Add proto_common.direct_source_infos

This change adds a helper to extract information about direct sources
of `ProtoInfo` providers.

Design doc:
https://docs.google.com/document/d/1u95vlQ1lWeQNR4bUw5T4cMeHTGJla2_e1dHHx7v4Dvg/edit#

Note that this was originally named `proto_common.protos_to_generate`,
but was renamed because it applies more broadly.

.bazelci/presubmit.yml

@@ -5,20 +5,30 @@ buildifier:
 platforms:
   macos:
     build_targets:
-      - "..."
+      - "//..."
+    test_targets:
+      - "//..."
 
   rbe_ubuntu1604:
     build_targets:
-      - "..."
+      - "//..."
+    test_targets:
+      - "//..."
 
   ubuntu1604:
     build_targets:
-      - "..."
+      - "//..."
+    test_targets:
+      - "//..."
 
   ubuntu1804:
     build_targets:
-      - "..."
+      - "//..."
+    test_targets:
+      - "//..."
 
   windows:
     build_targets:
-      - "..."
+      - "//..."
+    test_targets:
+      - "//..."

WORKSPACE

@@ -7,6 +7,10 @@ rules_proto_dependencies()
 
 rules_proto_toolchains()
 
+load("@bazel_skylib//lib:unittest.bzl", "register_unittest_toolchains")
+
+register_unittest_toolchains()
+
 http_archive(
     name = "bazel_toolchains",
     sha256 = "b663c411acc9cf191679823aa1eb9d665358239e8bf9e6f7cbb302b41f57317c",

proto/defs.bzl

@@ -14,7 +14,8 @@
 
 """Starlark rules for building protocol buffers."""
 
-load("//proto/private:native.bzl", "NativeProtoInfo", "native_proto_common")
+load("//proto/private:native.bzl", "NativeProtoInfo")
+load("//proto/private/utils:direct_source_infos.bzl", "direct_source_infos")
 
 _MIGRATION_TAG = "__PROTO_RULES_MIGRATION_DO_NOT_USE_WILL_BREAK__"
 
@@ -57,4 +58,6 @@ ProtoInfo = NativeProtoInfo
 # Utilities for protocol buffers.
 #
 # https://docs.bazel.build/versions/master/skylark/lib/proto_common.html
-proto_common = native_proto_common
+proto_common = struct(
+    direct_source_infos = direct_source_infos,
+)

proto/private/utils/BUILD

@@ -0,0 +1 @@
+# Intentionally left empty (for now).

proto/private/utils/direct_source_infos.bzl

@@ -0,0 +1,68 @@
+# Copyright 2019 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Contains the implementation for `proto_common.direct_source_infos`."""
+
+# TODO(yannic): Remove this suppression when
+# https://github.com/bazelbuild/buildtools/issues/774 has been fixed.
+# buildifier: disable=function-docstring-args
+def direct_source_infos(proto_info, *, provided_sources = []):
+    """Returns information about `proto_info`'s direct sources.
+
+    Files that are both in `proto_info`'s direct sources and in
+    `provided_sources` are skipped. This is useful, e.g., for well-known
+    protos that are already provided by the Protobuf runtime.
+
+    Args:
+      proto_info: An instance of `ProtoInfo`.
+      provided_sources: Optional. A sequence of import paths to ignore.
+
+    Returns:
+      A sequence of structs containing information about `proto_info`'s direct
+      sources. Each struct contains the following fields:
+        - `file`: The `.proto` file.
+        - `import_path`: The import path of the `.proto` file.
+    """
+
+    files = [_info(f, proto_info) for f in proto_info.direct_sources]
+    return [f for f in files if f.import_path not in provided_sources]
+
+def _info(file, proto_info):
+    """Computes information about a single `.proto` file.
+
+    Args:
+      file: The `.proto` file to generate info for. Must be in
+          `direct_sources` of `proto_info`.
+      proto_info: An instance of `ProtoInfo`.
+
+    Returns: A struct. Consult the documented return type of
+        `direct_source_infos` for documentation about its fields.
+    """
+
+    if "." == proto_info.proto_source_root:
+        # The `proto_library` didn't specify `import_prefix` or
+        # `strip_import_prefix`, and `file` is a regular source file
+        # (i.e. not generated) in the main workspace.
+
+        return struct(
+            file = file,
+            import_path = file.path,
+        )
+
+    source_root = proto_info.proto_source_root
+    offset = len(source_root) + 1  # + '/'.
+    return struct(
+        file = file,
+        import_path = file.path[offset:],
+    )

tests/BUILD

@@ -1,8 +1,115 @@
 load("//proto:defs.bzl", "proto_library")
 
+WORKSPACE_PREFIX = ""  # copybara-workspace-prefix(WORKSPACE_PREFIX)
+
+proto_library(
+    name = "multiple_srcs_proto",
+    srcs = [
+        "empty.proto",
+        "prefix/empty.proto",
+    ],
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
 proto_library(
     name = "empty_proto",
     srcs = [
         "empty.proto",
     ],
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
+proto_library(
+    name = "empty_with_prefix_proto",
+    srcs = [
+        "prefix/empty.proto",
+    ],
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
+proto_library(
+    name = "empty_with_absolute_strip_prefix_proto",
+    srcs = [
+        "empty.proto",
+    ],
+    strip_import_prefix = "/" + WORKSPACE_PREFIX + "tests",
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
+proto_library(
+    name = "empty_with_relative_strip_prefix_proto",
+    srcs = [
+        "prefix/empty.proto",
+    ],
+    strip_import_prefix = "prefix",
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
+proto_library(
+    name = "empty_with_empty_strip_prefix_proto",
+    srcs = [
+        "empty.proto",
+    ],
+    strip_import_prefix = "",
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
+proto_library(
+    name = "empty_with_add_and_absolute_strip_prefix_proto",
+    srcs = [
+        "empty.proto",
+    ],
+    import_prefix = "foo",
+    strip_import_prefix = "/" + WORKSPACE_PREFIX + "tests",
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
+proto_library(
+    name = "empty_with_add_and_relative_strip_prefix_proto",
+    srcs = [
+        "prefix/empty.proto",
+    ],
+    import_prefix = "foo",
+    strip_import_prefix = "prefix",
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
+proto_library(
+    name = "empty_with_add_and_empty_strip_prefix_proto",
+    srcs = [
+        "empty.proto",
+    ],
+    import_prefix = "foo",
+    strip_import_prefix = "",
+    visibility = [
+        "//tests:__subpackages__",
+    ],
+)
+
+proto_library(
+    name = "empty_with_add_and_empty_strip_prefix_proto_in_subdir",
+    srcs = [
+        "prefix/empty.proto",
+    ],
+    import_prefix = "foo",
+    strip_import_prefix = "",
+    visibility = [
+        "//tests:__subpackages__",
+    ],
 )

tests/analysis/BUILD

@@ -0,0 +1,5 @@
+load("//tests/analysis:proto_common_contains_native_fields_test.bzl", "proto_common_contains_native_fields_test")
+
+proto_common_contains_native_fields_test(
+    name = "proto_common_contains_native_fields_test",
+)

tests/analysis/proto_common_contains_native_fields_test.bzl

@@ -0,0 +1,45 @@
+# Copyright 2019 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unit-test to verify that the Starlark `proto_common` shim contains all fields
+of the native version of `proto_common`, excluding fields that are considered
+to be an implementation detail (thus not part of the public API).
+"""
+
+load("@bazel_skylib//lib:unittest.bzl", "asserts", "unittest")
+load("//proto:defs.bzl", "proto_common")
+load("//proto/private:native.bzl", "native_proto_common")  # buildifier: disable=bzl-visibility
+
+def _impl(ctx):
+    """Verifies that the Starlark `proto_common` contains all necessary fields.
+
+    Args:
+      ctx: The rule context.
+
+    Returns: A (not further specified) sequence of providers.
+    """
+
+    env = unittest.begin(ctx)
+
+    for field in dir(native_proto_common):
+        # Starlark `proto_common` only exports fields that are part of the
+        # stable and supported API of native `proto_common`.
+        if not field.endswith("_do_not_use_or_we_will_break_you_without_mercy"):
+            asserts.true(env, hasattr(proto_common, field))
+        else:
+            asserts.false(env, hasattr(proto_common, field))
+
+    return unittest.end(env)
+
+proto_common_contains_native_fields_test = unittest.make(_impl)

tests/prefix/empty.proto

@@ -0,0 +1,17 @@
+// Copyright 2019 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package rules_proto.tests.prefix;