no-empty-interface: allow providing type arguments for extended type (p…

…alantir#3260)

[bugfix] `no-empty-interface` allows providing type arguments for extended type
Fixes: palantir#3256

src/rules/noEmptyInterfaceRule.ts

@@ -45,13 +45,22 @@ function walk(ctx: Lint.WalkContext<void>) {
     return ts.forEachChild(ctx.sourceFile, function cb(node: ts.Node): void {
         if (isInterfaceDeclaration(node) &&
             node.members.length === 0 &&
-            (node.heritageClauses === undefined ||
-             // allow interfaces that extend 2 or more interfaces
-             node.heritageClauses[0].types.length < 2)) {
+            (node.heritageClauses === undefined || extendsOneTypeWithoutTypeArguments(node.heritageClauses[0]))) {
             return ctx.addFailureAtNode(
                 node.name,
                 node.heritageClauses !== undefined ? Rule.FAILURE_STRING_FOR_EXTENDS : Rule.FAILURE_STRING);
         }
         return ts.forEachChild(node, cb);
     });
 }
+
+function extendsOneTypeWithoutTypeArguments({types}: ts.HeritageClause): boolean {
+    switch (types.length) {
+        case 0:
+            return true; // don't crash on empty extends list
+        case 1:
+            return types[0].typeArguments === undefined; // allow interfaces that provide type arguments for the extended type
+        default:
+            return false; // allow interfaces extending more than one types
+    }
+}

test/rules/no-empty-interface/test.ts.lint

@@ -10,3 +10,5 @@ interface L extends J, K {} // extending more than one interface is ok, as it ca
 
 interface M extends {} // don't crash on empty extends list
           ~               [An interface declaring no members is equivalent to its supertype.]
+
+interface N extends Promise<string|number> {}