After installing the module and going to the upgrade status report page, I encountered an error alert: Scanning is not possible until this is resolved.
and indeed was unable to click the button to scan selected modules/themes.
This error occurred due to a stray "z" that was prepending the composer.json file. I did not notice initially because the composer.json file I was using was not inside the web directory, but was actually up a level. Leaving this note here for anyone else who encounters this error. After finding and removing this "z", I next encountered the error documented in this other issue 💬 PHPStan binary was not found in the default vendor directory Postponed: needs info , for which there is a helpful fix in the comments.
The takeaway is that if you see this error, and are confused because your composer.json looks perfectly fine, check to make sure that you are looking at the same composer.json file that Drupal is looking at.
Maybe there is some way to tell upgrade status or Drupal to look at the correct composer.json.
Closed: works as designed
3.0
Code
Per the description, a solution has already been reached, but maybe there is still room for improvement?
The error already includes the file path which is the most we can do to help resolve the issue.
throw new \Exception('Unable to decode composer information from ' . $composer_json_path . '.');