Non-go deps built twice with gotags

[ripatel-fd]

What version of rules_go are you using?

v0.38.0

What version of Bazel are you using?

6.0.0

Does this issue reproduce with the latest releases of all the above?

Yes

What operating system and processor architecture are you using?

amd64 RHEL 8

Any other potentially useful information about your toolchain?

GCC 8.5.0

What did you do?

Run https://github.com/terorie/rules_go_bug

What did you expect to see?

Dep tree as follows go_test -> go_library -> cc_library.

The go_test has one string in gotags set.

When I bazel build the go_test and go_library, I expect cc_library to be only built once.

What did you see instead?

cc_library is built twice.

Related

• Trim transitioned Go settings on non-Go dependencies #3108 (The PR that was originally supported to fix it)
• Transition on edges not self #3116 (suspected regression)

[ripatel-fd]

cc @fmeum @illicitonion I hope this bug report helps. I would be happy to fix it myself but I lack understanding of how transitions work in rules_go

[fmeum]

I don't think this is a regression. With v0.33.0, which doesn't contain b0b7d85, running bazel build --nobuild //... && bazel cquery //clib:clib (twice, not sure why that's necessary), you can see that the C library is built twice.

The fix is to use a recent version of rules_go, Bazel 6, and the flag --experimental_output_directory_naming_scheme=diff_against_baseline. I am working on getting this enabled by default in Bazel 6.1.

[ripatel-fd]

Thanks a lot 🙏 So is this a problem with Bazel, not rules_go?

[fmeum]

Well, let's call it a missing optimization. But yes, short of ditching transitions entirely or using quite complex and fragile tricks, there is nothing rules_go can do about this by itself.

[fmeum]

Will be fixed by default in Bazel 7 and can be fixed by setting --experimental_output_directory_naming_scheme=diff_against_dynamic_baseline in Bazel 6.4.0.