bzlmod: override_target_build_script and override_target_proc_macro are silent no-ops (override_targets key mismatch)

[zertosh]

The bzlmod module extension reconstructs override_targets from the four split override_target_* attributes using the keys "build_script" and "proc_macro":

https://github.com/bazelbuild/rules_rust/blob/main/crate_universe/extensions.bzl (search for override_target_build_script)

replacement = annotation_dict.pop("override_target_proc_macro")
if replacement:
    annotation_dict["override_targets"]["proc_macro"] = str(replacement)

replacement = annotation_dict.pop("override_target_build_script")
if replacement:
    annotation_dict["override_targets"]["build_script"] = str(replacement)

But rendering looks the rule up by its cargo-metadata Target.kind via override_target_key(), which returns "proc-macro" and "custom-build":

https://github.com/bazelbuild/rules_rust/blob/main/crate_universe/src/context/crate_context.rs (override_target_key)

pub(crate) fn override_target_key(&self) -> &'static str {
    match self {
        Self::Library(..) => "lib",
        Self::ProcMacro(..) => "proc-macro",
        Self::Binary(..) => "bin",
        Self::BuildScript(..) => "custom-build",
    }
}

"lib" and "bin" agree in both spellings, so those overrides work. "build_script" and "proc_macro" never match, so under bzlmod override_target_build_script and override_target_proc_macro are silently ignored: the generated BUILD keeps its own cargo_build_script instead of emitting the alias to the override label. No error or warning is produced.

The non-bzlmod crate.annotation(override_targets = ...) documents the kind-style vocabulary ("Keys can be proc-macro, custom-build, lib, bin" in crate_universe/private/crate.bzl), which is presumably why this went unnoticed: WORKSPACE users pass the dict directly with the correct keys.

Repro: annotate any crate that has a build script with override_target_build_script = "//some:target" under bzlmod, repin, and inspect the generated BUILD: it still contains the generated cargo_build_script rather than an alias to //some:target.

Fix: align the two keys in extensions.bzl with the documented vocabulary:

-                annotation_dict["override_targets"]["proc_macro"] = str(replacement)
+                annotation_dict["override_targets"]["proc-macro"] = str(replacement)
...
-                annotation_dict["override_targets"]["build_script"] = str(replacement)
+                annotation_dict["override_targets"]["custom-build"] = str(replacement)

We are running with exactly this two-line patch applied to 0.70.0 and override_target_build_script works as documented with it.