Use StackId instead of String in contexts (#173)

CHANGELOG.md

@@ -36,5 +36,6 @@
 - New trait design for `LayerLifecycle` which also was renamed to `Layer`.
 - Removed low-level layer functions from `BuildContext`. They don't fit well with the design of the library at this
   point and are potential footguns. Implementing a `Layer` should work for all use-cases.
+- The `stack_id` field in `BuildContext` and `DetectContext` is now of type `StackId` instead of `String`.
 
 ## [0.3.0] 2021/09/17

libcnb/src/build.rs

@@ -6,14 +6,15 @@ use crate::buildpack::Buildpack;
 use crate::data::store::Store;
 use crate::layer::{HandleLayerErrorOrBuildpackError, Layer, LayerData};
 
+use crate::data::buildpack::StackId;
 use crate::data::{buildpack::BuildpackToml, buildpack_plan::BuildpackPlan, launch::Launch};
 
 /// Context for the build phase execution.
 pub struct BuildContext<B: Buildpack + ?Sized> {
     pub layers_dir: PathBuf,
     pub app_dir: PathBuf,
     pub buildpack_dir: PathBuf,
-    pub stack_id: String,
+    pub stack_id: StackId,
     pub platform: B::Platform,
     pub buildpack_plan: BuildpackPlan,
     pub buildpack_descriptor: BuildpackToml<B::Metadata>,

libcnb/src/detect.rs

@@ -4,13 +4,14 @@ use std::fmt::Debug;
 use std::path::PathBuf;
 
 use crate::buildpack::Buildpack;
+use crate::data::buildpack::StackId;
 use crate::{data::build_plan::BuildPlan, data::buildpack::BuildpackToml};
 
 /// Context for the detect phase execution.
 pub struct DetectContext<B: Buildpack + ?Sized> {
     pub app_dir: PathBuf,
     pub buildpack_dir: PathBuf,
-    pub stack_id: String,
+    pub stack_id: StackId,
     pub platform: B::Platform,
     pub buildpack_descriptor: BuildpackToml<B::Metadata>,
 }

libcnb/src/error.rs

@@ -1,3 +1,4 @@
+use crate::data::buildpack::StackIdError;
 use crate::data::launch::ProcessTypeError;
 use crate::layer::HandleLayerError;
 use crate::toml_file::TomlFileError;
@@ -17,6 +18,9 @@ pub enum Error<E: Debug + Display> {
     #[error("Process type error: {0}")]
     ProcessTypeError(#[from] ProcessTypeError),
 
+    #[error("Stack ID error: {0}")]
+    StackIdError(#[from] StackIdError),
+
     #[error("Could not determine app directory: {0}")]
     CannotDetermineAppDirectory(std::io::Error),
 

libcnb/src/runtime.rs

@@ -8,7 +8,7 @@ use serde::de::DeserializeOwned;
 
 use crate::build::{BuildContext, InnerBuildResult};
 use crate::buildpack::Buildpack;
-use crate::data::buildpack::BuildpackToml;
+use crate::data::buildpack::{BuildpackToml, StackId};
 use crate::detect::{DetectContext, InnerDetectResult};
 use crate::error::Error;
 use crate::platform::Platform;
@@ -86,7 +86,9 @@ fn libcnb_runtime_detect<B: Buildpack>(buildpack: &B) -> Result<(), B::Error> {
 
     let app_dir = env::current_dir().map_err(Error::CannotDetermineAppDirectory)?;
 
-    let stack_id: String = env::var("CNB_STACK_ID").map_err(Error::CannotDetermineStackId)?;
+    let stack_id: StackId = env::var("CNB_STACK_ID")
+        .map_err(Error::CannotDetermineStackId)
+        .and_then(|stack_id_string| stack_id_string.parse().map_err(Error::StackIdError))?;
 
     let platform = B::Platform::from_path(&args.platform_dir_path)
         .map_err(Error::CannotCreatePlatformFromPath)?;
@@ -121,7 +123,9 @@ fn libcnb_runtime_build<B: Buildpack>(buildpack: &B) -> Result<(), B::Error> {
 
     let app_dir = env::current_dir().map_err(Error::CannotDetermineAppDirectory)?;
 
-    let stack_id: String = env::var("CNB_STACK_ID").map_err(Error::CannotDetermineStackId)?;
+    let stack_id: StackId = env::var("CNB_STACK_ID")
+        .map_err(Error::CannotDetermineStackId)
+        .and_then(|stack_id_string| stack_id_string.parse().map_err(Error::StackIdError))?;
 
     let platform = B::Platform::from_path(&args.platform_dir_path)
         .map_err(Error::CannotCreatePlatformFromPath)?;