bazel compilation with emscripten failed

[wzheng21]

Hi we are recently trying to compile glog to wasm using bazel. The commit we are compiling is this. The crucial part of the error message is

Compiling src/raw_logging.cc failed: (Exit 1): emcc.sh failed: error executing command external/emsdk/emscripten_toolchain/emcc.sh '--sysroot=external/emscripten_bin_linux/emscripten/cache/sysroot' -fdiagnostics-color -fno-exceptions -fno-strict-aliasing -funsigned-char ... (remaining 53 arguments skipped)

Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
external/com_googlesource_code_glog/src/raw_logging.cc:162:14: error: use of undeclared identifier 'STDERR_FILENO'
  safe_write(STDERR_FILENO, buffer, strlen(buffer));
             ^
1 error generated.

The root cause seems to be that wasm_copts misses -DHAVE_MODE_T and -DHAVE_UNISTD_H, both of which are defined in linux_or_darwin_copts, so when the platform is wasm, then compilation failed.

The quick fix I did is to move those two macro definitions to wasm_copts. Let me know if there's a more correct way of handling this or I missed anything.

[drigz]

Hey Victor! Let me know if you feel comfortable sending a PR to https://github.com/google/glog/blob/master/bazel/glog.bzl to fix this - also, if you depend on the wasm support maybe you could think about how to add CI for this in either https://github.com/google/glog/blob/master/.bazelci/presubmit.yml or https://github.com/google/glog/tree/master/.github/workflows, as I'm not sure how we can prevent future wasm breakage (it was added by a contributor but I haven't heard anything from them for some time).

[wzheng21]

Hi @drigz I'm happy to send a PR. There's really not much to do. But it's a bit hard for me to do the CICD stuff with bazel + WASM.

[drigz]

But it's a bit hard for me to do the CICD stuff with bazel + WASM.

NP, don't block the fix on CI suggestion. Feel free to ignore that (and maybe revisit if you observe more breakage in future).