- Proposal: SE-00XX
- Author(s): Erica Sadun
- Status: TBD
- Review manager: TBD
Expanding the configuration test suite to include Darwin support (to test
for Apple platforms) was first introduced
on the Swift-Evolution list by
Lily Ballard. Her idea was greeted warmly and quickly expanded upon by developers
looking to introduce the kinds of conditional configuration they're used to
in other languages. This proposal introduces a subset of the configurations
requested on that thread.
SE-0020
added #if swift to enable code to compile with specific versions of the Swift language.
This proposal introduces several further compile-time configuration,
adding configuration tests for x, y, z, and w.
This proposal was discussed on-list in the thread.
Swift currently supports the following configuration tests:
- The literals
trueandfalse - The
os()function that tests forOSX, iOS, watchOS, tvOS, and Linux - The
arch()function that tests forx86_64, arm, arm64, and i386 - The
swift()function that tests for specific Swift language releases, e.g.swift(>=2.2)
As Swift expands to a growing developer base and to new platforms, the existing suite of
configuration tests begins to show strain. Shortcuts taking advantage of current
limitations introduce fragility. For example, testing #if os(iOS) || os(OSX) || os(watchOS) || os(tvOS) may
miss new platform targets and #if !os(Linux) may introduce errors should Swift extend to
other non-Apple platforms, such as Windows.
Swift also misses a built-in #if debug test. Although you can specify command-line flags
using -D <#flag#> (e.g. -D debug) and test in-code (#if debug), there's no consistent
system-supplied way to differentiate code meant only for debug builds.
This proposal introduces a minimal set of utility configuration tests.
#if platform(Apple)tests for platform families, including Apple, Linux, Unix, Windows#if imports(UIKit)tests for module support, differentiating, for example, Mac code from iOS and tvOS code.#if target(simulator)and#if target(device)represent a common categorization requirement, such as Metal, Keychain, and AVFoundation Camera code.#if bitwidth(32)and#if bitwidth(64)tests for 32 and 64 bit architecture families.#if endian(big)and#if endian(little)tests for big and little endianness.#if config(debug)tests for debug builds.
Joe Groff writes, "We specifically avoided making debug/release an #if condition because we considered #if to be the wrong point at which to start conditionalizing code generation for assertions. Though the final executable image's behavior is unavoidably dependent on whether asserts are enabled, we didn't want the SIL for inlineable code to be, since that would mean libraries with inlineable code would need to ship three times the amount of serialized SIL to support the right behavior in -Onone, -O, and -Ounchecked builds. Instead, the standard library has some hidden helper functions,
_isDebugAssertConfiguration,_isReleaseAssertConfiguration, and_isFastAssertConfiguration, which are guaranteed to be constant-folded away before final code generation."
Not included in this proposal at this time: "Is the target built for running tests", #if destination() tests for specific destinations, #if destination(BSD), #if destination(Ubuntu, >=14.04) to establish common-ground calls for, for example, BSD destinations or specific Linux distros, or "Has a module been imported elsewhere in my project?, e.g. #if imported(UIKit)"
There are no alternatives considered.