grpc: C++ GRPC targets fail to build with import_prefix or strip_import_prefix in Bazel

GRPC Bazel targets (cc_grpc_library) fail to build when proto_library sources contain import_prefix and/or strip_import_prefix options.

What version of gRPC and what language are you using?

1.24.2 (latest master)

What operating system (Linux, Windows,…) and version?

Ubuntu Linux 18.04

What runtime / compiler are you using (e.g. python version or version of gcc)

clang 6.0 with bazel 0.29.1

What did you do?

Created a simple GRPC target (using the HelloService), where the proto_library contains configuration for import_prefix and strip_import_prefix. To reproduce, in the grpc repository:

1. Cherry pick this commit: https://github.com/grpc/grpc/commit/6f1c7150d1d25674d53c8715ddf060d46199f0b4
2. run bazel build //examples/cpp/strip_prefix:service_cc_grpc

What did you expect to see?

Target builds successfully.

What did you see instead?

INFO: Found 1 target...
ERROR: /home/cbills/git/grpc-coopeyb/examples/cpp/strip_prefix/BUILD:15:1: C++ compilation of rule '//examples/cpp/strip_prefix:service_cc_grpc' failed (Exit 1) clang failed: error executing command /usr/bin/clang -U_FORTIFY_SOURCE -fstack-protector -Wall -Wthread-safety -Wself-assign -fcolor-diagnostics -fno-omit-frame-pointer '-std=c++0x' -MD -MF ... (remaining 46 argument(s) skipped)

Use --sandbox_debug to see verbose messages from the sandbox
bazel-out/k8-fastbuild/bin/examples/cpp/strip_prefix/_virtual_imports/service_proto/custom/prefix/service.grpc.pb.cc:5:10: fatal error: 'examples/cpp/strip_prefix/_virtual_imports/service_proto/custom/prefix/service.pb.h' file not found
#include "examples/cpp/strip_prefix/_virtual_imports/service_proto/custom/prefix/service.pb.h"
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
Target //examples/cpp/strip_prefix:service_cc_grpc failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 0.709s, Critical Path: 0.59s
INFO: 0 processes.
FAILED: Build did NOT complete successfully

Worth noting: poking around the sandbox after the failed build, service.pb.h exists, but under _virtual_includes instead of _virtual_imports.

Anything else we should know about your project / environment?

We’re having issues in our repository as well. We need the stirp_import_prefix and import_prefix options for integrating with our existing codebases and consider this issue to be a blocking item to migrate to Bazel.