make translate-c self-hosted

[andrewrk]

Here's the plan:

1. Separate translate_c.cpp into zig_clang.h/zig_clang.cpp and translate_c.cpp. The wrapper simply creates a C interface on top of the C++ clang API, and translate_c.cpp goes through the wrapper API. This transition is complete.
2. Create src-self-hosted/clang.zig which is a Zig version of the src/zig_clang.h file. These will have to be kept in sync in order to prevent a dependency loop.
3. Port src/translate_c.cpp to src-self-hosted/translate_c.zig and then delete src/translate_c.cpp. This step was completed by @Vexu in Translate-c-2 the rest #3935.

Currently, zig translate-c and @cImport are implemented with translate_c.cpp and zig translate-c-2 is implemented with translate_c.zig. There will be a separate set of translate-c tests specifically for the Zig implementation, until finally the Zig implementation passes all the tests and step 3 is completed.

[andrewrk]

I did a sort of proof-of-concept with zig fmt in ba56f36

[andrewrk]

I started on step 1 in 356cfa0. The last puzzle piece to fit in here is that, until we get self-hosted and start shipping stage2 (#89), we will have an interesting build process:

• Build zig/zig.exe - the stage1 compiler with @cImport and translate-c capabilities disabled.
• One of the artifacts from the previous step is zig_cpp.a/zig_cpp.lib. Using that and .zig translate-c source code, build translate_c.a/translate_c.lib.
• Build zig/zig.exe - the stage1 compiler again, this time with @cImport and translate-c capabilities enabled. Link with translate_c.a/translate_c.lib.

I will note this negates the "small stage1 performance price today" I mentioned earlier. We can have our 🍰 and eat it too!

[andrewrk]

Marking this as contributor friendly since you can follow the pattern I've started in the latest commit (c3c92ca). The goal is to delete these lines from translate_c.cpp:

#include <clang/Frontend/ASTUnit.h>
#include <clang/Frontend/CompilerInstance.h>
#include <clang/AST/Expr.h>

Instead relying only on the decls in zig_clang.h. Once that's done we can proceed to steps 2 and 3. If you want to contribute on this you can look for clang::Foo in translate_c.cpp and try to make the code use decls from zig_clang.h instead of the clang::Foo thing.

[andrewrk]

C API Progress Bar (grep 'clang::' ../src/translate_c.cpp | wc -l and then 1137 minus that number out of 1137):

• 100%

[andrewrk]

Now that #2295 is merged, all the proofs of concept are completed, the plan is working, and the rest of this issue is just porting the C++ translate-c code to Zig. We have zig translate-c-2 coexisting with zig translate-c for now. Once the self-hosted version is on par with the C++ version we'll delete the C++ version.

[andrewrk]

Progress:

[andrewrk]

Progress:

[nix-shell:~/downloads/zig/build]$ cat foo.c
void foo(void);
int x;

[nix-shell:~/downloads/zig/build]$ ./zig translate-c-2 foo.c 
// foo.c:1:6: warning: unsupported type: 'FunctionProto'
// foo.c:1:6: warning: unable to resolve prototype of function 'foo'
// foo.c:2:5: warning: TODO implement translate-c for variables

[andrewrk]

Progress:

[nix-shell:~/downloads/zig/build]$ cat foo.c
int x;
void __attribute__((noreturn)) foo(void);

[nix-shell:~/downloads/zig/build]$ ./zig translate-c-2 foo.c
// foo.c:1:5: warning: TODO implement translate-c for variables
extern fn () noreturn;
// foo.c:2:32: warning: TODO implement more translate-c for function decls

[shawnl]

My "get_c_type for vectors" patch allows generating header files for @Vector() arguments and return values, but we also need support interfacing with libclang's parsing of Vector. #2945 (Can't link to patch, cause this patch-set is getting constantly rebased)

• Vector type support for header files

(trying to translate use of vector types is probably not worth it)

[andrewrk]

Huge thanks to @Vexu for doing most of the porting of translate-c to stage2!

This project is now complete.