Parsing for `-enable-upcoming-feature` and `-enable-experimental-feature` is
lenient by default because some projects need to be compatible with multiple
language versions and compiler toolchains simultaneously, and strict
diagnostics would be a nuisance. On the other hand, though, it would be useful
to get feedback from the compiler when you attempt to enable a feature that
doesn't exist. This change splits the difference by introducing new diagnostics
for potential feature enablement misconfigurations but leaves those diagnostics
ignored by default. Projects that wish to use them can specify `-Wwarning
StrictLanguageFeatures`.
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.
If an upcoming feature was enabled by passing it via `-enable-experimental-feature`,
downgrade the `already enabled` diagnostic to a warning.
Resolves rdar://139087679.
During the lifecycle of a feature, it may start as an experimental feature and
then graduate to become an upcoming feature. To preserve compatibility with
projects that adopted the feature when it was experimental,
`-enable-experimental-feature` ought to be able to enable upcoming features,
too.
Since projects may use `-enable-experimental-feature` for compatibility with an
older toolchain that does not have the feature as an upcoming feature, there is
no warning when the flag is used to enable an upcoming feature.
Note that if the semantics of a feature change when it graduates from
experimental to upcoming, then the feature must be renamed so that projects
using the experimental feature have an opportunity opt-in to the new semantics
of the upcoming feature.
Resolves rdar://134276783.
Introduce the `-enable-upcoming-feature X` command-line argument to
allow one to opt into features that will be enabled in an upcoming language
mode. Stage in several features this way (`ConciseMagicFile`,
`ForwardTrailingClosures`, `BareSlashRegexLiterals`).
