suggest_borrow_generic_arg: erase regions sooner

Author: dianne

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -666,6 +666,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             return None;
         }
 
+        // Erase region variables before performing any substitutions (#133118)
+        let moved_arg_ty = tcx.erase_regions(moved_arg_ty);
+
         // Try borrowing a shared reference first, then mutably.
         if let Some(mutbl) = [ty::Mutability::Not, ty::Mutability::Mut].into_iter().find(|&mutbl| {
             let re = self.infcx.tcx.lifetimes.re_erased;

tests/ui/moves/region-var-in-moved-ty-issue-133118.rs

@@ -0,0 +1,25 @@
+//! regression test for #133118
+
+pub trait Alpha {
+    fn y(self) -> usize;
+}
+
+pub trait Beta {
+    type Gamma;
+    fn gamma(&self) -> Self::Gamma;
+}
+
+pub fn a<T: Alpha>(_x: T) -> usize {
+    todo!();
+}
+
+pub fn x<B>(beta: &B) -> usize
+where
+    for<'a> &'a B: Beta,
+    for<'a> <&'a B as Beta>::Gamma: Alpha,
+{
+    let g1 = beta.gamma();
+    a(g1) + a(g1) //~ ERROR use of moved value: `g1` [E0382]
+}
+
+pub fn main() {}

tests/ui/moves/region-var-in-moved-ty-issue-133118.stderr

@@ -0,0 +1,21 @@
+error[E0382]: use of moved value: `g1`
+  --> $DIR/region-var-in-moved-ty-issue-133118.rs:22:15
+   |
+LL |     let g1 = beta.gamma();
+   |         -- move occurs because `g1` has type `<&B as Beta>::Gamma`, which does not implement the `Copy` trait
+LL |     a(g1) + a(g1)
+   |       --      ^^ value used here after move
+   |       |
+   |       value moved here
+   |
+note: consider changing this parameter type in function `a` to borrow instead if owning the value isn't necessary
+  --> $DIR/region-var-in-moved-ty-issue-133118.rs:12:24
+   |
+LL | pub fn a<T: Alpha>(_x: T) -> usize {
+   |        -               ^ this parameter takes ownership of the value
+   |        |
+   |        in this function
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0382`.