Supress swapping lhs and rhs in equality suggestion in extern macro

Signed-off-by: xizheyin <[email protected]>

Author: xizheyin

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -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 is in an external macro,
+            // 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;
+            }
+
             if let Ok(rhs_snippet) = sm.span_to_snippet(rhs_expr.span)
                 && let Ok(lhs_snippet) = sm.span_to_snippet(lhs_expr.span)
             {

tests/ui/typeck/suggestions/sugg-swap-equality-in-macro-issue-139050.rs

@@ -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() {}

tests/ui/typeck/suggestions/sugg-swap-equality-in-macro-issue-139050.stderr

@@ -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`.