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Add more documentation about code generation (#83)
Motivation: Users (especially new ones) often have issues with generating code. This package provide a number of ways to do this but doesn't do a good job of explaining the pros and cons of each method or how to use each of them. Modifications: - Split up the generating stubs doc into four parts: one article for each method explaining how to use that approach. For the build plugin and protoc the content was more or less directly moves from the existing doc. - Reprurpose the existing generating stubs doc to explain the pros and cons of each approach to make it easier for users to decide. Result: Better docs
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‎Sources/GRPCProtobuf/Documentation.docc/Articles/Code-generation-with-protoc.md‎

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# Code generation with protoc
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This article describes how to use the Swift Package Manager build plugin to
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generate gRPC Swift and Swift Protobuf code from your Protocol Buffers `.proto` files.
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## Overview
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If you've used Protocol Buffers before then generating gRPC Swift stubs should be simple. If you're
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unfamiliar with Protocol Buffers then you should get comfortable with the concepts before
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continuing; the [Protocol Buffers website](https://protobuf.dev/) is a great place to start.
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If you haven't installed `protoc` yet refer to <doc:Installing-protoc> for
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instructions.
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## Using protoc
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The [`grpc-swift-protobuf`](https://github.com/grpc/grpc-swift-protobuf) package provides
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`protoc-gen-grpc-swift-2`, a program which is a plugin for the Protocol Buffers compiler, `protoc`.
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To generate gRPC stubs for your `.proto` files directly you must run the `protoc` command with
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the `--grpc-swift-2_out=<DIRECTORY>` option:
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```console
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protoc --grpc-swift-2_out=. my-service.proto
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```
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> `protoc-gen-grpc-swift-2` only generates gRPC stubs, it doesn't generate messages. You must use
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> `protoc-gen-swift` to generate messages in addition to gRPC Stubs.
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The presence of `--grpc-swift-2_out` tells `protoc` to use the `protoc-gen-grpc-swift-2` plugin. By
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default it'll look for the plugin in your `PATH`. You can also specify the path to the plugin
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explicitly:
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```console
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protoc --plugin=/path/to/protoc-gen-grpc-swift-2 --grpc-swift-2_out=. my-service.proto
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```
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You can specify various options to `protoc-gen-grpc-swift-2` via `protoc` using
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the `--grpc-swift-2_opt` argument:
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```console
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protoc --grpc-swift-2_opt=<OPTION_NAME>=<OPTION_VALUE> --grpc-swift-2_out=.
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```
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You can specify multiple options by repeating the `--grpc-swift-2_opt` argument:
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```console
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protoc \
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--grpc-swift-2_opt=<OPTION_NAME1>=<OPTION_VALUE1> \
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--grpc-swift-2_opt=<OPTION_NAME2>=<OPTION_VALUE2> \
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--grpc-swift-2_out=.
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```
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### Generator options
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| Name | Possible Values | Default | Description |
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|---------------------------|---------------------------------------------|-----------------|----------------------------------------------------------|
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| `Visibility` | `Public`, `Package`, `Internal` | `Internal` | Access level for generated stubs |
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| `Server` | `True`, `False` | `True` | Generate server stubs |
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| `Client` | `True`, `False` | `True` | Generate client stubs |
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| `FileNaming` | `FullPath`, `PathToUnderscores`, `DropPath` | `FullPath` | How generated source files should be named. † |
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| `ProtoPathModuleMappings` | | | Path to module map `.asciipb` file. ‡ |
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| `UseAccessLevelOnImports` | `True`, `False` | `False` | Whether imports should have explicit access levels. |
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| `GRPCModuleName` | | `GRPCCore` | The name of the `GRPCCore` module. |
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| `GRPCProtobufModuleName` | | `GRPCProtobuf` | The name of the `GRPCProtobuf` module. |
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| `SwiftProtobufModuleName` | | `SwiftProtobuf` | The name of the `SwiftProtobuf` module. |
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| `Availability` | String, in the form `OS Version` | | Platform availability to use in generated code. § |
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† The `FileNaming` option has three possible values, for an input of `foo/bar/baz.proto` the following
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output file will be generated:
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- `FullPath`: `foo/bar/baz.grpc.swift`.
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- `PathToUnderscores`: `foo_bar_baz.grpc.swift`
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- `DropPath`: `baz.grpc.swift`
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‡ The code generator assumes all inputs are generated into the same module, `ProtoPathModuleMappings`
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allows you to specify a mapping from `.proto` files to the Swift module they are generated in. This
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allows the code generator to add appropriate imports to your generated stubs. This is described in
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more detail in the [SwiftProtobuf documentation](https://github.com/apple/swift-protobuf/blob/main/Documentation/PLUGIN.md).
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§ If unspecified the following availability is used: macOS 15, iOS 18, tvOS 18,
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watchOS 11, visionOS 2. The `Availability` option may be specified multiple
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times, where each value is a space delimited pair of platform and version, e.g.
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`Availability=macOS 15.0`.
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### Building the protoc plugin
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> The version of `protoc-gen-grpc-swift-2` you use mustn't be newer than the version of
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> the `grpc-swift-protobuf` you're using.
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If your package depends on `grpc-swift-protobuf` then you can get a copy of `protoc-gen-grpc-swift-2`
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by building it directly:
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```console
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swift build --product protoc-gen-grpc-swift-2
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```
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This command will build the plugin into `.build/debug` directory. You can get the full path using
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`swift build --show-bin-path`.

‎Sources/GRPCProtobuf/Documentation.docc/Articles/Code-generation-with-the-build-plugin.md‎

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# Code generation with the build plugin
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This article describes how to use `protoc` to generate stubs for gRPC Swift and
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Swift Protobuf from your Protocol Buffers `.proto` files.
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## Overview
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The build plugin (`GRPCProtobufGenerator`) is a great choice for convenient
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dynamic code generation, however it does come with some limitations. Because it
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generates the gRPC Swift stubs as part of the build it has the requirement that
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`protoc` must be available at compile time. This requirement means it is not a
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good fit for library authors who do not have direct control over this.
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To learn more about other options for code generation see <doc:Generating-stubs>.
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The build plugin works by detecting `.proto` files in the source tree and
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invokes `protoc` once for each file (caching results and performing the
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generation as necessary).
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If you haven't installed `protoc` yet refer to <doc:Installing-protoc> for
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instructions.
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### Adoption
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You must adopt Swift Package Manager build plugins on a per-target basis by
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modifying your package manifest (`Package.swift` file). To do this, declare the
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`grpc-swift-protobuf` package as a dependency and add the plugin to your desired
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targets.
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For example, to make use of the plugin for generating gRPC Swift stubs as part
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of the `echo-server` target:
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```swift
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targets: [
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.executableTarget(
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name: "echo-server",
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dependencies: [
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// ...
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],
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plugins: [
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.plugin(
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name: "GRPCProtobufGenerator",
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package: "grpc-swift-protobuf"
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)
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]
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)
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]
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```
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Once this is done you need to ensure that the `.proto` files to be used for
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generation are included in the target's source directory and that you have
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defined a configuration file.
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## Configuration
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You must provide a configuration file named
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`grpc-swift-proto-generator-config.json` in the directory which encloses all
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`.proto` files (in the same directory as the files or a parent directory). The
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configuration file tells the build plugin about the options used for `protoc`
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invocations.
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> Warning:
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> The name of the config file is important and must match exactly, the
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> plugin won't be applied if it can't find the config file.
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You can use the following as a starting point for your configuration:
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```json
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{
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"generate": {
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"clients": true,
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"servers": true,
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"messages": true
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}
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}
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```
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By default clients, servers, and messages will be generated with the `internal`
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access level.
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The full structure of the config file looks like this:
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```json
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{
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"generate": {
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"clients": true,
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"servers": true,
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"messages": true
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},
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"generatedSource": {
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"accessLevelOnImports": false,
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"accessLevel": "internal"
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},
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"protoc": {
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"executablePath": "/opt/homebrew/bin/protoc",
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"importPaths": [
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"../directory_1"
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]
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}
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}
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```
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Each of the options are described below:
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| Name | Possible Values | Default | Description |
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|----------------------------------------|--------------------------------------------|--------------|-----------------------------------------------------|
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| `generate.servers` | `true`, `false` | `true` | Generate server stubs |
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| `generate.clients` | `true`, `false` | `true` | Generate client stubs |
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| `generate.messages` | `true`, `false` | `true` | Generate message stubs |
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| `generatedSource.accessLevelOnImports` | `true`, `false` | `false` | Whether imports should have explicit access levels |
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| `generatedSource.accessLevel` | `"public"`, `"package"`, `"internal"` | `"internal"` | Access level for generated stubs |
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| `protoc.executablePath` | N/A | `null`† | Path to the `protoc` executable |
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| `protoc.importPaths` | N/A | `null`‡ | Import paths passed to `protoc` |
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† The Swift Package Manager build plugin infrastructure will attempt to discover
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the executable's location if you don't provide one.
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‡ If you don't provide any import paths then the path to the configuration file
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will be used on a per-source-file basis.
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Many of these options map to `protoc-gen-grpc-swift-2` and `protoc-gen-swift`
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options.
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If you require greater flexibility you may specify more than one configuration
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file. Configuration files apply to all `.proto` files equal to or below it in
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the file hierarchy. A configuration file lower in the file hierarchy supersedes
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one above it.

‎Sources/GRPCProtobuf/Documentation.docc/Articles/Code-generation-with-the-command-plugin.md‎

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# Code generation with generate-grpc-code-from-protos
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This article describes how to use the `generate-grpc-code-from-protos` Swift
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Package Manager command plugin to generate gRPC Swift and Swift Protobuf code
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from your Protocol Buffers `.proto` files.
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This plugin is particularly useful for:
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- **Manual, on-demand code generation:** When you prefer to explicitly generate
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code rather than relying on a build tool plugin.
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- **Libraries:** For Swift packages intended as libraries, where generated
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source code should be checked into your repository to avoid external `protoc`
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dependencies for your library's consumers.
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If you haven't installed `protoc` yet refer to <doc:Installing-protoc> for
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instructions.
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## Adding the Plugin to Your Package
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To use `generate-grpc-code-from-protos` your package needs to depend on
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`grpc-swift-protobuf`. You **don't** need to add a dependency on each target
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like you would for the build plugin.
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## Basic Usage
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Once your package depends on `grpc-swift-protobuf` you can invoke it using:
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```sh
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swift package generate-grpc-code-from-protos path/to/YourService.proto path/to/YourMessages.proto
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```
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If you've organised your protos within a single directory then you can
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pass the path of the directory as an argument instead, the plugin will find
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all `.proto` files nested within that directory:
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```sh
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swift package generate-grpc-code-from-protos Protos
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```
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By default the plugin generates code for gRPC servers, clients, and Protobuf
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messages into the current working directory. To change where the code is
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generated you can specify the `--output-path` option:
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```sh
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swift package generate-grpc-code-from-protos --output-path Sources/Generated -- Protos
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```
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> Important: The "`--`" separates options and inputs passed to the plugin.
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>
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> Everything after "`--`" is treated as an input (a `.proto` file or a
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> directory), everything before "`--`" is treated as an option with a value or
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> a flag. If there is no "`--`" then all arguments are treated as input.
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You should now have a basic understanding of how to use the plugin. You can
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configure how the code is generated via a number of options, a few commonly used
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ones are:
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- `--no-client` disables client code generation,
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- `--no-server` disables server code generation,
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- `--no-messages` disables message code generation,
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- `--access-level <access>` specifies the access level of the generated code,
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(`<access>` must be one of "internal", "package", or "public").
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You can read about other options by referring to the `--help` text:
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```sh
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swift package generate-grpc-code-from-protos --help
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```
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### Permissions
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Swift Package Manager command plugins require permission to create files. You'll
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be prompted to give `generate-grpc-code-from-protos` permission when running it.
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To avoid being prompted you can grant permissions ahead of time by specifying
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`--allow-writing-to-package-directory` to the `swift package` command. For
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example:
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```sh
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swift package --allow-writing-to-package-directory generate-grpc-code-from-protos Protos
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```

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