How do I provide a file as a dependency to an external crate's build.rs?

[akesling]

I'm trying to link in pyo3 with a custom build of Python and a pyo3 build config file. This is normally passed as an absolute path via the PYO3_CONFIG_FILE environment variable. I've figured out how to pass the appropriate environment variable, but I don't yet know the most ergonomic way to both A) make a file available at build script execution time to the appropriate crate (pyo3-ffi in this case), and B) set PYO3_CONFIG_FILE to an absolute path which points at said provided file.

Any ideas?

For context, the cargo command I'd use alternatively would look something like: PYO3_CONFIG_FILE="$(pwd)/pyo3_build_config.txt" PYO3_NO_PYTHON=1 cargo build --release --bin runtime -p python-embedder

[illicitonion]

You probably need to add the file as a label to build_script_data annotation attribute for the crate, and then you can use $(execpath //that:label) in the value of build_script_env on the annotation to get an absolute path to that file.

[akesling]

@illicitonion thank you for the pointers!

Here's what I'm trying now:

...
    annotations = {
        # Set pyo3 FFI build flags when building pyo3-ffi dep
        "pyo3-ffi": [crate.annotation(
            build_script_data = ["//python_embedder:pyo3_build_config.txt"],
            build_script_env = {
                "PYO3_NO_PYTHON": "1",
                "PYO3_CONFIG_FILE": "$(execpath //python_embedder:pyo3_build_config.txt)",
            },
        )],
    },
...

But when I build, I get the following: ERROR: /private/var/tmp/_bazel_akesling/72b5820b02a477ec8ed97bd441726217/external/crates__pyo3-ffi-0.19.2/BUILD.bazel:90:19: no such package '@crates__pyo3-ffi-0.19.2//python_embedder': BUILD file not found in directory 'python_embedder' of external repository @crates__pyo3-ffi-0.19.2. Add a BUILD file to a directory to mark it as a package. and referenced by '@crates__pyo3-ffi-0.19.2//:pyo3-ffi_build_script' .

It looks like the path is being interpreted as being relative to some pyo3-ffi root and not my repo. Any advice here?

[illicitonion]

Try throwing in a @ before the // for both labels - @// means "in the root repo":

...
    annotations = {
        # Set pyo3 FFI build flags when building pyo3-ffi dep
        "pyo3-ffi": [crate.annotation(
            build_script_data = ["@//python_embedder:pyo3_build_config.txt"],
            build_script_env = {
                "PYO3_NO_PYTHON": "1",
                "PYO3_CONFIG_FILE": "$(execpath @//python_embedder:pyo3_build_config.txt)",
            },
        )],
    },
...

[akesling]

Thank you so much for the help!

To close the loop here (in case someone stumbles across this looking for how to actually get this working w/ PyO3):

To get the equivalent of PYO3_CONFIG_FILE="$(pwd)/pyo3_build_config.txt" PYO3_NO_PYTHON=1 cargo build --release --bin runtime -p python-embedder, the following annotations work....

...
    annotations = {
        "pyo3-build-config": [crate.annotation(
            build_script_data = ["@//python_embedder:pyo3_build_config.txt"],
            build_script_env = {
                "PYO3_NO_PYTHON": "1",
                "PYO3_CONFIG_FILE": "$(execpath @//python_embedder:pyo3_build_config.txt)",
            },
        )],
    },
...

Note that we're directly using the pyo3 crate, but we fundamentally depend on pyo3-build-config to consume the PyO3 build configuration.