fix: Include signature type parameters, too.

Author: cartant

source/rules/prefer-interface.ts

@@ -57,9 +57,12 @@ const rule = ruleCreator({
           return;
         }
         function fix(fixer: eslint.RuleFixer) {
-          const typeParameters = typeAliasNode.typeParameters
+          const interfaceTypeParameters = typeAliasNode.typeParameters
             ? context.getSourceCode().getText(typeAliasNode.typeParameters)
             : "";
+          const functionTypeParameters = functionTypeNode.typeParameters
+            ? context.getSourceCode().getText(functionTypeNode.typeParameters)
+            : "";
           const params = functionTypeNode.params
             .map((param) => context.getSourceCode().getText(param))
             .join(",");
@@ -71,7 +74,7 @@ const rule = ruleCreator({
             : "void";
           return fixer.replaceText(
             typeAliasNode,
-            `interface ${typeAliasNode.id.name}${typeParameters} { (${params}): ${returnType}; }`
+            `interface ${typeAliasNode.id.name}${interfaceTypeParameters} { ${functionTypeParameters}(${params}): ${returnType}; }`
           );
         }
         context.report({

tests/rules/prefer-interface.ts

@@ -132,13 +132,23 @@ ruleTester({ types: true }).run("prefer-interface", rule, {
     ),
     fromFixture(
       stripIndent`
-        export type Identity<T> = (value: T) => T;
-                    ~~~~~~~~ [forbidden]
+        type Identity<T> = (value: T) => T;
+             ~~~~~~~~ [forbidden]
+      `,
+      {
+        output: stripIndent`
+          interface Identity<T> { (value: T): T; }
+        `,
+      }
+    ),
+    fromFixture(
+      stripIndent`
+        type Func<Foo> = <Bar>(foo: Foo) => Bar;
+             ~~~~ [forbidden]
       `,
       {
-        options: [{ allowLocal: true }],
         output: stripIndent`
-          export interface Identity<T> { (value: T): T; }
+          interface Func<Foo> { <Bar>(foo: Foo): Bar; }
         `,
       }
     ),