Make rules_swift work with virtual import directories.

swift/internal/proto_gen_utils.bzl

@@ -15,9 +15,9 @@
 """Utility functions shared by rules/aspects that generate sources from .proto files."""
 
 load("@bazel_skylib//lib:paths.bzl", "paths")
-load(":utils.bzl", "workspace_relative_path")
+load(":utils.bzl", "proto_import_path")
 
-def declare_generated_files(name, actions, extension_fragment, proto_srcs):
+def declare_generated_files(name, actions, extension_fragment, proto_source_root, proto_srcs):
     """Declares generated `.swift` files that correspond to a list of `.proto` files.
 
     Args:
@@ -26,18 +26,19 @@ def declare_generated_files(name, actions, extension_fragment, proto_srcs):
         extension_fragment: An extension fragment that precedes `.swift` on the end of the
             generated files. In other words, the file `foo.proto` will generate a file named
             `foo.{extension_fragment}.swift`.
+        proto_source_root: the source root of the `.proto` files in `proto_srcs`.
         proto_srcs: A list of `.proto` files.
 
     Returns:
         A list of files that map one-to-one to `proto_srcs` but with `.{extension_fragment}.swift`
         extensions instead of `.proto`.
     """
     return [
-        actions.declare_file(_generated_file_path(name, extension_fragment, f))
+        actions.declare_file(_generated_file_path(name, extension_fragment, proto_source_root, f))
         for f in proto_srcs
     ]
 
-def extract_generated_dir_path(name, extension_fragment, generated_files):
+def extract_generated_dir_path(name, extension_fragment, proto_source_root, generated_files):
     """Extracts the full path to the directory where `.swift` files are generated.
 
     This dance is required because we cannot get the full (repository-relative) path to the
@@ -52,6 +53,8 @@ def extract_generated_dir_path(name, extension_fragment, generated_files):
         extension_fragment: An extension fragment that precedes `.swift` on the end of the
             generated files. In other words, the file `foo.proto` will generate a file named
             `foo.{extension_fragment}.swift`.
+        proto_source_root: the source root for the `.proto` files `generated_files` are generated
+            from.
         generated_files: A list of generated `.swift` files, one of which will be used to extract
             the directory path.
 
@@ -62,7 +65,7 @@ def extract_generated_dir_path(name, extension_fragment, generated_files):
         return None
 
     first_path = generated_files[0].path
-    dir_name = _generated_file_path(name, extension_fragment)
+    dir_name = _generated_file_path(name, extension_fragment, proto_source_root)
     offset = first_path.find(dir_name)
     return first_path[:offset + len(dir_name)]
 
@@ -88,7 +91,7 @@ def register_module_mapping_write_action(name, actions, module_mappings):
 
     return mapping_file
 
-def _generated_file_path(name, extension_fragment, proto_file = None):
+def _generated_file_path(name, extension_fragment, proto_source_root, proto_file = None):
     """Returns the short path of a generated `.swift` file corresponding to a `.proto` file.
 
     The returned workspace-relative path should be used to declare output files so that they are
@@ -102,6 +105,7 @@ def _generated_file_path(name, extension_fragment, proto_file = None):
         extension_fragment: An extension fragment that precedes `.swift` on the end of the
             generated files. In other words, the file `foo.proto` will generate a file named
             `foo.{extension_fragment}.swift`.
+        proto_source_root: The source root for the `.proto` file.
         proto_file: The `.proto` file whose generated `.swift` path should be computed.
 
     Returns:
@@ -115,7 +119,7 @@ def _generated_file_path(name, extension_fragment, proto_file = None):
     )
     if proto_file:
         generated_file_path = paths.replace_extension(
-            workspace_relative_path(proto_file),
+            proto_import_path(proto_file, proto_source_root),
             ".{}.swift".format(extension_fragment),
         )
         return paths.join(dir_path, generated_file_path)

swift/internal/swift_grpc_library.bzl

@@ -26,12 +26,19 @@ load(
     "register_module_mapping_write_action",
 )
 load(":providers.bzl", "SwiftInfo", "SwiftProtoInfo", "SwiftToolchainInfo")
-load(":utils.bzl", "compact", "create_cc_info", "get_providers", "workspace_relative_path")
+load(
+    ":utils.bzl",
+    "compact",
+    "create_cc_info",
+    "get_providers",
+    "proto_import_path",
+)
 
 def _register_grpcswift_generate_action(
         label,
         actions,
         direct_srcs,
+        proto_source_root,
         transitive_descriptor_sets,
         module_mapping_file,
         mkdir_and_run,
@@ -46,6 +53,7 @@ def _register_grpcswift_generate_action(
         actions: The context's actions object.
         direct_srcs: The direct `.proto` sources belonging to the target being analyzed, which
             will be passed to `protoc`.
+        proto_source_root: the source root for `direct_srcs`.
         transitive_descriptor_sets: The transitive `DescriptorSet`s from the `proto_library` being
             analyzed.
         module_mapping_file: The `File` containing the mapping between `.proto` files and Swift
@@ -61,8 +69,19 @@ def _register_grpcswift_generate_action(
     Returns:
         A list of generated `.grpc.swift` files corresponding to the `.proto` sources.
     """
-    generated_files = declare_generated_files(label.name, actions, "grpc", direct_srcs)
-    generated_dir_path = extract_generated_dir_path(label.name, "grpc", generated_files)
+    generated_files = declare_generated_files(
+        label.name,
+        actions,
+        "grpc",
+        proto_source_root,
+        direct_srcs,
+    )
+    generated_dir_path = extract_generated_dir_path(
+        label.name,
+        "grpc",
+        proto_source_root,
+        generated_files,
+    )
 
     mkdir_args = actions.args()
     mkdir_args.add(generated_dir_path)
@@ -107,7 +126,7 @@ def _register_grpcswift_generate_action(
         )
     protoc_args.add("--descriptor_set_in")
     protoc_args.add_joined(transitive_descriptor_sets, join_with = ":")
-    protoc_args.add_all([workspace_relative_path(f) for f in direct_srcs])
+    protoc_args.add_all([proto_import_path(f, proto_source_root) for f in direct_srcs])
 
     additional_command_inputs = []
     if module_mapping_file:
@@ -168,6 +187,7 @@ def _swift_grpc_library_impl(ctx):
         ctx.label,
         ctx.actions,
         direct_srcs,
+        ctx.attr.srcs[0][ProtoInfo].proto_source_root,
         transitive_descriptor_sets,
         transitive_module_mapping_file,
         ctx.executable._mkdir_and_run,

swift/internal/swift_protoc_gen_aspect.bzl

@@ -25,7 +25,13 @@ load(
     "register_module_mapping_write_action",
 )
 load(":providers.bzl", "SwiftInfo", "SwiftProtoInfo", "SwiftToolchainInfo")
-load(":utils.bzl", "compact", "create_cc_info", "get_providers", "workspace_relative_path")
+load(
+    ":utils.bzl",
+    "compact",
+    "create_cc_info",
+    "get_providers",
+    "proto_import_path",
+)
 
 # The paths of proto files bundled with the runtime. This is mainly the well
 # known type protos, but also includes descriptor.proto to make generation of
@@ -67,11 +73,12 @@ This provider is an implementation detail not meant to be used by clients.
     },
 )
 
-def _filter_out_well_known_types(srcs):
+def _filter_out_well_known_types(srcs, proto_source_root):
     """Returns the given list of files, excluding any well-known type protos.
 
     Args:
       srcs: A list of `.proto` files.
+      proto_source_root: the source root where the `.proto` files are.
 
     Returns:
       The given list of files with any well-known type protos (those living under
@@ -80,13 +87,14 @@ def _filter_out_well_known_types(srcs):
     return [
         f
         for f in srcs
-        if workspace_relative_path(f) not in _RUNTIME_BUNDLED_PROTO_FILES
+        if proto_import_path(f, proto_source_root) not in _RUNTIME_BUNDLED_PROTO_FILES
     ]
 
 def _register_pbswift_generate_action(
         label,
         actions,
         direct_srcs,
+        proto_source_root,
         transitive_descriptor_sets,
         module_mapping_file,
         mkdir_and_run,
@@ -99,6 +107,7 @@ def _register_pbswift_generate_action(
         actions: The context's actions object.
         direct_srcs: The direct `.proto` sources belonging to the target being analyzed, which
             will be passed to `protoc-gen-swift`.
+        proto_source_root: the source root where the `.proto` files are.
         transitive_descriptor_sets: The transitive `DescriptorSet`s from the `proto_library` being
             analyzed.
         module_mapping_file: The `File` containing the mapping between `.proto` files and Swift
@@ -112,8 +121,19 @@ def _register_pbswift_generate_action(
     Returns:
         A list of generated `.pb.swift` files corresponding to the `.proto` sources.
     """
-    generated_files = declare_generated_files(label.name, actions, "pb", direct_srcs)
-    generated_dir_path = extract_generated_dir_path(label.name, "pb", generated_files)
+    generated_files = declare_generated_files(
+        label.name,
+        actions,
+        "pb",
+        proto_source_root,
+        direct_srcs,
+    )
+    generated_dir_path = extract_generated_dir_path(
+        label.name,
+        "pb",
+        proto_source_root,
+        generated_files,
+    )
 
     mkdir_args = actions.args()
     mkdir_args.add(generated_dir_path)
@@ -142,7 +162,9 @@ def _register_pbswift_generate_action(
         )
     protoc_args.add("--descriptor_set_in")
     protoc_args.add_joined(transitive_descriptor_sets, join_with = ":")
-    protoc_args.add_all([workspace_relative_path(f) for f in direct_srcs])
+    protoc_args.add_all(
+        [proto_import_path(f, proto_source_root) for f in direct_srcs],
+    )
 
     additional_command_inputs = []
     if module_mapping_file:
@@ -195,12 +217,13 @@ def _build_swift_proto_info_provider(
         ),
     )
 
-def _build_module_mapping_from_srcs(target, proto_srcs):
+def _build_module_mapping_from_srcs(target, proto_srcs, proto_source_root):
     """Returns the sequence of module mapping `struct`s for the given sources.
 
     Args:
       target: The `proto_library` target whose module mapping is being rendered.
       proto_srcs: The `.proto` files that belong to the target.
+      proto_source_root: The source root for `proto_srcs`.
 
     Returns:
       A string containing the module mapping for the target in protobuf text
@@ -216,7 +239,7 @@ def _build_module_mapping_from_srcs(target, proto_srcs):
     # update to protoc-gen-swift?
     return struct(
         module_name = swift_common.derive_module_name(target.label),
-        proto_file_paths = [workspace_relative_path(f) for f in proto_srcs],
+        proto_file_paths = [proto_import_path(f, proto_source_root) for f in proto_srcs],
     )
 
 def _gather_transitive_module_mappings(targets):
@@ -250,7 +273,10 @@ def _gather_transitive_module_mappings(targets):
 def _swift_protoc_gen_aspect_impl(target, aspect_ctx):
     swift_toolchain = aspect_ctx.attr._toolchain[SwiftToolchainInfo]
 
-    direct_srcs = _filter_out_well_known_types(target[ProtoInfo].direct_sources)
+    direct_srcs = _filter_out_well_known_types(
+        target[ProtoInfo].direct_sources,
+        target[ProtoInfo].proto_source_root,
+    )
 
     # 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
@@ -264,7 +290,11 @@ def _swift_protoc_gen_aspect_impl(target, aspect_ctx):
     minimal_module_mappings = []
     if direct_srcs:
         minimal_module_mappings.append(
-            _build_module_mapping_from_srcs(target, direct_srcs),
+            _build_module_mapping_from_srcs(
+                target,
+                direct_srcs,
+                target[ProtoInfo].proto_source_root,
+            ),
         )
     if proto_deps:
         minimal_module_mappings.extend(_gather_transitive_module_mappings(proto_deps))
@@ -283,6 +313,7 @@ def _swift_protoc_gen_aspect_impl(target, aspect_ctx):
             target.label,
             aspect_ctx.actions,
             direct_srcs,
+            target[ProtoInfo].proto_source_root,
             transitive_descriptor_sets,
             transitive_module_mapping_file,
             aspect_ctx.executable._mkdir_and_run,

swift/internal/utils.bzl

@@ -251,3 +251,20 @@ def workspace_relative_path(file):
     """
     workspace_path = paths.join(file.root.path, file.owner.workspace_root)
     return paths.relativize(file.path, workspace_path)
+
+def proto_import_path(f, proto_source_root):
+    """ Returns the import path of a `.proto` file given its path.
+
+    Args:
+        f: The `File` object representing the `.proto` file.
+        proto_source_root: The source root for the `.proto` file.
+
+    Returns:
+        The path the `.proto` file should be imported at.
+    """
+    if f.path.startswith(proto_source_root):
+        return f.path[len(proto_source_root) + 1:]
+    else:
+        # Happens before Bazel 1.0, where proto_source_root was not
+        # guaranteed to be a parent of the .proto file
+        return workspace_relative_path(f)