Fix logic for package manager detection

Author: cknitt

src/PackageManagers.res

@@ -1,11 +1,21 @@
+open Node
+
 @scope(("process", "env"))
-external execpath: option<string> = "npm_execpath"
+external npm_execpath: option<string> = "npm_execpath"
+
+let compatiblePackageManagers = ["pnpm", "npm", "yarn", "bun"]
+
+let isCompatiblePackageManager = execPath => {
+  let filename = Path.parse(execPath).name
 
-// pnpm must be before npm in this array, as npm is a substring of it
-let packageManagers = ["pnpm", "npm", "yarn", "bun"]
-let defaultPackageManager = "npm"
+  // Note: exec path may be something like
+  // /usr/local/lib/node_modules/npm/bin/npm-cli.js
+  // So we have to check for substrings here.
+  compatiblePackageManagers->Array.some(pm => filename->String.includes(pm))
+}
 
 let getActivePackageManager = () =>
-  execpath
-  ->Option.flatMap(execpath => packageManagers->Array.find(pm => execpath->String.includes(pm)))
-  ->Option.getOr(defaultPackageManager)
+  switch npm_execpath {
+  | Some(execPath) if isCompatiblePackageManager(execPath) => execPath
+  | _ => "npm"
+  }

src/bindings/Node.res

@@ -38,6 +38,16 @@ module Path = {
   external join: array<string> => string = "join"
 
   @module("node:path") external join2: (string, string) => string = "join"
+
+  type parseResult = {
+    root: string,
+    dir: string,
+    base: string,
+    ext: string,
+    name: string,
+  }
+
+  @module("node:path") external parse: string => parseResult = "parse"
 }
 
 module Process = {