Its not possible for humans to determine if a work qualify under copyright, so getting a computer to do it is about as impossible task as one can make it.
You can put in arbitrary heuristics and argue how many expressions, lines, or words should be required for copyright status, but then there will always be up to a judge if you guessed right.
The options here seems to either not include any detection for the copyright scope, or try invent something and hope that people will send in patches when it hit a false positive.
If you think such plugin should detect something as trivial code which it currently classify as not, send in a patch.
You can put in arbitrary heuristics and argue how many expressions, lines, or words should be required for copyright status, but then there will always be up to a judge if you guessed right.
The options here seems to either not include any detection for the copyright scope, or try invent something and hope that people will send in patches when it hit a false positive.
If you think such plugin should detect something as trivial code which it currently classify as not, send in a patch.