Rollup merge of #122835 - compiler-errors:deref-pure, r=Nadrieril

Require `DerefMut` and `DerefPure` on `deref!()` patterns when appropriate

Waiting on the deref pattern syntax pr to merge

r? nadrieril

compiler/rustc_hir/src/lang_items.rs

@@ -199,6 +199,7 @@ language_item_table! {
 
     Deref,                   sym::deref,               deref_trait,                Target::Trait,          GenericRequirement::Exact(0);
     DerefMut,                sym::deref_mut,           deref_mut_trait,            Target::Trait,          GenericRequirement::Exact(0);
+    DerefPure,               sym::deref_pure,          deref_pure_trait,           Target::Trait,          GenericRequirement::Exact(0);
     DerefTarget,             sym::deref_target,        deref_target,               Target::AssocTy,        GenericRequirement::None;
     Receiver,                sym::receiver,            receiver_trait,             Target::Trait,          GenericRequirement::None;
 

compiler/rustc_hir_typeck/src/pat.rs

@@ -2002,8 +2002,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         pat_info: PatInfo<'tcx, '_>,
     ) -> Ty<'tcx> {
         let tcx = self.tcx;
-        // FIXME(deref_patterns): use `DerefPure` for soundness
-        // FIXME(deref_patterns): use `DerefMut` when required
+        // Register a `DerefPure` bound, which is required by all `deref!()` pats.
+        self.register_bound(
+            expected,
+            tcx.require_lang_item(hir::LangItem::DerefPure, Some(span)),
+            self.misc(span),
+        );
         // <expected as Deref>::Target
         let ty = Ty::new_projection(
             tcx,
@@ -2013,6 +2017,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let ty = self.normalize(span, ty);
         let ty = self.try_structurally_resolve_type(span, ty);
         self.check_pat(inner, ty, pat_info);
+
+        // Check if the pattern has any `ref mut` bindings, which would require
+        // `DerefMut` to be emitted in MIR building instead of just `Deref`.
+        // We do this *after* checking the inner pattern, since we want to make
+        // sure to apply any match-ergonomics adjustments.
+        if self.typeck_results.borrow().pat_has_ref_mut_binding(inner) {
+            self.register_bound(
+                expected,
+                tcx.require_lang_item(hir::LangItem::DerefMut, Some(span)),
+                self.misc(span),
+            );
+        }
+
         expected
     }
 

compiler/rustc_middle/src/ty/typeck_results.rs

@@ -430,6 +430,31 @@ impl<'tcx> TypeckResults<'tcx> {
         LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.pat_adjustments }
     }
 
+    /// Does the pattern recursively contain a `ref mut` binding in it?
+    ///
+    /// This is used to determined whether a `deref` pattern should emit a `Deref`
+    /// or `DerefMut` call for its pattern scrutinee.
+    ///
+    /// This is computed from the typeck results since we want to make
+    /// sure to apply any match-ergonomics adjustments, which we cannot
+    /// determine from the HIR alone.
+    pub fn pat_has_ref_mut_binding(&self, pat: &'tcx hir::Pat<'tcx>) -> bool {
+        let mut has_ref_mut = false;
+        pat.walk(|pat| {
+            if let hir::PatKind::Binding(_, id, _, _) = pat.kind
+                && let Some(ty::BindByReference(ty::Mutability::Mut)) =
+                    self.pat_binding_modes().get(id)
+            {
+                has_ref_mut = true;
+                // No need to continue recursing
+                false
+            } else {
+                true
+            }
+        });
+        has_ref_mut
+    }
+
     /// For a given closure, returns the iterator of `ty::CapturedPlace`s that are captured
     /// by the closure.
     pub fn closure_min_captures_flattened(

compiler/rustc_span/src/symbol.rs

@@ -674,6 +674,7 @@ symbols! {
         deref_mut,
         deref_mut_method,
         deref_patterns,
+        deref_pure,
         deref_target,
         derive,
         derive_const,