Cannot inline refactor method that is invoked using a cascade operator

[alanrussian]

When I try to refactor a Dart method that is invoked using the cascade operator, I get this error: "Cannot inline cascade invocation." This appears to be coming from here:

sdk/pkg/analysis_server/lib/src/services/refactoring/legacy/inline_method.dart

Line 546 in 53fb57e

'Cannot inline cascade invocation.', newLocation_fromNode(usage));

For example:

class Foo {
  void bar() {
    baz();
  }

  void baz() {}
}

void main() {
  final myFoo = Foo()..bar();
}

1. Copy this into VSCode.
2. Right click bar, click refactor, then click inline.

Expected:

class Foo {
  void baz() {}
}

void main() {
  final myFoo = Foo()..baz();
}

• Dart version and tooling diagnostic info (dart info): The current one in google3 (not sure if I can share here)
• Whether you are using Windows, macOS, or Linux (if applicable): Linux
• Whether you are using Chrome, Safari, Firefox, Edge (if applicable): N/A

[scheglov]

We could theoretically do a few simple operations, e.g. like here - replace one invocation with another, but in general cascades are quite limiting in the set of operations that you can include there. Do you envision this as just such limited extension of the inline method refactoring, or saw in the past the need to expand it wider?

[alanrussian]

Our codebase has a testing library with many void methods and it's a common pattern to use the cascade operator to chain the operations. We had one case which came up where the inlining would be very straightforward and I imagine could be covered.

[scheglov]

Alan, you mentioned a degraded experience option, inline where possible, and leave the rest as is.

It almost works, from the InlineMethodRefactoringImpl point of view.
We actually report it as addError(), not addFatalError().
A fatal error would mean that the server completely refuses to do it.
A non-fatal error means that some changes might be invalid.

It is up to the IDE to decide how to handle these statuses.
Unfortunately, all IDEs after Dart Editor decided that even a warning is a fatal problem, and the refactoring cannot be done.

So, in the test it could work like this.
Of course here we could inline even the cascade, but I'm showing just what results we have right now, without changing much implementation in the server, and what could work in general case, if test() has multiple statements.

  Future<void> solo_test_bad_cascadeInvocation() async {
    await indexTestUnit(r'''
class A {
  foo() {}
  bar() {}
  baz() {}
  test() {
    baz();
  }
}
void f() {
 A a = new A();
 a..foo()..test()..bar();
 a.test();
}
''');
    _createRefactoring('test() {');
    // error
    var status = await refactoring.checkAllConditions();
    var location = SourceRange(findOffset('..test()'), '..test()'.length);
    assertRefactoringStatus(status, RefactoringProblemSeverity.ERROR,
        expectedMessage: 'Cannot inline cascade invocation.',
        expectedContextRange: location);
    // change
    var change = await refactoring.createChange();
    refactoringChange = change;
    assertTestChangeResult(r'''
class A {
  foo() {}
  bar() {}
  baz() {}
}
void f() {
 A a = new A();
 a..foo()..test()..bar();
 a.baz();
}
''');
  }