1819643 - downloads.download should report accurate error for clearly invalid filenames

Status: NEW

(WebExtensions :: General, enhancement, P5)

Description

[Rob Wu [:robwu]]

This is a follow-up to https://bugzilla.mozilla.org/show_bug.cgi?id=1810793#c40 . The test case in that comment triggers "Error: filename must not contain illegal characters", even though the more correct error would be something like "Invalid filename" (if an error were to be reported at all - bug 1791530).

Here is a different test case that fails to report the correct error.
STR:

1. Load an extension with the "downloads" permission, and run the following snippet:

chrome.downloads.download({
  url: URL.createObjectURL(new Blob(["x"])),
  filename: "dir/isthisadir/",
  saveAs: false,
});

Expected:

• Should throw an error about the filename being invalid. E.g. Chrome does not download and the error "Invalid filename" is logged.

Actual:

• with saveAs: false,: directory dir/isthisadir is created, and a file is saved at dir/isthisadir(1)
• with saveAs: false,: directory dir/isthisadir is created, and the file picker proposes a file called "isthisadir(1)" within that new directory.