2021 prelude collision lint expands macros when used as an expression

[ehuss]

The rust_2021_prelude_collisions lint suggestion seems to expand the expression for a macro, but I don't think it should. The following:

#![warn(rust_2021_prelude_collisions)]

fn bar() {}

macro_rules! foo {
    () => {{
        $crate::bar();
        S
    }};
}

trait MyTry<T> {
    fn try_into(self) -> Result<T, ()>;
}

struct S;

impl MyTry<i32> for S {
    fn try_into(self) -> Result<i32, ()> {
        unimplemented!();
    }
}

fn main() {
    foo!().try_into().unwrap();
}

The suggestion recommends replacing it with:

    MyTry::try_into({
        $crate::bar();
        S
    }).unwrap();

which will not compile. I would expect it to suggest:

MyTry::try_into(foo!()).unwrap();

Found during the crater run for:

• https://github.com/cedric-h/sorry - https://crater-reports.s3.amazonaws.com/pr-87190-3/try%23a7a572ce3edd6d476191fbfe92c9c1986e009b34/gh/cedric-h.sorry/log.txt

Meta

rustc --version --verbose:

rustc 1.56.0-nightly (b03ccace5 2021-08-24)
binary: rustc
commit-hash: b03ccace573bb91e27625c190a0f7807045a1012
commit-date: 2021-08-24
host: x86_64-apple-darwin
release: 1.56.0-nightly
LLVM version: 13.0.0

[m-ou-se]

This is basically the same issue as #87955, and probably happens in many more places. The solution is simple, but this would be the third place we add a loop to follow spans up expansions until the right one is found. So I'll see if I can put it into a method on span.

(Something like Span::find_parent_inside(outer: Span) -> Option<Span> or something. Or maybe we can somehow fix it in a more general way.)

[m-ou-se]

The same happens for arguments, not just for the receiver:

#![warn(rust_2021_prelude_collisions)]

fn bar() {}

macro_rules! foo {
    () => {{
        $crate::bar();
        S
    }};
}

trait MyTry<T> {
    fn try_into(self, _: u8);
}

struct S;

impl MyTry<i32> for S {
    fn try_into(self, _: u8) {}
}

fn main() {
    foo!().try_into(todo!());
}

help: disambiguate the associated function
   |
29 ~     MyTry::try_into({
30 +         $crate::bar();
31 +         S
32 ~     }, $crate::panicking::panic($msg));
   |

And worse: if the source code of todo!() in core isn't available, this ICEs.