Rollup merge of rust-lang#58199 - clintfred:partial-move-err-msg, r=estebank

Add better error message for partial move

closes rust-lang#56657

r? @davidtwco

Author: Mark-Simulacrum

src/librustc_mir/borrow_check/error_reporting.rs

@@ -130,6 +130,11 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
             );
 
             let mut is_loop_move = false;
+            let is_partial_move = move_site_vec.iter().any(|move_site| {
+                let move_out = self.move_data.moves[(*move_site).moi];
+                let moved_place = &self.move_data.move_paths[move_out.path].place;
+                used_place != moved_place && used_place.is_prefix_of(moved_place)
+            });
             for move_site in &move_site_vec {
                 let move_out = self.move_data.moves[(*move_site).moi];
                 let moved_place = &self.move_data.move_paths[move_out.path].place;
@@ -175,8 +180,9 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                 err.span_label(
                     span,
                     format!(
-                        "value {} here after move",
-                        desired_action.as_verb_in_past_tense()
+                        "value {} here {}",
+                        desired_action.as_verb_in_past_tense(),
+                        if is_partial_move { "after partial move" } else { "after move" },
                     ),
                 );
             }

src/test/ui/borrowck/borrowck-uninit-field-access.mir.stderr

@@ -20,7 +20,7 @@ error[E0382]: use of moved value: `line2`
 LL |     let _moved = (line2.origin, line2.middle);
    |                                 ------------ value moved here
 LL |     line2.consume(); //[ast]~ ERROR use of partially moved value: `line2` [E0382]
-   |     ^^^^^ value used here after move
+   |     ^^^^^ value used here after partial move
    |
    = note: move occurs because `line2.middle` has type `Point`, which does not implement the `Copy` trait
 

src/test/ui/nll/move-subpaths-moves-root.stderr

@@ -4,7 +4,7 @@ error[E0382]: use of moved value: `x`
 LL |     drop(x.0);
    |          --- value moved here
 LL |     drop(x); //~ ERROR use of moved value
-   |          ^ value used here after move
+   |          ^ value used here after partial move
    |
    = note: move occurs because `x.0` has type `std::vec::Vec<i32>`, which does not implement the `Copy` trait