fix(runtime): explain package.json parse errors

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/command_install_invalid_package_json/snapshots.toml

@@ -0,0 +1,8 @@
+[[case]]
+name = "command_install_invalid_package_json"
+vp = "global"
+steps = [
+  { argv = ["vpt", "write-file", ".node-version", "22.18.0"], snapshot = false },
+  { argv = ["vpt", "write-file", "package.json", "not-json"], snapshot = false },
+  { argv = ["vp", "install"], comment = "should name the package.json that failed to parse", continue-on-failure = true },
+]

crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/command_install_invalid_package_json/snapshots/command_install_invalid_package_json.md

@@ -0,0 +1,19 @@
+# command_install_invalid_package_json
+
+## `vpt write-file .node-version 22.18.0`
+
+
+## `vpt write-file package.json not-json`
+
+
+## `vp install`
+
+should name the package.json that failed to parse
+
+**Exit code:** 1
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+error: Failed to download Node.js runtime: Failed to parse <workspace>/package.json: expected ident at line 1 column 2
+```

crates/vp_js_runtime/src/error.rs

@@ -1,4 +1,5 @@
 use thiserror::Error;
+use vt_path::AbsolutePath;
 use vt_str::Str;
 
 /// Errors that can occur during JavaScript runtime management
@@ -40,6 +41,10 @@ pub enum Error {
     #[error("Failed to parse version index: {reason}")]
     VersionIndexParseFailed { reason: Str },
 
+    /// Failed to parse package.json
+    #[error("Failed to parse {path}: {reason}")]
+    PackageJsonParseFailed { path: Box<AbsolutePath>, reason: Str },
+
     /// No version matching the requirement found
     #[error("No version matching '{version_req}' found")]
     NoMatchingVersion { version_req: Str },

crates/vp_js_runtime/src/runtime.rs

@@ -667,7 +667,11 @@ pub async fn read_package_json(
     }
 
     let content = tokio::fs::read_to_string(package_json_path).await?;
-    let pkg: PackageJson = serde_json::from_str(&content)?;
+    let pkg: PackageJson =
+        serde_json::from_str(&content).map_err(|e| Error::PackageJsonParseFailed {
+            path: package_json_path.as_absolute_path().into(),
+            reason: vt_str::format!("{e}"),
+        })?;
     Ok(Some(pkg))
 }
 
@@ -992,6 +996,70 @@ mod tests {
         .await;
     }
 
+    #[tokio::test]
+    async fn test_read_package_json_invalid_json_names_file() {
+        let temp_dir = TempDir::new().unwrap();
+        let temp_path = AbsolutePathBuf::new(temp_dir.path().to_path_buf()).unwrap();
+
+        // Write invalid package.json file
+        let package_json_path = temp_path.join("package.json");
+        tokio::fs::write(&package_json_path, "not-json").await.unwrap();
+
+        let error = read_package_json(&package_json_path).await.unwrap_err();
+
+        // Should be the dedicated package.json error variant
+        assert!(
+            matches!(error, Error::PackageJsonParseFailed { .. }),
+            "unexpected error: {error:?}"
+        );
+
+        // Should name the file, line & column that failed to parse
+        assert_eq!(
+            error.to_string(),
+            format!(
+                "Failed to parse {}: expected ident at line 1 column 2",
+                package_json_path.as_absolute_path()
+            )
+        );
+    }
+
+    #[tokio::test]
+    async fn test_download_runtime_for_project_invalid_package_json() {
+        let vp_home = TempDir::new().unwrap();
+        vp_shared::EnvConfig::with_vars_async(
+            [(env_vars::VP_HOME, vp_home.path().as_os_str())],
+            |_| async {
+                let temp_dir = TempDir::new().unwrap();
+                let temp_path = AbsolutePathBuf::new(temp_dir.path().to_path_buf()).unwrap();
+
+                // Write invalid package.json file
+                tokio::fs::write(temp_path.join("package.json"), "not-json").await.unwrap();
+
+                // Write sibling .node-version to trigger proceeding to package.json re-read
+                tokio::fs::write(temp_path.join(".node-version"), "22.18.0\n").await.unwrap();
+
+                let error = download_runtime_for_project(&temp_path).await.unwrap_err();
+
+                // Should fail on the package.json re-read
+                assert!(
+                    matches!(error, Error::PackageJsonParseFailed { .. }),
+                    "unexpected error: {error:?}"
+                );
+
+                // Should name the file, line & column that failed to parse
+                let package_json_path = temp_path.join("package.json");
+                assert_eq!(
+                    error.to_string(),
+                    format!(
+                        "Failed to parse {}: expected ident at line 1 column 2",
+                        package_json_path.as_absolute_path()
+                    )
+                );
+            },
+        )
+        .await;
+    }
+
     #[tokio::test]
     async fn test_download_runtime_for_project_inherits_parent_node_version() {
         let vp_home = shared_vp_home();