Env helper layers

CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- `libherokubuildpack`: Add `env::DefaultEnvLayer` and `env::ConfigureEnvLayer` structs for setting environment variables ([#598](https://github.com/heroku/libcnb.rs/pull/598))
 
 ## [0.17.0] - 2023-12-06
 

libherokubuildpack/Cargo.toml

@@ -18,9 +18,10 @@ all-features = true
 workspace = true
 
 [features]
-default = ["command", "download", "digest", "error", "log", "tar", "toml", "fs", "write"]
+default = ["command", "download", "digest", "error", "env_layer", "log", "tar", "toml", "fs", "write"]
 download = ["dep:ureq", "dep:thiserror"]
 digest = ["dep:sha2"]
+env_layer = ["dep:libcnb"]
 error = ["log", "dep:libcnb"]
 log = ["dep:termcolor"]
 tar = ["dep:tar", "dep:flate2"]

libherokubuildpack/src/env_layer.rs

@@ -0,0 +1,125 @@
+use libcnb::build::BuildContext;
+use libcnb::data::layer_content_metadata::LayerTypes;
+use libcnb::generic::GenericMetadata;
+use libcnb::layer::{Layer, LayerResult, LayerResultBuilder};
+use libcnb::layer_env::LayerEnv;
+use std::marker::PhantomData;
+use std::path::Path;
+
+/// Convenience layer for setting environment variables
+///
+/// If you do not need to modify files on disk or cache metadata, you can use this layer along with
+/// [`BuildContext::handle_layer`] to apply results of [`LayerEnv::chainable_insert`] to build and
+/// launch (runtime) environments.
+///
+/// Example:
+///
+/// ```no_run
+///# use libcnb::build::{BuildContext, BuildResult, BuildResultBuilder};
+///# use libcnb::data::launch::{LaunchBuilder, ProcessBuilder};
+///# use libcnb::data::process_type;
+///# use libcnb::detect::{DetectContext, DetectResult, DetectResultBuilder};
+///# use libcnb::generic::{GenericError, GenericMetadata, GenericPlatform};
+///# use libcnb::{buildpack_main, Buildpack};
+///# use libcnb::data::layer::LayerName;
+///
+///# pub(crate) struct HelloWorldBuildpack;
+///
+/// use libcnb::Env;
+/// use libcnb::data::layer_name;
+/// use libcnb::layer_env::{LayerEnv, ModificationBehavior, Scope};
+/// use libherokubuildpack::env_layer;
+///
+///# impl Buildpack for HelloWorldBuildpack {
+///#     type Platform = GenericPlatform;
+///#     type Metadata = GenericMetadata;
+///#     type Error = GenericError;
+///
+///#     fn detect(&self, _context: DetectContext<Self>) -> libcnb::Result<DetectResult, Self::Error> {
+///#         todo!()
+///#     }
+///
+///#     fn build(&self, context: BuildContext<Self>) -> libcnb::Result<BuildResult, Self::Error> {
+///         let env = Env::from_current();
+///
+///         let env = {
+///             let layer = context.handle_layer(
+///                 layer_name!("configure_env"),
+///                 env_layer::ConfigureEnvLayer::new(
+///                     LayerEnv::new()
+///                         .chainable_insert(
+///                             Scope::All,
+///                             ModificationBehavior::Override,
+///                             "BUNDLE_GEMFILE", // Tells bundler where to find the `Gemfile`
+///                             context.app_dir.join("Gemfile"),
+///                         )
+///                         .chainable_insert(
+///                             Scope::All,
+///                             ModificationBehavior::Override,
+///                             "BUNDLE_CLEAN", // After successful `bundle install` bundler will automatically run `bundle clean`
+///                             "1",
+///                         )
+///                         .chainable_insert(
+///                             Scope::All,
+///                             ModificationBehavior::Override,
+///                             "BUNDLE_DEPLOYMENT", // Requires the `Gemfile.lock` to be in sync with the current `Gemfile`.
+///                             "1",
+///                         )
+///                         .chainable_insert(
+///                             Scope::All,
+///                             ModificationBehavior::Default,
+///                             "MY_ENV_VAR",
+///                             "Whatever I want",
+///                         ),
+///                 ),
+///             )?;
+///             layer.env.apply(Scope::Build, &env)
+///         };
+///
+///#        todo!()
+///#     }
+///# }
+/// ```
+pub struct ConfigureEnvLayer<B: libcnb::Buildpack> {
+    pub(crate) data: LayerEnv,
+    pub(crate) _buildpack: std::marker::PhantomData<B>,
+}
+
+impl<B> ConfigureEnvLayer<B>
+where
+    B: libcnb::Buildpack,
+{
+    #[must_use]
+    pub fn new(env: LayerEnv) -> Self {
+        ConfigureEnvLayer {
+            data: env,
+            _buildpack: PhantomData,
+        }
+    }
+}
+
+impl<B> Layer for ConfigureEnvLayer<B>
+where
+    B: libcnb::Buildpack,
+{
+    type Buildpack = B;
+    type Metadata = GenericMetadata;
+
+    fn types(&self) -> LayerTypes {
+        LayerTypes {
+            build: true,
+            launch: true,
+            cache: false,
+        }
+    }
+
+    fn create(
+        &self,
+        _context: &BuildContext<Self::Buildpack>,
+        _layer_path: &Path,
+    ) -> Result<LayerResult<Self::Metadata>, B::Error> {
+        LayerResultBuilder::new(GenericMetadata::default())
+            .env(self.data.clone())
+            .build()
+    }
+}

libherokubuildpack/src/lib.rs

@@ -6,6 +6,8 @@ pub mod command;
 pub mod digest;
 #[cfg(feature = "download")]
 pub mod download;
+#[cfg(feature = "env_layer")]
+pub mod env_layer;
 #[cfg(feature = "error")]
 pub mod error;
 #[cfg(feature = "fs")]