0.19.1: @bazel_tools//tools/cpp:cc-compiler-local-k8' is not a cc_toolchain rule

[scottmin0r]

Description of the problem / feature request:

C++ builds fail with:

ERROR: The label '@bazel_tools//tools/cpp:cc-compiler-local-k8' is not a cc_toolchain rule

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

On Linux/amd64, in an otherwise empty workspace with an empty WORKSPACE file, run:

bazel build --crosstool_top=@bazel_tools//tools/cpp:default-toolchain //...

What operating system are you running Bazel on?

Linux (Debian variant)

What's the output of bazel info release?

release 0.19.1

Have you found anything relevant by searching the web?

In the file https://github.com/bazelbuild/bazel/blob/0.19.1/tools/cpp/BUILD:

On the 0.19.0 tag, this line refers to cc-compiler-local, a cc_toolchain rule that exists.

On the 0.19.1 tag, this line refers to cc-compiler-local-k8, a cc_toolchain rule that does not exist.

This appears to be the cause of the issue, although I am not sure why this was changed.

[katre]

You're right about the cause, I'm not sure what those changed lines are about. Adding @mhlopko and @lberki to try and help figure it out.

[nlopezgi]

#6665 might be related. Perhaps this is also due to 6bc4528 not being included in 0.19.1

[gelrom]

Could the following output have the same underlying cause?
...in cc_toolchain rule @local_config_cc//:cc-compiler-k8: Error while selecting cc_toolchain: Toolchain identifier 'local' was not found, valid identifiers are...
This break occurs at 0.19.1. I've been unable to determine if it also occurs at 0.19, but 0.18 was definitely working. Note that this still breaks even if all backward breaking flags that were flipped in 0.19 are set to false.

edit: If this is irrelevant, I can delete this comment and file a separate issue.

[scentini]

@gelrom can you share the build command? Seems close enough, but not quite the same.

[scentini]

@gelrom also, could you please provide the list of valid identifiers in the error message?

[scentini]

@scottminor-google, we've confirmed that @bazel_tools//tools/cpp:default-toolchain is in error.
Why do you need to set --crosstool_top=@bazel_tools//tools/cpp:default-toolchain ? I'm trying to determine the scope of the issue.
Thanks.

[gelrom]

@scentini bazel build --crosstool_top=//lib/bazel:toolchain //...
the list of identifiers is of each of our toolchain's toolchain_identifier

[scottmin0r]

We have a long-ish bazelrc that is explicit about each crosstool_top and host_crosstool_top that is used for each config that we define, to keep the toolchain selection as obvious and understandable as possible. default-toolchain is what we use mostly for host_crosstool_top (although that will change shortly, as we don't want to rely on a user-installed toolchain in any part of the build by default).

Is there a different spelling for the same behavior/toolchain as default-toolchain that works in 0.19.1 and is backwards-compatible to at least 0.18.0 that we should be using instead?

[scottmin0r]

Thanks for the fix! I rebuilt bazel from 94d51fc to test/verify this fix against our codebase. Unfortunately, I'm running into another error:

ERROR: /usr/local/google/home/minors/.cache/bazel/_bazel_minors/32b2ee46dce03a213358bafd92f1c3ce/external/local_config_cc/BUILD:57:1: in cc_toolchain rule @local_config_cc//:cc-compiler-k8: Error while selecting cc_toolchain: Toolchain identifier 'local' was not found, valid identifiers are [stub_armeabi-v7a, local_linux, local_darwin, local_freebsd, local_windows_mingw, local_windows_msys64_mingw64, local_windows_clang, local_windows_msys64, vc_14_0_x64]
ERROR: Analysis of target '//:hello_world' failed; build aborted: Analysis of target '@local_config_cc//:cc-compiler-k8' failed; build aborted

This is reproduced in a workspace with:

• an empty WORKSPACE file
• //hello_world.cpp:

  #include <iostream>
  
  int main() {
    std::cout << "Hello, world!" << std::endl;
    return 0;
  }
  

• //BUILD:

  cc_binary(
      name = "hello_world",
      srcs = ["hello_world.cpp"],
  )
  

Bazel builds successfully when doing:

bazel build //...

but fails with the above error when specifying default-toolchain:

bazel build //... --crosstool_top=@bazel_tools//tools/cpp:default-toolchain

[scottmin0r]

In our codebase, the error is a little different - it still complains about @local_config_cc//:cc-compiler-k8, but the available toolchain identifiers is one element - the toolchain_identifier specified in our custom CROSSTOOL. I have no idea why that would be interacting with @local_config_cc (or even what that is supposed to be).

Is there anything I can read up on to better understand C/C++ toolchain resolution and what best practices are? I feel woefully uneducated when it comes to this area of Bazel.

[wjywbs]

I'm encountering an issue similar to this. I took some time to make a minimal repro in https://github.com/wjywbs/bazel-cc-toolchain-bug, and posted the outputs of bazel 0.18.1, 0.19.0 and 0.19.1 in there.

[scentini]

Thanks for the repro, looking into it.

[katre]

It looks like cherrypicking 683c302 will fix this (but, it changes how crosstool_top is selected). @scottminor-google, can you add that cherrypick on top of the existing release-0.19.2 branch and let me know if it works?

[katre]

I've pushed the cherrypick into the RC, please let me know if there are still issues.

[scottmin0r]

I built bazel from f2be11dda2 and it successfully builds a C++ target from our codebase with no additional flags. Thanks for the fix!

[katre]

Closing since 0.19.2 will be released shortly.