Fix flags presets (#96)

- Fixes https://github.com/aspect-build/toolchains_protoc/issues/85
- Closes https://github.com/aspect-build/toolchains_protoc/pull/93

MODULE.bazel

diff --git a/MODULE.bazel b/MODULE.bazel
index c98de63..ddaa68c 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -12,6 +12,7 @@
 
 bazel_dep(name = "aspect_bazel_lib", version = "2.8.1", dev_dependency = True)
 bazel_dep(name = "buildifier_prebuilt", version = "6.1.2", dev_dependency = True)
+bazel_dep(name = "bazelrc-preset.bzl", version = "1.2.0", dev_dependency = True)
 
 protoc = use_extension("@toolchains_protoc//protoc:extensions.bzl", "protoc")
 protoc.toolchain(

protoc/flags.bzl

diff --git a/protoc/flags.bzl b/protoc/flags.bzl
index 88bc01c..23eaed4 100644
--- a/protoc/flags.bzl
+++ b/protoc/flags.bzl
@@ -8,20 +8,26 @@
         That flag ALSO decouples how each built-in language rule (Java, Python, C++, etc.) locates the runtime.
         """,
     ),
-    "per_file_copt": struct(
-        default = "external/.*protobuf.*@--PROTOBUF_WAS_NOT_SUPPOSED_TO_BE_BUILT",
-        description = "Make sure protobuf is not built from source",
-    ),
-    "host_per_file_copt": struct(
-        default = "external/.*protobuf.*@--PROTOBUF_WAS_NOT_SUPPOSED_TO_BE_BUILT",
-        description = "Make sure protobuf is not built from source",
-    ),
-    "per_file_copt": struct(
-        default = "external/.*grpc.*@--GRPC_WAS_NOT_SUPPOSED_TO_BE_BUILT",
-        description = "Make sure grpc is not built from source",
-    ),
-    "host_per_file_copt": struct(
-        default = "external/.*grpc.*@--GRPC_WAS_NOT_SUPPOSED_TO_BE_BUILT",
-        description = "Make sure grpc is not built from source",
-    ),
+    "per_file_copt": [
+        struct(
+            default = "external/.*protobuf.*@--PROTOBUF_WAS_NOT_SUPPOSED_TO_BE_BUILT",
+            description = "Make sure protobuf is not built from source",
+        ),
+        struct(
+            default = "external/.*grpc.*@--GRPC_WAS_NOT_SUPPOSED_TO_BE_BUILT",
+            description = "Make sure grpc is not built from source",
+            allow_repeated = True,
+        ),
+    ],
+    "host_per_file_copt": [
+        struct(
+            default = "external/.*protobuf.*@--PROTOBUF_WAS_NOT_SUPPOSED_TO_BE_BUILT",
+            description = "Make sure protobuf is not built from source",
+        ),
+        struct(
+            default = "external/.*grpc.*@--GRPC_WAS_NOT_SUPPOSED_TO_BE_BUILT",
+            description = "Make sure grpc is not built from source",
+            allow_repeated = True,
+        ),
+    ],
 }

tests/BUILD.bazel

diff --git a/tests/BUILD.bazel b/tests/BUILD.bazel
new file mode 100644
index 0000000..09a9d15
--- /dev/null
+++ b/tests/BUILD.bazel
@@ -0,0 +1,7 @@
+load("@bazelrc-preset.bzl", "bazelrc_preset_test")
+load("//protoc:flags.bzl", "PROTOC_TOOLCHAIN_FLAGS")
+
+bazelrc_preset_test(
+    name = "test_protoc_toolchain_flags",
+    extra_presets = PROTOC_TOOLCHAIN_FLAGS,
+)