From 5ddaa2d5e53344ff8b88d98e61e3dd36edb803e9 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 6 Mar 2022 17:21:39 -0800
Subject: [PATCH] Erase regions when checking for missing Copy predicates

---
 .../src/diagnostics/conflict_errors.rs          | 12 ++++++++++--
 .../ui/borrowck/copy-suggestion-region-vid.rs   | 17 +++++++++++++++++
 .../borrowck/copy-suggestion-region-vid.stderr  | 14 ++++++++++++++
 3 files changed, 41 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/borrowck/copy-suggestion-region-vid.rs
 create mode 100644 src/test/ui/borrowck/copy-suggestion-region-vid.stderr

diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index 684a3ced5a070..2a74e1ce8b1b1 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -448,8 +448,16 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                                 self.mir_hir_id(),
                                 rustc_infer::traits::ObligationCauseCode::MiscObligation,
                             );
-                            fulfill_cx.register_bound(&infcx, self.param_env, ty, copy_did, cause);
-                            let errors = fulfill_cx.select_where_possible(&infcx);
+                            fulfill_cx.register_bound(
+                                &infcx,
+                                self.param_env,
+                                // Erase any region vids from the type, which may not be resolved
+                                infcx.tcx.erase_regions(ty),
+                                copy_did,
+                                cause,
+                            );
+                            // Select all, including ambiguous predicates
+                            let errors = fulfill_cx.select_all_or_error(&infcx);
 
                             // Only emit suggestion if all required predicates are on generic
                             errors
diff --git a/src/test/ui/borrowck/copy-suggestion-region-vid.rs b/src/test/ui/borrowck/copy-suggestion-region-vid.rs
new file mode 100644
index 0000000000000..dff95283459b6
--- /dev/null
+++ b/src/test/ui/borrowck/copy-suggestion-region-vid.rs
@@ -0,0 +1,17 @@
+pub struct DataStruct();
+
+pub struct HelperStruct<'n> {
+    pub helpers: [Vec<&'n i64>; 2],
+    pub is_empty: bool,
+}
+
+impl DataStruct {
+    pub fn f(&self) -> HelperStruct {
+        let helpers = [vec![], vec![]];
+
+        HelperStruct { helpers, is_empty: helpers[0].is_empty() }
+        //~^ ERROR borrow of moved value
+    }
+}
+
+fn main() {}
diff --git a/src/test/ui/borrowck/copy-suggestion-region-vid.stderr b/src/test/ui/borrowck/copy-suggestion-region-vid.stderr
new file mode 100644
index 0000000000000..f03cdd84d75f8
--- /dev/null
+++ b/src/test/ui/borrowck/copy-suggestion-region-vid.stderr
@@ -0,0 +1,14 @@
+error[E0382]: borrow of moved value: `helpers`
+  --> $DIR/copy-suggestion-region-vid.rs:12:43
+   |
+LL |         let helpers = [vec![], vec![]];
+   |             ------- move occurs because `helpers` has type `[Vec<&i64>; 2]`, which does not implement the `Copy` trait
+LL | 
+LL |         HelperStruct { helpers, is_empty: helpers[0].is_empty() }
+   |                        -------            ^^^^^^^^^^^^^^^^^^^^^ value borrowed here after move
+   |                        |
+   |                        value moved here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0382`.