How to I set an ENV VAR in my WORKSPACE in Bazel - bazel

Question

I am trying to use Bazel with Pybind, and it requires that I set the following variables:
"""Repository rule for Python autoconfiguration.
`python_configure` depends on the following environment variables:
* `PYTHON_BIN_PATH`: location of python binary.
* `PYTHON_LIB_PATH`: Location of python libraries.
"""
https://github.com/pybind/pybind11_bazel/blob/master/python_configure.bzl
I dont want to have to pass it in manually when building my libraries, how can i hardcode these env vars in my WORKSPACE?

Answer 1

To (always) set environmental variable for a repository rule consumption, you case use --repo_env command line option. And if you want to include those with every invocation in your workspace, you can set add these flags to your .bazelrc file therein.
Now the wisdom of doing that could be questioned. If it's actually a project (repo) and not build host configuration, it would probably make more sense, be more targeted and more explicit, if it was an attribute of the given rule which was then checked in with the rest of the build configuration.
And looking at the name, there may be another question about specifying python configuration (from outside the bazel build) instead of actually using correctly resolved python toolchain (but there I have to say have no background in what the given rule is about and what is it trying to accomplish to render judgment, this is just a general comment).
To address your comment... I don't what other factors make it "not accept" or what exactly does that actually look like, but if I have this mini-example:
.
├── BUILD
├── WORKSPACE
└── customrule.bzl
Where customrule.bzl reads:
def _run_me(repo_ctx):
repo_ctx.file(
"WORKSPACE",
'workspace(name = "{}")\n'.format(repo_ctx.name),
executable = False,
)
repo_ctx.file(
"BUILD",
'exports_files(["var.sh"], visibility=["//visibility:public"])',
executable = False,
)
repo_ctx.file(
"var.sh",
"echo {}\n".format(repo_ctx.os.environ.get("var1")),
executable = True,
)
wsrule = repository_rule(
implementation = _run_me,
environ = ["var1"],
)
The WORKSPACE is:
load(":customrule.bzl", "wsrule")
wsrule(
name = "extdep"
)
And BUILD:
sh_binary(
name = "tgt",
srcs = ["#extdep//:var.sh"],
)
Then I do get:
$ bazel run --repo_env var1=val1 tgt
val1
and:
$ bazel run --repo_env var1=val2 tgt
val2
I.e. this is a way to pass variables to a repo rule and it does (as such) work.
If you absolutely know, you must call a build with some variable set to certain value (which as mentioned above is itself a requirement that is worth closer examination) and you want these to be associated with the project / repo. You can always check in a build.sh or any such file that wraps your bazel call to be exactly what it must be. But again, this looks more likely to not be really entirely "The Right Thing" to do or want.