fix(npm): improve error message on directory import in npm package (#19538)

Co-authored-by: David Sherret <dsherret@users.noreply.github.com>

1 files changed, 27 insertions, 6 deletions

diff --git a/cli/module_loader.rs b/cli/module_loader.rs
index 9e814662c..54efcd9dd 100644
--- a/cli/module_loader.rs
+++ b/cli/module_loader.rs
@@ -748,13 +748,34 @@ impl NpmModuleLoader {
       .read_to_string(&file_path)
       .map_err(AnyError::from)
       .with_context(|| {
-        let mut msg = "Unable to load ".to_string();
-        msg.push_str(&file_path.to_string_lossy());
-        if let Some(referrer) = &maybe_referrer {
-          msg.push_str(" imported from ");
-          msg.push_str(referrer.as_str());
+        if file_path.is_dir() {
+          // directory imports are not allowed when importing from an
+          // ES module, so provide the user with a helpful error message
+          let dir_path = file_path;
+          let mut msg = "Directory import ".to_string();
+          msg.push_str(&dir_path.to_string_lossy());
+          if let Some(referrer) = &maybe_referrer {
+            msg.push_str(" is not supported resolving import from ");
+            msg.push_str(referrer.as_str());
+            let entrypoint_name = ["index.mjs", "index.js", "index.cjs"]
+              .iter()
+              .find(|e| dir_path.join(e).is_file());
+            if let Some(entrypoint_name) = entrypoint_name {
+              msg.push_str("\nDid you mean to import ");
+              msg.push_str(entrypoint_name);
+              msg.push_str(" within the directory?");
+            }
+          }
+          msg
+        } else {
+          let mut msg = "Unable to load ".to_string();
+          msg.push_str(&file_path.to_string_lossy());
+          if let Some(referrer) = &maybe_referrer {
+            msg.push_str(" imported from ");
+            msg.push_str(referrer.as_str());
+          }
+          msg
         }
-        msg
       })?;
 
     let code = if self.cjs_resolutions.contains(specifier) {