A protoc plugin that generates Cargo crates and include files.
When used in projects that use only Rust code, the preferred mechanism for
generating protobuf definitions with Prost! is to use [prost-build] from
within a build.rs file. However, when working in polyglot environments,
it can be advantageous to utilize common tooling in the Protocol Buffers
ecosystem. One common tool used for this purpose is [buf], which simplifies
the code generation process and includes several useful features, including
linting, package management, and breaking change detection.
Ensure that protoc-gen-prost-crate has been installed within a directory on your
$PATH. Then invoke protoc from the command line as follows:
shell
protoc --prost-crate_out=proto/gen -I proto proto/greeter/v1/greeter.proto
The following options can be specified:
default_package_filename=<value>: This should match the value of the
main protoc-gen-prost step so that the include file references the correct
output file. (see also [default package filename] from prost-build)include_file(=<value>): Sets the name for the generated include file. If
not specified, then the default value depends on whether gen_crate is
specified. If it is, then <value> defaults to src/lib.rs. Otherwise, it
defaults to mod.rs. The generated include file will add feature markers
to each produced module to allow for faster compilation and reduced sizes
for unnecessary features. This can be disabled by specifying no_features.only_include=<proto_path>: Will only include packages with the specified
prefix in the generated include file and generated features list, if enabled.
Paths must be fully-qualified and begin with ..gen_crate(=<template_path>): Indicates that a Cargo crate should be
generated with the manifest based on the template at the path provided. The
template should include a placeholder to inject the crate features graph
unless no_features is specified. The template generation does not take
into account crate dependencies. These must be managed separately. If not
specified, Cargo.toml is assumed. This allows automatic updating of the
features in the Cargo manifest.no_features(=<boolean>): Disables the generation of feature flags in the
include file or in the Cargo manifest.A note on parameter values:
(=<boolean>): Boolean values may be specified after a parameter, but if
not, the value is assumed to be true by virtue of having listed the
parameter.When used with buf, options can be specified in the buf.gen.yaml file.
This plugin must be run with strategy: all in order to have a complete
view of the protobuf schemas and correctly identify dependencies for the
input files.
The following will just produce an include file mod.rs in the output gen
directory without any conditional compilation feature flags:
yaml
version: v1
plugins:
- name: prost-crate
out: gen
strategy: all
opt:
- no_features
When using the gen_crate option, later Rust generators should generate
into the src directory which will be created by this plugin:
yaml
version: v1
plugins:
- name: prost
out: gen/src
opt:
- bytes=.
- file_descriptor_set
- name: prost-crate
out: gen
strategy: all
opt:
- gen_crate
When working with private, vendored package dependencies, buf tends to
push more files for output than desired. To limit the packages that get
put into the include file, used the only_include option:
yaml
version: v1
plugins:
- name: prost
out: gen/src
opt:
- bytes=.
- file_descriptor_set
- name: prost-crate
out: gen
strategy: all
opt:
- gen_crate
- only_include=.my_company
The protoc-gen-prost-crate plugin is also published on the Buf Schema Registry as
a plugin which you can execute remotely, without needing to explicitly install
this tool. See the plugin listing to identify the latest published version
for use. Note that the remote plugin form is not compatible with the gen_crate
option, as the plugin is executed outside the context of the current file system,
so template information cannot be used. The plugin is referenced as follows:
yaml
version: v1
plugins:
- remote: buf.build/prost/plugins/crate:v0.1.5-2
out: gen
When using the gen_crate option, the template specified will be placed in
the output folder. The template should include a commented insertion point
that can be referenced for the placement of the features dependency graph.
The template will be Cargo.toml by default, and will do an in-place update
of the Cargo.toml file, updating the exposed features to match the generated
code.
protoc will insert the computed dependency graph above the insertion point.
If this commented line is not included, then protoc will not know where to
place the features list and the insertion will be silently skipped.
```toml [package] name = "my-cool-proto-defs" version = "0.1.0" edition = "2021"
[dependencies] prost = "0.10.0"
[features] default = []
```
Once generated, the manifest will include a set of features that allow limiting the compilation to only those modules that are required. Each feature will automatically activate the relevant features required.
```toml [package] name = "my-cool-proto-defs" version = "0.1.0" edition = "2021"
[dependencies] prost = "0.10.0"
[features] default = []
protofull = ["helloworldv1", "greeterv1"] greeterv1 = ["helloworldv1"] helloworldv1 = []
```
In general, I counsel against manually editing the generated code files. Doing
so makes it more difficult to evolve your schema, as regenerating the code
will result in needing to manually edit again in order to re-add the
customizations. Instead, I recommend using a subdirectory to host the generated
code and include that file in src/lib.rs as in the build-with-buf example.
src/lib.rs:
```no_compile
include!("gen/mod.rs");
// Any additional traits or other impls can go here or in other related files. // These won't be touched by the code generation process. ```
Cargo.toml (prior to first generation):
```toml
[package]
name = "my-cool-proto-defs"
version = "0.1.0"
edition = "2021"
[features] default = ["proto_full"]
[dependencies] prost = "0.10.0" ```
buf.gen.yaml:
yaml
version: v1
plugins:
- name: prost
out: src
opt:
- bytes=.
- file_descriptor_set
- name: prost-crate
out: gen
strategy: all
opt:
- include_file=src/gen/mod.rs
- gen_crate