nobzlmod behaves very differently than bzlmod

[mvukov]

Related to #2650 , now I made small minimum example in a separate repo: https://github.com/mvukov/rules_rust_bzlmod_vs_nobzlmod.

bzlmod works as expected:

cd rules_rust_bzlmod
bazel run //:rust_main
# add a comment in BUILD.bazel (just edit it)
bazel run //:rust_main # nothing happens as expected

nobzlmod behaves funky:

cd rules_rust_nobzlmod
REPIN=1 bazel run //:rust_main
# add a comment in BUILD.bazel (just edit it)
bazel run //:rust_main

and now the drama starts, the first thing I see is:

Another command (pid=3841104) is running. Waiting for it to complete on the server (server_pid=3804232)...

and after a couple of seconds:

Computing main repo mapping: 
    Fetching repository @@crates; starting
    Fetching repository @@rust_linux_x86_64__x86_64-unknown-linux-gnu__stable_tools; starting

... where this step also takes some seconds to complete.

My machine runs on Ubuntu 22.04, Bazel version is 7.1.2.

I'd like to help, but honestly I don't know where to start.

[matts1]

@Wyverald might know more.

You might want to try USE_BAZEL_VERSION=6.5.0 (with bazelisk). Bazel 7.0 flipped bzlmod on by default, so it could be related to that.

[illicitonion]

I don't reproduce this. My guess from the "Another command is running" part is that you have rust analyzer or something running in the repo, and that it's running a bazel command with a different configuration (e.g. different env vars set) which is thrashing your in-memory caches?

[otiv-milan]

I thought about that. The steps I listed above are from a single terminal session, no e.g. vscode terminal. FWIW, my installation doesn't have rust-analyzer. Digging deeper...

[mvukov]

OK, this issue seems to be related to vscode Bazel extension. I just removed it and I don't observe the behavior above. It's not a big issue for me as I used the extension only for syntax highlighting anyway. On the other hand, this is very strange, as this behavior only happens with rules_rust.