Remove unnecessary `&*` sigil pairs in derived code.

By producing `&T` expressions for fields instead of `T`. This matches
what the existing comments (e.g. on `FieldInfo`) claim is happening, and
it's also what most of the trait-specific code needs.

The exception is `PartialEq`, which needs `T` expressions for lots of
special case error messaging to work. So we now convert the `&T` back to
a `T` for `PartialEq`.

7 files changed, 65 insertions, 39 deletions

diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
index 9cd72ed0c67..72aa8e17d01 100644
--- a/compiler/rustc_builtin_macros/src/deriving/clone.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -161,7 +161,7 @@ fn cs_clone(
     let all_fields;
     let fn_path = cx.std_path(&[sym::clone, sym::Clone, sym::clone]);
     let subcall = |cx: &mut ExtCtxt<'_>, field: &FieldInfo| {
-        let args = vec![cx.expr_addr_of(field.span, field.self_expr.clone())];
+        let args = vec![field.self_expr.clone()];
         cx.expr_call_global(field.span, fn_path.clone(), args)
     };
 
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
index 859e995356e..aad0ab3f5bb 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
@@ -63,10 +63,7 @@ pub fn cs_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> Bl
                 let [other_expr] = &field.other_selflike_exprs[..] else {
                         cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`");
                     };
-                let args = vec![
-                    cx.expr_addr_of(field.span, field.self_expr.clone()),
-                    cx.expr_addr_of(field.span, other_expr.clone()),
-                ];
+                let args = vec![field.self_expr.clone(), other_expr.clone()];
                 cx.expr_call_global(field.span, cmp_path.clone(), args)
             }
             CsFold::Combine(span, expr1, expr2) => {
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
index 724c639984c..83534b62b46 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
@@ -2,7 +2,8 @@ use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::{path_local, path_std};
 
-use rustc_ast::{BinOpKind, MetaItem};
+use rustc_ast::ptr::P;
+use rustc_ast::{BinOpKind, BorrowKind, Expr, ExprKind, MetaItem, Mutability};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
@@ -32,7 +33,21 @@ pub fn expand_deriving_partial_eq(
                     let [other_expr] = &field.other_selflike_exprs[..] else {
                         cx.span_bug(field.span, "not exactly 2 arguments in `derive(PartialEq)`");
                     };
-                    cx.expr_binary(field.span, op, field.self_expr.clone(), other_expr.clone())
+
+                    // We received `&T` arguments. Convert them to `T` by
+                    // stripping `&` or adding `*`. This isn't necessary for
+                    // type checking, but it results in much better error
+                    // messages if something goes wrong.
+                    let convert = |expr: &P<Expr>| {
+                        if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, inner) =
+                            &expr.kind
+                        {
+                            inner.clone()
+                        } else {
+                            cx.expr_deref(field.span, expr.clone())
+                        }
+                    };
+                    cx.expr_binary(field.span, op, convert(&field.self_expr), convert(other_expr))
                 }
                 CsFold::Combine(span, expr1, expr2) => cx.expr_binary(span, combiner, expr1, expr2),
                 CsFold::Fieldless => cx.expr_bool(span, base),
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
index 3f9843922da..ce45b0e1965 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -71,10 +71,7 @@ pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_
                 let [other_expr] = &field.other_selflike_exprs[..] else {
                         cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`");
                     };
-                let args = vec![
-                    cx.expr_addr_of(field.span, field.self_expr.clone()),
-                    cx.expr_addr_of(field.span, other_expr.clone()),
-                ];
+                let args = vec![field.self_expr.clone(), other_expr.clone()];
                 cx.expr_call_global(field.span, partial_cmp_path.clone(), args)
             }
             CsFold::Combine(span, expr1, expr2) => {
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
index b99198054de..5de20520486 100644
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -95,9 +95,8 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
                 );
                 args.push(name);
             }
-            // Use double indirection to make sure this works for unsized types
+            // Use an extra indirection to make sure this works for unsized types.
             let field = cx.expr_addr_of(field.span, field.self_expr.clone());
-            let field = cx.expr_addr_of(field.span, field);
             args.push(field);
         }
         let expr = cx.expr_call_global(span, fn_path_debug, args);
@@ -115,9 +114,9 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
                 ));
             }
 
-            // Use double indirection to make sure this works for unsized types
-            let value_ref = cx.expr_addr_of(field.span, field.self_expr.clone());
-            value_exprs.push(cx.expr_addr_of(field.span, value_ref));
+            // Use an extra indirection to make sure this works for unsized types.
+            let field = cx.expr_addr_of(field.span, field.self_expr.clone());
+            value_exprs.push(field);
         }
 
         // `let names: &'static _ = &["field1", "field2"];`
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index dbac6e61ea9..a5d5782dbd2 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -1004,7 +1004,7 @@ impl<'a> MethodDef<'a> {
     /// ```
     /// #[derive(PartialEq)]
     /// # struct Dummy;
-    /// struct A { x: i32, y: i32 }
+    /// struct A { x: u8, y: u8 }
     ///
     /// // equivalent to:
     /// impl PartialEq for A {
@@ -1016,9 +1016,9 @@ impl<'a> MethodDef<'a> {
     /// But if the struct is `repr(packed)`, we can't use something like
     /// `&self.x` on a packed type (as required for e.g. `Debug` and `Hash`)
     /// because that might cause an unaligned ref. So we use let-destructuring
-    /// instead.
+    /// instead. If the struct impls `Copy`:
     /// ```
-    /// # struct A { x: i32, y: i32 }
+    /// # struct A { x: u8, y: u8 }
     /// impl PartialEq for A {
     ///     fn eq(&self, other: &A) -> bool {
     ///         let Self { x: __self_0_0, y: __self_0_1 } = *self;
@@ -1027,6 +1027,19 @@ impl<'a> MethodDef<'a> {
     ///     }
     /// }
     /// ```
+    /// If it doesn't impl `Copy`:
+    /// ```
+    /// # struct A { x: u8, y: u8 }
+    /// impl PartialEq for A {
+    ///     fn eq(&self, other: &A) -> bool {
+    ///         let Self { x: ref __self_0_0, y: ref __self_0_1 } = *self;
+    ///         let Self { x: ref __self_1_0, y: ref __self_1_1 } = *other;
+    ///         *__self_0_0 == *__self_1_0 && *__self_0_1 == *__self_1_1
+    ///     }
+    /// }
+    /// ```
+    /// This latter case only works if the fields match the alignment required
+    /// by the `packed(N)` attribute.
     fn expand_struct_method_body<'b>(
         &self,
         cx: &mut ExtCtxt<'_>,
@@ -1058,9 +1071,9 @@ impl<'a> MethodDef<'a> {
         } else {
             let prefixes: Vec<_> =
                 (0..selflike_args.len()).map(|i| format!("__self_{}", i)).collect();
-            let no_deref = always_copy;
+            let addr_of = always_copy;
             let selflike_fields =
-                trait_.create_struct_pattern_fields(cx, struct_def, &prefixes, no_deref);
+                trait_.create_struct_pattern_fields(cx, struct_def, &prefixes, addr_of);
             let mut body = mk_body(cx, selflike_fields);
 
             let struct_path = cx.path(span, vec![Ident::new(kw::SelfUpper, type_ident.span)]);
@@ -1194,9 +1207,9 @@ impl<'a> MethodDef<'a> {
                 // A single arm has form (&VariantK, &VariantK, ...) => BodyK
                 // (see "Final wrinkle" note below for why.)
 
-                let no_deref = false; // because enums can't be repr(packed)
+                let addr_of = false; // because enums can't be repr(packed)
                 let fields =
-                    trait_.create_struct_pattern_fields(cx, &variant.data, &prefixes, no_deref);
+                    trait_.create_struct_pattern_fields(cx, &variant.data, &prefixes, addr_of);
 
                 let sp = variant.span.with_ctxt(trait_.span.ctxt());
                 let variant_path = cx.path(sp, vec![type_ident, variant.ident]);
@@ -1512,7 +1525,7 @@ impl<'a> TraitDef<'a> {
         cx: &mut ExtCtxt<'_>,
         struct_def: &'a VariantData,
         prefixes: &[String],
-        no_deref: bool,
+        addr_of: bool,
     ) -> Vec<FieldInfo> {
         self.create_fields(struct_def, |i, _struct_field, sp| {
             prefixes
@@ -1520,7 +1533,7 @@ impl<'a> TraitDef<'a> {
                 .map(|prefix| {
                     let ident = self.mk_pattern_ident(prefix, i);
                     let expr = cx.expr_path(cx.path_ident(sp, ident));
-                    if no_deref { expr } else { cx.expr_deref(sp, expr) }
+                    if addr_of { cx.expr_addr_of(sp, expr) } else { expr }
                 })
                 .collect()
         })
@@ -1536,17 +1549,20 @@ impl<'a> TraitDef<'a> {
             selflike_args
                 .iter()
                 .map(|selflike_arg| {
-                    // Note: we must use `struct_field.span` rather than `span` in the
+                    // Note: we must use `struct_field.span` rather than `sp` in the
                     // `unwrap_or_else` case otherwise the hygiene is wrong and we get
                     // "field `0` of struct `Point` is private" errors on tuple
                     // structs.
-                    cx.expr(
+                    cx.expr_addr_of(
                         sp,
-                        ast::ExprKind::Field(
-                            selflike_arg.clone(),
-                            struct_field.ident.unwrap_or_else(|| {
-                                Ident::from_str_and_span(&i.to_string(), struct_field.span)
-                            }),
+                        cx.expr(
+                            sp,
+                            ast::ExprKind::Field(
+                                selflike_arg.clone(),
+                                struct_field.ident.unwrap_or_else(|| {
+                                    Ident::from_str_and_span(&i.to_string(), struct_field.span)
+                                }),
+                            ),
                         ),
                     )
                 })
diff --git a/compiler/rustc_builtin_macros/src/deriving/hash.rs b/compiler/rustc_builtin_macros/src/deriving/hash.rs
index 2213cd6d37d..52239eff5da 100644
--- a/compiler/rustc_builtin_macros/src/deriving/hash.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/hash.rs
@@ -52,14 +52,13 @@ fn hash_substructure(
     let [state_expr] = substr.nonselflike_args else {
         cx.span_bug(trait_span, "incorrect number of arguments in `derive(Hash)`");
     };
-    let call_hash = |span, thing_expr| {
+    let call_hash = |span, expr| {
         let hash_path = {
             let strs = cx.std_path(&[sym::hash, sym::Hash, sym::hash]);
 
             cx.expr_path(cx.path_global(span, strs))
         };
-        let ref_thing = cx.expr_addr_of(span, thing_expr);
-        let expr = cx.expr_call(span, hash_path, vec![ref_thing, state_expr.clone()]);
+        let expr = cx.expr_call(span, hash_path, vec![expr, state_expr.clone()]);
         cx.stmt_expr(expr)
     };
     let mut stmts = Vec::new();
@@ -67,11 +66,14 @@ fn hash_substructure(
     let fields = match substr.fields {
         Struct(_, fs) | EnumMatching(_, 1, .., fs) => fs,
         EnumMatching(.., fs) => {
-            let variant_value = deriving::call_intrinsic(
-                cx,
+            let variant_value = cx.expr_addr_of(
                 trait_span,
-                sym::discriminant_value,
-                vec![cx.expr_self(trait_span)],
+                deriving::call_intrinsic(
+                    cx,
+                    trait_span,
+                    sym::discriminant_value,
+                    vec![cx.expr_self(trait_span)],
+                ),
             );
 
             stmts.push(call_hash(trait_span, variant_value));