conflicts caused by implicit using Base and importall Base.Operators

[JeffBezanson]

If a module M exports a name that's also exported by Base, using M leads to the new warning Warning: both M and Base export "sin"; uses of it in module Main must be qualified. This makes it very hard to make packages that override Base functions.

One workaround is to use import M.sin instead of using, however that fails for operators because of the implicit importall Base.Operators. You get for example Warning: ignoring conflicting import of M.+ into Main.

These warnings are great for usings and imports that are written explicitly, e.g. if you write import A.x; import B.x, but they're annoying in the case of the default imports.

Some mitigation ideas:

• Remove the implicit importall Base.Operators
• Allow other modules to silently override names brought in by the implicit using Base

[vtjnash]

ref #8113

[mauro3]

Shouldn't it be the case that functions of Base should almost never be overridden? Overriding them silently seems bad. My vote goes to option one of the mitigation ideas.

[Sisyphuss]

3 questions:

1. We made using the same functions drop both. Why we want to override the Base.function now?
2. How does the import M.sin walk around?
3. If Module A imports Module S, Module B imports Module S and Module A, what will happen?

[mauro3]

Not sure about answers to your questions. But this issue was resolved by #12235, I think.

[Sisyphuss]

These questions go beyond this issue. Knowing the answers to these questions will help the development in other situations.