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fix(sysroot): take the std module source from the sysroot's libc++ release

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A cross build against a sysroot whose libc++ differs from the
toolchain's failed while precompiling the std module, with a page of
"no member named 'runtime_format' in namespace 'std'". The module source
is a list of using-declarations for what one libc++ release declares, so
it only compiles against that release's headers. BuildStdPcm wants the
sysroot's own <sysroot>/usr/share/libc++/v1/std.cppm, but Alpine
packages the headers without it, and the fallback was the toolchain's
copy whatever its release. That held while the compiler came from the
same distro as the sysroot; with the Flatpak's libc++ 22.1.8 and Alpine
edge on 23.1.2 it no longer does.

The release is now read from _LIBCPP_VERSION in the sysroot's and the
toolchain's <__config>, and SysrootStdModule picks in this order: the
sysroot's own source, the toolchain's when both are the same major
release (a release branch only takes fixes), the copy crafter-build
ships for that release under share/crafter-build/libc++-modules/<major>.
When none fits the build stops with one line naming both releases and
the directory the matching source belongs in, before clang is run. If
either release cannot be read the toolchain's source is tried as
before, since there is nothing to compare.

Matching sources live in crafter-build's own share directory rather
than the LLVM prefix: they are data this tool ships for sysroots, not
part of any one compiler install, and "sources ship" already describes
that directory. `--version` prints the toolchain's libc++ release and
the releases sources are shipped for, the first thing to look at when
such a build fails.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
This commit is contained in:
Jorijn van der Graaf 2026-10-03 16:37:00 +02:00
commit e15cd3c14d
Signed by: jorijnvdgraaf
GPG key ID: 2937E59CDCC1BCFB
4 changed files with 112 additions and 14 deletions
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14
implementations/Crafter.Build-Clang.cpp
View file

@ -1537,6 +1537,20 @@ static void PrintVersion() {
return;
}
std::println("compiler {} ({})", tc.clangVersion, tc.clangxx.string());
if (tc.libcxxVersion != 0) {
// A sysroot on another libc++ release builds only when its std
// module source is in the sysroot or among these; printed here
// because that is the first question when such a build fails.
std::vector<std::string> shipped;
std::error_code ec;
for (const fs::directory_entry& entry : fs::directory_iterator(tc.stdModulesDir, ec)) {
if (fs::exists(entry.path() / "std.cppm")) shipped.push_back(entry.path().filename().string());
}
std::ranges::sort(shipped);
std::string also;
for (const std::string& release : shipped) also += std::format(", {}", release);
std::println("libc++ {}{}", LibcxxVersionString(tc.libcxxVersion), also.empty() ? std::string() : std::format(" (std module sources for sysroots also for{})", also.substr(1)));
}
std::println("host {}", tc.hostTriple);
}