[SR-13388] Add Fix-Its to "override" mismatch

[DougGregor]

Previous ID	SR-13388
Radar	rdar://problem/66539331
Original Reporter	@DougGregor
Type	Improvement
Status	In Progress
Resolution

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Improvement, StarterBug
Assignee	RoyCao (JIRA)
Priority	Medium

md5: be871146c13ac26dbbf04275c83c2233

Issue Description:

For code like this following:

class Base {
  func foo(a: Int, b: Int) {}
}
class C: Base {
  override func foo(a: Int) {} // error: method does not override any method from its superclass
}

we should provide a Fix-It that adds ", b: Int" to C.foo.

[typesanitizer]

@swift-ci create

[swift-ci]

Comment by CaoMing (JIRA)

I am interested in implementing this🙂

[typesanitizer]

Sure thing. Check out our README for instructions on how to understand the workflow of submitting a PR and building the compiler.

In this particular case, you can check which parts of the compiler emit the error by searching for the error string and working backwards from there (error string -> error name -> places which emit the error).

Once you find that, you'll need to see which potential methods could've been over-ridden (but aren't because of the type mismatch). There may be zero or more "matches". The zero match case will not require any fix-its. The one match case will have one fix-it (search for fixit and fixitReplace in the compiler to see examples). When there is more than one match, there is a design decision to be made:

1. If there are multiple matches, show multiple fix-its. This may get overwhelming if there are too many matches.
2. If there are multiple matches, just list the potential matches somehow but no fix-it.
3. If there are multiple matches, don't do anything extra.

[swift-ci]

Comment by CaoMing (JIRA)

Very detailed guidance, thank you very much

[slavapestov]

> Once you find that, you'll need to see which potential methods could've been over-ridden (but aren't because of the type mismatch).

This should already be available in some form. Override matching does a name lookup to find candidates, and then filters this list by argument label and type. You can preserve the original list, and use it to emit diagnostics if the final set of candidates is empty.

[swift-ci]

Comment by CaoMing (JIRA)

class Base {
func foo(a: Int, b: Int, c) {}
}

class C: Base {
override func foo(a: Int) {} // error: method does not override any method from its superclass

}

In this case, we should provide a Fix-It that adds ", b: Int, c: Int" to C.foo, right?

class Base {
func foo(a: Int, b: Int, c: Int) {}
}

class C: Base {
override func foo(a: Int, b: Int) {} // error: method does not override any method from its superclass

}

In this case, we should provide a Fix-It that adds ", c: Int" to C.foo, right?

class Base {
func foo(a: Int, b: Int, c) {}
func foo(a: Int, b: Int, c: Int) {}
}

class C: Base {
override func foo(a: Int) {} // error: method does not override any method from its superclass

}

In this case, we should provide a Fix-It that adds ", b: Int" to C.foo, right?

[theblixguy]

Yeah, that makes sense to me, there will be one fix-it for each “near-match”.

[swift-ci]

Comment by CaoMing (JIRA)

class Base {

func foo(a: Int, b: Int) {}

}

class C: Base {

override func foo() {} // error: method does not override any method from its superclass

}

In this case, do we provide a Fix-It that adds "a: Int, b: Int" to C.foo?

theindigamer (JIRA User) @theblixguy

[swift-ci]

Comment by CaoMing (JIRA)

@slavapestov @theblixguy Could you help to review and give me some suggestion? Thank you.

#34003