Honor the feature flag to enable generation from raw proto sources.

The DescriptorSets ProtoInfo exposes don't have source info, so the generated
source don't have the comment. bazelbuild/bazel#9337
is open to attempt to get that, but this provides a way to opt into forcing it.

This does come with a minor risk for cross repository and/or generated proto
files where the protoc command line might not be crafted correctly, so it
remains opt in.

This is followup to the previous change that did this for swift_proto_library.

NOTE: The current version of swift grpc depended on doesn't include comments,
but the NIO version appears to support it for methods, so landing the work
in advance of things updating to that version.

RELNOTES: None
PiperOrigin-RevId: 330729710

swift/internal/swift_grpc_library.bzl

@@ -23,6 +23,7 @@ load(
 load(
     ":feature_names.bzl",
     "SWIFT_FEATURE_ENABLE_TESTING",
+    "SWIFT_FEATURE_GENERATE_FROM_RAW_PROTO_FILES",
     "SWIFT_FEATURE_NO_GENERATED_HEADER",
 )
 load(":linking.bzl", "register_libraries_to_link")
@@ -49,6 +50,7 @@ def _register_grpcswift_generate_action(
         proto_source_root,
         transitive_descriptor_sets,
         module_mapping_file,
+        generate_from_proto_sources,
         mkdir_and_run,
         protoc_executable,
         protoc_plugin_executable,
@@ -69,6 +71,10 @@ def _register_grpcswift_generate_action(
             target being analyzed. May be `None`, in which case no module
             mapping will be passed (the case for leaf nodes in the dependency
             graph).
+        generate_from_proto_sources: True/False for is generation should happen
+            from proto source file vs just via the DescriptorSets. The Sets
+            don't have source info, so the generated sources won't have
+            comments (https://github.com/bazelbuild/bazel/issues/9337).
         mkdir_and_run: The `File` representing the `mkdir_and_run` executable.
         protoc_executable: The `File` representing the `protoc` executable.
         protoc_plugin_executable: The `File` representing the `protoc` plugin
@@ -135,14 +141,34 @@ def _register_grpcswift_generate_action(
             module_mapping_file,
             format = "--swiftgrpc_opt=ProtoPathModuleMappings=%s",
         )
-    protoc_args.add("--descriptor_set_in")
-    protoc_args.add_joined(transitive_descriptor_sets, join_with = ":")
+
+    protoc_args.add_joined(
+        transitive_descriptor_sets,
+        join_with = ":",
+        format_joined = "--descriptor_set_in=%s",
+        omit_if_empty = True,
+    )
+
+    if generate_from_proto_sources:
+        # ProtoCompileActionBuilder.java's XPAND_TRANSITIVE_PROTO_PATH_FLAGS
+        # leaves this off also.
+        if proto_source_root != ".":
+            protoc_args.add(proto_source_root, format = "--proto_path=%s")
+
+        # Follow ProtoCompileActionBuilder.java's
+        # ExpandImportArgsFn::expandToCommandLine() logic and provide a mapping
+        # for each file to the proto path.
+        for f in direct_srcs:
+            protoc_args.add("-I%s=%s" % (proto_import_path(f, proto_source_root), f.path))
+
     protoc_args.add_all([
         proto_import_path(f, proto_source_root)
         for f in direct_srcs
     ])
 
     additional_command_inputs = []
+    if generate_from_proto_sources:
+        additional_command_inputs.extend(direct_srcs)
     if module_mapping_file:
         additional_command_inputs.append(module_mapping_file)
 
@@ -181,16 +207,41 @@ def _swift_grpc_library_impl(ctx):
 
     swift_toolchain = ctx.attr._toolchain[SwiftToolchainInfo]
 
-    # Direct sources are passed as arguments to protoc to generate *only* the
-    # files in this target, but we need to pass the transitive sources as inputs
-    # to the generating action so that all the dependent files are available for
-    # protoc to parse.
-    # Instead of providing all those files and opening/reading them, we use
-    # protoc's support for reading descriptor sets to resolve things.
-    direct_srcs = ctx.attr.srcs[0][ProtoInfo].direct_sources
-    transitive_descriptor_sets = (
-        ctx.attr.srcs[0][ProtoInfo].transitive_descriptor_sets
+    unsupported_features = ctx.disabled_features
+    if ctx.attr.flavor != "client_stubs":
+        unsupported_features.append(SWIFT_FEATURE_ENABLE_TESTING)
+
+    feature_configuration = swift_common.configure_features(
+        ctx = ctx,
+        requested_features = ctx.features + [SWIFT_FEATURE_NO_GENERATED_HEADER],
+        swift_toolchain = swift_toolchain,
+        unsupported_features = unsupported_features,
+    )
+
+    generate_from_proto_sources = swift_common.is_enabled(
+        feature_configuration = feature_configuration,
+        feature_name = SWIFT_FEATURE_GENERATE_FROM_RAW_PROTO_FILES,
     )
+
+    srcs_proto_info = ctx.attr.srcs[0][ProtoInfo]
+
+    # Only the files for direct sources should be generated, but the
+    # transitive descriptor sets are still need to be able to parse/load
+    # those descriptors.
+    direct_srcs = srcs_proto_info.direct_sources
+    if generate_from_proto_sources:
+        # Take the transitive descriptor sets from the proto_library deps,
+        # so the direct sources won't be in any descriptor sets to reduce
+        # the input to the action (and what protoc has to parse).
+        direct_descriptor_set = srcs_proto_info.direct_descriptor_set
+        transitive_descriptor_sets = depset(direct = [
+            x
+            for x in srcs_proto_info.transitive_descriptor_sets.to_list()
+            if x != direct_descriptor_set
+        ])
+    else:
+        transitive_descriptor_sets = srcs_proto_info.transitive_descriptor_sets
+
     deps = ctx.attr.deps
 
     minimal_module_mappings = deps[0][SwiftProtoInfo].module_mappings
@@ -209,9 +260,10 @@ def _swift_grpc_library_impl(ctx):
         ctx.label,
         ctx.actions,
         direct_srcs,
-        ctx.attr.srcs[0][ProtoInfo].proto_source_root,
+        srcs_proto_info.proto_source_root,
         transitive_descriptor_sets,
         transitive_module_mapping_file,
+        generate_from_proto_sources,
         ctx.executable._mkdir_and_run,
         ctx.executable._protoc,
         ctx.executable._protoc_gen_swiftgrpc,
@@ -225,17 +277,6 @@ def _swift_grpc_library_impl(ctx):
     # action.
     compile_deps = deps + ctx.attr._proto_support
 
-    unsupported_features = ctx.disabled_features
-    if ctx.attr.flavor != "client_stubs":
-        unsupported_features.append(SWIFT_FEATURE_ENABLE_TESTING)
-
-    feature_configuration = swift_common.configure_features(
-        ctx = ctx,
-        requested_features = ctx.features + [SWIFT_FEATURE_NO_GENERATED_HEADER],
-        swift_toolchain = swift_toolchain,
-        unsupported_features = unsupported_features,
-    )
-
     module_name = swift_common.derive_module_name(ctx.label)
 
     compilation_outputs = swift_common.compile(