Auto merge of #113376 - Nilstrieb:pointer-coercions-are-not-casts-because-that-sounds-way-to-general-aaaa, r=oli-obk

Rename `adjustment::PointerCast` and variants using it to `PointerCoercion`

It makes it sounds like the `ExprKind` and `Rvalue` are supposed to represent all pointer related casts, when in reality their just used to share a little enum variants. Make it clear there these are only coercions and that people who see this and think "why are so many pointer related casts not in these variants" aren't insane.

This enum was added in #59987. I'm not sure whether the variant sharing is actually worth it, but this at least makes it less confusing.

r? oli-obk

compiler/rustc_middle/src/mir/mod.rs

@@ -2014,7 +2014,7 @@ impl<'tcx> Rvalue<'tcx> {
                 | CastKind::IntToFloat
                 | CastKind::FnPtrToPtr
                 | CastKind::PtrToPtr
-                | CastKind::Pointer(_)
+                | CastKind::PointerCoercion(_)
                 | CastKind::PointerFromExposedAddress
                 | CastKind::DynStar
                 | CastKind::Transmute,

compiler/rustc_middle/src/mir/syntax.rs

@@ -7,7 +7,7 @@ use super::{BasicBlock, Constant, Local, SwitchTargets, UserTypeProjection};
 
 use crate::mir::coverage::{CodeRegion, CoverageKind};
 use crate::traits::Reveal;
-use crate::ty::adjustment::PointerCast;
+use crate::ty::adjustment::PointerCoercion;
 use crate::ty::subst::SubstsRef;
 use crate::ty::{self, List, Ty};
 use crate::ty::{Region, UserTypeAnnotationIndex};
@@ -1230,9 +1230,9 @@ pub enum CastKind {
     /// An address-to-pointer cast that picks up an exposed provenance.
     /// See the docs on `from_exposed_addr` for more details.
     PointerFromExposedAddress,
-    /// All sorts of pointer-to-pointer casts. Note that reference-to-raw-ptr casts are
+    /// Pointer related casts that are done by coercions. Note that reference-to-raw-ptr casts are
     /// translated into `&raw mut/const *r`, i.e., they are not actually casts.
-    Pointer(PointerCast),
+    PointerCoercion(PointerCoercion),
     /// Cast into a dyn* object.
     DynStar,
     IntToInt,

compiler/rustc_middle/src/thir.rs

@@ -18,7 +18,7 @@ use rustc_index::IndexVec;
 use rustc_middle::middle::region;
 use rustc_middle::mir::interpret::AllocId;
 use rustc_middle::mir::{self, BinOp, BorrowKind, FakeReadCause, Mutability, UnOp};
-use rustc_middle::ty::adjustment::PointerCast;
+use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, AdtDef, FnSig, List, Ty, UpvarSubsts};
 use rustc_middle::ty::{CanonicalUserType, CanonicalUserTypeAnnotation};
@@ -329,9 +329,10 @@ pub enum ExprKind<'tcx> {
     NeverToAny {
         source: ExprId,
     },
-    /// A pointer cast. More information can be found in [`PointerCast`].
-    Pointer {
-        cast: PointerCast,
+    /// A pointer coercion. More information can be found in [`PointerCoercion`].
+    /// Pointer casts that cannot be done by coercions are represented by [`ExprKind::Cast`].
+    PointerCoercion {
+        cast: PointerCoercion,
         source: ExprId,
     },
     /// A `loop` expression.

compiler/rustc_middle/src/thir/visit.rs

@@ -65,7 +65,7 @@ pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Exp
         Cast { source } => visitor.visit_expr(&visitor.thir()[source]),
         Use { source } => visitor.visit_expr(&visitor.thir()[source]),
         NeverToAny { source } => visitor.visit_expr(&visitor.thir()[source]),
-        Pointer { source, cast: _ } => visitor.visit_expr(&visitor.thir()[source]),
+        PointerCoercion { source, cast: _ } => visitor.visit_expr(&visitor.thir()[source]),
         Let { expr, .. } => {
             visitor.visit_expr(&visitor.thir()[expr]);
         }

compiler/rustc_middle/src/ty/adjustment.rs

@@ -6,7 +6,7 @@ use rustc_span::Span;
 use rustc_target::abi::FieldIdx;
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
-pub enum PointerCast {
+pub enum PointerCoercion {
     /// Go from a fn-item type to a fn-pointer type.
     ReifyFnPointer,
 
@@ -99,7 +99,7 @@ pub enum Adjust<'tcx> {
     /// Take the address and produce either a `&` or `*` pointer.
     Borrow(AutoBorrow<'tcx>),
 
-    Pointer(PointerCast),
+    Pointer(PointerCoercion),
 
     /// Cast into a dyn* object.
     DynStar,

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -332,7 +332,7 @@ TrivialTypeTraversalAndLiftImpls! {
     crate::ty::IntVarValue,
     crate::ty::ParamConst,
     crate::ty::ParamTy,
-    crate::ty::adjustment::PointerCast,
+    crate::ty::adjustment::PointerCoercion,
     crate::ty::RegionVid,
     crate::ty::UniverseIndex,
     crate::ty::Variance,