So you’re saying “style” wasn’t supposed to be used, and all style-related rules should go under “convention”? (I looked up all rules with the style tag, and there are only 15, which are the same two rules repeated for various relevant languages.)
Actually, a style tag might be useful – if done consistently. There are currently 46 rules with the convention tag (48 if you move the two style-tagged rules there). It seems like the ones related purely to syntax, like the curly-brace ones, indentation, etc., would be better in a separate category, especially as those are often used in many languages, whereas things like “X should implement Y” are semantic and very language-specific.
Just to make a suggestion: I think Sonar should think about having some internal documentation about API’s to ensure that developers do things consistently. For instance, there are a lot of cases in web_api where two functions will use different names for the exact same parameter. It appears that different developers went off in separate corners, each implementing their own function independently.