fix(npm): use ntfs junctions in node_modules folder on Windows (#16061)

cli/Cargo.toml

@@ -111,6 +111,7 @@ zstd = '=0.11.2'
 
 [target.'cfg(windows)'.dependencies]
 fwdansi = "=1.1.0"
+junction = "=0.2.0"
 winapi = { version = "=0.3.9", features = ["knownfolders", "mswsock", "objbase", "shlobj", "tlhelp32", "winbase", "winerror", "winsock2"] }
 
 [dev-dependencies]

cli/npm/resolvers/local.rs

@@ -323,9 +323,44 @@ fn symlink_package_dir(
 
   // need to delete the previous symlink before creating a new one
   let _ignore = fs::remove_dir_all(new_path);
+
+  #[cfg(windows)]
+  return junction_or_symlink_dir(old_path, new_path);
+  #[cfg(not(windows))]
   fs_util::symlink_dir(old_path, new_path)
 }
 
+#[cfg(windows)]
+fn junction_or_symlink_dir(
+  old_path: &Path,
+  new_path: &Path,
+) -> Result<(), AnyError> {
+  // Use junctions because they're supported on ntfs file systems without
+  // needing to elevate privileges on Windows
+  match junction::create(old_path, new_path) {
+    Ok(()) => Ok(()),
+    Err(junction_err) => {
+      if cfg!(debug) {
+        // When running the tests, junctions should be created, but if not then
+        // surface this error.
+        log::warn!("Error creating junction. {:#}", junction_err);
+      }
+
+      match fs_util::symlink_dir(old_path, new_path) {
+        Ok(()) => Ok(()),
+        Err(symlink_err) => bail!(
+          concat!(
+            "Failed creating junction and fallback symlink in node_modules folder.\n\n",
+            "{:#}\n\n{:#}",
+          ),
+          junction_err,
+          symlink_err,
+        ),
+      }
+    }
+  }
+}
+
 fn join_package_name(path: &Path, package_name: &str) -> PathBuf {
   let mut path = path.to_path_buf();
   // ensure backslashes are used on windows