fix(fetch): clearer errors for non-string / host-less URLs

src/runtime/webcore/fetch.rs

@@ -272,7 +272,7 @@ fn bun_fetch_preconnect(
         return Err(global_object
             .err(
                 jsc::ErrorCode::INVALID_ARG_TYPE,
-                format_args!("fetch() URL must not be a blank string."),
+                format_args!("fetch() URL must have a hostname"),
             )
             .throw());
     }
@@ -310,10 +310,18 @@ impl StringOrURL {
         }
 
         let out = jsc::URL::href_from_js(value, global_this)?;
-        if out.tag() == BunStringTag::Dead {
-            return Ok(None);
+        if out.tag() != BunStringTag::Dead {
+            return Ok(Some(out));
+        }
+        // RequestInit objects keep the url property path; other values stringify.
+        if value.is_object() {
+            if let Some(url_prop) = value.fast_get(global_this, jsc::BuiltinName::Url)? {
+                if !url_prop.is_undefined() {
+                    return Ok(None);
+                }
+            }
         }
-        Ok(Some(out))
+        Ok(Some(BunString::from_js(value, global_this)?))
     }
 }
 
@@ -588,6 +596,17 @@ fn fetch_impl<const ALLOW_GET_BODY: bool>(
         url_type = URLType::Blob;
     }
 
+    if url_type == URLType::Remote
+        && (url.is_http() || url.is_https() || url.is_s3())
+        && url.hostname.is_empty()
+    {
+        let err = ctx.to_type_error(
+            jsc::ErrorCode::INVALID_URL,
+            format_args!("fetch() URL must have a hostname"),
+        );
+        return Ok(JSPromise::rejected_promise(global_this, err).to_js());
+    }
+
     // **Start with the harmless ones.**
 
     // "method"

test/js/web/fetch/fetch-args.test.ts

@@ -166,6 +166,9 @@ describe.concurrent("fetch() early rejections are reported when unhandled", () =
   const cases: [name: string, code: string, expectedStderr: string][] = [
     ["no arguments", `fetch()`, "fetch() expects a string but received no arguments"],
     ["blank url", `fetch("")`, "fetch() URL must not be a blank string"],
+    ["number url", `fetch(123)`, "fetch() URL is invalid"],
+    ["undefined url", `fetch(undefined)`, "fetch() URL is invalid"],
+    ["relative toString url", `fetch({ toString() { return "/some_path"; } })`, "fetch() URL is invalid"],
     ["invalid url", `fetch("not a url")`, "fetch() URL is invalid"],
     ["unsupported protocol", `fetch("gopher://example.com/")`, "protocol must be http:, https: or s3:"],
     // No host may be read behind the second scheme, and the request still has to be refused.