Bazel produces an over-aggressive instrumentation_filter

[linzhp]

Description of the problem / feature request:

If one of the targets passed to bazel coverage is one level below the root of the repo (e.g., //foo in bazel coverage //foo:go_default_test //bar/baz:go_default_test), Bazel would infer the --instrumentation_filter to be //. This is undesirable, because it will instrument the test coverage for the whole transitive dependency of both //foo:go_default_test and //bar:go_default_test, including third-party libraries.

When we run bazel coverage //foo:go_default_test //bar/baz:go_default_test, we are only interested in the test coverage of those two packages, so only those two packages need to be instrumented. When we run bazel test //foo:go_default_test //bar/baz:go_default_test and then bazel coverage //foo:go_default_test //bar/baz:go_default_test, we would expect only //foo:go_default_test and //bar/baz:go_default_test are rebuilt because of the extra instrumentation code. Their dependencies should not need rebuild. Due to the over-instrumentation, the whole transitive graph is rebuilt.

Even for targets deep below, the behavior is not desirable either. For example, bazel coverage //foo/bar:go_default_test //foo/baz:go_default_test would have --instrumentation_filter=//foo[:/] by default. As a result all transitive dependencies under //foo/ will have to rebuild between bazel coverage and bazel test, even when only //foo/bar and //foo/baz need to be instrumented for test coverage.

I think Bazel should either turn off such optimization entirely, or only optimize for certain wildcard patterns such as //foo/..., such bazel test and bazel coverage can share cache except the tested targets.

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

bazel coverage --announce_rc //foo:go_default_test //bar/baz:go_default_test

What operating system are you running Bazel on?

macOS

What's the output of bazel info release?

release 3.4.1-homebrew

Have you found anything relevant by searching the web?

optimizeFilterSet transformed packageFilters from {"foo", "bar/baz"} to {""}, which becomes //[/:] later. Then this line further transformed it into //.