I don't really know what to say here. What you were doing isn't a supported use case. @slavapestov?

@belkadan I understand that but without that it'd be so slow that it's unusable...

ping @slavapestov, this will unfortunately get very important for us as soon as Swift 4.2 will be released. The only (really bad) option I see to remain warning-free is to change our @_inlineable s to @inline(_always) which is really wrong and bad. But we can't just remove them and regress really badly in performance for all of our users.

ok, what we could do is release SwiftNIO 2.0 with Swift 4.2 an just drop Swift 4.0 support, if we can get the @inlineable and @usableFromInline spellings into Swift 4.1.(n+1) but I reckon that's quite unlikely too, right?

Apart from only taking maintenance fixes at this point (if even that), Swift 4.1 had a bunch of bugs around inlining that we fixed in Swift 4.2. So no, we're not going to add the new spelling to the Swift 4.1 series.

Yeah, your best bet is dropping Swift 4.0/4.1 support as soon as 4.2 is out, or living with warnings.

@slavapestov actually, we do explicitly ask for the Swift language version 4 which seems to mean 4.0 and 4.1 but not 4.2. So why can't we have this warning only in 4.2?

swift-version 4:

$ swiftc -swift-version 4 test.swift
test.swift:1:2: warning: '@_inlineable' has been renamed to '@inlinable'
@_inlineable
 ^~~~~~~~~~~
 inlinable

seems to be the same as swift-version 4.1 (which is illegal)

$ swiftc -swift-version 4.1 test.swift
<unknown>:0: error: invalid value '4.1' in '-swift-version 4.1'
<unknown>:0: note: use major version, as in '-swift-version 4'
test.swift:1:2: warning: '@_inlineable' has been renamed to '@inlinable'
@_inlineable
 ^~~~~~~~~~~
 inlinable

but 4.2 is not:

$ swiftc -swift-version 4.2 test.swift
test.swift:1:2: warning: '@_inlineable' has been renamed to '@inlinable'
@_inlineable
 ^~~~~~~~~~~
 inlinable

so really, this warning should not be enabled for swift-version 4 but can be enabled for 4.2

Why is it important to compile without warnings on older releases of Swift?

@slavapestov the problem is that we'll compile with warnings on newer releases of Swift. If it were only for older releases that might be acceptable because at least the warning is actionable (ie. upgrade to get rid of it).

But generally the problems with warnings is that many people want to compile with 'warnings to errors' (especially in CI) which many consider to be good style. But even without it's really bad if you get 100 warnings each time you build. You're bound to miss one warning that is actually important.

We seem to have two bad options:

1. spell it @_inlineable and compile fine on 4.0 & 4.1 but with loads of warnings on 4.2

2. spell it @inlinable and only compile on 4.2

My argument is that 4.2 already got its on -swift-version anyway so I don't understand what's wrong with having both spellings be fine for -swift-version 4 but issuing a warning on -swift-version 4.2 for the old spelling.

Ok, you win 🙂 I'll look into muffling the warning in 4.2 mode. There is another issue where 4.1 did not enforce @usableFromInline on type aliases correctly; I might have to bypass that enforcement in -swift-version 4 as well.

I think it's okay to add correct enforcements to the model as long as you can deal with them in 4.1.

@slavapestov Thank you very much, that makes the whole situation much much better. Ideally, we want the higher-level libraries to adopt new Swift versions the fastest and usually I think that's what's happening as higher level libraries want to use cool new language features like say Codable more often than low-level libraries. And when most clients have deprecated a certain old Swift version low-level libraries such as SwiftNIO can follow and also drop those versions asap. In the case of @inlinable however it was a bit unfortunate as the higher-level libraries don't need them but the low-level ones really do.

@swift-ci create

#17090

4.2 branch?

#17091

👍

thanks you @slavapestov, that's awesome!!

@slavapestov thanks very much for that. Just tried to compile NIO again and loads of warnings are indeed gone. However there are still a lot of warnings left:

/Users/johannes/devel/swift-nio/Sources/NIO/ByteBuffer-core.swift:348:18: warning: '@inlinable' declaration is already '@usableFromInline'
    @_inlineable @_versioned
                 ^~~~~~~~~~~

which is correct. Removing the @_versioned however leads to a compile error in 4.1:

$ jw-swift-4.1 swift build
Compile CNIOLinux shim.c
Compile CNIOSHA1 c_nio_sha1.c
Compile CNIODarwin shim.c
Compile CNIOZlib empty.c
Compile CNIOAtomics src/c-atomics.c
Compile CNIOHTTPParser c_nio_http_parser.c
Compile Swift Module 'NIOPriorityQueue' (2 sources)
Compile Swift Module 'NIOConcurrencyHelpers' (2 sources)
Compile Swift Module 'NIO' (52 sources)
/Users/johannes/devel/swift-nio/Sources/NIO/ByteBuffer-core.swift:354:5: error: '@_inlineable' attribute can only be applied to public declarations, but '_moveWriterIndex' is internal
    @_inlineable
    ^~~~~~~~~~~~
    
/Users/johannes/devel/swift-nio/Sources/NIO/ByteBuffer-core.swift:354:5: error: '@_inlineable' attribute can only be applied to public declarations, but '_moveWriterIndex' is internal
    @_inlineable
    ^~~~~~~~~~~~
    
/Users/johannes/devel/swift-nio/Sources/NIO/ByteBuffer-core.swift:363:14: error: instance method '_moveWriterIndex(to:)' is internal and cannot be referenced from an '@_inlineable' function
        self._moveWriterIndex(to: newIndex)
             ^
/Users/johannes/devel/swift-nio/Sources/NIO/ByteBuffer-core.swift:355:19: note: instance method '_moveWriterIndex(to:)' is not '@_versioned' or public
    mutating func _moveWriterIndex(to newIndex: Index) {
                  ^
/Users/johannes/devel/swift-nio/Sources/NIO/ByteBuffer-core.swift:483:14: error: instance method '_moveWriterIndex(to:)' is internal and cannot be referenced from an '@_inlineable' function
        self._moveWriterIndex(to: self._writerIndex + _toIndex(bytesWritten))
             ^
/Users/johannes/devel/swift-nio/Sources/NIO/ByteBuffer-core.swift:355:19: note: instance method '_moveWriterIndex(to:)' is not '@_versioned' or public
    mutating func _moveWriterIndex(to newIndex: Index) {
                  ^
/Users/johannes/devel/swift-nio/Sources/NIO/ByteBuffer-core.swift:354:5: error: '@_inlineable' attribute can only be applied to public declarations, but '_moveWriterIndex' is internal
    @_inlineable
    ^~~~~~~~~~~~
    
error: terminated(1): /Library/Developer/Toolchains/swift-4.1-RELEASE.xctoolchain/usr/bin/swift-build-tool -f /Users/johannes/devel/swift-nio/.build/debug.yaml main output:

so the cheapest way to fix this is probably to ignore this warning too in language mode 4.

#17314

thanks very much!

confirmed working now on very recent 4.2 snapshots.