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Supress swapping lhs and rhs in equality suggestion in extern macro #144266

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Supress swapping lhs and rhs in equality suggestion in extern macro #144266

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6 changes: 6 additions & 0 deletions compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3533,6 +3533,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
.must_apply_modulo_regions()
{
let sm = self.tcx.sess.source_map();
// If the span of rhs_expr or lhs_expr is in an external macro,
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There is another copy of suggest_swapping_lhs_and_rhs in rustc_trait_selection. Could you please add this check to that, too, since I think it suffers from the same issue.

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Yeah, I'll also look for a test case for that tomorrow.

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I don't really think it needs a test case, but if you want to add one it's probably something like:

upstream crate:

macro_rules! eq {
    ($a:expr) => { $a == () }
}

downstream crate:

struct Foo;

impl PartialEq<Foo> for () {
    fn eq(&self, _: &Foo) -> bool { todo!() }
}

fn main() {
    let _ = eq!(Foo);
}

Pay attention to the fact that it's a trait error and there may already be some macro suppression going on there 🤔

// we should not suggest to swap the equality. See issue #139050
if rhs_expr.span.in_external_macro(sm) || lhs_expr.span.in_external_macro(sm) {
return;
}

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Now I checked both.

if let Ok(rhs_snippet) = sm.span_to_snippet(rhs_expr.span)
&& let Ok(lhs_snippet) = sm.span_to_snippet(lhs_expr.span)
{
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13 changes: 13 additions & 0 deletions tests/ui/typeck/suggestions/sugg-swap-equality-in-macro-issue-139050.rs
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@@ -0,0 +1,13 @@
// if we use lhs == rhs in a macro, we should not suggest to swap the equality
// because the origin span of lhs and rhs can not be found. See issue #139050

use std::fmt::Debug;

pub fn foo<I: Iterator>(mut iter: I, value: &I::Item)
where
Item: Eq + Debug, //~ ERROR cannot find type `Item` in this scope [E0412]
{
debug_assert_eq!(iter.next(), Some(value)); //~ ERROR mismatched types [E0308]
assert_eq!(iter.next(), Some(value)); //~ ERROR mismatched types [E0308]
}
fn main() {}
28 changes: 28 additions & 0 deletions tests/ui/typeck/suggestions/sugg-swap-equality-in-macro-issue-139050.stderr
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@@ -0,0 +1,28 @@
error[E0412]: cannot find type `Item` in this scope
--> $DIR/sugg-swap-equality-in-macro-issue-139050.rs:8:5
|
LL | Item: Eq + Debug,
| ^^^^ not found in this scope

error[E0308]: mismatched types
--> $DIR/sugg-swap-equality-in-macro-issue-139050.rs:10:35
|
LL | debug_assert_eq!(iter.next(), Some(value));
| ^^^^^^^^^^^ expected `Option<<I as Iterator>::Item>`, found `Option<&<I as Iterator>::Item>`
|
= note: expected enum `Option<_>`
found enum `Option<&_>`

error[E0308]: mismatched types
--> $DIR/sugg-swap-equality-in-macro-issue-139050.rs:11:29
|
LL | assert_eq!(iter.next(), Some(value));
| ^^^^^^^^^^^ expected `Option<<I as Iterator>::Item>`, found `Option<&<I as Iterator>::Item>`
|
= note: expected enum `Option<_>`
found enum `Option<&_>`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0308, E0412.
For more information about an error, try `rustc --explain E0308`.
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