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[SR-7247] Misleading type inference error message for extensions #49795

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swift-ci opened this issue Mar 21, 2018 · 6 comments
Closed

[SR-7247] Misleading type inference error message for extensions #49795

swift-ci opened this issue Mar 21, 2018 · 6 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis

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@swift-ci
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Previous ID SR-7247
Radar rdar://problem/38716444
Original Reporter gmilos (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

4.1 development snapshot (LLVM 260a172ffb, Clang cd84be6c42, Swift 04baf31).

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, TypeChecker
Assignee gmilos (JIRA)
Priority Medium

md5: 2640556cbadebf5abba890a0ac38cfe1

Issue Description:

The following distills the issue I hit (in larger body of code):

/***************** File1.swift *****************/
struct SomeType<T> {
}
/***************** File2.swift *****************/
extension SomeType {
 static func someFunc<R>(r: () -> R) {
 }
}
SomeType.someFunc { "hi" }

The compiler gives the following error:

error: repl.swift:11:19: error: cannot convert value of type '() -> String' to expected argument type '() -> _'
SomeType.someFunc { "hi" }
 ^~~~~~~~

But of course the issue is unknown generic type on SomeType, i.e. the fix is:

SomeType<Any>.someFunc { "hi" }

Reproduces on current 4.1 development snapshot (LLVM 260a172ffb, Clang cd84be6c42, Swift 04baf31).
@belkadan
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@xedin, do you have a dup for this?

@xedin
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xedin commented Mar 21, 2018

Unfortunately diagnostics for generic parameters are currently not great 🙁 I'll create a radar anyway and dup it later.

@xedin
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xedin commented Mar 21, 2018

@swift-ci create

@mdiep
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mdiep commented Jun 10, 2018

This is unrelated to the fact that the function is an extension. This also reproduces the issue:

struct SomeType<T> {
 static func someFunc<R>(r: () -> R) {
 }
}

SomeType.someFunc { "hi" }

Note that the error is that T can't be inferred, not R.

Removing the parameter does give a proper error about T.

@mdiep
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mdiep commented Jun 12, 2018

Curiously, if you put the closure inside () s to make it non-trailing, then you get the correct error.

@xedin
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xedin commented Feb 5, 2020

Looks like compiler produces much better message how (since 5.2):

error: generic parameter 'T' could not be inferred
SomeType.someFunc { "hi" }
^
 note: 'T' declared as parameter to type 'SomeType'
struct SomeType<T> {
                ^
note: explicitly specify the generic arguments to fix this issue
SomeType.someFunc { "hi" }
^
        <Any>

gmilos (JIRA User) Please use the latest master/5.2 snapshot to verify and close.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis
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@mdiep @xedin @belkadan @swift-ci