The patch adding support for `__ENVIRONMENT_OS_VERSION_MIN_REQUIRED__`
to clang has been backported to all versions of clang in nixpkgs (except
for clang 12), allowing this workaround to be dropped.
While it would be nice if this could be split, there are too many
changes as part of the cleanup and improvements, including:
- Refactoring all propagated packages into functions that can be used to
ensure that packages are propagated only at the expected stages;
- Using a sanity-checking merge function to ensure that packages are
only propagated by one of the above functions;
- Reducing the number of Python builds during the bootstrap to one;
- Removing the extra sysctl stage;
- Using the LLVM bootstrap to build LLVM, clang, libc++, etc;
- Propagating llvmPackages_<version> in the final stdenv, so that
packages needing that version specifically don’t have to rebuild it;
- Bootstrapping with the new Darwin SDK; and
- Reducing the overall number of paths build during a bootstrap by ~33%.
Using the bootstrap stdenv avoids an infinite recursion from xcbuild
depending on zlib depending on xcrun from xcbuild, which is propagated
by the non-bootstrap stdenv.
macOS ships with several stubs in `/usr/bin` that invoke `xcrun` to run
the tools from the active SDK. When `/usr/bin` is in `PATH`, this will
cause `xcrun` from xcbuild to invoke itself over and over. Filtering
`/usr/bin` from `xcrun`’s search path prevents this from happening.
xcbuild determines the SDK dynamically, so overriding the `sdkVer` no
longer works. If packages want to change the SDK, they need to add one
of the SDK packages to their inputs.
Take advantage of the new Darwin SDKs to dynamically determine SDK
information such as path, version, and binaries (via `xcrun --find`).
This is accomplished by relying on the existance of `DEVELOPER_DIR`,
which the SDK will set up in nixpkgs.
Using the bootstrap stdenv avoids an infinite recursion from xcbuild
depending on ncurses depending on xcrun from xcbuild, which is
propagated by the non-bootstrap stdenv.
When using the LLVM bootstrap to build LLVM and its libraries,
overriding just LLVM to disable tests during the first build doesn’t
seem to work. This stage name should remain stable, so check for it and
disable tests when building in it.
When compiler-rt targets Darwin, it is built with `-target`, which
causes clang to try to invoke `ld` without a target prefix (e.g., it
will try to exec `ld` instead of `x86_64-apple-darwin-ld` on a
cross-build to x86_64-darwin). Specifying `--ld-path` overrides that
behavior, allowing it to find the appropriate cross-linker.
The first build of compiler-rt in the LLVM bootstrap is build without
libc++ being available, which causes support for the `-g` flag to be
detected incorrectly on Darwin. Overriding the check by specifying that
it’s usable allows the first build of compiler-rt to succeed.
compiler-rt supports specifying the SDK path and version, so do that to
avoid needing to include `xcrun` as a native build input, which
simplifies the bootstrap.
Instead of using overrides in the stdenv bootstrap, Darwin will be
relying on the LLVM bootstrap to build compiler-rt. The only special
handling it needs is to use a stdenv with a bootstrap SDK instead of the
default one (to avoid infinite recursions).
While the Darwin stdenv bootstrap sets up its own clang wrappers and
doesn’t provide these wrappers in the final stdenv, it does use them
indirectly via the LLVM bootstrap to build LLVM and its libraries.
Note on using the system libunwind: It is possible to build and use the
LLVM libunwind on Darwin, but using the system by default one ensures
everything is using the same unwinder.
Using the bootstrap stdenv avoids an infinite recursion from xcbuild
depending on libxml2 depending on xcrun from xcbuild, which is
propagated by the non-bootstrap stdenv.
