Improve Yarn errors (#1079)

* Improve Yarn errors

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

* Update CHANGELOG.md

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

* Fixed lint errors

---------

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

Author: colincasey

Diff for: Cargo.lock

@@ -7,7 +7,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added 
+
 - Added Yarn version 4.9.0.
+
+### Changed
+
+- Updated error messages and formatting. ([#1074](https://github.com/heroku/buildpacks-nodejs/pull/1074))
+  
 ## [3.6.0] - 2025-04-09
 
 - No changes.

Diff for: buildpacks/nodejs-yarn/CHANGELOG.md

@@ -10,6 +10,7 @@ workspace = true
 bullet_stream = "0.7"
 fun_run = "0.5"
 heroku-nodejs-utils.workspace = true
+indoc = "2"
 libcnb = { version = "=0.28.1", features = ["trace"] }
 libherokubuildpack = { version = "=0.28.1", default-features = false, features = [
     "download",
@@ -18,10 +19,11 @@ libherokubuildpack = { version = "=0.28.1", default-features = false, features =
 ] }
 serde = "1"
 tempfile = "3"
-thiserror = "2"
 toml = "0.8"
 
 [dev-dependencies]
-indoc = "2"
+insta = "1"
 libcnb-test = "=0.28.1"
 test_support.workspace = true
+serde_json = "1"
+ureq = "3"

Diff for: buildpacks/nodejs-yarn/Cargo.toml

@@ -2,68 +2,51 @@ use crate::yarn::Yarn;
 use bullet_stream::state::SubBullet;
 use bullet_stream::{style, Print};
 use fun_run::{CmdError, CommandWithName};
-use heroku_nodejs_utils::vrs::Version;
+use heroku_nodejs_utils::vrs::{Version, VersionError};
 use libcnb::Env;
 use std::io::Stderr;
 use std::{
     path::{Path, PathBuf},
-    process::{Command, Stdio},
+    process::Command,
 };
 
-#[derive(thiserror::Error, Debug)]
-pub(crate) enum Error {
-    #[error("Couldn't start yarn command: {0}")]
-    Spawn(std::io::Error),
-    #[error("Couldn't finish yarn  command: {0}")]
-    Wait(std::io::Error),
-    #[error("Yarn command finished with a non-zero exit code: {0}")]
-    Exit(std::process::ExitStatus),
-    #[error("Yarn output couldn't be parsed: {0}")]
-    Parse(String),
+#[derive(Debug)]
+pub(crate) enum YarnVersionError {
+    Command(CmdError),
+    Parse(String, VersionError),
 }
 
 /// Execute `yarn --version` to determine what version of `yarn` is in effect
 /// for this codebase.
-pub(crate) fn yarn_version(env: &Env) -> Result<Version, Error> {
-    let output = Command::new("yarn")
+pub(crate) fn yarn_version(env: &Env) -> Result<Version, YarnVersionError> {
+    Command::new("yarn")
         .arg("--version")
         .envs(env)
-        .stdout(Stdio::piped())
-        .spawn()
-        .map_err(Error::Spawn)?
-        .wait_with_output()
-        .map_err(Error::Wait)?;
-
-    output
-        .status
-        .success()
-        .then_some(())
-        .ok_or(Error::Exit(output.status))?;
-    let stdout = String::from_utf8_lossy(&output.stdout);
-    stdout
-        .parse()
-        .map_err(|_| Error::Parse(stdout.into_owned()))
+        .named_output()
+        .map_err(YarnVersionError::Command)
+        .and_then(|output| {
+            let stdout = output.stdout_lossy();
+            stdout
+                .parse::<Version>()
+                .map_err(|e| YarnVersionError::Parse(stdout, e))
+        })
 }
 
 /// Execute `yarn config get` to determine where the yarn cache is.
-pub(crate) fn yarn_get_cache(yarn_line: &Yarn, env: &Env) -> Result<PathBuf, Error> {
-    let mut args = vec!["config", "get"];
+pub(crate) fn yarn_get_cache(yarn_line: &Yarn, env: &Env) -> Result<PathBuf, CmdError> {
+    let mut cmd = Command::new("yarn");
+    cmd.envs(env);
+
+    cmd.arg("config");
+    cmd.arg("get");
     if yarn_line == &Yarn::Yarn1 {
-        args.push("cache-folder");
+        cmd.arg("cache-folder");
     } else {
-        args.push("cacheFolder");
+        cmd.arg("cacheFolder");
     }
-    let output = Command::new("yarn")
-        .args(args)
-        .envs(env)
-        .stdout(Stdio::piped())
-        .spawn()
-        .map_err(Error::Spawn)?
-        .wait_with_output()
-        .map_err(Error::Wait)?;
 
-    let stdout = String::from_utf8_lossy(&output.stdout).trim().to_string();
-    Ok(stdout.into())
+    cmd.named_output()
+        .map(|output| PathBuf::from(output.stdout_lossy().trim()))
 }
 
 /// Execute `yarn config set` to set the yarn cache to a specfic location.

Diff for: buildpacks/nodejs-yarn/src/cmd.rs

@@ -1,3 +1,5 @@
+use crate::yarn::Yarn;
+use crate::{cmd, YarnBuildpack, YarnBuildpackError};
 use bullet_stream::state::SubBullet;
 use bullet_stream::Print;
 use libcnb::build::BuildContext;
@@ -9,10 +11,7 @@ use libcnb::Env;
 use serde::{Deserialize, Serialize};
 use std::fs;
 use std::io::Stderr;
-use thiserror::Error;
-
-use crate::yarn::Yarn;
-use crate::{cmd, YarnBuildpack, YarnBuildpackError};
+use std::path::PathBuf;
 
 /// `DepsLayer` is a layer for caching yarn dependencies from build to build.
 /// This layer is irrelevant in zero-install mode, as cached dependencies are
@@ -62,8 +61,9 @@ pub(crate) fn configure_yarn_cache(
                 cache_usage_count: new_metadata.cache_usage_count + 1.0,
                 ..new_metadata
             })?;
-            fs::create_dir(deps_layer.path().join(CACHE_DIR))
-                .map_err(DepsLayerError::CreateCacheDir)?;
+
+            let cache_dir = deps_layer.path().join(CACHE_DIR);
+            fs::create_dir(&cache_dir).map_err(|e| DepsLayerError::CreateCacheDir(cache_dir, e))?;
         }
     }
 
@@ -86,11 +86,9 @@ pub(crate) struct DepsLayerMetadata {
     yarn: Yarn,
 }
 
-#[derive(Error, Debug)]
+#[derive(Debug)]
 pub(crate) enum DepsLayerError {
-    #[error("Couldn't create yarn dependency cache: {0}")]
-    CreateCacheDir(std::io::Error),
-    #[error("Couldn't set yarn cache folder: {0}")]
+    CreateCacheDir(PathBuf, std::io::Error),
     YarnCacheSet(fun_run::CmdError),
 }