[SR-7046] Autocomplete suggests methods that can't be called on certain instances

[AnthonyLatsis]

Previous ID	SR-7046
Radar	rdar://problem/45340583
Original Reporter	@AnthonyLatsis
Type	Bug
Status	Resolved
Resolution	Done

Attachment: Download

Environment

Xcode Version 9.2 (9C40b)

Additional Detail from JIRA

Votes	3
Component/s	CodeCompletion
Labels	Bug
Assignee	@rintaro
Priority	Medium

md5: 2666fe154a7afbbb66b70fdd218be9a2

relates to:

• SR-9027 SourceKit suggests autocomplete for unavailable constrained methods
• SR-9396 Nonsensical error message related to constrained extensions

Issue Description:

On the screenshot, `foo` can't be called on b, and the compiler will rightly show an error if I hit enter on the Autocomplete suggestion below.


I am not sure if Autocomplete is currently meant to be this smart, but if by any chance it is, here you go.

Another example:

extension Array { 
   func foo(...) where Element == Int { ... }
 // This method will also always be visible in code completion, regardless of what type Element is
} 

[swift-ci]

Comment by Will Lisac (JIRA)

Using a protocol in the where clause is a possible workaround for this code completion issue.

class A<T> { }

extension A where T == String {
    // This method will always be visible in code completion
    func fooString() { }
}

extension A where T: StringProtocol {
    // This method will only be visible when T conforms to StringProtocol
    func fooStringProtocol() { }
}

let example = A<Bool>()
example.foo

[jepers]

The protocol-workaround only works when all code is in the same swift file, if you put the class and extensions and the calling code in separate files, it will list all extensions again.

Another very similar attempted workaround detailed example here will show the same behavior, ie working only if all code is in the same file.

[jepers]

I guess the following might be another manifestation of this issue:

let floatRange = Float(0) ..< Float(1)
floatRange.cou // ERROR: Value of type 'Range<Float>' has no member 'cou'; did you mean 'count'?
floatRange.count // ERROR: Type 'Float' does not conform to protocol 'SignedInteger'

I mean the supposedly helpful "did you mean `count`?" and the fact that `.count` is in the list of code completions, even though `Range<Float>` does not have a `.count` member.

[rintaro]

This has been fixed in #23065

[rintaro]

let floatRange = Float(0) ..< Float(1)
floatRange.cou // ERROR: Value of type 'Range<Float>' has no member 'cou'; did you mean 'count'?

This has been fixed in #23332

[AnthonyLatsis]

Thanks, Rintaro!

[jepers]

Is this supposed to be fixed in the default toolchain of Xcode 10.2.1?

I see Rintaro saying above that it has been fixed but the issue as described here (in SR-7046) and in the linked SR-9396 remains as of default toolchain of Xcode 10.2.1. That is, for example the following is still what happens in Xcode 10.2.1:

let floatRange = Float(0) ..< Float(1)
floatRange.cou // ERROR: Value of type 'Range<Float>' has no member 'cou'; did you mean 'count'?

even though Range<Float> has no property called count.

[rintaro]

Not for Xcode 10.2.1 (Swift 5.0.1). Please wait for Swift 5.1.