Include file downloaded by Bazel http_file

Question

I'm using Bazel to build my project. I'd like to use the single-header test framework, Catch v2 . I decided to use the http_file rule to make Bazel download the catch header. My WORKSPACE file looks like this:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_file")

http_file(
  name = "catch",
  downloaded_file_path = "catch.hpp",
  sha256 = "cc6cc272cf84d8e10fb28f66f52584dedbb80d1234aae69e6a1027af4f31ae6f",
  urls = ["https://github.com/catchorg/Catch2/releases/download/v2.4.2/catch.hpp"],
)

According to the doc, the test depends on the generated package like this:

cc_test(
  name = "my_test",
  srcs = ["@catch//file", "my_test.cc"]
)

The test file my_test.cc can't get any simpler:

#include "catch.hpp"

However, I get the following error:

$ bazel test --config=opt -s //...
WARNING: [...]/BUILD:25:10: in srcs attribute of cc_test rule //test:my_test: please do not import '@catch//file:catch.hpp' directly. You should either move the file to this package or depend on an appropriate rule there
SUBCOMMAND: # //test:my_test [action 'Compiling test/my_test.cc']
(cd [...] && \
  exec env - [...] \
  /usr/bin/gcc
 -U_FORTIFY_SOURCE -fstack-protector -Wall -B/usr/bin -B/usr/bin -Wunused-but-set-parameter -Wno-free-nonheap-object -fno-omit-frame-pointer '-std=c++0x' -MD -MF [...].d '-frandom-seed=[...].o' -fPIC
 -iquote .
 -iquote bazel-out/k8-fastbuild/genfiles
 -iquote bazel-out/k8-fastbuild/bin
 -iquote external/bazel_tools
 -iquote bazel-out/k8-fastbuild/genfiles/external/bazel_tools
 -iquote bazel-out/k8-fastbuild/bin/external/bazel_tools
 -fno-canonical-system-headers -Wno-builtin-macro-redefined '-D__DATE__="redacted"' '-D__TIMESTAMP__="redacted"' '-D__TIME__="redacted"' -c test/my_test.cc
 -o [...].o)
ERROR: [...]/BUILD:23:1: C++ compilation of rule '//test:my_test' failed (Exit 1)
test/my_test.cc:1:28: fatal error: catch.hpp: No such file or directory
compilation terminated.
[...]
FAILED: Build did NOT complete successfully

Creating a cc_library wrapper, or including catch/catch.hpp , catch/file/catch.hpp produces the same error.

Answer 1

By default, files downloaded by http_file can be included as:

#include "external/<name>/file/<file_name>"

In this specific case:

#include "external/catch/file/catch.hpp"

However, this include path is ugly, it should be wrapped by a cc_library . Furthermore, compiling the full catch header file for each test will make the build slow. According to the catch docs , the implementation part of the catch header should be compiled separately. Like this:

test/BUILD:

cc_library(
  name = "catch",
  hdrs = ["@catch//file"],
  srcs = ["catch.cpp"],
  visibility = ["//visibility:public"],
  strip_include_prefix = "/external/catch/file",
  include_prefix = "catch",
  linkstatic = True,   # otherwise main() will could end up in a .so
)

cc_test(
  name = "my_test",
  deps = ["//test:catch"],
  srcs = ["my_test.cc"],
)

test/catch.cpp:

#define CATCH_CONFIG_MAIN
#include "catch/catch.hpp"

test/my_test.cc:

#include "catch/catch.hpp"

TEST_CASE("my_test", "[main]") { /* ... */ }

This way catch.cpp will not be re-compiled if only my_test.cc changes, saving precious seconds.