Adds example of importing protobuf well-known-types in golang.

- Partially addresses issue #22.

.travis.yml

@@ -35,6 +35,7 @@ script:
       examples/helloworld/go/... \
       examples/helloworld/java/... \
       examples/helloworld/closure/... \
+      examples/wkt/... \
       $FLAGS
 
 notifications:

examples/wkt/go/BUILD

@@ -0,0 +1,41 @@
+package(default_visibility = ["//visibility:public"])
+
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_test")
+
+load("//go:rules.bzl", "go_proto_library")
+
+#
+# Demonstration of importing the protobuf well-known types.
+#
+
+go_proto_library(
+    name = "protolib",
+    protos = ["wkt.proto"],
+    imports = [
+        'external/com_github_google_protobuf/src',
+    ],
+    importmap = {
+        'google/protobuf/descriptor.proto': 'github.com/golang/protobuf/protoc-gen-go/descriptor',
+        'google/protobuf/compiler/plugin.proto': 'github.com/golang/protobuf/protoc-gen-go/plugin',
+    },
+    deps = [
+        "@com_github_golang_protobuf//:ptypes/any",
+        "@com_github_golang_protobuf//:ptypes/duration",
+        "@com_github_golang_protobuf//:ptypes/timestamp",
+        "@com_github_golang_protobuf//:ptypes/empty",
+        "@com_github_golang_protobuf//:ptypes/struct",
+        "@com_github_golang_protobuf//:ptypes/wrappers",
+        "@com_github_golang_protobuf//:protoc-gen-go/descriptor",
+        "@com_github_golang_protobuf//:protoc-gen-go/plugin",
+    ],
+)
+
+go_test(
+    name = "wkt_test",
+    size = "small",
+    srcs = ["wkt_test.go"],
+    deps = [
+        "protolib",
+        "@com_github_golang_protobuf//:protoc-gen-go/descriptor",
+    ],
+)

examples/wkt/go/wkt.proto

@@ -0,0 +1,26 @@
+syntax = "proto3";
+
+import "google/protobuf/any.proto";
+import "google/protobuf/duration.proto";
+import "google/protobuf/timestamp.proto";
+import "google/protobuf/empty.proto";
+import "google/protobuf/struct.proto";
+import "google/protobuf/wrappers.proto";
+import "google/protobuf/descriptor.proto";
+import "google/protobuf/compiler/plugin.proto";
+
+message Message {
+  string id = 1;
+  google.protobuf.FileDescriptorProto file = 2;
+  google.protobuf.Any any = 3;
+  google.protobuf.Duration duration = 4;
+  google.protobuf.Timestamp ts = 5;
+  google.protobuf.Empty empty = 6;
+  google.protobuf.Struct struct = 7;
+  google.protobuf.BytesValue bytes_wrapper = 8;
+  google.protobuf.compiler.CodeGeneratorRequest code_generator_request = 9;
+}
+
+extend google.protobuf.MessageOptions {
+  string my_option = 10001;
+}

examples/wkt/go/wkt_test.go

@@ -0,0 +1,27 @@
+package wkt_test
+
+import (
+	"testing"
+	wkt "github.com/pubref/rules_protobuf/examples/wkt/go/protolib"
+	fd "github.com/golang/protobuf/protoc-gen-go/descriptor"
+)
+
+
+func TestWkt(t *testing.T) {
+	filename := "wkt.proto"
+
+	message := &wkt.Message{
+		Id: "foo",
+		File: &fd.FileDescriptorProto{
+			Name: &filename,
+		},
+	}
+
+	if message.Id != "foo" {
+		t.Error("Expected foo, got ", message.Id)
+	}
+
+	if *message.File.Name != filename {
+		t.Error("Expected %s, got %s", filename, message.File.Name)
+	}
+}

go/README.md

@@ -134,3 +134,56 @@ When this name is chosen, part 3 is not needed and should be omitted.
 Consult source files in the
 [examples/helloworld/go](../examples/helloworld/go) directory
 for additional information.
+
+---
+
+## Well-Known Protobuf Import Mappings
+
+This demonstrates one way to incorporate the so-called *well-known*
+protos in your proto definitions.  Protoc will look to find the proto
+file in the `google/protobuf/src` directory in the external workspace.
+The `protoc-gen-go` plugin then performs the importmapping according
+to the `importmap` attribute.  Pregenerated protobuf dependencies are
+provided by the `@com_github_golang_protobuf` workspace.  A minimally
+functional example is provided in
+[examples/wkt/go](https://github.com/pubref/rules_protobuf/tree/master/examples/wkt/go).
+
+```c
+// foo.proto
+syntax = "proto3";
+import "{A}";
+...
+```
+
+```python
+# BUILD
+go_proto_library(
+  name = "protolib",
+  protos = ["foo.proto"],
+  importmap = {
+    "{A}": "github.com/golang/protobuf/{B}",
+  },
+  imports = ["external/com_github_google_protobuf/src"],
+  deps = [
+    "@com_github_golang_protobuf//:{B}",
+  ],
+)
+```
+
+```go
+// foo.go
+import (
+	"github.com/golang/protobuf/{B}"
+)
+```
+
+| Proto Filename (A) | Import Name Suffix and Target Name (B) |
+| ---                | ---           | -----                  |
+| `google/protobuf/any.proto` |  `ptypes/any` |
+| `google/protobuf/duration.proto` |  `ptypes/duration` |
+| `google/protobuf/timestamp.proto` |  `ptypes/timestamp` |
+| `google/protobuf/empty.proto` |  `ptypes/empty` |
+| `google/protobuf/struct.proto` |  `ptypes/struct` |
+| `google/protobuf/wrappers.proto` |  `ptypes/wrappers` |
+| `google/protobuf/descriptor.proto` |  `protoc-gen-go/descriptor` |
+| `google/protobuf/compiler/plugin.proto` |  `protoc-gen-go/plugin` |

go/rules.bzl

@@ -31,6 +31,7 @@ def go_proto_library(
     name,
     langs = [str(Label("//go"))],
     protos = [],
+    importmap = {},
     imports = [],
     inputs = [],
     proto_deps = [],
@@ -62,6 +63,7 @@ def go_proto_library(
     "protos": protos,
     "deps": [dep + ".pb" for dep in proto_deps],
     "langs": langs,
+    "importmap": importmap,
     "imports": imports,
     "inputs": inputs,
     "pb_options": pb_options,