Begin accepting `-swift-version 7` in asserts compilers so that we can begin to
test source-breaking changes intended for the next language version mode, such
as diagnostics that need to be staged in without breaking existing code. There
are no announced plans yet for a language mode after Swift 6, so 7 serves as a
placeholder for some future language mode.
Tests that wish to use `-swift-version 7` currently must be marked with
`REQUIRES: swift7` or they will fail in no-asserts bots. The simplest pattern
is probably to duplicate part or all of the pre-Swift 7 test to check that will
behave as intended in Swift 7.
This was a nice feature when people said "-swift-version 3.1"...
up until we got "-swift-version 4.2" as an actual valid version.
Just drop the special case.
https://bugs.swift.org/browse/SR-8850
Put in a general mechanism for mapping user-specified "compatibility
versions" to proper "effective versions" (what #if and @available
checking should respect). This may still be different from the
intrinsic "language version"; right now master is considered a "3.1"
compiler with a "Swift 4 mode", and we plan to ship a "4.0" compiler
with a "Swift 3 mode" that will have a version number of something
like "3.2".
rdar://problem/29884401 / SR-3791
This flag switches the "effective language version" of the compiler,
at least to any version supported (as of this change: "3" or "3.0").
At the moment nothing uses it except the language version build
configuration statements (#if swift(...)) and various other places
that report, encode, or otherwise check version numbers.
In the future, it's intended as scaffolding for backwards compatibility.
Fixes SR-2582
