bazel: Build 5.0.0-pre.20211011.2 fails with "file is generated by these conflicting actions"

Description of the problem / feature request:

When using 5.0.0-pre.20211011.2, calling a rule with testonly=True fails with the following error (see repro):

bazel build //...                                                                                                           
Sandboxfs is activated
Running bazel with args: ['build', '//...']
ERROR: file 'repro/_objs/test/x.test.pic.o' is generated by these conflicting actions:
Label: //repro:test
RuleClass: cc_test rule
Configuration: eb5aa7e35a39550df811eb60154df7436a41dfb63084ca9e51c1a541bf5afff6, ee8d6eaa0d889f4c6823cf490fda5a6abbd816f2da1fb3ea369bdb12bcf6f68a
Mnemonic: CppCompile
Action key: 02da5c72aa15f35128a4e61749fbf1fbb8059850f350c190718a92f0c93c84fe
Progress message: Compiling repro/x.test.cpp
PrimaryInput: File:[/Users/dhavenstein/Desktop/bazel5repro[source]]repro/x.test.cpp
PrimaryOutput: File:[[<execution_root>]bazel-out/darwin-fastbuild/bin]repro/_objs/test/x.test.pic.o
Owner information: ConfiguredTargetKey{label=//repro:test, config=BuildConfigurationValue.Key[eb5aa7e35a39550df811eb60154df7436a41dfb63084ca9e51c1a541bf5afff6]}, ConfiguredTargetKey{label=//repro:test, config=BuildConfigurationValue.Key[ee8d6eaa0d889f4c6823cf490fda5a6abbd816f2da1fb3ea369bdb12bcf6f68a]}
MandatoryInputs: are equal
Outputs: are equal
ERROR: com.google.devtools.build.lib.skyframe.ArtifactConflictFinder$ConflictException: com.google.devtools.build.lib.actions.MutableActionGraph$ActionConflictException: for repro/_objs/test/x.test.pic.o, previous action: action 'Compiling repro/x.test.cpp', attempted action: action 'Compiling repro/x.test.cpp'

Feature requests: what underlying problem are you trying to solve with this feature?

Trying out new Bazel version on existing, large codebase

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

In an empty dir, create empty WORKSPACE file, and the following files:

cat .bazelversion
5.0.0-pre.20211011.2

cat repro/BUILD.bazel
load("@rules_cc//cc:defs.bzl", "cc_test")
load(":helpers.bzl", "dummy")
cc_test(
    name = "test",
    srcs = glob([
        "*.cpp",
        "*.hpp",
    ]),
)
dummy(name="d",binary=":test", testonly=True)

cat repro/helpers.bzl
def _dummy(ctx):
    return [DefaultInfo(files = depset(direct = []))]
dummy = rule(
    implementation = _dummy,
    attrs = {
      "binary" : attr.label(),
    }
)

cat repro/x.test.cpp
int main() {
   return 0;
}

What operating system are you running Bazel on?

MacOS BigSur

What’s the output of bazel info release?

release 5.0.0-pre.20211011.2

If bazel info release returns “development version” or “(@non-git)”, tell us how you built Bazel.

Downloaded from Releases page

What’s the output of git remote get-url origin ; git rev-parse master ; git rev-parse HEAD ?

Does not apply

Have you found anything relevant by searching the web?

No, found no similar issues reported

Any other information, logs, or outputs that you want to share?

You can reach out to me directly on Slack if I can help out with the repro