go/types, types2: missing types for unions #50093
Description
Pointed out in slack by @dominikh, we're not recording types for union (T1 | T2) or approximation (~T) elements in interfaces, or inlined in constraints. This is inconsistent and may be the first time we don't record a type for a binary or unary expression.
We should consider changing this behavior to record the relevant union type. It is not clear what to do in the case of A | B | C: this expression consists of two binary expressions, but we only build one union in the type checker.