Merging upstream version 1.68.2+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

23 files changed, 155 insertions, 73 deletions

diff --git a/compiler/rustc_builtin_macros/src/alloc_error_handler.rs b/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
index 95e38e4b0..dcf500ddb 100644
--- a/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
+++ b/compiler/rustc_builtin_macros/src/alloc_error_handler.rs
@@ -32,7 +32,7 @@ pub fn expand(
             (item, true, ecx.with_def_site_ctxt(fn_kind.sig.span))
         } else {
             ecx.sess.parse_sess.span_diagnostic.span_err(item.span(), "alloc_error_handler must be a function");
-            return vec![orig_item.clone()];
+            return vec![orig_item];
         };
 
     // Generate a bunch of new items using the AllocFnFactory
diff --git a/compiler/rustc_builtin_macros/src/asm.rs b/compiler/rustc_builtin_macros/src/asm.rs
index 900c44274..925392b50 100644
--- a/compiler/rustc_builtin_macros/src/asm.rs
+++ b/compiler/rustc_builtin_macros/src/asm.rs
@@ -352,7 +352,7 @@ pub fn parse_asm_args<'a>(
 ///
 /// This function must be called immediately after the option token is parsed.
 /// Otherwise, the suggestion will be incorrect.
-fn err_duplicate_option<'a>(p: &mut Parser<'a>, symbol: Symbol, span: Span) {
+fn err_duplicate_option(p: &mut Parser<'_>, symbol: Symbol, span: Span) {
     let mut err = p
         .sess
         .span_diagnostic
diff --git a/compiler/rustc_builtin_macros/src/concat.rs b/compiler/rustc_builtin_macros/src/concat.rs
index e2d71825d..7da9bdc38 100644
--- a/compiler/rustc_builtin_macros/src/concat.rs
+++ b/compiler/rustc_builtin_macros/src/concat.rs
@@ -4,14 +4,12 @@ use rustc_expand::base::{self, DummyResult};
 use rustc_session::errors::report_lit_error;
 use rustc_span::symbol::Symbol;
 
-use std::string::String;
-
 pub fn expand_concat(
     cx: &mut base::ExtCtxt<'_>,
     sp: rustc_span::Span,
     tts: TokenStream,
 ) -> Box<dyn base::MacResult + 'static> {
-    let Some(es) = base::get_exprs_from_tts(cx, sp, tts) else {
+    let Some(es) = base::get_exprs_from_tts(cx, tts) else {
         return DummyResult::any(sp);
     };
     let mut accumulator = String::new();
diff --git a/compiler/rustc_builtin_macros/src/concat_bytes.rs b/compiler/rustc_builtin_macros/src/concat_bytes.rs
index d1124145d..4f1a7d709 100644
--- a/compiler/rustc_builtin_macros/src/concat_bytes.rs
+++ b/compiler/rustc_builtin_macros/src/concat_bytes.rs
@@ -69,7 +69,7 @@ fn invalid_type_err(
         Ok(ast::LitKind::Int(_, _)) => {
             cx.span_err(span, "numeric literal is not a `u8`");
         }
-        Ok(ast::LitKind::ByteStr(_) | ast::LitKind::Byte(_)) => unreachable!(),
+        Ok(ast::LitKind::ByteStr(..) | ast::LitKind::Byte(_)) => unreachable!(),
         Err(err) => {
             report_lit_error(&cx.sess.parse_sess, err, token_lit, span);
         }
@@ -97,7 +97,7 @@ fn handle_array_element(
             )) if val <= u8::MAX.into() => Some(val as u8),
 
             Ok(ast::LitKind::Byte(val)) => Some(val),
-            Ok(ast::LitKind::ByteStr(_)) => {
+            Ok(ast::LitKind::ByteStr(..)) => {
                 if !*has_errors {
                     cx.struct_span_err(expr.span, "cannot concatenate doubly nested array")
                         .note("byte strings are treated as arrays of bytes")
@@ -137,7 +137,7 @@ pub fn expand_concat_bytes(
     sp: rustc_span::Span,
     tts: TokenStream,
 ) -> Box<dyn base::MacResult + 'static> {
-    let Some(es) = base::get_exprs_from_tts(cx, sp, tts) else {
+    let Some(es) = base::get_exprs_from_tts(cx, tts) else {
         return DummyResult::any(sp);
     };
     let mut accumulator = Vec::new();
@@ -174,7 +174,7 @@ pub fn expand_concat_bytes(
                 Ok(ast::LitKind::Byte(val)) => {
                     accumulator.push(val);
                 }
-                Ok(ast::LitKind::ByteStr(ref bytes)) => {
+                Ok(ast::LitKind::ByteStr(ref bytes, _)) => {
                     accumulator.extend_from_slice(&bytes);
                 }
                 _ => {
@@ -196,7 +196,7 @@ pub fn expand_concat_bytes(
         }
     }
     if !missing_literals.is_empty() {
-        let mut err = cx.struct_span_err(missing_literals.clone(), "expected a byte literal");
+        let mut err = cx.struct_span_err(missing_literals, "expected a byte literal");
         err.note("only byte literals (like `b\"foo\"`, `b's'`, and `[3, 4, 5]`) can be passed to `concat_bytes!()`");
         err.emit();
         return base::MacEager::expr(DummyResult::raw_expr(sp, true));
diff --git a/compiler/rustc_builtin_macros/src/derive.rs b/compiler/rustc_builtin_macros/src/derive.rs
index fa5a45730..2a8dc0284 100644
--- a/compiler/rustc_builtin_macros/src/derive.rs
+++ b/compiler/rustc_builtin_macros/src/derive.rs
@@ -1,7 +1,7 @@
 use crate::cfg_eval::cfg_eval;
 
 use rustc_ast as ast;
-use rustc_ast::{token, GenericParamKind, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
+use rustc_ast::{GenericParamKind, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
 use rustc_errors::{struct_span_err, Applicability};
 use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier};
 use rustc_feature::AttributeTemplate;
@@ -130,9 +130,11 @@ fn report_bad_target(sess: &Session, item: &Annotatable, span: Span) -> bool {
 }
 
 fn report_unexpected_meta_item_lit(sess: &Session, lit: &ast::MetaItemLit) {
-    let help_msg = match lit.token_lit.kind {
-        token::Str if rustc_lexer::is_ident(lit.token_lit.symbol.as_str()) => {
-            format!("try using `#[derive({})]`", lit.token_lit.symbol)
+    let help_msg = match lit.kind {
+        ast::LitKind::Str(_, ast::StrStyle::Cooked)
+            if rustc_lexer::is_ident(lit.symbol.as_str()) =>
+        {
+            format!("try using `#[derive({})]`", lit.symbol)
         }
         _ => "for example, write `#[derive(Debug)]` for `Debug`".to_string(),
     };
diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
index d59b3b8c8..ef5a75f42 100644
--- a/compiler/rustc_builtin_macros/src/deriving/clone.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -20,7 +20,7 @@ pub fn expand_deriving_clone(
     // some additional `AssertParamIsClone` assertions.
     //
     // We can use the simple form if either of the following are true.
-    // - The type derives Copy and there are no generic parameters.  (If we
+    // - The type derives Copy and there are no generic parameters. (If we
     //   used the simple form with generics, we'd have to bound the generics
     //   with Clone + Copy, and then there'd be no Clone impl at all if the
     //   user fills in something that is Clone but not Copy. After
@@ -82,7 +82,7 @@ pub fn expand_deriving_clone(
             nonself_args: Vec::new(),
             ret_ty: Self_,
             attributes: attrs,
-            unify_fieldless_variants: false,
+            fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
             combine_substructure: substructure,
         }],
         associated_types: Vec::new(),
@@ -177,7 +177,9 @@ fn cs_clone(
             all_fields = af;
             vdata = &variant.data;
         }
-        EnumTag(..) => cx.span_bug(trait_span, &format!("enum tags in `derive({})`", name,)),
+        EnumTag(..) | AllFieldlessEnum(..) => {
+            cx.span_bug(trait_span, &format!("enum tags in `derive({})`", name,))
+        }
         StaticEnum(..) | StaticStruct(..) => {
             cx.span_bug(trait_span, &format!("associated function in `derive({})`", name))
         }
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
index f861d47ed..3e994f037 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs
@@ -36,7 +36,7 @@ pub fn expand_deriving_eq(
             nonself_args: vec![],
             ret_ty: Unit,
             attributes: attrs,
-            unify_fieldless_variants: true,
+            fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
             combine_substructure: combine_substructure(Box::new(|a, b, c| {
                 cs_total_eq_assert(a, b, c)
             })),
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
index 96d18c7af..a926fca4e 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
@@ -29,7 +29,7 @@ pub fn expand_deriving_ord(
             nonself_args: vec![(self_ref(), sym::other)],
             ret_ty: Path(path_std!(cmp::Ordering)),
             attributes: attrs,
-            unify_fieldless_variants: true,
+            fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
             combine_substructure: combine_substructure(Box::new(|a, b, c| cs_cmp(a, b, c))),
         }],
         associated_types: Vec::new(),
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 7f95551fc..9051fe0b2 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_eq.rs
@@ -76,7 +76,7 @@ pub fn expand_deriving_partial_eq(
         nonself_args: vec![(self_ref(), sym::other)],
         ret_ty: Path(path_local!(bool)),
         attributes: attrs,
-        unify_fieldless_variants: true,
+        fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
         combine_substructure: combine_substructure(Box::new(|a, b, c| cs_eq(a, b, c))),
     }];
 
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 5c4e5b7f8..c9dc89212 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -28,7 +28,7 @@ pub fn expand_deriving_partial_ord(
         nonself_args: vec![(self_ref(), sym::other)],
         ret_ty,
         attributes: attrs,
-        unify_fieldless_variants: true,
+        fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
         combine_substructure: combine_substructure(Box::new(|cx, span, substr| {
             cs_partial_cmp(cx, span, substr)
         })),
diff --git a/compiler/rustc_builtin_macros/src/deriving/debug.rs b/compiler/rustc_builtin_macros/src/deriving/debug.rs
index 544d971b2..e0f487e86 100644
--- a/compiler/rustc_builtin_macros/src/deriving/debug.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/debug.rs
@@ -2,6 +2,7 @@ use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 use crate::deriving::path_std;
 
+use ast::EnumDef;
 use rustc_ast::{self as ast, MetaItem};
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_span::symbol::{sym, Ident, Symbol};
@@ -31,7 +32,8 @@ pub fn expand_deriving_debug(
             nonself_args: vec![(fmtr, sym::f)],
             ret_ty: Path(path_std!(fmt::Result)),
             attributes: ast::AttrVec::new(),
-            unify_fieldless_variants: false,
+            fieldless_variants_strategy:
+                FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless,
             combine_substructure: combine_substructure(Box::new(|a, b, c| {
                 show_substructure(a, b, c)
             })),
@@ -43,16 +45,18 @@ pub fn expand_deriving_debug(
 }
 
 fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> BlockOrExpr {
+    // We want to make sure we have the ctxt set so that we can use unstable methods
+    let span = cx.with_def_site_ctxt(span);
+
     let (ident, vdata, fields) = match substr.fields {
         Struct(vdata, fields) => (substr.type_ident, *vdata, fields),
         EnumMatching(_, _, v, fields) => (v.ident, &v.data, fields),
+        AllFieldlessEnum(enum_def) => return show_fieldless_enum(cx, span, enum_def, substr),
         EnumTag(..) | StaticStruct(..) | StaticEnum(..) => {
             cx.span_bug(span, "nonsensical .fields in `#[derive(Debug)]`")
         }
     };
 
-    // We want to make sure we have the ctxt set so that we can use unstable methods
-    let span = cx.with_def_site_ctxt(span);
     let name = cx.expr_str(span, ident.name);
     let fmt = substr.nonselflike_args[0].clone();
 
@@ -117,8 +121,7 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
         // `let names: &'static _ = &["field1", "field2"];`
         let names_let = if is_struct {
             let lt_static = Some(cx.lifetime_static(span));
-            let ty_static_ref =
-                cx.ty_rptr(span, cx.ty_infer(span), lt_static, ast::Mutability::Not);
+            let ty_static_ref = cx.ty_ref(span, cx.ty_infer(span), lt_static, ast::Mutability::Not);
             Some(cx.stmt_let_ty(
                 span,
                 false,
@@ -138,13 +141,13 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
         );
         let ty_slice = cx.ty(
             span,
-            ast::TyKind::Slice(cx.ty_rptr(span, ty_dyn_debug, None, ast::Mutability::Not)),
+            ast::TyKind::Slice(cx.ty_ref(span, ty_dyn_debug, None, ast::Mutability::Not)),
         );
         let values_let = cx.stmt_let_ty(
             span,
             false,
             Ident::new(sym::values, span),
-            Some(cx.ty_rptr(span, ty_slice, None, ast::Mutability::Not)),
+            Some(cx.ty_ref(span, ty_slice, None, ast::Mutability::Not)),
             cx.expr_array_ref(span, value_exprs),
         );
 
@@ -174,3 +177,47 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
         BlockOrExpr::new_mixed(stmts, Some(expr))
     }
 }
+
+/// Special case for enums with no fields. Builds:
+/// ```text
+/// impl ::core::fmt::Debug for A {
+///     fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
+///          ::core::fmt::Formatter::write_str(f,
+///             match self {
+///                 A::A => "A",
+///                 A::B() => "B",
+///                 A::C {} => "C",
+///             })
+///     }
+/// }
+/// ```
+fn show_fieldless_enum(
+    cx: &mut ExtCtxt<'_>,
+    span: Span,
+    def: &EnumDef,
+    substr: &Substructure<'_>,
+) -> BlockOrExpr {
+    let fmt = substr.nonselflike_args[0].clone();
+    let arms = def
+        .variants
+        .iter()
+        .map(|v| {
+            let variant_path = cx.path(span, vec![substr.type_ident, v.ident]);
+            let pat = match &v.data {
+                ast::VariantData::Tuple(fields, _) => {
+                    debug_assert!(fields.is_empty());
+                    cx.pat_tuple_struct(span, variant_path, vec![])
+                }
+                ast::VariantData::Struct(fields, _) => {
+                    debug_assert!(fields.is_empty());
+                    cx.pat_struct(span, variant_path, vec![])
+                }
+                ast::VariantData::Unit(_) => cx.pat_path(span, variant_path),
+            };
+            cx.arm(span, pat, cx.expr_str(span, v.ident.name))
+        })
+        .collect::<Vec<_>>();
+    let name = cx.expr_match(span, cx.expr_self(span), arms);
+    let fn_path_write_str = cx.std_path(&[sym::fmt, sym::Formatter, sym::write_str]);
+    BlockOrExpr::new_expr(cx.expr_call_global(span, fn_path_write_str, vec![fmt, name]))
+}
diff --git a/compiler/rustc_builtin_macros/src/deriving/decodable.rs b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
index 62af02c2b..5f9519dad 100644
--- a/compiler/rustc_builtin_macros/src/deriving/decodable.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
@@ -49,7 +49,7 @@ pub fn expand_deriving_rustc_decodable(
                 PathKind::Std,
             )),
             attributes: ast::AttrVec::new(),
-            unify_fieldless_variants: false,
+            fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
             combine_substructure: combine_substructure(Box::new(|a, b, c| {
                 decodable_substructure(a, b, c, krate)
             })),
diff --git a/compiler/rustc_builtin_macros/src/deriving/default.rs b/compiler/rustc_builtin_macros/src/deriving/default.rs
index eb66c4a69..182707472 100644
--- a/compiler/rustc_builtin_macros/src/deriving/default.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/default.rs
@@ -34,7 +34,7 @@ pub fn expand_deriving_default(
             nonself_args: Vec::new(),
             ret_ty: Self_,
             attributes: attrs,
-            unify_fieldless_variants: false,
+            fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
             combine_substructure: combine_substructure(Box::new(|cx, trait_span, substr| {
                 match substr.fields {
                     StaticStruct(_, fields) => {
diff --git a/compiler/rustc_builtin_macros/src/deriving/encodable.rs b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
index 68bc0ff2e..2afeed927 100644
--- a/compiler/rustc_builtin_macros/src/deriving/encodable.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
@@ -133,7 +133,7 @@ pub fn expand_deriving_rustc_encodable(
                 PathKind::Std,
             )),
             attributes: AttrVec::new(),
-            unify_fieldless_variants: false,
+            fieldless_variants_strategy: FieldlessVariantsStrategy::Default,
             combine_substructure: combine_substructure(Box::new(|a, b, c| {
                 encodable_substructure(a, b, c, krate)
             })),
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index beac591bf..17b7ac0eb 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -222,14 +222,27 @@ pub struct MethodDef<'a> {
 
     pub attributes: ast::AttrVec,
 
-    /// Can we combine fieldless variants for enums into a single match arm?
-    /// If true, indicates that the trait operation uses the enum tag in some
-    /// way.
-    pub unify_fieldless_variants: bool,
+    pub fieldless_variants_strategy: FieldlessVariantsStrategy,
 
     pub combine_substructure: RefCell<CombineSubstructureFunc<'a>>,
 }
 
+/// How to handle fieldless enum variants.
+#[derive(PartialEq)]
+pub enum FieldlessVariantsStrategy {
+    /// Combine fieldless variants into a single match arm.
+    /// This assumes that relevant information has been handled
+    /// by looking at the enum's discriminant.
+    Unify,
+    /// Don't do anything special about fieldless variants. They are
+    /// handled like any other variant.
+    Default,
+    /// If all variants of the enum are fieldless, expand the special
+    /// `AllFieldLessEnum` substructure, so that the entire enum can be handled
+    /// at once.
+    SpecializeIfAllVariantsFieldless,
+}
+
 /// All the data about the data structure/method being derived upon.
 pub struct Substructure<'a> {
     /// ident of self
@@ -264,9 +277,14 @@ pub enum StaticFields {
 
 /// A summary of the possible sets of fields.
 pub enum SubstructureFields<'a> {
-    /// A non-static method with `Self` is a struct.
+    /// A non-static method where `Self` is a struct.
     Struct(&'a ast::VariantData, Vec<FieldInfo>),
 
+    /// A non-static method handling the entire enum at once
+    /// (after it has been determined that none of the enum
+    /// variants has any fields).
+    AllFieldlessEnum(&'a ast::EnumDef),
+
     /// Matching variants of the enum: variant index, variant count, ast::Variant,
     /// fields: the field name is only non-`None` in the case of a struct
     /// variant.
@@ -1086,8 +1104,8 @@ impl<'a> MethodDef<'a> {
     /// ```
     /// Creates a tag check combined with a match for a tuple of all
     /// `selflike_args`, with an arm for each variant with fields, possibly an
-    /// arm for each fieldless variant (if `!unify_fieldless_variants` is not
-    /// true), and possibly a default arm.
+    /// arm for each fieldless variant (if `unify_fieldless_variants` is not
+    /// `Unify`), and possibly a default arm.
     fn expand_enum_method_body<'b>(
         &self,
         cx: &mut ExtCtxt<'_>,
@@ -1101,7 +1119,8 @@ impl<'a> MethodDef<'a> {
         let variants = &enum_def.variants;
 
         // Traits that unify fieldless variants always use the tag(s).
-        let uses_tags = self.unify_fieldless_variants;
+        let unify_fieldless_variants =
+            self.fieldless_variants_strategy == FieldlessVariantsStrategy::Unify;
 
         // There is no sensible code to be generated for *any* deriving on a
         // zero-variant enum. So we just generate a failing expression.
@@ -1161,23 +1180,35 @@ impl<'a> MethodDef<'a> {
         // match is necessary.
         let all_fieldless = variants.iter().all(|v| v.data.fields().is_empty());
         if all_fieldless {
-            if uses_tags && variants.len() > 1 {
-                // If the type is fieldless and the trait uses the tag and
-                // there are multiple variants, we need just an operation on
-                // the tag(s).
-                let (tag_field, mut tag_let_stmts) = get_tag_pieces(cx);
-                let mut tag_check = self.call_substructure_method(
-                    cx,
-                    trait_,
-                    type_ident,
-                    nonselflike_args,
-                    &EnumTag(tag_field, None),
-                );
-                tag_let_stmts.append(&mut tag_check.0);
-                return BlockOrExpr(tag_let_stmts, tag_check.1);
-            }
-
-            if variants.len() == 1 {
+            if variants.len() > 1 {
+                match self.fieldless_variants_strategy {
+                    FieldlessVariantsStrategy::Unify => {
+                        // If the type is fieldless and the trait uses the tag and
+                        // there are multiple variants, we need just an operation on
+                        // the tag(s).
+                        let (tag_field, mut tag_let_stmts) = get_tag_pieces(cx);
+                        let mut tag_check = self.call_substructure_method(
+                            cx,
+                            trait_,
+                            type_ident,
+                            nonselflike_args,
+                            &EnumTag(tag_field, None),
+                        );
+                        tag_let_stmts.append(&mut tag_check.0);
+                        return BlockOrExpr(tag_let_stmts, tag_check.1);
+                    }
+                    FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless => {
+                        return self.call_substructure_method(
+                            cx,
+                            trait_,
+                            type_ident,
+                            nonselflike_args,
+                            &AllFieldlessEnum(enum_def),
+                        );
+                    }
+                    FieldlessVariantsStrategy::Default => (),
+                }
+            } else if variants.len() == 1 {
                 // If there is a single variant, we don't need an operation on
                 // the tag(s). Just use the most degenerate result.
                 return self.call_substructure_method(
@@ -1187,7 +1218,7 @@ impl<'a> MethodDef<'a> {
                     nonselflike_args,
                     &EnumMatching(0, 1, &variants[0], Vec::new()),
                 );
-            };
+            }
         }
 
         // These arms are of the form:
@@ -1198,7 +1229,7 @@ impl<'a> MethodDef<'a> {
         let mut match_arms: Vec<ast::Arm> = variants
             .iter()
             .enumerate()
-            .filter(|&(_, v)| !(self.unify_fieldless_variants && v.data.fields().is_empty()))
+            .filter(|&(_, v)| !(unify_fieldless_variants && v.data.fields().is_empty()))
             .map(|(index, variant)| {
                 // A single arm has form (&VariantK, &VariantK, ...) => BodyK
                 // (see "Final wrinkle" note below for why.)
@@ -1249,7 +1280,7 @@ impl<'a> MethodDef<'a> {
         // Add a default arm to the match, if necessary.
         let first_fieldless = variants.iter().find(|v| v.data.fields().is_empty());
         let default = match first_fieldless {
-            Some(v) if self.unify_fieldless_variants => {
+            Some(v) if unify_fieldless_variants => {
                 // We need a default case that handles all the fieldless
                 // variants. The index and actual variant aren't meaningful in
                 // this case, so just use dummy values.
@@ -1296,7 +1327,7 @@ impl<'a> MethodDef<'a> {
         // If the trait uses the tag and there are multiple variants, we need
         // to add a tag check operation before the match. Otherwise, the match
         // is enough.
-        if uses_tags && variants.len() > 1 {
+        if unify_fieldless_variants && variants.len() > 1 {
             let (tag_field, mut tag_let_stmts) = get_tag_pieces(cx);
 
             // Combine a tag check with the match.
@@ -1580,5 +1611,6 @@ where
             }
         }
         StaticEnum(..) | StaticStruct(..) => cx.span_bug(trait_span, "static function in `derive`"),
+        AllFieldlessEnum(..) => cx.span_bug(trait_span, "fieldless enum in `derive`"),
     }
 }
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
index eaa488190..c6f5f5d08 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/ty.rs
@@ -97,7 +97,7 @@ impl Ty {
         match self {
             Ref(ty, mutbl) => {
                 let raw_ty = ty.to_ty(cx, span, self_ty, self_generics);
-                cx.ty_rptr(span, raw_ty, None, *mutbl)
+                cx.ty_ref(span, raw_ty, None, *mutbl)
             }
             Path(p) => p.to_ty(cx, span, self_ty, self_generics),
             Self_ => cx.ty_path(self.to_path(cx, span, self_ty, self_generics)),
diff --git a/compiler/rustc_builtin_macros/src/deriving/hash.rs b/compiler/rustc_builtin_macros/src/deriving/hash.rs
index c136bb714..f8570d8f8 100644
--- a/compiler/rustc_builtin_macros/src/deriving/hash.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/hash.rs
@@ -33,7 +33,7 @@ pub fn expand_deriving_hash(
             nonself_args: vec![(Ref(Box::new(Path(arg)), Mutability::Mut), sym::state)],
             ret_ty: Unit,
             attributes: AttrVec::new(),
-            unify_fieldless_variants: true,
+            fieldless_variants_strategy: FieldlessVariantsStrategy::Unify,
             combine_substructure: combine_substructure(Box::new(|a, b, c| {
                 hash_substructure(a, b, c)
             })),
diff --git a/compiler/rustc_builtin_macros/src/env.rs b/compiler/rustc_builtin_macros/src/env.rs
index 0b4e545f7..e5a5e6069 100644
--- a/compiler/rustc_builtin_macros/src/env.rs
+++ b/compiler/rustc_builtin_macros/src/env.rs
@@ -1,4 +1,4 @@
-// The compiler code necessary to support the env! extension.  Eventually this
+// The compiler code necessary to support the env! extension. Eventually this
 // should all get sucked into either the compiler syntax extension plugin
 // interface.
 //
@@ -30,7 +30,7 @@ pub fn expand_option_env<'cx>(
                 sp,
                 true,
                 cx.std_path(&[sym::option, sym::Option, sym::None]),
-                vec![GenericArg::Type(cx.ty_rptr(
+                vec![GenericArg::Type(cx.ty_ref(
                     sp,
                     cx.ty_ident(sp, Ident::new(sym::str, sp)),
                     Some(lt),
@@ -52,7 +52,7 @@ pub fn expand_env<'cx>(
     sp: Span,
     tts: TokenStream,
 ) -> Box<dyn base::MacResult + 'cx> {
-    let mut exprs = match get_exprs_from_tts(cx, sp, tts) {
+    let mut exprs = match get_exprs_from_tts(cx, tts) {
         Some(exprs) if exprs.is_empty() => {
             cx.span_err(sp, "env! takes 1 or 2 arguments");
             return DummyResult::any(sp);
diff --git a/compiler/rustc_builtin_macros/src/format.rs b/compiler/rustc_builtin_macros/src/format.rs
index 8b07c1106..9f4bbbc62 100644
--- a/compiler/rustc_builtin_macros/src/format.rs
+++ b/compiler/rustc_builtin_macros/src/format.rs
@@ -333,7 +333,7 @@ pub fn make_format_args(
             parse::Piece::String(s) => {
                 unfinished_literal.push_str(s);
             }
-            parse::Piece::NextArgument(parse::Argument { position, position_span, format }) => {
+            parse::Piece::NextArgument(box parse::Argument { position, position_span, format }) => {
                 if !unfinished_literal.is_empty() {
                     template.push(FormatArgsPiece::Literal(Symbol::intern(&unfinished_literal)));
                     unfinished_literal.clear();
@@ -583,7 +583,7 @@ fn report_missing_placeholders(
     if detect_foreign_fmt {
         use super::format_foreign as foreign;
 
-        // The set of foreign substitutions we've explained.  This prevents spamming the user
+        // The set of foreign substitutions we've explained. This prevents spamming the user
         // with `%d should be written as {}` over and over again.
         let mut explained = FxHashSet::default();
 
@@ -638,7 +638,7 @@ fn report_missing_placeholders(
                 if show_doc_note {
                     diag.note(concat!(
                         stringify!($kind),
-                        " formatting not supported; see the documentation for `std::fmt`",
+                        " formatting is not supported; see the documentation for `std::fmt`",
                     ));
                 }
                 if suggestions.len() > 0 {
diff --git a/compiler/rustc_builtin_macros/src/format_foreign.rs b/compiler/rustc_builtin_macros/src/format_foreign.rs
index 6f7fc3a95..bd9e903b6 100644
--- a/compiler/rustc_builtin_macros/src/format_foreign.rs
+++ b/compiler/rustc_builtin_macros/src/format_foreign.rs
@@ -253,7 +253,7 @@ pub(crate) mod printf {
     #[derive(Copy, Clone, PartialEq, Debug)]
     pub enum Num {
         // The range of these values is technically bounded by `NL_ARGMAX`... but, at least for GNU
-        // libc, it apparently has no real fixed limit.  A `u16` is used here on the basis that it
+        // libc, it apparently has no real fixed limit. A `u16` is used here on the basis that it
         // is *vanishingly* unlikely that *anyone* is going to try formatting something wider, or
         // with more precision, than 32 thousand positions which is so wide it couldn't possibly fit
         // on a screen.
diff --git a/compiler/rustc_builtin_macros/src/global_allocator.rs b/compiler/rustc_builtin_macros/src/global_allocator.rs
index 41531580c..f8761653b 100644
--- a/compiler/rustc_builtin_macros/src/global_allocator.rs
+++ b/compiler/rustc_builtin_macros/src/global_allocator.rs
@@ -35,7 +35,7 @@ pub fn expand(
             (item, true, ecx.with_def_site_ctxt(ty.span))
         } else {
             ecx.sess.parse_sess.span_diagnostic.span_err(item.span(), "allocators must be statics");
-            return vec![orig_item.clone()]
+            return vec![orig_item];
         };
 
     // Generate a bunch of new items using the AllocFnFactory
diff --git a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
index ece660cf6..21c8caa65 100644
--- a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
+++ b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
@@ -262,6 +262,7 @@ impl<'a> Visitor<'a> for CollectProcMacros<'a> {
 //          use proc_macro::bridge::client::ProcMacro;
 //
 //          #[rustc_proc_macro_decls]
+//          #[used]
 //          #[allow(deprecated)]
 //          static DECLS: &[ProcMacro] = &[
 //              ProcMacro::custom_derive($name_trait1, &[], ::$name1);
@@ -348,7 +349,7 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
         .item_static(
             span,
             Ident::new(sym::_DECLS, span),
-            cx.ty_rptr(
+            cx.ty_ref(
                 span,
                 cx.ty(
                     span,
@@ -364,6 +365,7 @@ fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
         )
         .map(|mut i| {
             i.attrs.push(cx.attr_word(sym::rustc_proc_macro_decls, span));
+            i.attrs.push(cx.attr_word(sym::used, span));
             i.attrs.push(cx.attr_nested_word(sym::allow, sym::deprecated, span));
             i
         });
diff --git a/compiler/rustc_builtin_macros/src/test.rs b/compiler/rustc_builtin_macros/src/test.rs
index f5f02fc77..729ae4071 100644
--- a/compiler/rustc_builtin_macros/src/test.rs
+++ b/compiler/rustc_builtin_macros/src/test.rs
@@ -239,8 +239,7 @@ pub fn expand_test_or_bench(
             cx.attr_nested_word(sym::cfg, sym::test, attr_sp),
             // #[rustc_test_marker = "test_case_sort_key"]
             cx.attr_name_value_str(sym::rustc_test_marker, test_path_symbol, attr_sp),
-        ]
-        .into(),
+        ],
         // const $ident: test::TestDescAndFn =
         ast::ItemKind::Const(
             ast::Defaultness::Final,