Remove forward declarations to cgo exported funcs

[iamcalledrob]

Parallel PR to crawshaw/sqlite#146 -- I feel like this one has a better chance of being merged than the crawshaw repo :)

Full details of the change in PR linked above.

tl;dr, fixes building on windows with clang, as well as a typo in readme.md

[iamcalledrob]

To hopefully save someone else some time

My personal use-case here is to easily cross-compile a project that uses sqlite.

https://github.com/zombiezen/go-sqlite would have been my first choice of sqlite driver, but the modernc/sqlite foundation it's built on doesn't support many GOOS/GOARCH combos. For example, Android (builds but makes prohibited syscalls), iOS, various BSDs.

Zig is great, and makes cross compilation a dream, e.g.
GOARGS GOOS=linux GOARCH=arm64 "CC=zig cc -target aarch64-linux-gnu" go build ... to build for arm64 linux.

Unfortunately, Zig uses clang internally, leading to the build errors on windows detailed in the main PR. This PR makes cross-compiling as "easy" as:
GOARGS GOOS=windows GOARCH=amd64 "CC=zig cc -target x86_64-windows-gnu" go build ...

Caveat: The zig toolchain is currently missing winpthreads for windows, so you'll need to build and link against winpthreads manually, e.g. by cross-compiling using https://github.com/kassane/winpthreads-zigbuild and passing zig-out/include and zig-out/winpthreads.lib into CGO_CFLAGS / CGO_LDFLAGS as appropriate/

[anacrolix]

@theraphim do you have any thoughts?

What version of Zig are you cross compiling with?

I have a project that I cross compile to Windows and I don't recall any errors but it's been a while. I'll try it with this PR.

Thanks for the PR!

[anacrolix]

I should mention that I've used zombiezen, and Zig for cross compilation too, so I understand the difficulty.

In my case I had to stop using zombiezen because I needed to use extensions, and I couldn't figure them out in Go with zombiezen, and couldn't call through to C extensions from zombiezen, and I started writing my extensions in Rust which was all too much to deal with.

[iamcalledrob]

@anacrolix Cross compiling with both Zig stable and nightly -- behaviour is the same!

I believe cross-compiling with a gcc based toolchain does work, but not with a clang-based one (i.e. zig, but also... clang).

I'm recklessly assuming you're not a Windows user, but you can verify the problem and fix on linux/macos because zig bundles a mingw64+clang cross compilation toolchain:

1. Install zig, e.g. via brew on macos brew install zig
2. Download then cross-compile winpthreads: cd /path/to/winpthreads; zig build -Dtarget=x86_64-windows-gnu -Dcpu=baseline. That will build in source into a "zig-out" dir.
3. Cross-compile a go project that depends on the sqlite driver, e.g.: GOARGS GOOS=windows GOARCH=amd64 CGO_CFLAGS="-I/path/to/winpthreads/zig-out/include" CGO_LDFLAGS="-L/path/to/winpthreads/zig-out/lib -lwinpthreads" CC=zig cc -target x86_64-windows-gnu" go build someproject
4. Witness the errors and warnings listed in Remove forward declarations to cgo exported funcs crawshaw/sqlite#146

[anacrolix]

Fantastic. Thanks for the thorough reproduction steps.