Proto: documentation to change dependencies (#173)

Compile dependencies for rust_proto_library and rust_grpc_library
documentation was incorrect. To work-around bazelbuild/bazel#6889,
the format has changed a little but the documentation did not
reflected that change.

Fixes #170

proto/README.md

@@ -211,9 +211,37 @@ rust_proto_toolchain(
 )
 ```
 
-Finally, now that you have your own toolchain, you need to register it by
+Now that you have your own toolchain, you need to register it by
 inserting the following statement in your `WORKSPACE` file:
 
 ```python
 register_toolchains(["//package:toolchain"])
 ```
+
+Finally, you might want to set the `rust_deps` attribute in
+`rust_proto_library` and `rust_grpc_library` to change the compile-time
+dependencies:
+
+```python
+rust_proto_library(
+    ...
+    rust_deps = ["//cargo_raze/remote:protobuf"],
+    ...
+)
+
+rust_grpc_library(
+    ...
+    rust_deps = [
+        "//cargo_raze/remote:protobuf",
+        "//cargo_raze/remote:grpc",
+        "//cargo_raze/remote:tls_api",
+        "//cargo_raze/remote:tls_api_stub",
+    ],
+    ...
+)
+```
+
+__Note__: Ideally, we would inject those dependencies from the toolchain,
+but due to [bazelbuild/bazel#6889](https://github.com/bazelbuild/bazel/issues/6889)
+all dependencies added via the toolchain ends-up being in the wrong
+configuration.

proto/toolchain.bzl

@@ -103,11 +103,9 @@ def _rust_proto_toolchain_impl(ctx):
     return platform_common.ToolchainInfo(
         protoc = ctx.executable.protoc,
         proto_plugin = ctx.file.proto_plugin,
-        proto_compile_deps = ctx.attr.proto_compile_deps,
         grpc_plugin = ctx.file.grpc_plugin,
-        grpc_compile_deps = ctx.attr.grpc_compile_deps,
         edition = ctx.attr.edition,
-    )
+   )
 
 PROTO_COMPILE_DEPS = [
     "@io_bazel_rules_rust//proto/raze:protobuf",
@@ -121,6 +119,9 @@ GRPC_COMPILE_DEPS = PROTO_COMPILE_DEPS + [
 ]
 """Default dependencies needed to compile gRPC stubs."""
 
+# TODO(damienmg): Once bazelbuild/bazel#6889 is fixed, reintroduce
+# proto_compile_deps and grpc_compile_deps and remove them from the
+# rust_proto_library and grpc_proto_library.
 rust_proto_toolchain = rule(
     _rust_proto_toolchain_impl,
     attrs = {
@@ -150,16 +151,6 @@ rust_proto_toolchain = rule(
             doc = "The edition used by the generated rust source.",
             default = "2015",
         ),
-        "proto_compile_deps": attr.label_list(
-            allow_files = True,
-            cfg = "target",
-            default = [Label(l) for l in PROTO_COMPILE_DEPS],
-        ),
-        "grpc_compile_deps": attr.label_list(
-            allow_files = True,
-            cfg = "target",
-            default = [Label(l) for l in GRPC_COMPILE_DEPS],
-        ),
     },
 )
 
@@ -176,8 +167,6 @@ Args:
   optional_output_wrapper: An executable
   grpc_plugin: The location of the Rust protobuf compiler pugin to generate
     gRPC stubs.
-  proto_compile_deps: dependencies for rust compilation of protobuf stubs.
-  grpc_compile_deps: dependencies for rust compilation of gRPC stubs.
 
 Example:
   Suppose a new nicer gRPC plugin has came out. Using this new plugin can be