Don't use thir::PatKind::DerefPattern for implicit pin-patterns

Author: Zalathar

compiler/rustc_mir_build/src/builder/matches/match_pair.rs

@@ -287,8 +287,9 @@ impl<'tcx> MatchPairTree<'tcx> {
                 None
             }
 
+            // FIXME: Pin-patterns should probably have their own pattern kind,
+            // instead of overloading `PatKind::Deref` via the pattern type.
             PatKind::Deref { ref subpattern }
-            | PatKind::DerefPattern { ref subpattern, borrow: ByRef::Yes(Pinnedness::Pinned, _) }
                 if let Some(ref_ty) = pattern.ty.pinned_ty()
                     && ref_ty.is_ref() =>
             {

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -11,7 +11,7 @@ use rustc_abi::{FieldIdx, Integer};
 use rustc_errors::codes::*;
 use rustc_hir::def::{CtorOf, DefKind, Res};
 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
-use rustc_hir::{self as hir, ByRef, LangItem, Mutability, Pinnedness, RangeEnd};
+use rustc_hir::{self as hir, LangItem, RangeEnd};
 use rustc_index::Idx;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::interpret::LitToConstInput;
@@ -114,16 +114,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                     let borrow = self.typeck_results.deref_pat_borrow_mode(adjust.source, pat);
                     PatKind::DerefPattern { subpattern: thir_pat, borrow }
                 }
-                PatAdjust::PinDeref => {
-                    let mutable = self.typeck_results.pat_has_ref_mut_binding(pat);
-                    PatKind::DerefPattern {
-                        subpattern: thir_pat,
-                        borrow: ByRef::Yes(
-                            Pinnedness::Pinned,
-                            if mutable { Mutability::Mut } else { Mutability::Not },
-                        ),
-                    }
-                }
+                PatAdjust::PinDeref => PatKind::Deref { subpattern: thir_pat },
             };
             Box::new(Pat { span, ty: adjust.source, kind })
         });