[swift-users] Airbnb's Swift 3 Migration Blog

[Chengyin Liu]

Thanks for the feedback!

> This is probably source-compatibility that you want, not necessarily ABI
compatibility.

You are right. Thank you for the correction.

> BTW, are you mixed-source? If so, were you able to try out PCH for
bridging headers as identified here: https://swift.org/blog/bridging-pch/?

We are. We are excited with PCH but currently compiler fails with segfault
using Xcode 8.3b2 for us. We are still investigating to provide the best
info there.

> If you can produce a test case that repros the blowup, can you put that
in a JIRA?

Filed: http://bugs.swift.org/browse/SR-3892. Notably this function builds
even slower with 3.1. (2.3: 0.6s → 3.0: 12s → 3.1: 22s)

> “Near misses” on Optional Protocol Method Implementations

I don't think those are actual bugs. From a compiler standpoint, the code
is fine. We did hit another issue with protocol near miss that may count as
a compiler issue. I will try to create a reproducible case.

On Tue, Feb 7, 2017 at 2:44 PM Michael Ilseman <milseman at apple.com> wrote:

> Comments:
>
> > Since the Swift ABI changed between versions 2 and 3, even correct Swift
> 3 code that imports Swift 2 libraries will not compile. This
> incompatibility made it difficult to parallelize code conversion.
>
> This is probably source-compatibility that you want, not necessarily ABI
> compatibility. Even if the ABI was stable, you still want to use the decls
> from the other module, and thus you’d still be in a rough spot. But, with
> source compatibility in Swift 4, the other modules could remain written in
> an older syntax/semantics while being compiled with the new compiler (and
> thus the new ABI). This would mean a gentle module-by-module incremental
> conversion regardless of the ABI for a Swift 3 to Swift 4 conversion.
>
> > Debug Build Time
>
> BTW, are you mixed-source? If so, were you able to try out PCH for
> bridging headers as identified here: https://swift.org/blog/bridging-pch/?
>
> > However, we did find a function...
>
> If you can produce a test case that repros the blowup, can you put that in
> a JIRA?
>
> > So, to complete the Swift 3 migration we strongly encouraged the entire
> team (minus the ones doing the migration) to really, truly take a Saturday
> off work 😄.
>
> Sounds like some good came of it after all!
>
> > “Near misses” on Optional Protocol Method Implementations
>
> These are great JIRA fodder too!
>
>
>
>
> On Feb 7, 2017, at 1:35 PM, Chengyin Liu via swift-users <
> swift-users at swift.org> wrote:
>
> Hi all,
>
> At Airbnb we recently migrated to Swift 3, just in time for Xcode 8.3. We
> waited as long as possible because our codebase is massive. We have
> hundreds thousands lines of Swift.
>
> In the end we were able to migrate without a code freeze. 3 engineers
> worked on it for 3 weeks without disrupting the normal development.
>
> We shared our experience in this blog post:
> https://medium.com/airbnb-engineering/getting-to-swift-3-at-airbnb-79a257d2b656#.j800yp6l8
> <https://medium.com/airbnb-engineering/getting-to-swift-3-at-airbnb-79a257d2b656>
>
> Feel free to reach out if you have any questions!
> --
> Chengyin
>
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>
>
> --
Chengyin
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