# zig rc: Add COFF object file creation for CMake cross-compilation use case · gitcafe/zig

[View on GitCafe](https://git.cafe/gitcafe/zig/commit/a502301b5eb84329c8c3ecb4b68bc52048f99cdc)

Repository: [gitcafe/zig](https://git.cafe/gitcafe/zig)

Visibility: public

Requested revision: a502301b5eb84329c8c3ecb4b68bc52048f99cdc

Requested commit: a502301b5eb84329c8c3ecb4b68bc52048f99cdc

Commit: a502301b5eb84329c8c3ecb4b68bc52048f99cdc

Tree: ad086cb9950be276b6688aef6abf6107391afb59

Author: Ryan Liptak

Committer: Andrew Kelley

## Message

```
zig rc: Add COFF object file creation for CMake cross-compilation use case

In #22522 I said:

> RC="zig rc" will now work in combination with zig cc and CMake. Here's an example of cross-compiling a simple Windows GUI CMake project
>
>    $ RC="zig rc" CC="zig cc --target=x86_64-windows-gnu" cmake .. -DCMAKE_SYSTEM_NAME=Windows -G Ninja

However, I didn't realize that the time that this only works because of the `-G Ninja` part. When not using Ninja as the build tool, CMake adds a workaround for 'very long lists of object files' where it takes all object files and runs them through `ar` to combine them into one archive:

https://github.com/Kitware/CMake/blob/4a11fd8dde745789f66d6500412d7f56607e9218/Modules/Platform/Windows-GNU.cmake#L141-L158

This is a problem for the Windows resource use-case, because `ar` doesn't know how to deal with `.res` files and so this object combining step fails with:

    unknown file type: foo.rc.res

Only the linker knows what to do with .res files (since it has its own `.res` -> `.obj` ('cvtres') conversion mechanism). So, when using Ninja, this object file combining step is skipped and the .res file gets passed to the linker and everyone is happy.

Note: When CMake thinks that its using `windres` as the Windows resource compiler, it will pass `-O coff` to windres which causes it to output a COFF object file instead of a `.res` file, which means that the `ar` step can succeed because it's only working on actual object files.

---

This commit gives `zig rc` the ability to output COFF object files directly when `/:output-format coff` is provided as an argument. This effectively matches what happens when CMake uses `windres` for resource compilation, but requires the argument to be provided explicitly.

So, after this change, the following CMake cross-compilation use case will work, even when not using Ninja as the generator:

    RC="zig rc /:output-format coff" CC="zig cc --target=x86_64-windows-gnu" cmake .. -DCMAKE_SYSTEM_NAME=Windows

```

## Parents

- [8683f25d24414f817e946ac5fe7c9f6eceb7bb09](https://git.cafe/gitcafe/zig/commit/8683f25d24414f817e946ac5fe7c9f6eceb7bb09?format=markdown)

[Source at this commit](https://git.cafe/gitcafe/zig/tree/a502301b5eb84329c8c3ecb4b68bc52048f99cdc?format=markdown)