What's the preferred way to get run_files directory?

[c...@nuro.ai]

Is using $0.runfiles/path the preferred way to get the runfile for a cc_binary?

I have a py_binary which executes another cc_binary, and I put the cc_binary as data dep of the py_binary.

cc_binary(
name = "main",
srcs = ["main.cc"],
data = [":runfile.txt"]
)

py_binary(
name = "py_main",
srcs = ["py_main.py"],
data = [":main"],
)

Inspecting the output directory hierarchy, I noticed the runfiles of py_binary contains the data needed for both, but there's no main.runfiles directory or symlink to the root of runfiles.

~/bazeltest (master) $ ls -R bazel-bin/py_main.runfiles
bazel-bin/py_main.runfiles:
__main__ MANIFEST

bazel-bin/py_main.runfiles/__main__:
main py_main py_main.py runfile.txt

That means, if I invoke the cc binary in the py, it cannot use $0.runfiles/runfile.txt because that will point to
bazel-bin/py_main.runfiles/__main__/main.runfiles/runfile.txt, which doesn't exist.

What's the best way for main to get the runfile, and works in both cases where it's directly executed or it's executed as part of py_binary?

[László Csomor]

Use the runfiles libraries built into Bazel:

- for Python: https://github.com/bazelbuild/bazel/blob/4e4c77ae96955138006af15664074123d6a4f51d/tools/python/runfiles/runfiles.py#L16

- for C++: https://github.com/bazelbuild/bazel/blob/4e4c77ae96955138006af15664074123d6a4f51d/tools/cpp/runfiles/runfiles.h#L15

See the comments I linked for full usage information, including the use case you described.

--
László Csomor | Software Engineer | laszlo...@google.com

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[petros.es...@gmail.com]

László, are there runfiles libraries for java binaries?

[petros.es...@gmail.com]

My apologies on the last message. I may have misinterpreted the intent
of the initial post (and also included a bunch of cruft).

Nevertheless, what I wanted to know was there an officially supported way to
obtain a path to the runfiles for a java_binary from a skylark rule?

Currently, I am leveraging an implementation detail in the java_binary
wrapper script to set a number of system properties, relative to the
runfiles path.

Concretely, in the macro that creates a java_binary, one of the
jvm_flags I use is

-Dsome.company.required.config=$(readlink -f ${RUNPATH:-.})/<path>

After the java_binary is compiled, the bazel-bin wrapper script contains
the above as a JVM_FLAG. This causes no issues since it explicitly defines
the RUNPATH variable earlier in the script [0].

The fundamental reason, I am doing all of this is that I need to define
a set of java system properties that require the paths of key configuration
files.

[0]https://github.com/bazelbuild/bazel/blob/master/src/main/java/com/google/devtools/build/lib/bazel/rules/java/java_stub_template.txt#L245

[László Csomor]

Hey Petros,

No worries! Yes, for the record there's a runfiles library for Java too, usage info is here [1].

My understanding is, you need this info in a *macro* (you said *rule* at some point).

There's a canonical way to solve the problem, without using the RUNPATH-based hackery: `java_binary.jvm_flags` supports make variable expansion [2], so you can use:

  jvm_flags=["-Dsome.company.required.config=$(location //path/to:data)"]

Does that help?

[1] https://github.com/bazelbuild/bazel/blob/4e4c77ae96955138006af15664074123d6a4f51d/src/tools/runfiles/java/com/google/devtools/build/runfiles/Runfiles.java#L30

[2] https://docs.bazel.build/versions/master/be/java.html#java_binary.jvm_flags

--
László Csomor | Software Engineer | laszlo...@google.com

Google Germany GmbH | Erika-Mann-Str. 33 | 80636 München | Germany
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado

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