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[SR-12259] Function Builders with types conforming to ExpressibleBy... #54687

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swift-ci opened this issue Feb 24, 2020 · 5 comments
Closed

[SR-12259] Function Builders with types conforming to ExpressibleBy... #54687

swift-ci opened this issue Feb 24, 2020 · 5 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself result builders Feature: Result builders type checker Area → compiler: Semantic analysis

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@swift-ci
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Previous ID SR-12259
Radar rdar://problem/59740177
Original Reporter mkao (JIRA User)
Type Bug
Status Resolved
Resolution Invalid

Attachment: Download

Environment

Xcode 11.3 Playground / Swift 5.1.3

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, FunctionBuilder, TypeChecker
Assignee None
Priority Medium

md5: f3685517f91c2b32760fd3296922b4f3

Issue Description:

When using a type conforming to ExpressibleByStringLiteral within the FunctionBuilder closure, the compiler seems to have issues.

Given the following type:

public enum Foo: ExpressibleByStringLiteral {
    case string(String)
    case other

    public init(stringLiteral value: String) {
        self = .string(value)
    }
}

And using the function builder:

@_functionBuilder
public class SomeBuilder {
    public static func buildBlock(_ values: Foo...) -> [Foo] {
        values
    }
}

public func call(@SomeBuilder values: () -> [Foo]) -> [Foo] {
    values()
}

public func call(@SomeBuilder values: () -> Foo) -> [Foo] {
    [values()]
}

I am able to get this working:

call {
    "foo"
}

But when adding another String, the compiler throws an error:

call {
    "foo"
    "bar" // Cannot invoke 'call' with an argument list of type '(@escaping () -> ())'
}

I could reproduce the same behavior when using ExpressibleByIntegerLiteral.
@typesanitizer
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@swift-ci create

@theblixguy
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On master:

/Users/suyashsrijan/Desktop/test.swift:26:3: error: cannot convert value of type 'String' to expected argument type 'Foo'
  "foo"
  ^
/Users/suyashsrijan/Desktop/test.swift:27:3: error: cannot convert value of type 'String' to expected argument type 'Foo'
  "bar"
  ^

@theblixguy
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The error seems to go away when you insert a cast:

call { 
  "foo" as Foo
  "bar" as Foo
}

@swift-ci
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swift-ci commented Mar 1, 2020

Comment by Michael Kao (JIRA)

Ah ok, haven't tried that. But isn't that something the compiler should be able to figure out?

@DougGregor
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This is intended behavior. Add

static func buildExpression(_ value: Foo) -> Foo { value }

to your function builder to affect how the expressions are type checked. See https://github.com/DougGregor/swift-evolution/blob/function-builders/proposals/XXXX-function-builders.md for more information.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself result builders Feature: Result builders type checker Area → compiler: Semantic analysis
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@DougGregor @theblixguy @typesanitizer @swift-ci