bazel 8 + bzlmod and child modules resolution

[mgenov]

VS Code Bazel extension does not respect root toolchains / .bazelrc in multi-module bzlmod monorepos

Problem description

When using Bazel with bzlmod in a monorepo, each app or library is its own Bazel module (apps/appX/MODULE.bazel, modules/shared/MODULE.bazel, etc.).
The monorepo root also has a MODULE.bazel where all toolchains and the main .bazelrc are centralized.

Expected behavior

• The VS Code Bazel extension should treat the monorepo root as the single Bazel workspace root.
• All build/test/run actions (CodeLens, Test UI, right-click commands) should run Bazel from the repo root, so that:
  • the root .bazelrc is applied,
  • toolchains registered in the root MODULE.bazel are available,
  • cross-module deps work (e.g. @other_module//path:target),
  • labels are consistent (//modules/transport/...:foo) rather than relative to a leaf folder.

Actual behavior

• The extension currently picks the nearest MODULE.bazel or WORKSPACE file to the open file and treats that as the workspace root.
• If I open apps/app-go/src/main.go and run “Bazel: Build Target”, the extension runs Bazel in apps/app-go/.
  • Labels resolve relative to that folder (e.g. //proto/... instead of //modules/transport/proto/...).
  • Toolchains defined in the root MODULE.bazel are not registered.
  • The root .bazelrc is ignored.
• This makes cross-module builds/tests fail when triggered from VS Code, even though they succeed when run manually from the monorepo root.

Why this matters

• With bzlmod, the recommended monorepo structure is multiple modules with a root module that wires toolchains and overrides.
• IDE users (VS Code) expect Bazel commands to “just work” without having to cd into the root manually.
• As of today, developers must either:
  • open only the repo root in VS Code (which breaks per-app workspace setups), or
  • duplicate toolchain registration and .bazelrc in every leaf module (which defeats the purpose of centralization).

Steps to reproduce

1. Create a monorepo with:
   MODULE.bazel # root, toolchains + local_path_override
   apps/app-go/MODULE.bazel # leaf module
2. Open apps/app-go/ in VS Code.
3. Run “Bazel: Build Target” on a file.
4. Observe: Bazel runs from apps/app-go/ instead of the monorepo root, toolchains are missing, and labels resolve incorrectly.

Desired solution

• Provide a VS Code setting to force Bazel commands to run from the top-level workspace root (not the nearest).
• Example: "bazel.workspaceRootMode": "repo-root-only".
• Or auto-detect the “primary” root (the one containing .git/ and MODULE.bazel) instead of treating every nested module as independent.
• At minimum, document that opening a leaf module as the VS Code workspace will break root toolchains/config.

Environment

• Bazel: 8.x with bzlmod enabled
• VS Code: latest
• Extension: vscode-bazel latest
• OS: Any

[cameron-martin]

Related:

• https://bazelbuild.slack.com/archives/C014RARENH0/p1702897315236089?thread_ts=1702897315.236089&cid=C014RARENH0
• Extension adds MODULE.bazel and MODULE.bazel.lock in local repositories #383