters.ts(39,5): error TS2322: Type '(x: number, y: number) => number' is not assignable to type '(x: number) => number'.
+  Target signature provides too few arguments. Expected 2 or more, but got 1.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignaturesWithOptionalParameters.ts(45,5): error TS2322: Type '(x: number, y: number) => number' is not assignable to type '(x: number) => number'.
+  Target signature provides too few arguments. Expected 2 or more, but got 1.
 
 
 ==== tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithCallSignaturesWithOptionalParameters.ts (7 errors) ====
@@ -26,18 +33,22 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a = (x: number) => 1; // error, too many required params
         ~
 !!! error TS2322: Type '(x: number) => number' is not assignable to type '() => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
         a = b.a; // ok
         a = b.a2; // ok
         a = b.a3; // error
         ~
 !!! error TS2322: Type '(x: number) => number' is not assignable to type '() => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
         a = b.a4; // error
         ~
 !!! error TS2322: Type '(x: number, y?: number) => number' is not assignable to type '() => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
         a = b.a5; // ok
         a = b.a6; // error
         ~
 !!! error TS2322: Type '(x: number, y: number) => number' is not assignable to type '() => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 0.
 
     var a2: (x?: number) => number; 
         a2 = () => 1; // ok, same number of required params
@@ -51,6 +62,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a2 = b.a6; // error
         ~~
 !!! error TS2322: Type '(x: number, y: number) => number' is not assignable to type '(x?: number) => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 1.
 
     var a3: (x: number) => number; 
         a3 = () => 1; // ok, fewer required params
@@ -59,6 +71,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a3 = (x: number, y: number) => 1;  // error, too many required params
         ~~
 !!! error TS2322: Type '(x: number, y: number) => number' is not assignable to type '(x: number) => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 1.
         a3 = b.a; // ok
         a3 = b.a2; // ok
         a3 = b.a3; // ok
@@ -67,6 +80,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a3 = b.a6; // error
         ~~
 !!! error TS2322: Type '(x: number, y: number) => number' is not assignable to type '(x: number) => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 1.
 
     var a4: (x: number, y?: number) => number;
         a4 = () => 1; // ok, fewer required params

tests/baselines/reference/assignmentCompatWithConstructSignaturesWithOptionalParameters.errors.txt

@@ -1,8 +1,13 @@
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignaturesWithOptionalParameters.ts(16,5): error TS2322: Type 'new (x: number) => number' is not assignable to type 'new () => number'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignaturesWithOptionalParameters.ts(17,5): error TS2322: Type 'new (x: number, y?: number) => number' is not assignable to type 'new () => number'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignaturesWithOptionalParameters.ts(19,5): error TS2322: Type 'new (x: number, y: number) => number' is not assignable to type 'new () => number'.
+  Target signature provides too few arguments. Expected 2 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignaturesWithOptionalParameters.ts(27,5): error TS2322: Type 'new (x: number, y: number) => number' is not assignable to type 'new (x?: number) => number'.
+  Target signature provides too few arguments. Expected 2 or more, but got 1.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignaturesWithOptionalParameters.ts(35,5): error TS2322: Type 'new (x: number, y: number) => number' is not assignable to type 'new (x: number) => number'.
+  Target signature provides too few arguments. Expected 2 or more, but got 1.
 
 
 ==== tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithConstructSignaturesWithOptionalParameters.ts (5 errors) ====
@@ -24,13 +29,16 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a = b.a3; // error
         ~
 !!! error TS2322: Type 'new (x: number) => number' is not assignable to type 'new () => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
         a = b.a4; // error
         ~
 !!! error TS2322: Type 'new (x: number, y?: number) => number' is not assignable to type 'new () => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
         a = b.a5; // ok
         a = b.a6; // error
         ~
 !!! error TS2322: Type 'new (x: number, y: number) => number' is not assignable to type 'new () => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 0.
 
     var a2: new (x?: number) => number; 
         a2 = b.a; // ok
@@ -41,6 +49,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a2 = b.a6; // error
         ~~
 !!! error TS2322: Type 'new (x: number, y: number) => number' is not assignable to type 'new (x?: number) => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 1.
 
     var a3: new (x: number) => number; 
         a3 = b.a; // ok
@@ -51,6 +60,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a3 = b.a6; // error
         ~~
 !!! error TS2322: Type 'new (x: number, y: number) => number' is not assignable to type 'new (x: number) => number'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 1.
 
     var a4: new (x: number, y?: number) => number;
         a4 = b.a; // ok

tests/baselines/reference/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.errors.txt

@@ -1,13 +1,17 @@
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(14,13): error TS2322: Type '(x: T) => any' is not assignable to type '() => T'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(23,13): error TS2322: Type '(x: T, y: T) => any' is not assignable to type '(x: T) => T'.
+  Target signature provides too few arguments. Expected 2 or more, but got 1.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(63,9): error TS2322: Type '() => T' is not assignable to type '<T>() => T'.
   Type 'T' is not assignable to type 'T'. Two different types with this name exist, but they are unrelated.
     'T' could be instantiated with an arbitrary type which could be unrelated to 'T'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(64,9): error TS2322: Type '(x?: T) => T' is not assignable to type '<T>() => T'.
   Type 'T' is not assignable to type 'T'. Two different types with this name exist, but they are unrelated.
     'T' could be instantiated with an arbitrary type which could be unrelated to 'T'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(65,9): error TS2322: Type '(x: T) => T' is not assignable to type '<T>() => T'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(66,9): error TS2322: Type '(x: T, y?: T) => T' is not assignable to type '<T>() => T'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(67,9): error TS2322: Type '(x?: T, y?: T) => T' is not assignable to type '<T>() => T'.
   Type 'T' is not assignable to type 'T'. Two different types with this name exist, but they are unrelated.
     'T' could be instantiated with an arbitrary type which could be unrelated to 'T'.
@@ -88,7 +92,9 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
     Type 'T' is not assignable to type 'T'. Two different types with this name exist, but they are unrelated.
       'T' could be instantiated with an arbitrary type which could be unrelated to 'T'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(107,13): error TS2322: Type '<T>(x: T) => any' is not assignable to type '<T>() => T'.
+  Target signature provides too few arguments. Expected 1 or more, but got 0.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts(116,13): error TS2322: Type '<T>(x: T, y: T) => any' is not assignable to type '<T>(x: T) => T'.
+  Target signature provides too few arguments. Expected 2 or more, but got 1.
 
 
 ==== tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithGenericCallSignaturesWithOptionalParameters.ts (29 errors) ====
@@ -108,6 +114,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
                 this.a = (x: T) => null; // error, too many required params
                 ~~~~~~
 !!! error TS2322: Type '(x: T) => any' is not assignable to type '() => T'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
 
                 this.a2 = () => null; // ok, same T of required params
                 this.a2 = (x?: T) => null; // ok, same T of required params
@@ -119,6 +126,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
                 this.a3 = (x: T, y: T) => null;  // error, too many required params
                 ~~~~~~~
 !!! error TS2322: Type '(x: T, y: T) => any' is not assignable to type '(x: T) => T'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 1.
 
                 this.a4 = () => null; // ok, fewer required params
                 this.a4 = (x?: T, y?: T) => null; // ok, fewer required params
@@ -173,9 +181,11 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
             b.a = t.a3;
             ~~~
 !!! error TS2322: Type '(x: T) => T' is not assignable to type '<T>() => T'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
             b.a = t.a4;
             ~~~
 !!! error TS2322: Type '(x: T, y?: T) => T' is not assignable to type '<T>() => T'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
             b.a = t.a5;
             ~~~
 !!! error TS2322: Type '(x?: T, y?: T) => T' is not assignable to type '<T>() => T'.
@@ -340,6 +350,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
                 this.a = <T>(x: T) => null; // error, too many required params
                 ~~~~~~
 !!! error TS2322: Type '<T>(x: T) => any' is not assignable to type '<T>() => T'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 1 or more, but got 0.
 
                 this.a2 = <T>() => null; // ok, same T of required params
                 this.a2 = <T>(x?: T) => null; // ok, same T of required params
@@ -351,6 +362,7 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
                 this.a3 = <T>(x: T, y: T) => null;  // error, too many required params
                 ~~~~~~~
 !!! error TS2322: Type '<T>(x: T, y: T) => any' is not assignable to type '<T>(x: T) => T'.
+!!! error TS2322:   Target signature provides too few arguments. Expected 2 or more, but got 1.
 
                 this.a4 = <T>() => null; // ok, fewer required params
                 this.a4 = <T>(x?: T, y?: T) => null; // ok, fewer required params