When compiling C++ files, Zig unconditionally passes -nostdinc++ and,
if link_libcpp is set, adds its bundled libc++/libc++abi include paths
as replacements (see Compilation.zig). On MSVC targets this conflicts
with the MSVC C++ runtime headers (vcruntime_typeinfo.h,
vcruntime_exception.h, etc.), causing compilation failures in SIMD
C++ code.
The fix is to use linkLibC instead of linkLibCpp on MSVC. Zig always
passes -nostdinc to strip default search paths, but LibCDirs.detect
re-adds the MSVC SDK include directories, which contain both C and
C++ standard library headers. This gives us proper access to MSVC's
own <optional>, <iterator>, <cstddef>, etc. without the libc++
conflicts.
For the package builds (highway, simdutf, utfcpp) this means
switching from linkLibCpp to linkLibC on MSVC. For SharedDeps and
GhosttyZig, linkLibC is already called separately, so we just skip
linkLibCpp.
Zig's bundled libc++/libc++abi conflicts with the MSVC C++ runtime
headers (vcruntime_typeinfo.h, vcruntime_exception.h, etc.) when
targeting native-native-msvc. This caused compilation failures in
the SIMD C++ code due to -nostdinc++ suppressing MSVC headers and
libc++ types clashing with MSVC runtime types.
Skip linkLibCpp() for MSVC targets across all packages (highway,
simdutf, utfcpp) and the main build (SharedDeps, GhosttyZig) since
MSVC provides its own C++ standard library natively. Also add
missing <iterator> and <cstddef> includes that were previously
pulled in transitively through libc++ headers but are not
guaranteed by MSVC's headers.
This causes linker issues for some libghostty users. I don't know why we
never saw these issues with Ghostty release builds, but generally
speaking I think its fine to do this for 3rd party code unless we've
witnessed an issue. And these deps have been stable for a long, long
time.
Hi there, this is just a low-hanging fruit and it also prepares the way
for the future 0.15, which removes addStaticLibrary.
Please, let me know what to do on the `// TODO` comments.
This fixes an issue where Ghostty would not build against the macOS 15.5 SDK.
What was happening was that Zig was adding its embedded libc paths to
the clang command line, which included old headers that were
incompatible with the latest (macOS 15.5) SDK. Ghostty was adding the
newer paths but they were being overridden by the embedded libc paths.
The reason this was happening is because Zig was using its own logic to
find the libc paths and this was colliding with the paths we were
setting manually. To fix this, we now use a `libc.txt` file that
explicitly tells Zig where to find libc, and we base this on our own SDK
search logic.
