Proposal Details

I propose adding the following method to go/types:

IsConstant reports whether tv represents a constant.
func (tv TypeAndValue) IsConstant() bool { return tv.Value != nil }

Calling tv.IsConstant() is clearer than writing tv.Value != nil, and avoids confusion with tv.IsValue(), which tests something different.

Motivation: much code in x/tools uses tv.Value != nil, often with no explanation, making challenging code even harder to understand.