1738179 - [meta] Remove, or rewrite and document, extensions inside `namespace std`

Status: NEW

(Firefox Build System :: General, task, P3)

Description

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Extending std is UB in most cases, with some specified exceptions.

As I write this, there are at least 55 of them in our code: https://searchfox.org/mozilla-central/search?q=namespace+std+{

E.g.:

• Overloading std::swap like we do for mozilla::UniquePtr is allowed before C++20, but not working fully as expected. In that case, swap should be a non-member function in the same namespace as the type, i.e. mozilla::. More about doing it correctly: https://quuxplusone.github.io/blog/2020/07/11/the-std-swap-two-step/
• OVerloading std::hash like we do for mozilla::wr::WeSpatialId is allowed, but it's recommended not to open namespace std { ... }, instead overload std::hash<...> directly.

Etc.
I would suggest filing bugs under this one to tackle each of these, or groups thereof.
And wherever we really want to overload something in std::, it should be explained with a comment.

Here are some more ideas about what can&should be done safely: https://quuxplusone.github.io/blog/2021/10/27/dont-reopen-namespace-std/

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The meta keyword is there, the bug doesn't depend on other bugs and there is no activity for 12 months.
:ahochheiden, maybe it's time to close this bug?

Comment 2

[Alex Hochheiden [:ahochheiden] (needinfo? me)]

I think this bug is still valid. It's just that nobody has gotten around to working on it yet.

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

The meta keyword is there, the bug doesn't depend on other bugs and there is no activity for 12 months.
:ahochheiden, maybe it's time to close this bug?

Comment 4

[Alex Hochheiden [:ahochheiden] (needinfo? me)]

Still valid (36 instances). Same justification as comment 2 for keeping this open.