This brings the internal package more in line with how the nixpkgs
package is built. It also handles recursive dependencies better than the
current system.
Because Zig does not fetch recursive dependencies when you run `zig build
--fetch` (see https://github.com/ziglang/zig/issues/20976) we need to do some
extra work to fetch everything that we actually need to build without Internet
access (such as when building a Nix package).
An example of this happening:
```
error: builder for '/nix/store/cx8qcwrhjmjxik2547fw99v5j6np5san-ghostty-0.1.0.drv' failed with exit code 1;
la/build/tmp.xgHOheUF7V/p/12208cfdda4d5fdbc81b0c44b82e4d6dba2d4a86bff644a153e026fdfc80f8469133/build.zig.zon:7:20: error: unable to discover remote git server capabilities: TemporaryNameServerFailure
> .url = "git+https://github.com/zigimg/zigimg#3a667bdb3d7f0955a5a51c8468eac83210c1439e",
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /build/tmp.xgHOheUF7V/p/12208cfdda4d5fdbc81b0c44b82e4d6dba2d4a86bff644a153e026fdfc80f8469133/build.zig.zon:16:20: error: unable to discover remote git server capabilities: TemporaryNameServerFailure
> .url = "git+https://github.com/mitchellh/libxev#f6a672a78436d8efee1aa847a43a900ad773618b",
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
For full logs, run 'nix log /nix/store/cx8qcwrhjmjxik2547fw99v5j6np5san-ghostty-0.1.0.drv'.
```
To update this script, add any failing URLs with a line like this:
```
zig fetch <url>
```
Periodically old URLs may need to be cleaned out.
Hopefully when the Zig issue is fixed this script can be eliminated in favor
of a plain `zig build --fetch`.
This adds a nix workflow that does the following:
* Checks to see if the Zig cache fixed derivation needs its hash
updated. It does this by downloading a new cache, calculating the
hash, and comparing it against what has already been set. If the hash
is different, the workflow fails.
* Runs a Nix build if the hash is OK, testing the build of
packages.ghostty (using "nix build .")
The cache workflow we use in the build job comes from:
https://github.com/DeterminateSystems/magic-nix-cache-action/Fixes#937.
