Adding checks to ensure that CMP0195 has the desired effect. If the
Swift compiler is too old and does not include the module triple in the
emitted target info, we won't set `CMAKE_Swift_MODULE_TRIPLE` and end up
with the flat directory structure. In this case, these tests won't have
the expected layout.
Issue: #28021
Update CMP0215 to avoid attempting to iterate through the flags
looking for `-emit-module-path` ins the user-specified flags. We don't
do this anywhere else in the code. The existing implementation didn't
handle correctly parsing the flag so `-I blah/my-emit-module-path/` and
`-Xcc -emit-module-path ...` would both trigger it, result in the
compiler not emitting any module. Furthermore, it didn't include the
user-specified module path as part of the build graph resulting in an
incorrect build graph that would never resolve.
The only two appropriate layouts for the module are either the flat
binary module file with the name `<module-name>.swiftmodule`, or the
nested form with
`<module-name>.swiftmodule/<module-triple>.swiftmodule`. The noted
Swift-Syntax situation passes the explicit `-emit-module-path` to get to
the latter form. This form is automatically emitted by CMake when
CMP0195 is `NEW`, removing the need for the flag. The Swift project
generally recommends the nested directory structure since it gathers all
of the generated interface outputs from the compiler (textual swift
interfaces, swiftdoc, sourceinfo, and the binary swiftmodule file) in a
single place, and since it uses the module triple in the filename,
cleanly allows fat mach-o binaries on Apple platforms.
Fixes: #28021
Add policy CMP0215 to emit `.swiftmodule` from a dedicated `-emit-module`
build edge for importable Swift targets in the Ninja generator.
Downstream targets can begin compiling as soon as the module interface
is ready, overlapping with upstream object compilation and linking.
When CMP0215 is NEW and CMP0157 is NEW, separate module emission is
enabled by default. The `Swift_SEPARATE_MODULE_EMISSION` target
property (initialized by the `CMAKE_Swift_SEPARATE_MODULE_EMISSION`
variable) can override this per target.
The compile edge still passes `-emit-module` so that swiftc continues
to produce `.swiftdoc`; only the `.swiftmodule` output moves to the new
edge.
Also fix swiftmodule dependency edges in cmNinjaNormalTargetGenerator
to use IsLanguageUsed instead of GetLinkerLanguage, so C/C++ targets
whose linker language propagated to Swift do not produce spurious
implicit dependencies.
Closes: #27748
Evan Wilde
Roman Lavrov