Error when build c/c++ dependencies: can't found

[zooeywm]

  cargo:warning=./src/handlers/my_handler.hpp:14:10: fatal error: 'X11/Xatom.h' file not found

  cargo:warning=#include <X11/Xatom.h>

  cargo:warning=         ^~~~~~~~~~~~~

I'm a C/C++ novice, I have a rust project that has C/C++ dependencies, X11/Xatom.h This library can be found during normal cargo build —target x86_64-unknown-linux-gnu compilation, when using zigbuild, the X11/Xatom.h` cannot be found when specifying any version of glibc on the same platform. Thanks for any help!

[polarathene]

Assuming that X11/Xatom.h is found at /usr/include, this should be fixable by including the system directory (which zig excludes when -nostdinc / -target is configured which cargo zigbuild sets).

This should work for you (RUSTFLAGS may not be necessary sometimes):

CFLAGS='-isystem /usr/include' RUSTFLAGS='-L /usr/lib64' cargo zigbuild --release --target x86_64-unknown-linux-gnu

Zig should provide it's own headers and those should be preferred when building for older glibc. You would not want to use -I /usr/include which would introduce conflicts. This should provide fallback to /usr/include for additional header files from other system packages.

Full explanation

The default system libs like /usr/include are excluded when you use zig with -target, but in the case of cargo-zigbuild it always enforces this regardless due to adding -nostdinc:

cargo-zigbuild/src/zig.rs

Lines 839 to 841 in eba2d7e

	// Never include default include directories,
	// otherwise `__has_include` will be totally confused.
	args.push("-nostdinc".to_owned());

To include that again you can use args like -isystem / -idirafter with /usr/include:

# `cargo-zigbuild` effectively runs `zig cc -nostdinc`,
# which excludes system include dir `/usr/include`, add it back via `-isystem`:
CC='zig cc -nostdinc -isystem /usr/include' make install

When you use -target with zig cc, such as -target x86_64-linux-gnu or the custom glibc target (eg: -target x86_64-linux-gnu.2.34), that will also exclude default search dirs for linking shared libraries (.so files), so you'll need to explicitly provide those too such as with -L /usr/lib64 (to zig cc like above with -isystem, or RUSTFLAGS).

---

These two extra flags need to be picked up separately usually if you've got a common command like cargo-zigbuild (which implicitly configures both CC and RUSTFLAGS='-C linker=...' for you).

• For zig cc there is the CFLAGS ENV, and for zig c++ you'd have CXXFLAGS equivalent as a way to pass extra options to the CC / CXX ENV or associated commands. Those same standard ENV work with gcc/g++ and clang. In Rust this can be relevant for build-time dependencies like -sys crates with their build.rs.
• Next is linking libs by the linker (RUSTFLAGS -C linker=...). zig / gcc / clang can leverage the LDFLAGS ENV for providing extra linker args, but for rustc you need to provide this information via RUSTFLAGS ENV so when crates have a build.rs that explicitly link libs via rustc-link-lib that it'll know about extra search directories.

Hence here's how zig cc could be used with a typical project that has a Makefile vs the equivalent for Rust via cargo:

CC='zig cc -target x86_64-linux-gnu' CFLAGS='-isystem /usr/include' LDFLAGS='-L /usr/lib64' make install

CFLAGS='-isystem /usr/include' RUSTFLAGS='-L /usr/lib64' cargo zigbuild --release --target x86_64-unknown-linux-gnu