Rollup merge of #99696 - WaffleLapkin:uplift, r=fee1-dead

Uplift `clippy::for_loops_over_fallibles` lint into rustc

This PR, as the title suggests, uplifts [`clippy::for_loops_over_fallibles`] lint into rustc. This lint warns for code like this:
```rust
for _ in Some(1) {}
for _ in Ok::<_, ()>(1) {}
```
i.e. directly iterating over `Option` and `Result` using `for` loop.

There are a number of suggestions that this PR adds (on top of what clippy suggested):
1. If the argument (? is there a better name for that expression) of a `for` loop is a `.next()` call, then we can suggest removing it (or rather replacing with `.by_ref()` to allow iterator being used later)
   ```rust
    for _ in iter.next() {}
    // turns into
    for _ in iter.by_ref() {}
    ```
2. (otherwise) We can suggest using `while let`, this is useful for non-iterator, iterator-like things like [async] channels
   ```rust
   for _ in rx.recv() {}
   // turns into
   while let Some(_) = rx.recv() {}
   ```
3. If the argument type is `Result<impl IntoIterator, _>` and the body has a `Result<_, _>` type, we can suggest using `?`
   ```rust
   for _ in f() {}
   // turns into
   for _ in f()? {}
   ```
4. To preserve the original behavior and clear intent, we can suggest using `if let`
   ```rust
   for _ in f() {}
   // turns into
   if let Some(_) = f() {}
   ```
(P.S. `Some` and `Ok` are interchangeable depending on the type)

I still feel that the lint wording/look is somewhat off, so I'll be happy to hear suggestions (on how to improve suggestions :D)!

Resolves #99272

[`clippy::for_loops_over_fallibles`]: https://rust-lang.github.io/rust-clippy/master/index.html#for_loops_over_fallibles

1 files changed, 3 insertions, 0 deletions

diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 070cccd141b..fee6e080c4f 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -52,6 +52,7 @@ mod early;
 mod enum_intrinsics_non_enums;
 mod errors;
 mod expect;
+mod for_loops_over_fallibles;
 pub mod hidden_unicode_codepoints;
 mod internal;
 mod late;
@@ -86,6 +87,7 @@ use rustc_span::Span;
 use array_into_iter::ArrayIntoIter;
 use builtin::*;
 use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
+use for_loops_over_fallibles::*;
 use hidden_unicode_codepoints::*;
 use internal::*;
 use let_underscore::*;
@@ -188,6 +190,7 @@ macro_rules! late_lint_mod_passes {
         $macro!(
             $args,
             [
+                ForLoopsOverFallibles: ForLoopsOverFallibles,
                 HardwiredLints: HardwiredLints,
                 ImproperCTypesDeclarations: ImproperCTypesDeclarations,
                 ImproperCTypesDefinitions: ImproperCTypesDefinitions,