Toolchain auto config error on Windows: `name 'arch' is not defined`

[stephen-ryan-ansys]

With Bazel 8.4.2, I am trying to add Windows support to an existing Linux C++ project that uses gRPC v1.76.0 as a direct dependency, and therefore rules_swift v3.1.2 as a transitive dependency, and I am getting the Bazel error when compiling my project on Windows x86_64:

ERROR: C:/users/xxxx/_bazel_xxxx/ls3vyc3v/external/rules_swift++non_module_deps+build_bazel_rules_swift_local_config/BUILD:54:58: name 'arch' is not defined
ERROR: package contains errors: : name 'arch' is not defined

My code does not use rules_swift directly, nor do I have any Swift source files.

I see that in the file swift/internal/swift_autoconfiguration.bzl, in the configuration of the windows-swift-toolchain-x86_64, there is a line with target_compatible_with = APPLE_PLATFORMS_CONSTRAINTS[arch]. In other toolchain configs in the file, there seems to be a list comprehension where the arch variable is defined (e.g., for arch in APPLE_PLATFORMS_CONSTRAINTS.keys() ) that is missing for the Windows toolchain. There does not seem to be a suitable value for APPLE_PLATFORMS_CONSTRAINTS for Windows in the configs/platforms.bzl file in the apple_support repo, so I am not sure if this is the correct thing to do here.

I was able to work around the error for my project by adding the following patch file:

diff --git a/swift/internal/swift_autoconfiguration.bzl b/swift/internal/swift_autoconfiguration.bzl
index 46f1f37..27a9965 100644
--- a/swift/internal/swift_autoconfiguration.bzl
+++ b/swift/internal/swift_autoconfiguration.bzl
@@ -364,7 +364,7 @@ toolchain(
         "@platforms//os:windows",
         "@platforms//cpu:x86_64",
     ],
-    target_compatible_with = APPLE_PLATFORMS_CONSTRAINTS[arch],
+    target_compatible_with = [],
     toolchain = ":windows-toolchain",
     toolchain_type = "{toolchain_type}",
     visibility = ["//visibility:public"],

and then using a single_version_override:

single_version_override(
    module_name = "rules_swift",
    version = "3.1.2",
    patches = ["//:fix_missing_arch_definition.patch"],
    patch_strip = 1,
)

Since I am not using Swift directly, I am not quite sure what actually needs to be done here to fix the issue.

[keith]

thanks for the report! i think #1616 is the right fix for now