feat: extra language inputs for bazel codegen #1904
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sgammon
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Sorry for delay. Multi language support is something I wanted to add myself. I was hoping to do it similar to the way protobuf is structured, but quickly ran into limitations of my bazel knowledge. This change looks much simpler, however I don't understand how does it help with the task? Where are additional plug-in arguments specified? Could you expand a little on the usage too? How do you use it to, generate another language? (Not sure what's your interest but I was looking into rust) |
| # process language extras, starting with files we should include | ||
| extra_inputs = ctx.files.language_extras or [] | ||
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| # then compute input flags, taking the parent of the first file in each extra as the include path | ||
| if len(ctx.attr.language_extras) > 0: | ||
| for extra in ctx.attr.language_extras: | ||
| files = extra.files.to_list() | ||
| if len(files) > 0: | ||
| args.add_all(["-I", files[0].dirname.removesuffix("/capnp")]) | ||
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| ctx.actions.run( | ||
| inputs = inputs + ctx.files._capnpc_cxx + ctx.files._capnpc_capnp + ctx.files._capnp_system, | ||
| inputs = inputs + ctx.files._capnpc_cxx + ctx.files._capnpc_capnp + ctx.files._capnp_system + extra_inputs, |
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@mikea Here's the entire change; the rest is wiring. If the user passes additional targets via the language_extras attribute, their files are included as inputs in the run, and each directory containing language extras is included via -I.
The effect is that the user can pass arbitrary dependencies to be exposed in the sandbox, and can include them easily within the capnp sources.
We're using this change downstream in an internal Bazel project, and it's working great, specifically to generate Java capnp sources.
I actually know exactly what you're talking about re/rules_proto. It is a little brain-melting to get aspects all working together properly, certainly not for the faint of heart. I've died on that same hill before.
So, I think you're right, it would be fantastic to get true first-class Bazel support for capnp in the same way Protocol Buffers is supported, including easy generation of different languages. But in the meantime, this gives capnp users an escape hatch in Bazel builds where there is no explicit support for their language yet.
Thus, these attributes could be kept to use in-house language implementations, or to facilitate easy testing, etc etc, alongside future attributes or rules or aspects which bring support to parity.
In other words, this change shouldn't preclude better support later.
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Usage example, which I'm happy to add to docs/README:
# ...
filegroup(
name = "capnpj_system_library",
srcs = [
"java.capnp",
],
visibility = ["//visibility:public"],
)
# ...
# ...
cc_capnp_library(
name = "some-capnp",
srcs = ["some.capnp"],
language_extras = ["@capnp-java//:capnpj_system_library"],
# ...
)
# ...
using Cxx = import "/capnp/c++.capnp";
using Java = import "/capnp/java.capnp";
# ... |
When using language plugins like Cap'n'proto for Java from Bazel, there needs to be a way to add language extras as inputs to the codegen phase. This is only needed when generating capnp code in multiple languages. Even if the generator is only producing a C++ in a given invocation, the imports for other languages will fail to be found due to Bazel's strict sandboxing. This new attribute fixes that condition. Fixes and closes capnproto#1903. Relates-To: elide-dev/bigtent#6 Relates-To: capnproto#1903 Signed-off-by: Sam Gammon <sam@elide.ventures>
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Summary
When using language plugins like Cap'n'proto for Java from Bazel, there needs to be a way to add language extras as inputs to the codegen phase.
This is only needed when generating capnp code in multiple languages. Even if the generator is only producing a C++ output in a given invocation, the imports for other languages will fail to be found due to Bazel's strict sandboxing. This new attribute fixes that condition.
Fixes and closes #1903.
Changelog
language_extrasargument tocc_capnp_librarymacrolanguage_extraslabel_listattribute to rule definitioninputsandargs(-I <parent_dir_of_extra>)