Generate import mappings.

Instead of generating a list of import paths based on the difnames of the
imported protos, generate maps to the package local names. This is needed to
handle the case of packages containing a proto with the same name.

An example here is the annotation.proto in this module.

Fixes grpc-ecosystem#633

protoc-gen-swagger/defs.bzl

@@ -1,39 +1,57 @@
 """Generated an open-api spec for a grpc api spec.
 
-Reads the the api spec in protobuf format and generate an open-api spec. 
+Reads the the api spec in protobuf format and generate an open-api spec.
 Optionally applies settings from the grpc-service configuration.
 """
-def _collect_includes(srcs):
-    includes = ["."]
+
+def _collect_includes(gen_dir, srcs):
+    """Build an include path mapping.
+
+    It is important to not just collect unique dirnames, to also support
+    proto files of the same name from different packages.
+
+    The implementation below is similar to what bazel does in its
+    ProtoCompileActionBuilder.java
+    """
+    includes = []
     for src in srcs:
-        include = src.dirname
-        if include and not include in includes:
-            includes += [include]
+        ref_path = src.path
+
+        if ref_path.startswith(gen_dir):
+            ref_path = ref_path[len(gen_dir):].lstrip("/")
+
+        if src.owner.workspace_root:
+            workspace_root = src.owner.workspace_root
+            ref_path = ref_path[len(workspace_root):].lstrip("/")
+
+        include = ref_path + "=" + src.path
+        if include not in includes:
+            includes.append(include)
 
     return includes
 
-def _run_proto_gen_swagger(direct_proto_srcs, transitive_proto_srcs, actions, protoc, protoc_gen_swagger, grpc_api_configuration):
+def _run_proto_gen_swagger(ctx, direct_proto_srcs, transitive_proto_srcs, actions, protoc, protoc_gen_swagger, grpc_api_configuration):
     swagger_files = []
     for proto in direct_proto_srcs:
       swagger_file = actions.declare_file(
           "%s.swagger.json" % proto.basename[:-len(".proto")],
           sibling = proto,
       )
-      
+
       inputs = direct_proto_srcs + transitive_proto_srcs + [protoc_gen_swagger]
-      
+
       options=["logtostderr=true"]
       if grpc_api_configuration:
           options.append("grpc_api_configuration=%s" % grpc_api_configuration.path)
           inputs.append(grpc_api_configuration)
 
+      includes = _collect_includes(ctx.genfiles_dir.path, direct_proto_srcs + transitive_proto_srcs)
+
       args = actions.args()
       args.add("--plugin=%s" % protoc_gen_swagger.path)
-      args.add("--swagger_out=%s:%s" % (",".join(options), swagger_file.dirname))
-      args.add("-Iexternal/com_google_protobuf/src")
-      args.add("-Iexternal/com_github_googleapis_googleapis")
-      args.add(["-I%s" % include for include in _collect_includes(direct_proto_srcs + transitive_proto_srcs)])
-      args.add(proto.basename)
+      args.add("--swagger_out=%s:%s" % (",".join(options), ctx.bin_dir.path))
+      args.add(["-I%s" % include for include in includes])
+      args.add(proto.path)
 
       actions.run(
           executable = protoc,
@@ -54,6 +72,7 @@ def _proto_gen_swagger_impl(ctx):
     return struct(
         files=depset(
             _run_proto_gen_swagger(
+                ctx,
                 direct_proto_srcs = proto.direct_sources,
                 transitive_proto_srcs = ctx.files._well_known_protos + proto.transitive_sources.to_list(),
                 actions = ctx.actions,