If you use a metric like that to affect my pay, I will happily maximize the metric to ensure I get paid as much as possible.
As a bonus for you, I will also try to write good code.
As a bonus for you, I will also try to write good code.
If you base someone's livelihood on a number, expect them to attempt to maximize that number, probably at the expense of other numbers that you may or may not be considering.
This is a big part of why we think engineering metrics are a tough nut to crack: there’s a fair bit of research that suggests tying KPIs to compensation is a huge anti-pattern for certain types of work (chiefly those involving lots of novel problem solving).
Highly recommend Daniel Pink’s “A Whole New Mind” on this topic; it’s pretty fascinating stuff.
Correction, the Pink title I was referring to was "Drive: The Surprising Truth About What Motivates Us"
Pink does a great job unpacking research that demonstrates how this type of 'affect my pay' dynamic backfires for engineering.