> ## Documentation Index > Fetch the complete documentation index at: https://bazel-pr-29804.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Protocol Buffer Rules ## Rules * [proto\_lang\_toolchain](#proto_lang_toolchain) * [proto\_library](#proto_library) ## proto\_lang\_toolchain [View rule sourceopen\_in\_new](https://github.com/bazelbuild/bazel/blob/master/src/main/java/com/google/devtools/build/lib/rules/proto/ProtoLangToolchainRule.java) ``` proto_lang_toolchain(name, blacklisted_protos, command_line, compatible_with, deprecation, distribs, exec_compatible_with, exec_properties, features, licenses, mnemonic, output_files, plugin, plugin_format_flag, progress_message, proto_compiler, restricted_to, runtime, tags, target_compatible_with, testonly, visibility) ``` If using Bazel, please load the rule from [https://github.com/bazelbuild/rules\_proto](https://github.com/bazelbuild/rules_proto). Specifies how a LANG\_proto\_library rule (e.g., `java_proto_library`) should invoke the proto-compiler. Some LANG\_proto\_library rules allow specifying which toolchain to use using command-line flags; consult their documentation. Normally you should not write those kind of rules unless you want to tune your Java compiler. There's no compiler. The proto-compiler is taken from the proto\_library rule we attach to. It is passed as a command-line flag to Blaze. Several features require a proto-compiler to be invoked on the proto\_library rule itself. It's beneficial to enforce the compiler that LANG\_proto\_library uses is the same as the one `proto_library` does. #### Examples A simple example would be: ``` proto_lang_toolchain( name = "javalite_toolchain", command_line = "--javalite_out=shared,immutable:$(OUT)", plugin = ":javalite_plugin", runtime = ":protobuf_lite", ) ``` ### Arguments | Attributes | | | -------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | `name` | [Name](/versions/7.7.1/concepts/labels#target-names); required A unique name for this target. | | `blacklisted_protos` | List of [labels](/versions/7.7.1/concepts/labels); default is `[]` No code will be generated for files in the `srcs` attribute of `blacklisted_protos`. This is used for .proto files that are already linked into proto runtimes, such as `any.proto`. | | `command_line` | String; required This value will be passed to proto-compiler to generate the code. Only include the parts specific to this code-generator/plugin (e.g., do not include -I parameters) \* `$(OUT)` is LANG\_proto\_library-specific. The rules are expected to define how they interpret this variable. For Java, for example, \$(OUT) will be replaced with the src-jar filename to create. | | `mnemonic` | String; default is `"GenProto"` This value will be set as the mnemonic on protoc action. | | `output_files` | String; default is `"legacy"` Controls how `$(OUT)` in `command_line` is formatted, either by a path to a single file or output directory in case of multiple files. Possible values are: "single", "multiple". | | `plugin` | [Label](/versions/7.7.1/concepts/labels); default is `None` If provided, will be made available to the action that calls the proto-compiler, and will be passed to the proto-compiler: `--plugin=protoc-gen-PLUGIN=.` | | `plugin_format_flag` | String; default is `""` If provided, this value will be passed to proto-compiler to use the plugin. The value must contain a single %s which is replaced with plugin executable. `--plugin=protoc-gen-PLUGIN=.` | | `progress_message` | String; default is `"Generating proto_library %{label}"` This value will be set as the progress message on protoc action. | | `proto_compiler` | [Label](/versions/7.7.1/concepts/labels); default is `None` The proto compiler executable. If provided, this target will be used as a proto-compiler to generate the code. | | `runtime` | [Label](/versions/7.7.1/concepts/labels); default is `None` A language-specific library that the generated code is compiled against. The exact behavior is LANG\_proto\_library-specific. Java, for example, should compile against the runtime. | ## proto\_library [View rule sourceopen\_in\_new](https://github.com/bazelbuild/bazel/blob/master/src/main/java/com/google/devtools/build/lib/rules/proto/BazelProtoLibraryRule.java) ``` proto_library(name, deps, srcs, data, allow_exports, compatible_with, deprecation, distribs, exec_compatible_with, exec_properties, exports, features, import_prefix, licenses, restricted_to, strip_import_prefix, tags, target_compatible_with, testonly, visibility) ``` Deprecated. Please use [https://github.com/bazelbuild/rules\_proto](https://github.com/bazelbuild/rules_proto) instead. Use `proto_library` to define libraries of protocol buffers which may be used from multiple languages. A `proto_library` may be listed in the `deps` clause of supported rules, such as `java_proto_library`. When compiled on the command-line, a `proto_library` creates a file named `foo-descriptor-set.proto.bin`, which is the descriptor set for the messages the rule srcs. The file is a serialized `FileDescriptorSet`, which is described in [https://developers.google.com/protocol-buffers/docs/techniques#self-description](https://developers.google.com/protocol-buffers/docs/techniques#self-description). It only contains information about the `.proto` files directly mentioned by a `proto_library` rule; the collection of transitive descriptor sets is available through the `[ProtoInfo].transitive_descriptor_sets` Starlark provider. See documentation in `ProtoInfo.java`. Recommended code organization: * One `proto_library` rule per `.proto` file.\* A file named `foo.proto` will be in a rule named `foo_proto`, which is located in the same package.\* A `[language]_proto_library` that wraps a `proto_library` named `foo_proto` should be called `foo_[language]_proto`, and be located in the same package. ### Arguments | Attributes | | | --------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `name` | [Name](/versions/7.7.1/concepts/labels#target-names); required A unique name for this target. | | `deps` | List of [labels](/versions/7.7.1/concepts/labels); default is `[]` The list of other `proto_library` rules that the target depends upon. A `proto_library` may only depend on other `proto_library` targets. It may not depend on language-specific libraries. | | `srcs` | List of [labels](/versions/7.7.1/concepts/labels); default is `[]` The list of `.proto` and `.protodevel` files that are processed to create the target. This is usually a non empty list. One usecase where `srcs` can be empty is an *alias-library*. This is a proto\_library rule having one or more other proto\_library in `deps`. This pattern can be used to e.g. export a public api under a persistent name. | | `allow_exports` | [Label](/versions/7.7.1/concepts/labels); default is `None` An optional allowlist that prevents proto library to be reexported or used in lang\_proto\_library that is not in one of the listed packages. | | `exports` | List of [labels](/versions/7.7.1/concepts/labels); default is `[]` List of proto\_library targets that can be referenced via "import public" in the proto source. | | `import_prefix` | String; default is `""` The prefix to add to the paths of the .proto files in this rule. When set, the .proto source files in the `srcs` attribute of this rule are accessible at is the value of this attribute prepended to their repository-relative path. The prefix in the `strip_import_prefix` attribute is removed before this prefix is added. | | `strip_import_prefix` | String; default is `""` The prefix to strip from the paths of the .proto files in this rule. When set, .proto source files in the `srcs` attribute of this rule are accessible at their path with this prefix cut off. If it's a relative path (not starting with a slash), it's taken as a package-relative one. If it's an absolute one, it's understood as a repository-relative path. The prefix in the `import_prefix` attribute is added after this prefix is stripped. |