Desugars drop and replace at MIR build

This commit desugars the drop and replace deriving from an
assignment at MIR build, avoiding the construction of the
DropAndReplace terminator (which will be removed in a followign PR)

In order to retain the same error messages for replaces a new
DesugaringKind::Replace variant is introduced.

1 files changed, 2 insertions, 0 deletions

diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index dee823eefde..9f22e9776d4 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -1151,6 +1151,7 @@ pub enum DesugaringKind {
     Await,
     ForLoop,
     WhileLoop,
+    Replace,
 }
 
 impl DesugaringKind {
@@ -1166,6 +1167,7 @@ impl DesugaringKind {
             DesugaringKind::OpaqueTy => "`impl Trait`",
             DesugaringKind::ForLoop => "`for` loop",
             DesugaringKind::WhileLoop => "`while` loop",
+            DesugaringKind::Replace => "drop and replace",
         }
     }
 }