fix: quickfix deletes active functionality when removing unused variable

[GuilhermeConstantino]

Description
This was an issue that I opened in a library very_good_analysis, they sugested I opened it here.
Linter will remove function calls when made to a unused variable, even though the function itself might still be needed.

System used:
Windows.

Steps To Reproduce
Create a variable that receives the result of a function but is unused
Accept the quickfix
Expected Behavior
Future _postSomething(var something) {
final result = sendPostRequest(something);
}
Now since I didn't do anything with the result, it will cause a unused_local_variable linter
And when I select the "Remove unused local variable" quickfix it will delete the whole send, not just the variable.

Wanted result:
Future _postSomething(var something) {
sendPostRequest(something);
}

Actual result:
Future _postSomething(var something) {
}

Additional Context
The linter deleted some of my app functionality instead of just the variable.

[FMorschel]

Hey @GuilhermeConstantino, could you please confirm the Dart version you're using?

I just tested on the latest main with the following code, and everything works as you asked, only the code before foo(1); gets removed:

int foo(int p) => 0;
void f(str) {
  final removed = foo(1);
}

We have a similar test case here (but for methods) that was added more than a year ago:

sdk/pkg/analysis_server/test/src/services/correction/fix/remove_unused_local_variable_test.dart

Lines 115 to 128 in ba40d9b

	Future<void> test_assigned_inDeclaration() async {
	await resolveTestCode(r'''
	List<String> l = [];
	void f(str) {
	final removed = l.remove(str);
	}
	''');
	await assertHasFix(r'''
	List<String> l = [];
	void f(str) {
	l.remove(str);
	}
	''');
	}

I still opened https://dart-review.googlesource.com/c/sdk/+/426380 to add a test for functions specifically.

If you can give more information, it would be great! If you want to test on the latest stable Dart and don't have it installed, you can test in https://dartpad.dev/ with no need to install anything else.

[GuilhermeConstantino]

Hello @FMorschel , aparently, it only happens when using await. Here is the code I used inside DartPad to verify it:

void f() async {
 final response = await test();
}

Future<String> test() async {
  return ('nothing');
}

If you paste the code and accept the quickfix, it will delete the function call. This was deleting my repository requests when using quickfix.

[GuilhermeConstantino]

@FMorschel My dart version is the following:

Dart SDK version: 3.7.0 (stable) (Wed Feb 5 04:53:58 2025 -0800) on "windows_x64"

But, the problem also happens inside DartPad.

[GuilhermeConstantino]

@FMorschel Just to clarify a bit more, this is not a problem with GET requests, as they return the result. But with POST requests, sometimes out of habit someone can assign the response of the request to a variable, but we used the try / catch to get any errors and did not use the response, in that situation, usign the quickfix would break the app, as the variable and the post request would be deleted.

[FMorschel]

Thanks for figuring out the problem and for opening this issue! I'll take a look at fixing it!

[FMorschel]

I've updated the above CL with the fix for this issue