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fix: key PCM and project.so freshness on content, not installed mtimes

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std.pcm was rebuilt when it was older than std.cppm, and project.so when
it was older than the crafter-build executable. Both inputs are installed
files, and an OSTree deployment (the Flatpak) gives every installed file
mtime 0: std.cppm and the executable always looked older than the cache,
so a clang bump would never rebuild std.pcm and a crafter-build update
would never recompile project.so. clang crashes on a PCM from another
compiler instead of reporting it, so the failure would have been a
backtrace on the user's first build after an update.

Each artifact now has a one-line stamp beside it. std.pcm's covers the
precompile command and the module source's bytes, which also catches a
libc++ update under the same clang. project.so's covers the crafter-build
version, the toolchain key, the module source stamp and the compile
command; project.cpp's and the pre-dependency artifacts' mtimes remain
inputs, since those live next to it with real timestamps. The module
source stamp stands in for the executable: project.so resolves Crafter::
symbols from the running binary, so only declarations matter, and an
implementation-only rebuild of crafter-build no longer recompiles it.
The std.pcm stamp folds into the module cache stamp, so a rebuilt
std.pcm rebuilds the PCMs that import it.

The cache directory carries the toolchain key
(<target>-<march>-<clang version>-<hash>), so a compiler bump starts
cold instead of handing the new clang PCMs it will crash on. LoadProject
and Build() now derive the directory from the same StdPcmDir. Old
<target>-<march> directories are left behind; `clean` never touched the
cache and still does not.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
This commit is contained in:
Jorijn van der Graaf 2026-10-02 22:32:35 +02:00
commit 59fc9501f1
Signed by: jorijnvdgraaf
GPG key ID: 2937E59CDCC1BCFB
4 changed files with 256 additions and 56 deletions
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13
implementations/Crafter.Build-Clang.cpp
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@ -246,11 +246,14 @@ void Configuration::GetInterfacesAndImplementations(std::span<fs::path> interfac
}
fs::path Crafter::StdPcmDir(const Configuration& config) {
// The std PCM is cached per target+march, but a wasm variant pass compiles
// it with extra codegen flags (e.g. -mrelaxed-simd) — its BMI must not be
// shared with the baseline's, or the consuming TUs see a target-feature
// mismatch. Suffix the cache dir with the variant flags when present.
std::string stdPcmKey = std::format("{}-{}", config.target, config.march);
// The std PCM is cached per target+march+toolchain: a PCM is only valid
// for the exact clang that wrote it, so a compiler bump starts a cold
// directory instead of handing the new clang a PCM it will crash on. A
// wasm variant pass compiles it with extra codegen flags (e.g.
// -mrelaxed-simd) — its BMI must not be shared with the baseline's, or
// the consuming TUs see a target-feature mismatch. Suffix the cache dir
// with the variant flags when present.
std::string stdPcmKey = std::format("{}-{}-{}", config.target, config.march, GetToolchain().Key());
for (const std::string& f : config.wasmVariantFlags) {
stdPcmKey += "+";
for (char c : f) stdPcmKey += (c == '/' || c == '\\') ? '_' : c;