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[SR-8295] Data.append(contentsOf: elements) has poor error message. #50823

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Dante-Broggi opened this issue Jul 17, 2018 · 3 comments
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[SR-8295] Data.append(contentsOf: elements) has poor error message. #50823

Dante-Broggi opened this issue Jul 17, 2018 · 3 comments
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@Dante-Broggi
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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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@Dante-Broggi
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Previous ID SR-8295
Radar None
Original Reporter @Dante-Broggi
Type Bug
Status Closed
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, TypeChecker
Assignee @Dante-Broggi
Priority Medium

md5: c0f367ff9627a115ed630e3d8228acf5

Issue Description:

When examining #SR-3566, I found it doesn't initialize the sequence it appends to a `Data`

So, I tried to make a sequence, but accidentally made it a sequence of `Int`, not `UInt8`, so it errored. However, it errored with an ambiguity error and not with eg. "Int != UInt8".

So, this is a report of poor compiler error message.

import Foundation
let elements = sequence(first: 1 /* should be "1 as UInt8" */) { _ in 1 }.prefix(5)
var d = Data()
d.append(contentsOf: elements) // Ambiguous reference to member 'append(contentsOf:)'
@belkadan
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   <stdin>:4:1: error: ambiguous reference to member 'append(contentsOf:)'
d.append(contentsOf: elements) 
^
Foundation.Data:48:26: note: found this candidate
    public mutating func append(contentsOf bytes: [UInt8])
                         ^
Foundation.Data:49:37: note: found this candidate
    @inlinable public mutating func append<S>(contentsOf newElements: S) where S : Sequence, S.Element == Data.Iterator.Element
                                    ^
Swift.RangeReplaceableCollection:5:37: note: found this candidate
    @inlinable public mutating func append<S>(contentsOf newElements: S) where S : Sequence, Self.Element == S.Element
                                    ^

cc @xedin

@xedin
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xedin commented Aug 30, 2018

Errors like that got improved on master, so now it's going to produce following:

error: instance method 'append(contentsOf:)' requires the types 'Int' and 'Data.Iterator.Element' (aka 'UInt8') be equivalent
d.append(contentsOf: elements)
  ^
Foundation.Data:49:37: note: where 'S.Element' = 'Int'
    @inlinable public mutating func append<S>(contentsOf newElements: S) where S : Sequence, S.Element == Data.Iterator.Element
                                    ^

@xedin
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xedin commented Aug 30, 2018

Thank you for reporting, @Dante-Broggi! Please use the latest nightly snapshot to verify.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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@Dante-Broggi Dante-Broggi

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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@xedin @belkadan @Dante-Broggi