Test BCR example in minimum bazel (#2613)

.bazelci/presubmit.yml

@@ -1,4 +1,5 @@
 ---
+minimum_bazel_version: &minimum_bazel_version "6.3.0"
 aspects_flags: &aspects_flags
   - "--config=rustfmt"
   - "--config=clippy"
@@ -232,7 +233,7 @@ tasks:
   ubuntu1804:
     name: "Min Bazel Version"
     # If updating the minimum bazel version, please also update /docs/index.md
-    bazel: "6.3.0"
+    bazel: *minimum_bazel_version
     platform: ubuntu1804
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
@@ -240,7 +241,7 @@ tasks:
     post_shell_commands: *coverage_validation_post_shell_commands
   ubuntu1804_with_aspects:
     name: "Min Bazel Version With Aspects"
-    bazel: "6.3.0"
+    bazel: *minimum_bazel_version
     platform: ubuntu1804
     build_targets: *default_linux_targets
     test_targets: *default_linux_targets
@@ -668,6 +669,19 @@ tasks:
       - "@rules_rust//tools/rust_analyzer:gen_rust_project"
     test_targets:
       - "//..."
+  ubuntu2004_bzlmod_minimum_bazel_bcr:
+    name: bzlmod BCR presubmit minimal bazel
+    bazel: *minimum_bazel_version
+    platform: ubuntu2004
+    working_directory: examples/bzlmod/hello_world
+    test_flags: *bzlmod_flags
+    shell_commands:
+      - "rm MODULE.bazel.lock"
+    run_targets:
+      - "//third-party:vendor"
+      - "@rules_rust//tools/rust_analyzer:gen_rust_project"
+    test_targets:
+      - "//..."
   macos_bzlmod_bcr:
     name: bzlmod BCR presubmit
     platform: macos

.bcr/presubmit.yml

@@ -9,6 +9,9 @@ bcr_test_module:
       name: "Run test module"
       platform: ${{ platform }}
       bazel: ${{ bazel }}
+      # Remove the lockfile because we generate on Bazel 7, but test on Bazel 6 which may not be able to parse a future-generated lockfile.
+      shell_commands:
+        - "rm MODULE.bazel.lock"
       run_targets:
         - "//third-party:vendor"
         - "@rules_rust//tools/rust_analyzer:gen_rust_project"
@@ -25,6 +28,9 @@ bcr_test_module_windows:
       name: "Run test module"
       platform: windows
       bazel: ${{ bazel }}
+      # Remove the lockfile because we generate on Bazel 7, but test on Bazel 6 which may not be able to parse a future-generated lockfile.
+      shell_commands:
+        - "rm MODULE.bazel.lock"
       run_targets:
         - "//third-party:vendor"
       build_targets:

rust/extensions.bzl

@@ -171,16 +171,20 @@ def _rust_host_tools_impl(module_ctx):
         **host_tools
     )
 
+    metadata_kwargs = {}
     if bazel_features.external_deps.extension_metadata_has_reproducible:
-        return module_ctx.extension_metadata(reproducible = True)
-    else:
-        return None
+        metadata_kwargs["reproducible"] = True
+    return module_ctx.extension_metadata(**metadata_kwargs)
+
+_conditional_rust_host_tools_args = {
+    "arch_dependent": True,
+    "os_dependent": True,
+} if bazel_features.external_deps.module_extension_has_os_arch_dependent else {}
 
 rust_host_tools = module_extension(
     implementation = _rust_host_tools_impl,
     tag_classes = {
         "host_tools": _RUST_HOST_TOOLS_TAG,
     },
-    os_dependent = True,
-    arch_dependent = True,
+    **_conditional_rust_host_tools_args
 )