rules_rust is failing to find _cc_toolchain in WORSPACE setup after updating to 0.57.1

[dunnock]

I am using WORKSPACE based setup with Bazel 7.4

bazel build is able to pick the _cc_toolchain on version 0.56, but failing with the following compile error after updating to 0.57.1 (redacted):

...
ERROR: .../external/rust_linux_x86_64__x86_64-unknown-linux-gnu__stable_tools/BUILD.bazel:96:15: in rust_toolchain rule @@rust_linux_x86_64__x86_64-unknown-linux-gnu__stable_tools//:rust_toolchain: 
Traceback (most recent call last):
        File ".../external/rules_rust/rust/toolchain.bzl", line 670, column 72, in _rust_toolchain_impl
                libstd_and_allocator_ccinfo = _make_libstd_and_allocator_ccinfo(ctx, rust_std, ctx.attr.allocator_library, "std"),
        File ".../external/rules_rust/rust/toolchain.bzl", line 159, column 60, in _make_libstd_and_allocator_ccinfo
                cc_toolchain, feature_configuration = find_cc_toolchain(ctx)
        File ".../external/rules_rust/rust/private/utils.bzl", line 55, column 43, in find_cc_toolchain
                cc_toolchain = find_rules_cc_toolchain(ctx)
        File ".../external/bazel_tools/tools/cpp/toolchain_utils.bzl", line 63, column 9, in find_cpp_toolchain
                fail("In order to use find_cpp_toolchain, you must define the '_cc_toolchain' attribute on your rule or aspect.")
Error in fail: In order to use find_cpp_toolchain, you must define the '_cc_toolchain' attribute on your rule or aspect.
...

[UebelAndre]

This was likely caused by #3116

cc @katre

[katre]

Hmm, checking the version of find_cpp_toolchain in Bazel 7.4.0, this appears to be following the "toolchain resolution for C++ not enabled" branch.

Are you explicitly disabling toolchain resolution for C++ (with the --incompatible_enable_cc_toolchain_resolution flag)? That's simply not compatible with recent Bazel rules (and, in Bazel 8.0, is an ignored flag).

If you have a reproduction I will take a look.

[dunnock]

Are you explicitly disabling toolchain resolution for C++ (with the --incompatible_enable_cc_toolchain_resolution flag)? That's simply not compatible with recent Bazel rules (and, in Bazel 8.0, is an ignored flag).

I am relatively new to bazel, integrating my Rust code base into large C++ project. But from what I can see I have this setting in the workspace root:

common --noincompatible_enable_cc_toolchain_resolution

From the comment it seems is present as a workaround for bazelbuild/bazel#21121

If you have a reproduction I will take a look.

This might be tricky but I will try. I thought it is a known issue but it seems it is rather an edge case.

[katre]

You should no longer be using either --noincompatible_enable_cc_toolchain_resolution or --crosstool_top: please see the documentation (especially those linked from bazelbuild/bazel#21121 (comment)) for the new flags to use.

We can no longer support those flags, so you'll need to update your project. There's really nothing I can do further, so no need to find a way for me to reproduce.