Add runfiles concept to documentation

[mering]

This has been requested for a long time and many projects have been documenting this downstream (for example Fuchsia).

Documenting this for C++, Go, Python, Shell as these are the languages we are using. Feel free to add additional languages in a follow-up.

I couldn't find a way to embed the example files directly in the documentation to ensure the examples can easily be tested, so I just copied the content in the MDX file.

The dependency to rules_go already existed transitively, so this is not newly added. Consider using a separate MODULE.bazel file for the examples folder in the future.

Fixes #10022.

[gemini-code-assist]

Code Review

This pull request adds valuable documentation for the runfiles concept, a long-requested feature. It provides examples for C++, Go, Python, and Shell, along with the necessary build configurations and source files to make them runnable. While the C++ and Go examples are correct, I've found critical errors in the Python and Shell examples that would prevent them from running as-is. The same errors are present in both the documentation and the example files. I've provided suggestions to correct these issues. With these fixes, this will be an excellent contribution.

[lberki]

Thanks for the PR! I only have minor stylistic nits.

[mering]

@lberki thanks for the review! I addressed your comments. PTAL.

[mering]

@lberki looks like some tests are using an old C++ toolchain without the filesystem include. Can I exclude these tests or specify some additional option to make this available?

[lberki]

Thanks and apologies for that space thing; for some reason, I didn't realize that there are newlines after.

re: #include <filesystem>, can you make do without? It looks like it's not a hard requirement for the example since runfiles.h takes an std::string. My C++ is somewhat rusty so I don't know if there is another officially blessed way to figure it out, but in the worst case #ifdef _WIN32 or hard-wiring a slash is preferable to disabling this test for some platforms.

[lberki]

Thanks! I assume this is now ready for review? (before I apply the "ready to merge" label)

[mering]

Thanks! I assume this is now ready for review? (before I apply the "ready to merge" label)

Yes indeed. I was only waiting for the test results before I planned to ping you again.

[lberki]

Oh sorry, I didn't realize I jumped the gun :) click

[iancha1992]

@mering Could you please make a change to runfile.py to address the below from our internal review?

Missing module docstring [missing-module-docstring]
//depot/google3/third_party/bazel/examples/py/runfile.py:1:1
Use implicit True/False evaluation [g-explicit-bool-comparison]
//depot/google3/third_party/bazel/examples/py/runfile.py:9:4