Don't ignore _ in type casts and ascriptions

src/librustc_typeck/check/mod.rs

@@ -2437,9 +2437,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         // types that involve projections, since those can resolve to
         // `'static` bounds (modulo #54940, which hopefully will be
         // fixed by the time you see this comment, dear reader,
-        // although I have my doubts). Other sorts of things are
-        // already sufficiently enforced with erased regions. =)
-        if ty.has_free_regions() || ty.has_projections() {
+        // although I have my doubts). Also pass in types with inference
+        // types, because they may be repeated. Other sorts of things
+        // are already sufficiently enforced with erased regions. =)
+        if ty.has_free_regions() || ty.has_projections() || ty.has_infer_types() {
             let c_ty = self.infcx.canonicalize_response(&UserType::Ty(ty));
             debug!("to_ty_saving_user_provided_ty: c_ty={:?}", c_ty);
             self.tables.borrow_mut().user_provided_types_mut().insert(ast_ty.hir_id, c_ty);

src/test/mir-opt/retag.rs

@@ -75,18 +75,18 @@ fn main() {
 //         _10 = move _8;
 //         Retag(_10);
 //         ...
-//         _14 = &mut (*_10);
-//         Retag(_14);
-//         _13 = move _14 as *mut i32 (Misc);
-//         Retag([raw] _13);
+//         _15 = &mut (*_10);
+//         Retag(_15);
+//         _14 = move _15 as *mut i32 (Misc);
+//         Retag([raw] _14);
 //         ...
-//         _17 = move _18(move _19) -> bb2;
+//         _18 = move _19(move _20) -> bb2;
 //     }
 //
 //     bb2: {
-//         Retag(_17);
+//         Retag(_18);
 //         ...
-//         _21 = const Test::foo_shr(move _22, move _24) -> bb3;
+//         _22 = const Test::foo_shr(move _23, move _25) -> bb3;
 //     }
 //
 //     bb3: {

src/test/ui/nll/user-annotations/issue-57731-ascibed-coupled-types.rs

@@ -0,0 +1,40 @@
+// Check that repeated type variables are correctly handled
+
+#![allow(unused)]
+#![feature(nll, type_ascription)]
+
+type PairUncoupled<'a, 'b, T> = (&'a T, &'b T);
+type PairCoupledTypes<T> = (T, T);
+type PairCoupledRegions<'a, T> = (&'a T, &'a T);
+
+fn uncoupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+    let ((y, _z),) = ((s, _x),): (PairUncoupled<_>,);
+    y // OK
+}
+
+fn coupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+    let ((y, _z),) = ((s, _x),): (PairCoupledTypes<_>,);
+    y //~ ERROR lifetime may not live long enough
+}
+
+fn coupled_regions_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+    let ((y, _z),) = ((s, _x),): (PairCoupledRegions<_>,);
+    y //~ ERROR lifetime may not live long enough
+}
+
+fn cast_uncoupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+    let ((y, _z),) = ((s, _x),) as (PairUncoupled<_>,);
+    y // OK
+}
+
+fn cast_coupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+    let ((y, _z),) = ((s, _x),) as (PairCoupledTypes<_>,);
+    y //~ ERROR lifetime may not live long enough
+}
+
+fn cast_coupled_regions_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+    let ((y, _z),) = ((s, _x),) as (PairCoupledRegions<_>,);
+    y //~ ERROR lifetime may not live long enough
+}
+
+fn main() {}

src/test/ui/nll/user-annotations/issue-57731-ascibed-coupled-types.stderr

@@ -0,0 +1,38 @@
+error: lifetime may not live long enough
+  --> $DIR/issue-57731-ascibed-coupled-types.rs:17:5
+   |
+LL | fn coupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+   |                      -- lifetime `'a` defined here
+LL |     let ((y, _z),) = ((s, _x),): (PairCoupledTypes<_>,);
+LL |     y //~ ERROR lifetime may not live long enough
+   |     ^ returning this value requires that `'a` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/issue-57731-ascibed-coupled-types.rs:22:5
+   |
+LL | fn coupled_regions_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+   |                        -- lifetime `'a` defined here
+LL |     let ((y, _z),) = ((s, _x),): (PairCoupledRegions<_>,);
+LL |     y //~ ERROR lifetime may not live long enough
+   |     ^ returning this value requires that `'a` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/issue-57731-ascibed-coupled-types.rs:32:5
+   |
+LL | fn cast_coupled_wilds_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+   |                           -- lifetime `'a` defined here
+LL |     let ((y, _z),) = ((s, _x),) as (PairCoupledTypes<_>,);
+LL |     y //~ ERROR lifetime may not live long enough
+   |     ^ returning this value requires that `'a` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/issue-57731-ascibed-coupled-types.rs:37:5
+   |
+LL | fn cast_coupled_regions_rhs<'a>(_x: &'a u32, s: &'static u32) -> &'static u32 {
+   |                             -- lifetime `'a` defined here
+LL |     let ((y, _z),) = ((s, _x),) as (PairCoupledRegions<_>,);
+LL |     y //~ ERROR lifetime may not live long enough
+   |     ^ returning this value requires that `'a` must outlive `'static`
+
+error: aborting due to 4 previous errors
+