Static Linking clang_sys on msvc/windows cannot find libraries, e.g. libclang.lib

[Cody-Duncan]

I ran into a bunch of problems to get clang_sys statically linking with binaries built via msvc on Windows
Documenting the found issues here for a future fix.

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Process to get static linking on clang 18.1.7

Stage 1: cmake configuration

Configuring cmake on llvm using the generator "Visual Studio 17 2022",
requires that LLVM_ENABLE_PIC also be turned off. Otherwise, it unsets LIBCLANG_BUILD_STATIC and builds shared DLL libraries.
-DLIBCLANG_BUILD_STATIC=ON
-DLLVM_ENABLE_PIC=OFF

Cmake configure command:
cmake -G "Visual Studio 17 2022" -A x64 -T host=x64 -DLLVM_TARGETS_TO_BUILD=X86 -DLIBCLANG_BUILD_STATIC=ON -DLLVM_ENABLE_PIC=OFF -S <path/to/llvm-project>/llvm -B <build_dir>

Then built the binaries in configuration RelWithDebInfo|x64.
devenv.com LLVM.sln /Build "RelWithDebInfo|x64"

Followed by cmake install command:
cmake --install <build_dir> --prefix <install_dir> --config RelWithDebInfo

Stage 2: Environment Variables

Created .cargo/config.toml containing

[env]
LLVM_CONFIG_PATH = '<install_dir>/bin/llvm-config.exe'
#LIBCLANG_PATH = '<install_dir>/bin/libclang.dll'
LIBCLANG_STATIC_PATH = '<install_dir>/lib/libclang.lib'
CLANG_PATH = '<install_dir>/bin/clang.exe'

Stage 3: fixing build/static.rs link() to find libraries

Problem: Could not find libclang.lib

• get_clang_libraries() searches for libclang*.a. Libraries on msvc are .lib.

Fix: changed get_clang_libraries() to switch the glob based on platform.

Problem: Could not find clang.lib.

• get_library_name() strips the lib prefix from the filename, turning libclang -> clang. clang.lib doesn't exist in the install libraries AFAICT. If it does, there's some configuration in cmake I don't know about, but I didn't need a clang.lib in the end.
• CLANG_LIBRARIES also refers to the nonexistent clang(.a/.lib).

Fix: removed get_library_name() call in get_clang_libraries(). Replaced it so it returned the filename libclang.lib

Problem: Unresolved external symbols (huge list here)

• get_library_name() wasn't returning any of the other clang libraries that were also dependencies. E.G. clangAST.lib and friends.

Fix: added logic to get_clang_libraries() so it returned libclang.lib and any clang*.lib libraries in the <install>/lib directory.

Problem: Unresolved external symbol GetFileVersionInfoSizeW + 2 more.

• This is from Version.lib, from C:/Program Files (x86)/Windows Kits/10/Lib/10.0.22621.0/um/x64

Fix: Added the appropriate cargo:rustc-link-search=C:/Program Files (x86)/Windows Kits/10/Lib/10.0.22621.0/um/x64 and cargo:rustc-link-lib=static=Version printlns at the end of link().
Caveat: I just hard-coded just to see if it will work. Need to find a more generic way to find Version.lib.

complete

And now it compiles and tests succeed with static linking.

Workflow Notes:

Need to compile using cargo test --features static -vv

• cargo build doesn't try to link against the library, so it false-positively succeeds building if it can find a libclang.lib. Use cargo test instead.
• --features static required to build with static linking from within the clang_sys crate
• -vv is "very verbose" and will emit the println outputs from build.rs and static.rs.