cc @Profpatsch @mboes @matthewbauer @LnL7

There is an interesting issue here: should the Bazel derivation declare all the Nix tools as dependencies? The resulting Bazel is fine to use without the Nix tools as long as no c/c++ code is built, or c/c++ code is built using custom CROSSTOOL files, instead of using the default ones.

It might be hard to find out which dependencies to use in your profile to use the default CROSSTOOL files if we don't include them unconditionally though.

The xcode_locator is still an issue though, right? The Hydra machines definitely don't have Xcode installed. I feel like that should be the focus - everything else is basically the same between linux & darwin. IIRC enableNixHacks will make sure NIX_LDFLAGS & NIX_CFLAGS_COMPILE are available. We might just need to make that default to true on Darwin or maybe even Linux as well for consistency. It might be better to try to upstream that match and make it conditional on some flag.

The xcode_locator.m thing is something that might be worth trying to convince Bazel maintainers is a VERY bad idea. They use LSCopyApplicationURLsForBundleIdentifier to find XCode.app locations which is both a very ugly hack and unfortunately does not respect sandboxing. Apple even provides xcode-select -p for the very purpose of locating XCode! This is something they should be using - not some obscure API that breaks sandboxing. I suspect they have some reasons for using it but they definitely need to make it possible to fallback to something for users that don't want to install XCode.

I will take a look on Monday. Please ping me if I forget.

The xcode_locator is still an issue though, right? The Hydra machines definitely don't have Xcode installed.

There are two xcode_locator related issues: one is that it's built during bootstrapping by hardcoding the compilation command:
https://github.com/bazelbuild/bazel/blob/696442c2cf3ab935b328000b78cac210300a7004/scripts/bootstrap/compile.sh#L317
This is fixed by this:
https://github.com/NixOS/nixpkgs/pull/44181/files#diff-4746b81564a01e241a84d455575437e7R80
The second issue is that it gets run to look for Xcode:
https://github.com/bazelbuild/bazel/blob/696442c2cf3ab935b328000b78cac210300a7004/tools/cpp/osx_cc_configure.bzl#L67
When that fails, it will fall back to the same logic Bazel uses on Linux:
https://github.com/bazelbuild/bazel/blob/696442c2cf3ab935b328000b78cac210300a7004/tools/cpp/osx_cc_configure.bzl#L160
So when building with Nix either on hydra or without Xcode installed it should all be ok.

Found out I misunderstood the purpose of the absolute paths in CROSSTOOL, they're just defaults. Also found out about BAZEL_USE_CPP_ONLY_TOOLCHAIN which disables the whole xcode locator part.

ping @Profpatsch

@GrahamcOfBorg build bazel

No attempt on aarch64-linux (full log)

The following builds were skipped because they don't evaluate on aarch64-linux: bazel

a) For `nixos-rebuild` you can set
  { nixpkgs.config.allowUnfree = true; }
in configuration.nix to override this.

b) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
  { allowUnfree = true; }
to ~/.config/nixpkgs/config.nix.

Success on x86_64-linux (full log)

Attempted: bazel

these paths will be fetched (98.80 MiB download, 101.39 MiB unpacked):
  /nix/store/gpirdnr7yl9wadd6hfc9my6yc4v93qry-bazel-0.15.2
  /nix/store/xkfg1m8q8zn0yc3fw8ds2d3sr6gcvfb5-bash
copying path '/nix/store/xkfg1m8q8zn0yc3fw8ds2d3sr6gcvfb5-bash' from 'https://cache.nixos.org'...
copying path '/nix/store/gpirdnr7yl9wadd6hfc9my6yc4v93qry-bazel-0.15.2' from 'https://cache.nixos.org'...
/nix/store/gpirdnr7yl9wadd6hfc9my6yc4v93qry-bazel-0.15.2

Success on x86_64-darwin (full log)

Attempted: bazel

//examples/cpp:hello-success_test                                        PASSED in 0.1s
//examples/java-native/src/test/java/com/example/myproject:hello         PASSED in 0.3s

Executed 2 out of 2 tests: 2 tests pass.
There were tests whose specified size is too big. Use the --test_verbose_timeout_warnings command line option to see which ones these are.
INFO: Build completed successfully, 20 total actions
installing
post-installation fixup
patching script interpreter paths in /nix/store/dyzwhqwpz12kvyd5p7cff9zhynnjssyp-bazel-0.15.2
/nix/store/dyzwhqwpz12kvyd5p7cff9zhynnjssyp-bazel-0.15.2

tbh I can’t say much about Darwin patches (no machine). But it looks like at least it builds on Darwin now. Adding a test might be a good idea.

Can you please add some comments to the bash code lines, explaining why the respective lines are needed? It seems to require some pretty arcane knowledge, so better document too much then too little.
Like basically everything in the comments here should go to the source code comments, otherwise it’s just lost information and time.

If you can, please shorten the lines a bit as well.

Will add comments.

Adding a test might be a good idea.

What kind of test? Doesn't the darwin build cover testing this?

What kind of test? Doesn't the darwin build cover testing this?

Ah, I mean some test that runs a simple build with bazel to check if it actually runs, not just builds.

@Profpatsch Added comments.

Ah, I mean some test that runs a simple build with bazel to check if it actually runs, not just builds.

We already do that by building and running the example tests:

That looks awesome! @mboes, I think we can merge?

ping @mboes

I will just merge now, feel free to revert if something’s not right.