Better documentation for disallowed_method lint

[juliancoffee]

https://rust-lang.github.io/rust-clippy/master/#disallowed_method
Doc on All Clippy Lints shows the example of how to use it with methods from the standard library, but no example on how to use it with user-defined types neither if this is possible to use with methods of user-defined types/imported items.

When I tried to use this with nightly-2021-07-06 in rust-toolchain I managed to get it to work with std::vec::Vec::append, but no luck with user-defined methods.

[juliancoffee]

Saw this commit
70ce0c2
if I understand correctly, this is worked on currently?

[Zenithsiz]

I believe local methods still can't be used with this lint.

For example, in a crate called my_crate with the following contents:

fn f() { }

fn g() {
    f();
}

And with the following clippy.toml

disallowed-methods = [
  "f"
]

The call in g isn't warned about.

Using crate::f, my_crate::f and ::my_crate::f also doesn't work.

[tisonkun]

As the clippy.toml can be defined for workspace, I suppose my_crate::f should work as a design (but it doesn't work yet).

[tisonkun]

Besides, I may want to disallow trait method for a specific implementation. Given -

trait A { fn f (); }
Struct B; impl A for B { ... }
Struct C; impl A for C { ... }

I'd like to forbit B.f() but not C.f(). It seems now we all resolved to A::f().

[tisonkun]

my_crate::f

I checked this way works now (may be related to #8852) and even with nested mod. My issue is the comment above #7479 (comment)

[9999years]

Note: Today (Rust 1.81, though it's probably worked for a while), this works in clippy.toml:

[[disallowed-methods]]
path = "std::fs::rename"
reason = "Use fs_err::rename"

However, the documentation only includes examples for methods on types, not methods on modules, so we should clean that up.