From e280c955f7c2da68154fa2cd722a4ef68c081349 Mon Sep 17 00:00:00 2001
From: Jorijn van der Graaf <jorijnvdgraaf@catcrafts.net>
Date: Tue, 6 Oct 2026 16:50:41 +0200
Subject: [PATCH] fix(host-cache): hash every part of the project.so stamp

The stamp that decides whether a compiled project file can be reused
was meant to cover the crafter-build version, the toolchain key, the
module-source stamp and the compile command. Only the version went in.
The four parts were joined by a format string with "\0" between the
fields, and a format string is read as a C string: it ended at the
first NUL, so std::format saw "{}" and dropped the other arguments
without a diagnostic.

A project.so is loaded into the crafter-build process and fills in
Configuration objects by their layout. With the stamp blind to the
declarations, one built against other module sources was loaded as
current whenever the version string was unchanged, which is every
working-tree build (`git describe --dirty` does not follow the tree's
contents) and every local Flatpak build. Growing a class that project
files construct then corrupts the heap: a project.so built while Shader
was 56 bytes, loaded after it had become 104, aborted with "free():
invalid size" as soon as it declared a shader. CI builds were spared
only because each carries its own version.

The parts are now appended to a std::string with NUL separators, the
way the other stamps in this file are built. Every existing project.so
carries a stamp of the version alone, so each is recompiled once.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 implementations/Crafter.Build-Platform.cpp | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/implementations/Crafter.Build-Platform.cpp b/implementations/Crafter.Build-Platform.cpp
index f8a7694..03cdba2 100644
--- a/implementations/Crafter.Build-Platform.cpp
+++ b/implementations/Crafter.Build-Platform.cpp
@@ -845,7 +845,18 @@ Configuration Crafter::LoadProject(const fs::path& projectFile, std::span<const
     // in for the executable: project.so resolves Crafter:: symbols from the
     // running binary, so only the declarations (the .cppm files) matter,
     // and an implementation-only rebuild of crafter-build leaves it valid.
-    const std::string projectStamp = HashStamp(std::format("{}\0{}\0{}\0{}", CrafterBuildVersion(), GetToolchain().Key(), sourcesStamp, compileCmd));
+    // The separators are appended, not written into a format string: a
+    // format string is read as a C string, so one with "\0" in it ends at the
+    // first NUL and everything after the version silently dropped out of the
+    // stamp. A project.so compiled against other declarations (a Shader with
+    // a different layout, say) was then loaded as current and corrupted the
+    // heap.
+    std::string projectStampInput(CrafterBuildVersion());
+    for (std::string_view part : {std::string_view(GetToolchain().Key()), std::string_view(sourcesStamp), std::string_view(compileCmd)}) {
+        projectStampInput += '\0';
+        projectStampInput += part;
+    }
+    const std::string projectStamp = HashStamp(projectStampInput);
 
     if (ProjectFileStale(soPath, absProject, projectStamp, preDeps)) {
         std::string result = RunBuildCommand(compileCmd);