Error on for (const x in never) (#22988)

* Error on `for (const x in never)`

* Update diagnostic

* Provide argument to diagnostic

Author: Andy

src/compiler/checker.ts

@@ -22590,8 +22590,8 @@ namespace ts {
 
             // unknownType is returned i.e. if node.expression is identifier whose name cannot be resolved
             // in this case error about missing name is already reported - do not report extra one
-            if (!isTypeAssignableToKind(rightType, TypeFlags.NonPrimitive | TypeFlags.InstantiableNonPrimitive)) {
-                error(node.expression, Diagnostics.The_right_hand_side_of_a_for_in_statement_must_be_of_type_any_an_object_type_or_a_type_parameter);
+            if (rightType === neverType || !isTypeAssignableToKind(rightType, TypeFlags.NonPrimitive | TypeFlags.InstantiableNonPrimitive)) {
+                error(node.expression, Diagnostics.The_right_hand_side_of_a_for_in_statement_must_be_of_type_any_an_object_type_or_a_type_parameter_but_here_has_type_0, typeToString(rightType));
             }
 
             checkSourceElement(node.statement);

src/compiler/diagnosticMessages.json

@@ -1372,7 +1372,7 @@
         "category": "Error",
         "code": 2406
     },
-    "The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.": {
+    "The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type '{0}'.": {
         "category": "Error",
         "code": 2407
     },

tests/baselines/reference/for-inStatements.errors.txt

@@ -1,6 +1,6 @@
 tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(33,18): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
 tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(50,18): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
-tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(79,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(79,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'Color.Blue'.
 
 
 ==== tests/cases/conformance/statements/for-inStatements/for-inStatements.ts (3 errors) ====
@@ -88,5 +88,5 @@ tests/cases/conformance/statements/for-inStatements/for-inStatements.ts(79,15):
     for (var x in Color) { }
     for (var x in Color.Blue) { }
                   ~~~~~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'Color.Blue'.
 

tests/baselines/reference/for-inStatementsInvalid.errors.txt

@@ -2,19 +2,19 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(2
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(5,6): error TS2405: The left-hand side of a 'for...in' statement must be of type 'string' or 'any'.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(8,6): error TS2405: The left-hand side of a 'for...in' statement must be of type 'string' or 'any'.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(10,10): error TS2404: The left-hand side of a 'for...in' statement cannot use a type annotation.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(13,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(17,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(18,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(19,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(20,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(22,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(29,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(13,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'void'.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(17,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(18,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(19,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(20,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(22,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(29,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(31,18): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(38,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(46,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(38,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(46,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
 tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(48,18): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type 'string', but here has type 'keyof this'.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(51,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
-tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(62,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(51,23): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
+tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(62,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
 
 
 ==== tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts (17 errors) ====
@@ -40,26 +40,26 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(6
     function fn(): void { }
     for (var x in fn()) { }
                   ~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'void'.
 
     var c : string, d:string, e;
 
     for (var x in c || d) { }
                   ~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
     for (var x in e ? c : d) { }
                   ~~~~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
     for (var x in 42 ? c : d) { }
                   ~~~~~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
     for (var x in '' ? c : d) { }
                   ~~~~~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
     for (var x in 42 ? d[x] : c[x]) { }
     for (var x in c[23]) { }
                   ~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'string'.
 
     for (var x in (<T>(x: T) => x)) { }
     for (var x in function (x: string, y: number) { return x + y }) { }
@@ -68,7 +68,7 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(6
         biz() : number{
             for (var x in this.biz()) { }
                           ~~~~~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
             for (var x in this.biz) { }
             for (var x in this) { }
                      ~
@@ -81,7 +81,7 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(6
             for (var x in this.baz) { }
             for (var x in this.baz()) { }
                           ~~~~~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
 
             return null;
         }
@@ -91,7 +91,7 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(6
         boz() {
             for (var x in this.biz()) { }
                           ~~~~~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
             for (var x in this.biz) { }
             for (var x in this) { }
                      ~
@@ -100,7 +100,7 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(6
             for (var x in super.biz) { }
             for (var x in super.biz()) { }
                           ~~~~~~~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
             return null;
         }
     }
@@ -113,5 +113,5 @@ tests/cases/conformance/statements/for-inStatements/for-inStatementsInvalid.ts(6
 
     for (var x in i[42]) { } 
                   ~~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
 

tests/baselines/reference/forIn2.errors.txt

@@ -1,8 +1,8 @@
-tests/cases/compiler/forIn2.ts(1,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+tests/cases/compiler/forIn2.ts(1,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type '1'.
 
 
 ==== tests/cases/compiler/forIn2.ts (1 errors) ====
     for (var i in 1) {
                   ~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type '1'.
     }

tests/baselines/reference/forInStatement2.errors.txt

@@ -1,9 +1,9 @@
-tests/cases/compiler/forInStatement2.ts(2,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+tests/cases/compiler/forInStatement2.ts(2,15): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
 
 
 ==== tests/cases/compiler/forInStatement2.ts (1 errors) ====
     var expr: number;
     for (var a in expr) {
                   ~~~~
-!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter.
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'number'.
     }

tests/baselines/reference/neverTypeErrors1.errors.txt

@@ -9,9 +9,10 @@ tests/cases/conformance/types/never/neverTypeErrors1.ts(13,5): error TS2322: Typ
 tests/cases/conformance/types/never/neverTypeErrors1.ts(17,5): error TS2322: Type '1' is not assignable to type 'never'.
 tests/cases/conformance/types/never/neverTypeErrors1.ts(20,16): error TS2534: A function returning 'never' cannot have a reachable end point.
 tests/cases/conformance/types/never/neverTypeErrors1.ts(23,17): error TS2488: Type 'never' must have a '[Symbol.iterator]()' method that returns an iterator.
+tests/cases/conformance/types/never/neverTypeErrors1.ts(24,17): error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'never'.
 
 
-==== tests/cases/conformance/types/never/neverTypeErrors1.ts (11 errors) ====
+==== tests/cases/conformance/types/never/neverTypeErrors1.ts (12 errors) ====
     function f1() {
         let x: never;
         x = 1;
@@ -57,4 +58,7 @@ tests/cases/conformance/types/never/neverTypeErrors1.ts(23,17): error TS2488: Ty
     for (const n of f4()) {}
                     ~~~~
 !!! error TS2488: Type 'never' must have a '[Symbol.iterator]()' method that returns an iterator.
+    for (const n in f4()) {}
+                    ~~~~
+!!! error TS2407: The right-hand side of a 'for...in' statement must be of type 'any', an object type or a type parameter, but here has type 'never'.
 

tests/baselines/reference/neverTypeErrors1.js

@@ -22,6 +22,7 @@ function f4(): never {
 }
 
 for (const n of f4()) {}
+for (const n in f4()) {}
 
 
 //// [neverTypeErrors1.js]
@@ -46,3 +47,4 @@ function f4() {
 for (var _i = 0, _a = f4(); _i < _a.length; _i++) {
     var n = _a[_i];
 }
+for (var n in f4()) { }

tests/baselines/reference/neverTypeErrors1.symbols

@@ -48,3 +48,7 @@ for (const n of f4()) {}
 >n : Symbol(n, Decl(neverTypeErrors1.ts, 22, 10))
 >f4 : Symbol(f4, Decl(neverTypeErrors1.ts, 17, 1))
 
+for (const n in f4()) {}
+>n : Symbol(n, Decl(neverTypeErrors1.ts, 23, 10))
+>f4 : Symbol(f4, Decl(neverTypeErrors1.ts, 17, 1))
+

tests/baselines/reference/neverTypeErrors1.types

@@ -62,3 +62,8 @@ for (const n of f4()) {}
 >f4() : never
 >f4 : () => never
 
+for (const n in f4()) {}
+>n : string
+>f4() : never
+>f4 : () => never
+