Stdlib is built 4 times

[linzhp]

For almost all go_library targets, rules_go builds 4 copies for stdlib: fastbuild vs opt (for tools), and cgo on vs. off. This happens to go_library targets that don't depend on cgo, e.g., @bazel_gazelle//cmd/gazelle:gazelle_lib. Also, I don't see a reason why we need to build stdlib for tools with both cgo on and off.

What version of rules_go are you using?

0.39.0

What version of gazelle are you using?

master branch

What version of Bazel are you using?

6.1.1

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

Yes

What operating system and processor architecture are you using?

macOS arm64

Any other potentially useful information about your toolchain?

What did you do?

Check out Gazelle repo and run bazel aquery 'mnemonic(GoStdlib, deps(//cmd/gazelle:gazelle_lib))'

What did you expect to see?

There are only 1-2 GoStdlib actions

What did you see instead?

4 GoStdlib actions, for fastbuild vs opt, and cgo on and off

[fmeum]

We can force any of these settings. Since only a tiny fraction of the stdlib is C, maybe we always want to build it with opt rather than fastbuild?

[linzhp]

yeah, we can force "opt" that except in dbg mode, where it may remove some symbols needed for debug.

What I wonder is why there are both cgo on and off configurations. Instead of forcing either cgo on or off, I think we should remove the additional transition.

[linzhp]

I just apply the patch below to force opt, but it doesn't stop bazel from build stdlib for 4 times though. There are other difference between "for tool" and regular builds:

• is exec configuration: true|false
• platform_suffix: exec-2B5CBBC6|null
• copt: [-g0] vs empty
• cxxopt: [-g0] vs empty
• strip: always|sometimes

diff --git a/go/private/rules/transition.bzl b/go/private/rules/transition.bzl
index 2883b982..c27bf1a3 100644
--- a/go/private/rules/transition.bzl
+++ b/go/private/rules/transition.bzl
@@ -272,12 +272,13 @@ def _go_stdlib_transition_impl(settings, _attr):
             settings[label] = value
     settings["//go/config:tags"] = [t for t in settings["//go/config:tags"] if t in _TAG_AFFECTS_STDLIB]
     settings["//go/private:bootstrap_nogo"] = False
+    settings["//command_line_option:compilation_mode"] = "opt"
     return settings
 
 go_stdlib_transition = transition(
     implementation = _go_stdlib_transition_impl,
-    inputs = _reset_transition_keys,
-    outputs = _reset_transition_keys,
+    inputs = _reset_transition_keys + ["//command_line_option:compilation_mode"],
+    outputs = _reset_transition_keys + ["//command_line_option:compilation_mode"],
 )

[fmeum]

Yes, for these differences getting rid of a separate exec build will be difficult without new Bazel features. My work on these features is progressing, but it will take more time before this can be used for rules_go.

I think that the best we can do for now is to get the count down to a single exec build of the stdlib.