[swift-dev] [swift-evolution] End of source-breaking changes for Swift 3

[Dave Abrahams]

on Wed Jul 27 2016, Ted Kremenek <kremenek-AT-apple.com> wrote:

> - swift-evolution, swift-evolution-announce
>
> Dave/Max: can you speak this?

>> On Jul 27, 2016, at 3:17 PM, Tony Allevato <allevato at google.com> wrote:
>> 
>> I noticed that while SE-0091 appears to be implemented (from a
>> cursory glance at some of the affected types like Equatable and
>> String), it looks like the named methods are still part of the
>> FloatingPoint protocol and they still use global operators.
>> 
>> Is anyone tracking the migration of that protocol (and possibly also
>> the new Integer protocols) to use the new operator technique? (I
>> have to apologize for not being able to update the proposal with
>> another PR that listed all those changes—my free time outside my day
>> job has been significantly reduced lately.)

I think we view those changes as implicitly approved along with SE-0091.
I was working on making them but we've run into bugs with the feature's
implementation during the migration.  When those are straightened out,
we can move forward with that cleanup.

>> On Wed, Jul 27, 2016 at 12:38 PM Ted Kremenek via swift-evolution
>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>>
>> wrote:
>> Dear friends,
>> 
>> Today is July 27 — and the last planned day to take source-breaking
>> changes for Swift 3. It has been an incredible ride to this point,
>> so let's take stock of where we are. Here are the list of currently
>> accepted — but not yet (fully) implemented — evolution proposals
>> (this is drawn from the "accepted" but not marked "implemented"
>> proposals from the swift-evolution
>> <https://github.com/apple/swift-evolution> repository):
>> 
>> SE-0025 - Scoped Access Level
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0025-scoped-access-level.md>
>> SE-0042 - Flattening the function type of unapplied method
>> references
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0042-flatten-method-types.md>
>> SE-0045 - Add scan, prefix(while:), drop(while:), and iterate to the
>> stdlib
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0045-scan-takewhile-dropwhile.md>
>> SE-0068 - Expanding Swift Self to class members and value types
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0068-universal-self.md>
>> SE-0075 - Adding a Build Configuration Import Test
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0075-import-test.md>
>> SE-0077 - Improved operator declarations
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0077-operator-precedence.md>
>> SE-0080 - Failable Numeric Conversion Initializers
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0080-failable-numeric-initializers.md>
>> SE-0081 - Move where clause to end of declaration
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0081-move-where-expression.md>
>> SE-0082 - Package Manager Editable Packages
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0082-swiftpm-package-edit.md>
>> SE-0088 - Modernize libdispatch for Swift 3 naming conventions
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0088-libdispatch-for-swift3.md>
>> SE-0089 - Renaming String.init<T>(_: T)
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0089-rename-string-reflection-init.md>
>> SE-0092 - Typealiases in protocols and protocol extensions
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0092-typealiases-in-protocols.md>
>> SE-0096 - Converting dynamicType from a property to an operator
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0096-dynamictype.md>
>> SE-0099 - Restructuring Condition Clauses
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0099-conditionclauses.md>
>> SE-0101 - Reconfiguring sizeof and related functions into a
>> unified MemoryLayout struct
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0101-standardizing-sizeof-naming.md>
>> SE-0102 - Remove @noreturn attribute and introduce an
>> empty Never type
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0102-noreturn-bottom-type.md>
>> SE-0103 - Make non-escaping closures the default
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0103-make-noescape-default.md>
>> SE-0104 - Protocol-oriented integers
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0104-improved-integers.md>
>> SE-0107 - UnsafeRawPointer API
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0107-unsaferawpointer.md>
>> SE-0110 - Distinguish between single-tuple and multiple-argument
>> function types
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0110-distingish-single-tuple-arg.md>
>> SE-0111 - Remove type system significance of function argument
>> labels
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0111-remove-arg-label-type-significance.md>
>> SE-0120 - Revise partition Method Signature
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0120-revise-partition-method.md>
>> SE-0127 - Cleaning up stdlib Pointer and Buffer Routines
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0127-cleaning-up-stdlib-ptr-buffer.md>
>> These are all changes the community has approved for Swift but did
>> not make today's cutoff. Some of these proposals have
>> implementations actively underway. For those proposals already in
>> active development — and near completion — I am okay with extending
>> the deadline for those changes to Friday, July 29. Such changes need
>> to be approved by the release manager (myself) and should be merged
>> into master via a pull request. When creating the pull request,
>> please assign it to me (tkremenek), and mention the pull request on
>> the swift-dev mailing list as well with the SE number in the email
>> title.
>> 
>> The rest of the unimplemented proposals do not make Swift 3. This
>> leaves us with the question of what to do with them. These proposals
>> represent the known and reviewed changes we want to make to Swift,
>> but inevitably there will also be changes that we don't even know
>> about today that we will want to take into Swift that can impact
>> core source stability. That said, we also have a very strong desire
>> to maintain source compatibility with Swift 3 and Swift 4 as much as
>> possible to provide some stability for which Swift users to build
>> upon. The challenge of course is reconciling these diametrically
>> opposing goals: maintaining source stability while having the
>> ability to incorporate more core (and important) language changes
>> that are possibly source-breaking.
>> 
>> The Swift team at Apple has reflected on this and decided what it
>> "means" for Swift 3 to be source compatible with Swift 4 and later
>> releases going forward. Our goal is to allow app developers to
>> combine a mix of Swift modules (e.g., SwiftPM packages), where each
>> module is known to compile with a specific version of the language
>> (module A works with Swift 3, module B works with Swift 3.1, etc.),
>> then combine those modules into a single binary. The key feature is
>> that a module can be migrated from Swift 3 to 3.1 to 4 (and beyond)
>> independently of its dependencies.
>> 
>> While the exact details of how we will accomplish this feat are
>> still being discussed, here is a sketch of how this will likely work
>> in the Swift 4 timeframe. The key enabler is a new compiler flag
>> that indicates the language version to compile for (e.g., similar to
>> the clang -std=c99 flag). The compiler flag will be provided by the
>> build system you are using (e.g., Xcode, SwiftPM, etc.) on a
>> per-module basis:
>> 
>> For language syntax/semantics, the compiler can use the language
>> mode to properly implement the language version being used by a
>> module.
>> 
>> For the Standard Library, additive and subtractive changes are
>> easily handled (the former by just adding them, the later by using
>> deprecation techniques). For semantics changes, things are much more
>> complicated, and will need further study.
>> 
>> The great thing about this approach is that a single Swift 4
>> compiler is building all of the sources in an application. This
>> allows us to roll out this approach before achieving full ABI
>> stability — something that will be a goal for Swift 4, but is
>> impractical to achieve for a Swift 3.x release. It also provides us
>> a general framework in the future for handling source compatibility
>> as Swift evolves.
>> 
>> To make this more concrete, suppose an application is written to use
>> Swift 4, but uses packages via SwiftPM that are written using Swift
>> 3. A single compiler would build both the app and the packages —
>> thus ensuring that all the compiled sources are binary
>> compatible. It would not be the case that a framework built with the
>> Swift 3 compiler could be used by an app built using the Swift 4
>> compiler. That kind of library binary stability (ABI) will be a key
>> goal of the Swift 4 release.
>> 
>> These constraints mentioned above will serve as scaffolding for
>> Swift 4 development. Discussion about Swift 4 commences on
>> Monday. Ahead of that, Chris Lattner plans to send out thoughts from
>> the Core team on some of the known key goals (and non-goals) for the
>> release. In the meantime, the focus over the next couple days should
>> be taking stock of what has landed for Swift 3 and to see if any of
>> the proposals mentioned above are close to being completed or are
>> truly out of scope.
>> 
>> Thank you again to everyone for making Swift 3 such as fantastic release!
>> 
>> Ted
>> 
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>

-- 
-Dave