Auto merge of #132275 - compiler-errors:deref-effects, r=fee1-dead

Register `~const` preds for `Deref` adjustments in HIR typeck

This doesn't *do* anything yet, since `Deref` and `DerefMut` aren't constified, and we explicitly don't error on calling non-const trait methods in HIR yet -- presumably that will wait until std is re-constified. But I'm confident this logic is correct, and this (afaict?) is the only major hole left in enforcing `~const` in HIR typeck.

r? fee1-dead

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -254,10 +254,32 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         for a in &adj {
-            if let Adjust::NeverToAny = a.kind {
-                if a.target.is_ty_var() {
-                    self.diverging_type_vars.borrow_mut().insert(a.target);
-                    debug!("apply_adjustments: adding `{:?}` as diverging type var", a.target);
+            match a.kind {
+                Adjust::NeverToAny => {
+                    if a.target.is_ty_var() {
+                        self.diverging_type_vars.borrow_mut().insert(a.target);
+                        debug!("apply_adjustments: adding `{:?}` as diverging type var", a.target);
+                    }
+                }
+                Adjust::Deref(Some(overloaded_deref)) => {
+                    self.enforce_context_effects(
+                        expr.span,
+                        overloaded_deref.method_call(self.tcx),
+                        self.tcx.mk_args(&[a.target.into()]),
+                    );
+                }
+                Adjust::Deref(None) => {
+                    // FIXME(effects): We *could* enforce `&T: ~const Deref` here.
+                }
+                Adjust::Pointer(_pointer_coercion) => {
+                    // FIXME(effects): We should probably enforce these.
+                }
+                Adjust::ReborrowPin(_mutability) => {
+                    // FIXME(effects): We could enforce these; they correspond to
+                    // `&mut T: DerefMut` tho, so it's kinda moot.
+                }
+                Adjust::Borrow(_) => {
+                    // No effects to enforce here.
                 }
             }
         }

compiler/rustc_hir_typeck/src/place_op.rs

@@ -296,6 +296,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             );
                         };
                         *deref = OverloadedDeref { mutbl, span: deref.span };
+                        self.enforce_context_effects(expr.span, method.def_id, method.args);
                         // If this is a union field, also throw an error for `DerefMut` of `ManuallyDrop` (see RFC 2514).
                         // This helps avoid accidental drops.
                         if inside_union

compiler/rustc_middle/src/ty/adjustment.rs

@@ -1,5 +1,6 @@
 use rustc_abi::FieldIdx;
 use rustc_hir as hir;
+use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
 use rustc_span::Span;
@@ -123,19 +124,18 @@ pub struct OverloadedDeref {
 }
 
 impl OverloadedDeref {
-    /// Get the zst function item type for this method call.
-    pub fn method_call<'tcx>(&self, tcx: TyCtxt<'tcx>, source: Ty<'tcx>) -> Ty<'tcx> {
+    /// Get the [`DefId`] of the method call for the given `Deref`/`DerefMut` trait
+    /// for this overloaded deref's mutability.
+    pub fn method_call<'tcx>(&self, tcx: TyCtxt<'tcx>) -> DefId {
         let trait_def_id = match self.mutbl {
             hir::Mutability::Not => tcx.require_lang_item(LangItem::Deref, None),
             hir::Mutability::Mut => tcx.require_lang_item(LangItem::DerefMut, None),
         };
-        let method_def_id = tcx
-            .associated_items(trait_def_id)
+        tcx.associated_items(trait_def_id)
             .in_definition_order()
             .find(|m| m.kind == ty::AssocKind::Fn)
             .unwrap()
-            .def_id;
-        Ty::new_fn_def(tcx, method_def_id, [source])
+            .def_id
     }
 }
 

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -136,7 +136,9 @@ impl<'tcx> Cx<'tcx> {
             Adjust::Deref(Some(deref)) => {
                 // We don't need to do call adjust_span here since
                 // deref coercions always start with a built-in deref.
-                let call = deref.method_call(self.tcx(), expr.ty);
+                let call_def_id = deref.method_call(self.tcx());
+                let overloaded_callee =
+                    Ty::new_fn_def(self.tcx(), call_def_id, self.tcx().mk_args(&[expr.ty.into()]));
 
                 expr = Expr {
                     temp_lifetime,
@@ -150,7 +152,13 @@ impl<'tcx> Cx<'tcx> {
 
                 let expr = Box::new([self.thir.exprs.push(expr)]);
 
-                self.overloaded_place(hir_expr, adjustment.target, Some(call), expr, deref.span)
+                self.overloaded_place(
+                    hir_expr,
+                    adjustment.target,
+                    Some(overloaded_callee),
+                    expr,
+                    deref.span,
+                )
             }
             Adjust::Borrow(AutoBorrow::Ref(m)) => ExprKind::Borrow {
                 borrow_kind: m.to_borrow_kind(),