Do not ICE on private type in field of unresolved struct

Author: estebank

compiler/rustc_resolve/src/diagnostics.rs

@@ -2179,9 +2179,9 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let ast::ExprKind::Struct(struct_expr) = &expr.kind else { return };
         // We don't have to handle type-relative paths because they're forbidden in ADT
         // expressions, but that would change with `#[feature(more_qualified_paths)]`.
-        let Some(Res::Def(_, def_id)) =
-            self.partial_res_map[&struct_expr.path.segments.iter().last().unwrap().id].full_res()
-        else {
+        let Some(segment) = struct_expr.path.segments.iter().last() else { return };
+        let Some(partial_res) = self.partial_res_map.get(&segment.id) else { return };
+        let Some(Res::Def(_, def_id)) = partial_res.full_res() else {
             return;
         };
         let Some(default_fields) = self.field_defaults(def_id) else { return };

tests/ui/structs/default-field-values/non-exhaustive-ctor-not-found.rs

@@ -0,0 +1,8 @@
+// Regression test for https://github.com/rust-lang/rust/issues/145367
+mod m {
+    struct Priv2;
+}
+fn main() {
+    WithUse { one: m::Priv2 } //~ ERROR: cannot find struct, variant or union type `WithUse` in this scope 
+    //~^ ERROR: unit struct `Priv2` is private
+}

tests/ui/structs/default-field-values/non-exhaustive-ctor-not-found.stderr

@@ -0,0 +1,22 @@
+error[E0422]: cannot find struct, variant or union type `WithUse` in this scope
+  --> $DIR/non-exhaustive-ctor-not-found.rs:6:5
+   |
+LL |     WithUse { one: m::Priv2 }
+   |     ^^^^^^^ not found in this scope
+
+error[E0603]: unit struct `Priv2` is private
+  --> $DIR/non-exhaustive-ctor-not-found.rs:6:23
+   |
+LL |     WithUse { one: m::Priv2 }
+   |                       ^^^^^ private unit struct
+   |
+note: the unit struct `Priv2` is defined here
+  --> $DIR/non-exhaustive-ctor-not-found.rs:3:5
+   |
+LL |     struct Priv2;
+   |     ^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0422, E0603.
+For more information about an error, try `rustc --explain E0422`.