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[SR-7108] Generic usage complication thru nesting leads to Compilation error: Generic parameter could not be inferred #49656

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swift-ci opened this issue Mar 2, 2018 · 4 comments
Closed

[SR-7108] Generic usage complication thru nesting leads to Compilation error: Generic parameter could not be inferred #49656

swift-ci opened this issue Mar 2, 2018 · 4 comments
Labels
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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swift-ci commented Mar 2, 2018

Previous ID SR-7108
Radar rdar://problem/38143705
Original Reporter melifaro (JIRA User)
Type Bug
Status Resolved
Resolution Done
Environment

macOS 10.13.3 (17D102)
Xcode 9.2
Apple Swift version 4.0.3 (swiftlang-900.0.74.1 clang-900.0.39.2)

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

md5: 9a7b97c03b4c56d3ca38833b490a79ec

Issue Description:

Consider following two examples. They are abstract. The first one is more complicated and produces compilation error: "Generic parameter could not be inferred" while the second - simplified version of the first compiles fine.

I expect no errors with the first example compilation as the type can be inferred in fact (and should).

First example (compiles with the error):

protocol FooProtocol {
    
    associatedtype Bar
    
    func doFoo(with bar: Bar)
}

class Bar {
    
}

class Foo: FooProtocol {
    
    func doFoo(with bar: Bar) {
        
        //..
    }
}

protocol ContainerProtocol {
    
    associatedtype Something
    
    func process(entity: Something)
}


class FooService<F: FooProtocol> {
    
    func doService<C>(container: C) -> C where C: ContainerProtocol, C.Something == F.Bar {
        
        return container
    }
}

protocol SomethingProtocol {
    
    associatedtype SomeType
    
    func doSomething(with value: SomeType)
}

class Container<S: SomethingProtocol>: ContainerProtocol {
    
    func process(entity: S) {
        //...
    }
}

class Something<S>: SomethingProtocol {
    
    func doSomething(with value: S) {
        //...
    }
}

class Client {
    
    init() {
        //ERROR HERE: Generic parameter 'C' could not be inferred
        let container: Container<Something<Bar>> = FooService<Foo>().doService(container: Container<Something<Bar>>())
    }
}

Second example (simplified, compiles fine):

protocol FooProtocol {
    
    associatedtype Bar
    
    func doFoo(with bar: Bar)
}

class Bar {
    
}

class Foo: FooProtocol {
    
    func doFoo(with bar: Bar) {
        
        //..
    }
}

protocol ContainerProtocol {
    
    associatedtype Something
    
    func process(entity: Something)
}


class FooService<F: FooProtocol> {
    
    func doService<C>(container: C) -> C where C: ContainerProtocol, C.Something == F.Bar {
        
        return container
    }
}

class Container<S>: ContainerProtocol {
    
    func process(entity: S) {
        
        //...
    }
}


class Client {
    
    init() {
        
        FooService<Foo>().doService(container: Container<Bar>())
    }
}
@belkadan
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belkadan commented Mar 5, 2018

There actually is a problem in your code: C.Something is 'Something<Bar>', but F.Bar is just 'Bar'. But it would be nice if the diagnostic were clearer, or at least didn't say the wrong thing.

cc @xedin

@xedin
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xedin commented Mar 5, 2018

@swift-ci create

@swift-ci
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swift-ci commented Mar 6, 2018

Comment by Igor Botov (JIRA)

Thanks Jordan! I'm apparently got confused with my own code - but agree that error message could be better)

@xedin
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xedin commented Sep 10, 2021

Diagnostic has been improved in Xcode 13:

error: instance method 'doService(container:)' requires the types 'Bar' and 'Something<Bar>' be equivalent
        let container: Container<Something<Bar>> = FooService<Foo>().doService(container: Container<Something<Bar>>())
                                                   ^
note: where 'F.Bar' = 'Bar', 'C.Something' = 'Something<Bar>'
    func doService<C>(container: C) -> C where C: ContainerProtocol, C.Something == F.Bar {
         ^

Please use either Xcode 13 or main branch 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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