Issue implicit any errors for mapped types without annotations (#21104)

* Fixed #21011

* Updated code of merged message

* Reversed message code change and moved error to it's appropriate position

* Applied suggested improvements

* Fixed wrong diagnostics message in checker

* Reverted diagnostic message change

src/compiler/checker.ts

@@ -11281,6 +11281,9 @@ namespace ts {
                     }
                     diagnostic = Diagnostics._0_which_lacks_return_type_annotation_implicitly_has_an_1_return_type;
                     break;
+                case SyntaxKind.MappedType:
+                    error(declaration, Diagnostics.Mapped_object_type_implicitly_has_an_any_template_type);
+                    return;
                 default:
                     diagnostic = Diagnostics.Variable_0_implicitly_has_an_1_type;
             }
@@ -20312,6 +20315,11 @@ namespace ts {
         function checkMappedType(node: MappedTypeNode) {
             checkSourceElement(node.typeParameter);
             checkSourceElement(node.type);
+
+            if (noImplicitAny && !node.type) {
+                reportImplicitAnyError(node, anyType);
+            }
+
             const type = <MappedType>getTypeFromMappedTypeNode(node);
             const constraintType = getConstraintTypeFromMappedType(type);
             checkTypeAssignableTo(constraintType, stringType, node.typeParameter.constraint);

src/compiler/diagnosticMessages.json

@@ -3571,7 +3571,10 @@
         "category": "Error",
         "code": 7038
     },
-
+    "Mapped object type implicitly has an 'any' template type.": {
+        "category": "Error",
+        "code": 7039
+    },
     "You cannot rename this element.": {
         "category": "Error",
         "code": 8000

tests/baselines/reference/anyMappedTypesError.errors.txt

@@ -0,0 +1,7 @@
+tests/cases/compiler/anyMappedTypesError.ts(1,12): error TS7039: Mapped object type implicitly has an 'any' template type.
+
+
+==== tests/cases/compiler/anyMappedTypesError.ts (1 errors) ====
+    type Foo = {[P in "bar"]};
+               ~~~~~~~~~~~~~~
+!!! error TS7039: Mapped object type implicitly has an 'any' template type.

tests/baselines/reference/anyMappedTypesError.js

@@ -0,0 +1,4 @@
+//// [anyMappedTypesError.ts]
+type Foo = {[P in "bar"]};
+
+//// [anyMappedTypesError.js]

tests/baselines/reference/anyMappedTypesError.symbols

@@ -0,0 +1,5 @@
+=== tests/cases/compiler/anyMappedTypesError.ts ===
+type Foo = {[P in "bar"]};
+>Foo : Symbol(Foo, Decl(anyMappedTypesError.ts, 0, 0))
+>P : Symbol(P, Decl(anyMappedTypesError.ts, 0, 13))
+

tests/baselines/reference/anyMappedTypesError.types

@@ -0,0 +1,5 @@
+=== tests/cases/compiler/anyMappedTypesError.ts ===
+type Foo = {[P in "bar"]};
+>Foo : Foo
+>P : P
+

tests/cases/compiler/anyMappedTypesError.ts

@@ -0,0 +1,3 @@
+// @noImplicitAny: true
+
+type Foo = {[P in "bar"]};