Quick fix for potentially uncalled decorators

src/compiler/diagnosticMessages.json

@@ -3709,6 +3709,10 @@
         "category": "Message",
         "code": 90027
     },
+    "Call decorator expression.": {
+        "category": "Message",
+        "code": 90028
+    },
 
     "Convert function to an ES2015 class": {
         "category": "Message",

src/services/codefixes/addMissingInvocationForDecorator.ts

@@ -0,0 +1,20 @@
+/* @internal */
+namespace ts.codefix {
+    registerCodeFix({
+        errorCodes: [Diagnostics._0_accepts_too_few_arguments_to_be_used_as_a_decorator_here_Did_you_mean_to_call_it_first_and_write_0.code],
+        getCodeActions: (context: CodeFixContext) => {
+            const sourceFile = context.sourceFile;
+            const token = getTokenAtPosition(sourceFile, context.span.start, /*includeJsDocComment*/ false);
+            const decorator = getAncestor(token, SyntaxKind.Decorator) as Decorator;
+            Debug.assert(!!decorator, "Expected position to be owned by a decorator.");
+            const replacement = createCall(decorator.expression, /*typeArguments*/ undefined, /*argumentsArray*/ undefined);
+            const changeTracker = textChanges.ChangeTracker.fromContext(context);
+            changeTracker.replaceNode(sourceFile, decorator.expression, replacement);
+
+            return [{
+                description: getLocaleSpecificMessage(Diagnostics.Call_decorator_expression),
+                changes: changeTracker.getChanges()
+            }];
+        }
+    });
+}

src/services/codefixes/fixes.ts

@@ -1,3 +1,4 @@
+/// <reference path="addMissingInvocationForDecorator.ts" />
 /// <reference path="correctQualifiedNameToIndexedAccessType.ts" />
 /// <reference path="fixClassIncorrectlyImplementsInterface.ts" />
 /// <reference path="fixAddMissingMember.ts" />

tests/cases/fourslash/codeFixAddForgottenDecoratorCall01.ts

@@ -0,0 +1,14 @@
+/// <reference path='fourslash.ts' />
+
+////declare function foo(): (...args: any[]) => void;
+////class C {
+////    [|@foo|]
+////    bar() {
+////
+////    }
+////}
+
+verify.codeFix({
+    description: "Call decorator expression.",
+    newRangeContent: `@foo()`
+});