Add more lint warnings

[MikePopoloski]

Ideas for things that should be checked:

• ~~Implicit conversions in constexprs that change value~~
• ~~empty loop/if body~~
• header guard mismatch
• misleading if else indentation
• ~~implicit conversions~~
• self-assign
• shadowing names
• ~~signedness issues~~
• ~~switch coverage of enum~~
• uninitialized vars in constexprs
• unreachable code
• ~~unused variables~~
• ~~unused typedef~~
• ~~unused parameters~~
• ~~posedge of multi-bit value~~
• latches, blocking assignments in ffs
• dangling else
• ~~missing return~~
• comparisons that always eval to same result
• ~~enums in set membership ops~~

[Sustrak]

Hi, I would like to add the following lint rule: Register only assigned on reset. The reason is that most synthesis tools will complain about this.

The following code snipped would trigger this warning:

logic my_register;
always_ff @(posedge clk or negedge rst) begin
    if (~rst) begin
        my_register <= '0;
    end else begin
        ...
        { other signals but no, my_register }
        ...
    end
end

Where it would be the best place to put the code to detect this scenario?

[MikePopoloski]

I think it would be easiest as a post-processing task once the AST is constructed. You can walk the tree, find all variables and then loop through their drivers by calling getFirstDriver() / getNextDriver() and look at the places it's assigned.