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build: non-root toolchain registration loads go_toolchains and rules_py constraint packages on every command (upstream) #9203
Description
Part of #8912. Found while profiling analysis of //cli/process/... on linux_x86_64 (origin/main 5cea169).
Toolchain registration from non-root modules loads packages that the scope never uses. The largest package creation spans after @rules_dotnet//dotnet are:
| package | package creation (s, loaded machine) | registered by |
|---|---|---|
@@llvm+//toolchain |
0.72 | root (@llvm//toolchain:all) |
@@rules_go++go_sdk+go_toolchains// |
0.59 | rules_go (non-root) |
@@rules_py+//uv/private/constraints/platform |
0.51 | rules_py (non-root) |
@@rules_python+//python/config_settings |
0.17 | rules_python |
In the Starlark CPU profile, declare_bazel_toolchains (go_toolchains) is 0.12s and generate_macos (rules_py uv constraints) 0.12s. Non-root register_toolchains cannot be removed from the root module, so this needs upstream changes.
Where
- rules_go
go/private/sdk.bzl/go_toolchainsrepo, rules_pyuv/private/constraints/platform.
Fix
- File upstream issues on bazel-contrib/rules_go and aspect-build/rules_py asking for lighter registered-toolchain packages (fewer generated
config_settings, or registration that does not need these packages). - No change in rules_dx until upstream lands; then measure with two evidence pairs.
🤖 Generated with Claude Code
Activity
TrapsterDK commentedon Nov 7, 2026
Upstream issues filed: bazel-contrib/rules_go#4779 (
go_toolchainspackage) and aspect-build/rules_py#1675 (uv/private/constraints/platform). No rules_dx change until they land.🤖 Generated with Claude Code
https://claude.ai/code/session_01Xut2hzpb4qWNZKpDCrwUz7
github-actions commentedon Nov 7, 2026
This issue has the
blockedlabel but noBlocked on:line in its body. Add one naming the blocking issue (#N), a pull request URL, or the owner action. See CONTRIBUTING.md.TrapsterDK commentedon Nov 7, 2026
Round 9 result (#9203, PR #9303): the rules_go
root_sdks_onlypatch and the rules_pyplatform_flags_packagepatch. They do what they should, but Windows is much slower, so this is dropped. PR #9303 is closed.Scope
//cli/process/..., task=test, linux_x86_64 and windows_x86_64. All four runs started at the same time and all passed. Branch head 62ea925.setup-bazel + "Run evidence task" step (s)
Bazel elapsed for the evidence task (s)
What the patches do:
@rules_py+//uv/private/constraints/platform(0.79s) and@go_toolchains//(0.37s) is gone.Why windows is slower, from the p1 profiles (main vs branch):
compute main repo mappingtakes 5.1s vs 2.2s.linux clears the 2s bar, but windows_x86_64 is more than 2s slower on both measures, so the change does not meet the rule. #9203 stays blocked until rules_go#4779 and rules_py#1675 land upstream. The patches are still on branch
issue-9203-toolchain-patchesif someone wants to measure again.🤖 Generated with Claude Code
https://claude.ai/code/session_01Xut2hzpb4qWNZKpDCrwUz7