flow - allow type parameter defaults in function declarations

packages/babel-parser/src/plugins/flow.js

@@ -798,9 +798,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       node.typeParameters = null;
 
       if (this.isRelational("<")) {
-        node.typeParameters = this.flowParseTypeParameterDeclaration(
-          /* allowDefault */ false,
-        );
+        node.typeParameters = this.flowParseTypeParameterDeclaration();
       }
 
       this.expect(tt.parenL);
@@ -1287,9 +1285,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
         case tt.relational:
           if (this.state.value === "<") {
-            node.typeParameters = this.flowParseTypeParameterDeclaration(
-              /* allowDefault */ false,
-            );
+            node.typeParameters = this.flowParseTypeParameterDeclaration();
             this.expect(tt.parenL);
             tmp = this.flowParseFunctionTypeParams();
             node.params = tmp.params;
@@ -2092,9 +2088,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       }
       delete (method: $FlowFixMe).variance;
       if (this.isRelational("<")) {
-        method.typeParameters = this.flowParseTypeParameterDeclaration(
-          /* allowDefault */ false,
-        );
+        method.typeParameters = this.flowParseTypeParameterDeclaration();
       }
 
       super.pushClassMethod(
@@ -2176,9 +2170,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
 
       // method shorthand
       if (this.isRelational("<")) {
-        typeParameters = this.flowParseTypeParameterDeclaration(
-          /* allowDefault */ false,
-        );
+        typeParameters = this.flowParseTypeParameterDeclaration();
         if (!this.match(tt.parenL)) this.unexpected();
       }
 
@@ -2386,9 +2378,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       // $FlowFixMe
       const kind = node.kind;
       if (kind !== "get" && kind !== "set" && this.isRelational("<")) {
-        node.typeParameters = this.flowParseTypeParameterDeclaration(
-          /* allowDefault */ false,
-        );
+        node.typeParameters = this.flowParseTypeParameterDeclaration();
       }
       super.parseFunctionParams(node, allowModifiers);
     }

packages/babel-parser/test/fixtures/flow/type-parameter-declaration/default-invalid-1/input.js

@@ -1,3 +1 @@
-(class A {
-  foo<T = string>() {}
-});
+declare function foo<T = string>() {}

packages/babel-parser/test/fixtures/flow/type-parameter-declaration/default-invalid-1/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected token (2:8)"
-}
+  "throws": "Unexpected token, expected \":\" (1:35)"
+}

packages/babel-parser/test/fixtures/flow/type-parameter-declaration/default-invalid-2/input.js

@@ -1 +1 @@
-({ foo<T = string>() {} });
+var x: Array<T = number>

packages/babel-parser/test/fixtures/flow/type-parameter-declaration/default-invalid-2/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected token (1:9)"
-}
+  "throws": "Unexpected token, expected \",\" (1:15)"
+}

packages/babel-parser/test/fixtures/flow/type-parameter-declaration/default-invalid-3/input.js

@@ -1 +1 @@
-declare class A { foo<T = string>(): void }
+class A extends B<T = number> {}

packages/babel-parser/test/fixtures/flow/type-parameter-declaration/default-invalid-3/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "Unexpected token (1:24)"
-}
+  "throws": "Unexpected token, expected \",\" (1:20)"
+}

packages/babel-parser/test/fixtures/flow/type-parameter-declaration/default/input.js

@@ -20,3 +20,13 @@ interface A19<T: ?string = string> {}
 interface A20<S, T: ?string = string> {}
 interface A21<S = number, T: ?string = string> {}
 type A22<T = void> = T
+function A26<T = string>() {}
+;({ A28<T = string>() {} });
+class A29 {
+  foo<T = string>() {}
+}
+;(class A30 {
+  foo<T = string>() {}
+});
+declare class A31 { foo<T = string>(): void }
+<T = string>() => 123;