Re: [swift-dev] Renamed types (Swift 3/4 Mix-and-Match)

[Jordan Rose via swift-dev]

> On Apr 20, 2017, at 18:25, Michael Ilseman  wrote:
> 
>> 
>> On Apr 20, 2017, at 4:55 PM, Jordan Rose via swift-dev > > wrote:
>> 
>> TLDR: Should we just always import C/ObjC types under their Swift 4 names, 
>> and use typealiases in Swift 3 mode?
>> 
>> ---
>> 
>> Hi, swift-dev. As my recent PRs have probably indicated, I've been working 
>> on the problems that can come up when mixing Swift 3 and Swift 4 code. Most 
>> of these problems have to do with C/ObjC APIs that might present themselves 
>> differently in Swift 3 and Swift 4, using the "API notes" feature in our 
>> downstream branch of Clang, and a good subset of these problems have to do 
>> with types getting renamed. (This includes being "renamed" into a member, 
>> such as NSNotificationName becoming (NS)Notification.Name in Swift.)
>> 
>> What's the problem? Well, there are a few. First of all, an API defined in 
>> terms of the Swift 3 name should still be callable in Swift 4. As an 
>> example, let's pretend NSNotification.Name was going to be renamed 
>> NSNotification.Identifier in Swift 4.
>> 
>> // Swift 3 library
>> public func postTestNotification(named name: NSNotification.Name) { … }
>> 
>> // Swift 4 app
>> let id: Notification.Identifier = …
>> postTestNotification(named: id) // should work
>> 
>> This means the reference to "NSNotification.Name" in the library's 
>> swiftmodule needs to still be resolvable. This isn't too bad if we leave 
>> behind a typealias for 'NSNotification.Name'. I have a reasonable (but too 
>> broad) implementation at https://github.com/apple/swift/pull/8737 
>> .
>> 
>> That just leads us to another problem, though: because Swift functions can 
>> be overloaded, the symbol name includes the type, and the type has changed. 
>> The Swift 3 library exposes a symbol 
>> '_T03Lib20postTestNotificationySo14NSNotificationC4NameV5named_tF', but the 
>> Swift 4 client expects 
>> '_T03Lib20postTestNotificationySo14NSNotificationC10IdentifierV5named_tF'.
>> 
>> My planned approach to combat this was to use the C name of the type in the 
>> mangling, producing 
>> '_T03Lib20postTestNotificationySo18NSNotificationNamea5named_tF'. This is 
>> prototyped in https://github.com/apple/swift/pull/8871 
>> .
>> 
>> 
>> At this point Slava pointed out I was chasing down a lot of issues when 
>> there's a much simpler solution for Swift 4: when importing types, always 
>> use the Swift 4 name, and use typealiases to handle Swift 3 compatibility. 
>> This defines both of the previous issues away, as well as any more that I 
>> just haven't thought of yet.
>> 
>> There are some downsides:
>> - We currently keep people from using Swift 4 names in Swift 3 code, and we 
>> wouldn't be able to do that, since the actual declaration of the type always 
>> needs to be available.
> 
> I don’t know if this is an important distinction to worry about. That code 
> will still be able to use features from Swift 4, and perhaps even Swift 4 
> only types (e.g. Substring from SE-0163).
> 
>> - We'd probably want to tweak the "aka" printing in diagnostics to not look 
>> through these typealiases. That's not hard, though.
>> - We can't keep doing this once we have ABI stability. Hopefully framework 
>> owners aren't going to continue changing Swift names of types, but we'll 
>> probably need to implement my "C name in the mangling" plan anyway, just in 
>> case.
>> 
> 
> Would this fall under the realm of library evolution, wherein name changes 
> should be versioned? In that case, would we need both symbols whether they 
> came from C or not?

I suspect we'll end up doing my appended follow-up for this: "mangle me as if 
my name were ___". That doesn't cover everything the importer does, though 
(turning enums into structs, swift_wrapper, import-as-member, etc).

I also hope we just don't have to deal with name changes very often in 
Swift-land.

Jordan

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Re: [swift-dev] Renamed types (Swift 3/4 Mix-and-Match)

[Michael Ilseman via swift-dev]

> On Apr 20, 2017, at 4:55 PM, Jordan Rose via swift-dev  
> wrote:
> 
> TLDR: Should we just always import C/ObjC types under their Swift 4 names, 
> and use typealiases in Swift 3 mode?
> 
> ---
> 
> Hi, swift-dev. As my recent PRs have probably indicated, I've been working on 
> the problems that can come up when mixing Swift 3 and Swift 4 code. Most of 
> these problems have to do with C/ObjC APIs that might present themselves 
> differently in Swift 3 and Swift 4, using the "API notes" feature in our 
> downstream branch of Clang, and a good subset of these problems have to do 
> with types getting renamed. (This includes being "renamed" into a member, 
> such as NSNotificationName becoming (NS)Notification.Name in Swift.)
> 
> What's the problem? Well, there are a few. First of all, an API defined in 
> terms of the Swift 3 name should still be callable in Swift 4. As an example, 
> let's pretend NSNotification.Name was going to be renamed 
> NSNotification.Identifier in Swift 4.
> 
> // Swift 3 library
> public func postTestNotification(named name: NSNotification.Name) { … }
> 
> // Swift 4 app
> let id: Notification.Identifier = …
> postTestNotification(named: id) // should work
> 
> This means the reference to "NSNotification.Name" in the library's 
> swiftmodule needs to still be resolvable. This isn't too bad if we leave 
> behind a typealias for 'NSNotification.Name'. I have a reasonable (but too 
> broad) implementation at https://github.com/apple/swift/pull/8737 
> .
> 
> That just leads us to another problem, though: because Swift functions can be 
> overloaded, the symbol name includes the type, and the type has changed. The 
> Swift 3 library exposes a symbol 
> '_T03Lib20postTestNotificationySo14NSNotificationC4NameV5named_tF', but the 
> Swift 4 client expects 
> '_T03Lib20postTestNotificationySo14NSNotificationC10IdentifierV5named_tF'.
> 
> My planned approach to combat this was to use the C name of the type in the 
> mangling, producing 
> '_T03Lib20postTestNotificationySo18NSNotificationNamea5named_tF'. This is 
> prototyped in https://github.com/apple/swift/pull/8871 
> .
> 
> 
> At this point Slava pointed out I was chasing down a lot of issues when 
> there's a much simpler solution for Swift 4: when importing types, always use 
> the Swift 4 name, and use typealiases to handle Swift 3 compatibility. This 
> defines both of the previous issues away, as well as any more that I just 
> haven't thought of yet.
> 
> There are some downsides:
> - We currently keep people from using Swift 4 names in Swift 3 code, and we 
> wouldn't be able to do that, since the actual declaration of the type always 
> needs to be available.

I don’t know if this is an important distinction to worry about. That code will 
still be able to use features from Swift 4, and perhaps even Swift 4 only types 
(e.g. Substring from SE-0163).

> - We'd probably want to tweak the "aka" printing in diagnostics to not look 
> through these typealiases. That's not hard, though.
> - We can't keep doing this once we have ABI stability. Hopefully framework 
> owners aren't going to continue changing Swift names of types, but we'll 
> probably need to implement my "C name in the mangling" plan anyway, just in 
> case.
> 

Would this fall under the realm of library evolution, wherein name changes 
should be versioned? In that case, would we need both symbols whether they came 
from C or not?

> What do people think?
> 
> Jordan
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Re: [swift-dev] Renamed types (Swift 3/4 Mix-and-Match)

[Jordan Rose via swift-dev]

> On Apr 20, 2017, at 16:55, Jordan Rose via swift-dev  
> wrote:
> 
> TLDR: Should we just always import C/ObjC types under their Swift 4 names, 
> and use typealiases in Swift 3 mode?
> 
> ---
> 
> Hi, swift-dev. As my recent PRs have probably indicated, I've been working on 
> the problems that can come up when mixing Swift 3 and Swift 4 code. Most of 
> these problems have to do with C/ObjC APIs that might present themselves 
> differently in Swift 3 and Swift 4, using the "API notes" feature in our 
> downstream branch of Clang, and a good subset of these problems have to do 
> with types getting renamed. (This includes being "renamed" into a member, 
> such as NSNotificationName becoming (NS)Notification.Name in Swift.)
> 
> What's the problem? Well, there are a few. First of all, an API defined in 
> terms of the Swift 3 name should still be callable in Swift 4. As an example, 
> let's pretend NSNotification.Name was going to be renamed 
> NSNotification.Identifier in Swift 4.
> 
> // Swift 3 library
> public func postTestNotification(named name: NSNotification.Name) { … }
> 
> // Swift 4 app
> let id: Notification.Identifier = …
> postTestNotification(named: id) // should work
> 
> This means the reference to "NSNotification.Name" in the library's 
> swiftmodule needs to still be resolvable. This isn't too bad if we leave 
> behind a typealias for 'NSNotification.Name'. I have a reasonable (but too 
> broad) implementation at https://github.com/apple/swift/pull/8737 
> .
> 
> That just leads us to another problem, though: because Swift functions can be 
> overloaded, the symbol name includes the type, and the type has changed. The 
> Swift 3 library exposes a symbol 
> '_T03Lib20postTestNotificationySo14NSNotificationC4NameV5named_tF', but the 
> Swift 4 client expects 
> '_T03Lib20postTestNotificationySo14NSNotificationC10IdentifierV5named_tF'.
> 
> My planned approach to combat this was to use the C name of the type in the 
> mangling, producing 
> '_T03Lib20postTestNotificationySo18NSNotificationNamea5named_tF'. This is 
> prototyped in https://github.com/apple/swift/pull/8871 
> .
> 
> 
> At this point Slava pointed out I was chasing down a lot of issues when 
> there's a much simpler solution for Swift 4: when importing types, always use 
> the Swift 4 name, and use typealiases to handle Swift 3 compatibility. This 
> defines both of the previous issues away, as well as any more that I just 
> haven't thought of yet.
> 
> There are some downsides:
> - We currently keep people from using Swift 4 names in Swift 3 code, and we 
> wouldn't be able to do that, since the actual declaration of the type always 
> needs to be available.
> - We'd probably want to tweak the "aka" printing in diagnostics to not look 
> through these typealiases. That's not hard, though.
> - We can't keep doing this once we have ABI stability. Hopefully framework 
> owners aren't going to continue changing Swift names of types, but we'll 
> probably need to implement my "C name in the mangling" plan anyway, just in 
> case.
> 
> What do people think?

Oh, I forgot there's one more option for fixing the mangling issue: save all 
mangled names into the swiftmodule. That also doesn't work once we have ABI 
stability, though, because you need to match the name for the previous release 
as well as the current one.

Jordan

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[swift-dev] Renamed types (Swift 3/4 Mix-and-Match)

[Jordan Rose via swift-dev]

TLDR: Should we just always import C/ObjC types under their Swift 4 names, and 
use typealiases in Swift 3 mode?

---

Hi, swift-dev. As my recent PRs have probably indicated, I've been working on 
the problems that can come up when mixing Swift 3 and Swift 4 code. Most of 
these problems have to do with C/ObjC APIs that might present themselves 
differently in Swift 3 and Swift 4, using the "API notes" feature in our 
downstream branch of Clang, and a good subset of these problems have to do with 
types getting renamed. (This includes being "renamed" into a member, such as 
NSNotificationName becoming (NS)Notification.Name in Swift.)

What's the problem? Well, there are a few. First of all, an API defined in 
terms of the Swift 3 name should still be callable in Swift 4. As an example, 
let's pretend NSNotification.Name was going to be renamed 
NSNotification.Identifier in Swift 4.

// Swift 3 library
public func postTestNotification(named name: NSNotification.Name) { … }

// Swift 4 app
let id: Notification.Identifier = …
postTestNotification(named: id) // should work

This means the reference to "NSNotification.Name" in the library's swiftmodule 
needs to still be resolvable. This isn't too bad if we leave behind a typealias 
for 'NSNotification.Name'. I have a reasonable (but too broad) implementation 
at https://github.com/apple/swift/pull/8737 
.

That just leads us to another problem, though: because Swift functions can be 
overloaded, the symbol name includes the type, and the type has changed. The 
Swift 3 library exposes a symbol 
'_T03Lib20postTestNotificationySo14NSNotificationC4NameV5named_tF', but the 
Swift 4 client expects 
'_T03Lib20postTestNotificationySo14NSNotificationC10IdentifierV5named_tF'.

My planned approach to combat this was to use the C name of the type in the 
mangling, producing 
'_T03Lib20postTestNotificationySo18NSNotificationNamea5named_tF'. This is 
prototyped in https://github.com/apple/swift/pull/8871 
.


At this point Slava pointed out I was chasing down a lot of issues when there's 
a much simpler solution for Swift 4: when importing types, always use the Swift 
4 name, and use typealiases to handle Swift 3 compatibility. This defines both 
of the previous issues away, as well as any more that I just haven't thought of 
yet.

There are some downsides:
- We currently keep people from using Swift 4 names in Swift 3 code, and we 
wouldn't be able to do that, since the actual declaration of the type always 
needs to be available.
- We'd probably want to tweak the "aka" printing in diagnostics to not look 
through these typealiases. That's not hard, though.
- We can't keep doing this once we have ABI stability. Hopefully framework 
owners aren't going to continue changing Swift names of types, but we'll 
probably need to implement my "C name in the mangling" plan anyway, just in 
case.

What do people think?

Jordan___
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