🔍 Detection of fragile unions and/or imports

[favonia]

Fragile = possibly changing the semantics when new top-level definitions are added in imported libraries.

Fragile code:

import "x.file" [a]
improt "y.file"

def c = a // future bindings from "y.file" can shadow "a"

Non-fragile code:

import "x.file" [a]
improt "y.file" [b]

def c = a // future bindings from "y.file" cannot shadow "a" because of the pattern [b]

The library should support giving warnings for these cases.