store the kind of pattern adjustments in pat_adjustments

This allows us to better distinguish builtin and overloaded implicit
dereferences.

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -1227,9 +1227,9 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
         // actually this is somewhat "disjoint" from the code below
         // that aims to account for `ref x`.
         if let Some(vec) = self.cx.typeck_results().pat_adjustments().get(pat.hir_id) {
-            if let Some(first_ty) = vec.first() {
-                debug!("pat_ty(pat={:?}) found adjusted ty `{:?}`", pat, first_ty);
-                return Ok(*first_ty);
+            if let Some(first_adjust) = vec.first() {
+                debug!("pat_ty(pat={:?}) found adjustment `{:?}`", pat, first_adjust);
+                return Ok(first_adjust.source);
             }
         } else if let PatKind::Ref(subpat, _) = pat.kind
             && self.cx.typeck_results().skipped_ref_pats().contains(pat.hir_id)

compiler/rustc_hir_typeck/src/pat.rs

@@ -29,6 +29,7 @@ use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::{ObligationCause, ObligationCauseCode};
 use tracing::{debug, instrument, trace};
 use ty::VariantDef;
+use ty::adjustment::{PatAdjust, PatAdjustment};
 
 use super::report_unexpected_variant_res;
 use crate::expectation::Expectation;
@@ -415,7 +416,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .pat_adjustments_mut()
                     .entry(pat.hir_id)
                     .or_default()
-                    .push(expected);
+                    .push(PatAdjustment { kind: PatAdjust::BuiltinDeref, source: expected });
 
                 let mut binding_mode = ByRef::Yes(match pat_info.binding_mode {
                     // If default binding mode is by value, make it `ref` or `ref mut`

compiler/rustc_middle/src/ty/adjustment.rs

@@ -214,3 +214,25 @@ pub enum CustomCoerceUnsized {
     /// Records the index of the field being coerced.
     Struct(FieldIdx),
 }
+
+/// Represents an implicit coercion applied to the scrutinee of a match before testing a pattern
+/// against it. Currently, this is used only for implicit dereferences.
+#[derive(Clone, Copy, TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
+pub struct PatAdjustment<'tcx> {
+    pub kind: PatAdjust,
+    /// The type of the scrutinee before the adjustment is applied, or the "adjusted type" of the
+    /// pattern.
+    pub source: Ty<'tcx>,
+}
+
+/// Represents implicit coercions of patterns' types, rather than values' types.
+#[derive(Clone, Copy, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
+#[derive(TypeFoldable, TypeVisitable)]
+pub enum PatAdjust {
+    /// An implicit dereference before matching, such as when matching the pattern `0` against a
+    /// scrutinee of type `&u8` or `&mut u8`.
+    BuiltinDeref,
+    /// An implicit call to `Deref(Mut)::deref(_mut)` before matching, such as when matching the
+    /// pattern `[..]` against a scrutinee of type `Vec<T>`.
+    OverloadedDeref,
+}

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -61,6 +61,12 @@ impl<'tcx> fmt::Debug for ty::adjustment::Adjustment<'tcx> {
     }
 }
 
+impl<'tcx> fmt::Debug for ty::adjustment::PatAdjustment<'tcx> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} -> {:?}", self.source, self.kind)
+    }
+}
+
 impl fmt::Debug for ty::BoundRegionKind {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {

compiler/rustc_middle/src/ty/typeck_results.rs

@@ -90,7 +90,7 @@ pub struct TypeckResults<'tcx> {
     ///
     /// See:
     /// <https://github.com/rust-lang/rfcs/blob/master/text/2005-match-ergonomics.md#definitions>
-    pat_adjustments: ItemLocalMap<Vec<Ty<'tcx>>>,
+    pat_adjustments: ItemLocalMap<Vec<ty::adjustment::PatAdjustment<'tcx>>>,
 
     /// Set of reference patterns that match against a match-ergonomics inserted reference
     /// (as opposed to against a reference in the scrutinee type).
@@ -403,11 +403,15 @@ impl<'tcx> TypeckResults<'tcx> {
         LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.pat_binding_modes }
     }
 
-    pub fn pat_adjustments(&self) -> LocalTableInContext<'_, Vec<Ty<'tcx>>> {
+    pub fn pat_adjustments(
+        &self,
+    ) -> LocalTableInContext<'_, Vec<ty::adjustment::PatAdjustment<'tcx>>> {
         LocalTableInContext { hir_owner: self.hir_owner, data: &self.pat_adjustments }
     }
 
-    pub fn pat_adjustments_mut(&mut self) -> LocalTableInContextMut<'_, Vec<Ty<'tcx>>> {
+    pub fn pat_adjustments_mut(
+        &mut self,
+    ) -> LocalTableInContextMut<'_, Vec<ty::adjustment::PatAdjustment<'tcx>>> {
         LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.pat_adjustments }
     }
 

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

@@ -5,7 +5,7 @@ use rustc_errors::MultiSpan;
 use rustc_hir::{BindingMode, ByRef, HirId, Mutability};
 use rustc_lint as lint;
 use rustc_middle::span_bug;
-use rustc_middle::ty::{self, Rust2024IncompatiblePatInfo, Ty, TyCtxt};
+use rustc_middle::ty::{self, Rust2024IncompatiblePatInfo, TyCtxt};
 use rustc_span::{Ident, Span};
 
 use crate::errors::{Rust2024IncompatiblePat, Rust2024IncompatiblePatSugg};
@@ -93,10 +93,10 @@ impl<'a> PatMigration<'a> {
     pub(super) fn visit_implicit_derefs<'tcx>(
         &mut self,
         pat_span: Span,
-        adjustments: &[Ty<'tcx>],
+        adjustments: &[ty::adjustment::PatAdjustment<'tcx>],
     ) -> Option<(Span, Mutability)> {
-        let implicit_deref_mutbls = adjustments.iter().map(|ref_ty| {
-            let &ty::Ref(_, _, mutbl) = ref_ty.kind() else {
+        let implicit_deref_mutbls = adjustments.iter().map(|adjust| {
+            let &ty::Ref(_, _, mutbl) = adjust.source.kind() else {
                 span_bug!(pat_span, "pattern implicitly dereferences a non-ref type");
             };
             mutbl

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

@@ -18,6 +18,7 @@ use rustc_middle::mir::interpret::LitToConstInput;
 use rustc_middle::thir::{
     Ascription, FieldPat, LocalVarId, Pat, PatKind, PatRange, PatRangeBoundary,
 };
+use rustc_middle::ty::adjustment::PatAdjustment;
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::{self, CanonicalUserTypeAnnotation, Ty, TyCtxt, TypingMode};
 use rustc_middle::{bug, span_bug};
@@ -63,7 +64,7 @@ pub(super) fn pat_from_hir<'a, 'tcx>(
 
 impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
     fn lower_pattern(&mut self, pat: &'tcx hir::Pat<'tcx>) -> Box<Pat<'tcx>> {
-        let adjustments: &[Ty<'tcx>] =
+        let adjustments: &[PatAdjustment<'tcx>] =
             self.typeck_results.pat_adjustments().get(pat.hir_id).map_or(&[], |v| &**v);
 
         // Track the default binding mode for the Rust 2024 migration suggestion.
@@ -102,11 +103,11 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
             _ => self.lower_pattern_unadjusted(pat),
         };
 
-        let adjusted_pat = adjustments.iter().rev().fold(unadjusted_pat, |thir_pat, ref_ty| {
-            debug!("{:?}: wrapping pattern with type {:?}", thir_pat, ref_ty);
+        let adjusted_pat = adjustments.iter().rev().fold(unadjusted_pat, |thir_pat, adjust| {
+            debug!("{:?}: wrapping pattern with type {:?}", thir_pat, adjust);
             Box::new(Pat {
                 span: thir_pat.span,
-                ty: *ref_ty,
+                ty: adjust.source,
                 kind: PatKind::Deref { subpattern: thir_pat },
             })
         });