To allow feature build settings to be composed more flexibly, allow an
`-enable-upcoming-feature` flag to be overridden by a
`-disable-upcoming-feature` flag. Whichever comes last on the command line
takes effect. Provide the same functionality for `-enable-experimental-feature`
as well.
Resolves rdar://126283879.
Find all the usages of `--enable-experimental-feature` or
`--enable-upcoming-feature` in the tests and replace some of the
`REQUIRES: asserts` to use `REQUIRES: swift-feature-Foo` instead, which
should correctly apply to depending on the asserts/noasserts mode of the
toolchain for each feature.
Remove some comments that talked about enabling asserts since they don't
apply anymore (but I might had miss some).
All this was done with an automated script, so some formatting weirdness
might happen, but I hope I fixed most of those.
There might be some tests that were `REQUIRES: asserts` that might run
in `noasserts` toolchains now. This will normally be because their
feature went from experimental to upcoming/base and the tests were not
updated.
This means that:
1. In test cases where minimal is the default (swift 5 without
-warn-concurrency), I added RUN lines for targeted, complete, and complete +
sns.
2. In test cases where complete is the default (swift 6, -warn-concurrency,
specified complete with -strict-concurrency), I added a send non-sendable run
line.
In each of these cases, I added additional expected-* lines as appropriate so
the tests can compile in each mode successfully.
Upcoming and experimental features are supported via command-line flags
and also in the SwiftPM manifest. Introduce it as an experimental
feature so that it can be enabled via SwiftPM without having to resort
to unsafe flags.
The `StrictConcurrency` experimental feature can also provide a
strictness level in the same manner as `-strict-concurrency`, e.g.,
`StrictConcurrency=targeted`. If the level is not provided, it'll be
`complete`.
Note that we do not introduce this as an "upcoming" feature, because
upcoming features should be in their final "Swift 6" form before
becoming available. We are still tuning the checking for concurrency.
