[Bug]: PROTOC_TOOLCHAIN_FLAGS contains duplicate keys in a dict

[mislavmandaricaxilis]

What happened?

We're trying out bazel-preset.bzl and as I was cleaning up our flags I stumbled upon PROTOC_TOOLCHAIN_FLAGS.

When testing it out from HEAD I got a build failure as the dict contains multiple flags. This should probably be resolved on bazel-preset.bzl level, because as it's public API defined right now, it's not possible to provide multiple values for the same flag (eg. can't set multiple --repo_env or --action_env flags).

ERROR: Traceback (most recent call last):
        File "/private/var/tmp/_bazel_username/f5a8e2c9b1d0f3a7e6b4c2d1f0a9b8c7/external/toolchains_protoc+/protoc/flags.bzl", line 19, column 20, in <toplevel>
                "per_file_copt": struct(
Error: dictionary expression has duplicate key: "per_file_copt"
WARNING: Target pattern parsing failed.
ERROR: Skipping '//tools/bazelrc_preset': error loading package 'tools/bazelrc_preset': initialization of module 'protoc/flags.bzl' failed
ERROR: error loading package 'tools/bazelrc_preset': initialization of module 'protoc/flags.bzl' failed
INFO: Elapsed time: 0.774s
INFO: 0 processes.
ERROR: Build did NOT complete successfully
ERROR: Build failed. Not running target

Version

Development (host) and target OS/architectures: darwin/arm64

Output of bazel --version: bazel 8.1.1

Version of the Aspect rules, or other relevant rules from your
WORKSPACE or MODULE.bazel file:
bazel_dep(name = "bazelrc-preset.bzl", version = "1.1.0")
bazel_dep(name = "toolchains_protoc", version = "0.4.3")

Language(s) and/or frameworks involved: /

How to reproduce

# MODULE.bazel
bazel_dep(name = "bazelrc-preset.bzl", version = "1.1.0")
bazel_dep(name = "toolchains_protoc", version = "0.4.3")
git_override(
    module_name = "toolchains_protoc",
    commit = "4ef6589ef740f70ef34f8b34474ebb36933b8803",
    remote = "https://github.com/aspect-build/toolchains_protoc",
)

# BUILD.bazel
load("@bazelrc-preset.bzl", "bazelrc_preset")
load("@toolchains_protoc//protoc:flags.bzl", "PROTOC_TOOLCHAIN_FLAGS")

bazelrc_preset(
    name = "preset",
    extra_presets = PROTOC_TOOLCHAIN_FLAGS,
)

Any other information?

No response

[mislavmandaricaxilis]

Issue was introduced in #84.

[alexeagle]

oops I just ran into this independently - FYI @hofbi

[hofbi]

Ups. I wanted to add https://github.com/bazel-contrib/bazelrc-preset.bzl/blob/26f5497a7991f7496f0e2faa64d779caa68cea58/tests/BUILD#L65-L69 to this repo once a new release of the presets is available on BCR to make sure this works as expected, but I think you were faster.

Because of #93 (comment), I don't think we can immediately solve. We could revert that PR and bring it back in a working state together with some tests once bazel-contrib/bazelrc-preset.bzl#72 is implemented.

Or as a super hacky workaround, we use common for one of the duplicated flag values and build, fetch, and query overrides for the other value. That would prevent running in the "duplicate command override error check", and only work in this case since we have 2 values.