Make index signature declarations without a type annotation an implicit any, not a grammar error

packages/typescript/src/ast/ast.generated.ts

@@ -754,7 +754,6 @@ export interface SetAccessorDeclaration extends NodeBase, DeclarationBase, Named
 }
 export interface IndexSignatureDeclaration extends NodeBase, DeclarationBase, ModifiersBase, FunctionLikeBase, TypeElementBase, ClassElementBase {
     readonly kind: SyntaxKind.IndexSignature;
-    readonly type: TypeNode;
 }
 export interface MethodSignatureDeclaration extends NodeBase, DeclarationBase, NamedMemberBase, FunctionLikeBase, TypeElementBase {
     readonly kind: SyntaxKind.MethodSignature;

packages/typescript/src/ast/factory.generated.ts

@@ -4357,7 +4357,7 @@ export function createSetAccessorDeclaration(modifiers: readonly ModifierLike[]
     }) as unknown as SetAccessorDeclaration;
 }
 
-export function createIndexSignatureDeclaration(modifiers: readonly ModifierLike[] | undefined, parameters: readonly ParameterDeclaration[], type: TypeNode): IndexSignatureDeclaration {
+export function createIndexSignatureDeclaration(modifiers: readonly ModifierLike[] | undefined, parameters: readonly ParameterDeclaration[], type?: TypeNode): IndexSignatureDeclaration {
     return new NodeObject(SyntaxKind.IndexSignature, {
         modifiers: modifiers ? createNodeArray(modifiers) : undefined,
         parameters: createNodeArray(parameters),
@@ -5591,7 +5591,7 @@ export function updateSetAccessorDeclaration(node: SetAccessorDeclaration, modif
     return node.modifiers !== modifiers || node.name !== name || node.typeParameters !== typeParameters || node.parameters !== parameters || node.type !== type || node.body !== body ? createSetAccessorDeclaration(modifiers, name, typeParameters, parameters, type, body) : node;
 }
 
-export function updateIndexSignatureDeclaration(node: IndexSignatureDeclaration, modifiers: readonly ModifierLike[] | undefined, parameters: readonly ParameterDeclaration[], type: TypeNode): IndexSignatureDeclaration {
+export function updateIndexSignatureDeclaration(node: IndexSignatureDeclaration, modifiers: readonly ModifierLike[] | undefined, parameters: readonly ParameterDeclaration[], type?: TypeNode): IndexSignatureDeclaration {
     return node.modifiers !== modifiers || node.parameters !== parameters || node.type !== type ? createIndexSignatureDeclaration(modifiers, parameters, type) : node;
 }
 

packages/typescript/test/sync/ast.test.ts

@@ -54,6 +54,7 @@ import {
     createFunctionDeclaration,
     createIdentifier,
     createIfStatement,
+    createIndexSignatureDeclaration,
     createMissingDeclaration,
     createNodeArray,
     createNumericLiteral,
@@ -108,6 +109,19 @@ describe("NodeObject + childrenIter", { concurrency }, () => {
     });
 });
 
+test("index signatures allow an omitted type", () => {
+    using api = spawnAPI();
+    const source = api.createSourceFile("/repro.ts", "interface I { [key: string]; next: number; }").sourceFile;
+    const declaration = source.statements[0];
+    assert.ok(astModule.isInterfaceDeclaration(declaration));
+    const signature = declaration.members[0];
+    assert.ok(astModule.isIndexSignatureDeclaration(signature));
+    const type: astModule.TypeNode | undefined = signature.type;
+    assert.strictEqual(type, undefined);
+    assert.strictEqual(createIndexSignatureDeclaration(undefined, signature.parameters).type, undefined);
+    assert.strictEqual(declaration.members.length, 2);
+});
+
 describe("AST property contracts", { concurrency }, () => {
     test("absent parser children have optional types", () => {
         const absent: {

tools/scripts/tsc/ast.json

@@ -2497,7 +2497,7 @@
                     {
                         "name": "Type",
                         "inherited": true,
-                        "optional": false
+                        "optional": true
                     }
                 ]
             },

tsc/internal/checker/checker.go

@@ -2834,6 +2834,8 @@ func (c *Checker) checkSignatureDeclaration(node *ast.Node) {
 			c.error(node, diagnostics.Construct_signature_which_lacks_return_type_annotation_implicitly_has_an_any_return_type)
 		case ast.KindCallSignature:
 			c.error(node, diagnostics.Call_signature_which_lacks_return_type_annotation_implicitly_has_an_any_return_type)
+		case ast.KindIndexSignature:
+			c.error(node, diagnostics.Index_signature_which_lacks_type_annotation_implicitly_has_an_any_type)
 		}
 	}
 	if returnTypeNode != nil {

tsc/internal/checker/grammarchecks.go

@@ -831,9 +831,6 @@ func (c *Checker) checkGrammarIndexSignatureParameters(node *ast.IndexSignatureD
 	if !everyType(t, c.isValidIndexKeyType) {
 		return c.grammarErrorOnNode(parameter.Name(), diagnostics.An_index_signature_parameter_type_must_be_string_number_symbol_or_a_template_literal_type)
 	}
-	if node.Type == nil {
-		return c.grammarErrorOnNode(node.AsNode(), diagnostics.An_index_signature_must_have_a_type_annotation)
-	}
 	return false
 }
 

tsc/internal/diagnostics/diagnosticMessages.generated.json

@@ -16,7 +16,6 @@
     "An_index_signature_parameter_cannot_have_an_accessibility_modifier_1018": "An index signature parameter cannot have an accessibility modifier.",
     "An_index_signature_parameter_cannot_have_a_question_mark_1019": "An index signature parameter cannot have a question mark.",
     "An_index_signature_parameter_cannot_have_an_initializer_1020": "An index signature parameter cannot have an initializer.",
-    "An_index_signature_must_have_a_type_annotation_1021": "An index signature must have a type annotation.",
     "An_index_signature_parameter_must_have_a_type_annotation_1022": "An index signature parameter must have a type annotation.",
     "readonly_modifier_can_only_appear_on_a_property_declaration_or_index_signature_1024": "'readonly' modifier can only appear on a property declaration or index signature.",
     "An_index_signature_cannot_have_a_trailing_comma_1025": "An index signature cannot have a trailing comma.",
@@ -1751,6 +1750,7 @@
     "This_syntax_is_reserved_in_files_with_the_mts_or_cts_extension_Use_an_as_expression_instead_7059": "This syntax is reserved in files with the .mts or .cts extension. Use an `as` expression instead.",
     "This_syntax_is_reserved_in_files_with_the_mts_or_cts_extension_Add_a_trailing_comma_or_explicit_cons_7060": "This syntax is reserved in files with the .mts or .cts extension. Add a trailing comma or explicit constraint.",
     "A_mapped_type_may_not_declare_properties_or_methods_7061": "A mapped type may not declare properties or methods.",
+    "Index_signature_which_lacks_type_annotation_implicitly_has_an_any_type_7062": "Index signature, which lacks type annotation, implicitly has an 'any' type.",
     "Declaration_emit_elides_private_members_but_0_refers_to_a_private_member_Write_an_explicit_type_here_7080": "Declaration emit elides private members, but '{0}' refers to a private member. Write an explicit type here.",
     "You_cannot_rename_this_element_8000": "You cannot rename this element.",
     "You_cannot_rename_elements_that_are_defined_in_the_standard_TypeScript_library_8001": "You cannot rename elements that are defined in the standard TypeScript library.",

tsc/internal/diagnostics/diagnosticMessages.json

@@ -67,10 +67,6 @@
         "category": "Error",
         "code": 1020
     },
-    "An index signature must have a type annotation.": {
-        "category": "Error",
-        "code": 1021
-    },
     "An index signature parameter must have a type annotation.": {
         "category": "Error",
         "code": 1022
@@ -7042,6 +7038,10 @@
         "category": "Error",
         "code": 7061
     },
+    "Index signature, which lacks type annotation, implicitly has an 'any' type.": {
+        "category": "Error",
+        "code": 7062
+    },
     "Declaration emit elides private members, but '{0}' refers to a private member. Write an explicit type here.": {
         "category": "Error",
         "code": 7080

tsc/testdata/baselines/reference/compiler/arraySigChecking.errors.txt

@@ -1,10 +1,11 @@
+arraySigChecking.ts(11,16): error TS7062: Index signature, which lacks type annotation, implicitly has an 'any' type.
 arraySigChecking.ts(11,17): error TS1268: An index signature parameter type must be 'string', 'number', 'symbol', or a template literal type.
 arraySigChecking.ts(18,27): error TS2322: Type 'void' is not assignable to type 'string'.
 arraySigChecking.ts(22,13): error TS2322: Type 'number' is not assignable to type 'number[]'.
 arraySigChecking.ts(22,16): error TS2322: Type 'number' is not assignable to type 'number[]'.
 
 
-==== arraySigChecking.ts (4 errors) ====
+==== arraySigChecking.ts (5 errors) ====
     declare namespace M {
         interface iBar { t: any; }
         interface iFoo extends iBar {
@@ -16,6 +17,8 @@ arraySigChecking.ts(22,16): error TS2322: Type 'number' is not assignable to typ
         }
 
         var foo: { [index: any]; }; // expect an error here
+                   ~~~~~~~~~~~~~
+!!! error TS7062: Index signature, which lacks type annotation, implicitly has an 'any' type.
                     ~~~~~
 !!! error TS1268: An index signature parameter type must be 'string', 'number', 'symbol', or a template literal type.
     }