feat: .node-version support

crates/volta-core/src/project/mod.rs

@@ -109,7 +109,10 @@ impl Project {
             extends = manifest.extends;
         }
 
-        let platform = platform.map(TryInto::try_into).transpose()?;
+        let platform = match platform.map(TryInto::try_into).transpose()? {
+            Some(platform) => Some(platform),
+            None => Self::platform_from_node_version(&manifest_file),
+        };
 
         Ok(Project {
             manifest_file,
@@ -119,6 +122,28 @@ impl Project {
         })
     }
 
+    /// Returns a Node.js version from .node_version_file
+    fn platform_from_node_version(manifest_file: &Path) -> Option<PlatformSpec> {
+        // project path without package.json
+        let project_path = manifest_file.parent()?;
+        let version_file_path = project_path.join(".node-version");
+        let version_content = std::fs::read_to_string(version_file_path).ok()?;
+        let version = version_content
+            .trim()
+            .strip_prefix('v')
+            .unwrap_or(version_content.trim());
+
+        match Version::parse(version) {
+            Ok(node) => Some(PlatformSpec {
+                node,
+                yarn: None,
+                npm: None,
+                pnpm: None,
+            }),
+            Err(_) => None,
+        }
+    }
+
     /// Returns a reference to the manifest file for the current project
     pub fn manifest_file(&self) -> &Path {
         &self.manifest_file