Improve pnpm install errors (#1078)

* Improve pnpm install errors

This PR adds detailed and consistent error messages for the pnpm install buildpack + includes snapshot testing for the output.

* Update CHANGELOG.md

Signed-off-by: Colin Casey <[email protected]>

---------

Signed-off-by: Colin Casey <[email protected]>

Author: colincasey

Diff for: Cargo.lock

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- Updated error messages and formatting. ([#1078](https://github.com/heroku/buildpacks-nodejs/pull/1078))
+
 ## [3.6.0] - 2025-04-09
 
 - No changes.

Diff for: buildpacks/nodejs-pnpm-install/CHANGELOG.md

@@ -16,5 +16,7 @@ serde = "1"
 toml = "0.8"
 
 [dev-dependencies]
+insta = "1"
 libcnb-test = "=0.28.1"
+serde_json = "1"
 test_support.workspace = true

Diff for: buildpacks/nodejs-pnpm-install/Cargo.toml

@@ -3,7 +3,7 @@ api = "0.10"
 [buildpack]
 id = "heroku/nodejs-pnpm-install"
 version = "3.6.0"
-name = "Heroku Node.js pnpm install"
+name = "Heroku Node.js pnpm Install"
 homepage = "https://github.com/heroku/buildpacks-nodejs"
 description = "Heroku's Node.js pnpm install buildpack. A component of the 'heroku/nodejs' buildpack."
 keywords = ["pnpm", "heroku"]

Diff for: buildpacks/nodejs-pnpm-install/buildpack.toml

@@ -50,7 +50,7 @@ pub(crate) fn configure_pnpm_store_directory(
     }
 
     cmd::pnpm_set_store_dir(env, &addressable_layer.path())
-        .map_err(PnpmInstallBuildpackError::PnpmDir)?;
+        .map_err(PnpmInstallBuildpackError::PnpmSetStoreDir)?;
 
     Ok(log)
 }

Diff for: buildpacks/nodejs-pnpm-install/src/configure_pnpm_store_directory.rs

@@ -26,19 +26,23 @@ pub(crate) fn configure_pnpm_virtual_store_directory(
     log = log.sub_bullet("Creating pnpm virtual store");
     let virtual_store_dir = virtual_layer.path().join("store");
     // Create a directory for dependencies in the virtual store.
-    create_dir(&virtual_store_dir).map_err(PnpmInstallBuildpackError::VirtualLayer)?;
+    create_dir(&virtual_store_dir)
+        .map_err(|e| PnpmInstallBuildpackError::CreateDirectory(virtual_store_dir.clone(), e))?;
+
     cmd::pnpm_set_virtual_dir(env, &virtual_store_dir)
-        .map_err(PnpmInstallBuildpackError::PnpmDir)?;
+        .map_err(PnpmInstallBuildpackError::PnpmSetVirtualStoreDir)?;
 
     // Install a symlink from {virtual_layer}/node_modules to
     // {app_dir}/node_modules, so that dependencies in
     // {virtual_layer}/store/ can find their dependencies via the Node
     // module loader's ancestor directory traversal.
-    symlink(
-        context.app_dir.join("node_modules"),
-        virtual_layer.path().join("node_modules"),
-    )
-    .map_err(PnpmInstallBuildpackError::VirtualLayer)?;
+    let from = context.app_dir.join("node_modules");
+    let to = virtual_layer.path().join("node_modules");
+    symlink(&from, &to).map_err(|source| PnpmInstallBuildpackError::CreateSymlink {
+        from,
+        to,
+        source,
+    })?;
 
     Ok(log)
 }