Auto merge of #102324 - matthiaskrgr:rollup-6l70oz3, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #101875 (Allow more `!Copy` impls)
 - #101996 (Don't duplicate region names for late-bound regions in print of Binder)
 - #102181 (Add regression test)
 - #102273 (Allow `~const` bounds on non-const functions)
 - #102286 (Recover some items that expect braces and don't take semicolons)

Failed merges:

 - #102314 (Add a label to struct/enum/union ident name)

r? `@ghost`
`@rustbot` modify labels: rollup

7 files changed, 124 insertions, 50 deletions

diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index b1d10e07ad0..ecf74c76020 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -1415,7 +1415,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     if !self.is_tilde_const_allowed {
                         self.err_handler()
                             .struct_span_err(bound.span(), "`~const` is not allowed here")
-                            .note("only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions")
+                            .note("only allowed on bounds on functions, traits' associated types and functions, const impls and its associated functions")
                             .emit();
                     }
                 }
@@ -1523,9 +1523,8 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             });
         }
 
-        let tilde_const_allowed =
-            matches!(fk.header(), Some(FnHeader { constness: Const::Yes(_), .. }))
-                || matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
+        let tilde_const_allowed = matches!(fk.header(), Some(FnHeader { .. }))
+            || matches!(fk.ctxt(), Some(FnCtxt::Assoc(_)));
 
         self.with_tilde_const(tilde_const_allowed, |this| visit::walk_fn(this, fk));
     }
diff --git a/compiler/rustc_error_messages/locales/en-US/parser.ftl b/compiler/rustc_error_messages/locales/en-US/parser.ftl
index 9459cfebde9..07dd03e6e50 100644
--- a/compiler/rustc_error_messages/locales/en-US/parser.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/parser.ftl
@@ -158,3 +158,6 @@ parser_remove_let = expected pattern, found `let`
 
 parser_use_eq_instead = unexpected `==`
     .suggestion = try using `=` instead
+
+parser_use_empty_block_not_semi = expected { "`{}`" }, found `;`
+    .suggestion = try using { "`{}`" } instead
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 99e5722ddad..70efa748846 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -1562,7 +1562,9 @@ pub struct FmtPrinterData<'a, 'tcx> {
     in_value: bool,
     pub print_alloc_ids: bool,
 
+    // set of all named (non-anonymous) region names
     used_region_names: FxHashSet<Symbol>,
+
     region_index: usize,
     binder_depth: usize,
     printed_type_count: usize,
@@ -2118,23 +2120,31 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
     where
         T: Print<'tcx, Self, Output = Self, Error = fmt::Error> + TypeFoldable<'tcx>,
     {
-        fn name_by_region_index(index: usize) -> Symbol {
-            match index {
-                0 => Symbol::intern("'r"),
-                1 => Symbol::intern("'s"),
-                i => Symbol::intern(&format!("'t{}", i - 2)),
+        fn name_by_region_index(
+            index: usize,
+            available_names: &mut Vec<Symbol>,
+            num_available: usize,
+        ) -> Symbol {
+            if let Some(name) = available_names.pop() {
+                name
+            } else {
+                Symbol::intern(&format!("'z{}", index - num_available))
             }
         }
 
+        debug!("name_all_regions");
+
         // Replace any anonymous late-bound regions with named
         // variants, using new unique identifiers, so that we can
         // clearly differentiate between named and unnamed regions in
         // the output. We'll probably want to tweak this over time to
         // decide just how much information to give.
         if self.binder_depth == 0 {
-            self.prepare_late_bound_region_info(value);
+            self.prepare_region_info(value);
         }
 
+        debug!("self.used_region_names: {:?}", &self.used_region_names);
+
         let mut empty = true;
         let mut start_or_continue = |cx: &mut Self, start: &str, cont: &str| {
             let w = if empty {
@@ -2151,13 +2161,24 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
 
         define_scoped_cx!(self);
 
+        let possible_names =
+            ('a'..='z').rev().map(|s| Symbol::intern(&format!("'{s}"))).collect::<Vec<_>>();
+
+        let mut available_names = possible_names
+            .into_iter()
+            .filter(|name| !self.used_region_names.contains(&name))
+            .collect::<Vec<_>>();
+        debug!(?available_names);
+        let num_available = available_names.len();
+
         let mut region_index = self.region_index;
-        let mut next_name = |this: &Self| loop {
-            let name = name_by_region_index(region_index);
+        let mut next_name = |this: &Self| {
+            let name = name_by_region_index(region_index, &mut available_names, num_available);
+            debug!(?name);
             region_index += 1;
-            if !this.used_region_names.contains(&name) {
-                break name;
-            }
+            assert!(!this.used_region_names.contains(&name));
+
+            name
         };
 
         // If we want to print verbosely, then print *all* binders, even if they
@@ -2178,6 +2199,7 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
                         ty::BrAnon(_) | ty::BrEnv => {
                             start_or_continue(&mut self, "for<", ", ");
                             let name = next_name(&self);
+                            debug!(?name);
                             do_continue(&mut self, name);
                             ty::BrNamed(CRATE_DEF_ID.to_def_id(), name)
                         }
@@ -2271,29 +2293,37 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
         Ok(inner)
     }
 
-    fn prepare_late_bound_region_info<T>(&mut self, value: &ty::Binder<'tcx, T>)
+    fn prepare_region_info<T>(&mut self, value: &ty::Binder<'tcx, T>)
     where
         T: TypeVisitable<'tcx>,
     {
-        struct LateBoundRegionNameCollector<'a, 'tcx> {
-            used_region_names: &'a mut FxHashSet<Symbol>,
+        struct RegionNameCollector<'tcx> {
+            used_region_names: FxHashSet<Symbol>,
             type_collector: SsoHashSet<Ty<'tcx>>,
         }
 
-        impl<'tcx> ty::visit::TypeVisitor<'tcx> for LateBoundRegionNameCollector<'_, 'tcx> {
+        impl<'tcx> RegionNameCollector<'tcx> {
+            fn new() -> Self {
+                RegionNameCollector {
+                    used_region_names: Default::default(),
+                    type_collector: SsoHashSet::new(),
+                }
+            }
+        }
+
+        impl<'tcx> ty::visit::TypeVisitor<'tcx> for RegionNameCollector<'tcx> {
             type BreakTy = ();
 
             fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
                 trace!("address: {:p}", r.0.0);
-                if let ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrNamed(_, name), .. }) = *r {
-                    self.used_region_names.insert(name);
-                } else if let ty::RePlaceholder(ty::PlaceholderRegion {
-                    name: ty::BrNamed(_, name),
-                    ..
-                }) = *r
-                {
+
+                // Collect all named lifetimes. These allow us to prevent duplication
+                // of already existing lifetime names when introducing names for
+                // anonymous late-bound regions.
+                if let Some(name) = r.get_name() {
                     self.used_region_names.insert(name);
                 }
+
                 r.super_visit_with(self)
             }
 
@@ -2309,12 +2339,9 @@ impl<'tcx> FmtPrinter<'_, 'tcx> {
             }
         }
 
-        self.used_region_names.clear();
-        let mut collector = LateBoundRegionNameCollector {
-            used_region_names: &mut self.used_region_names,
-            type_collector: SsoHashSet::new(),
-        };
+        let mut collector = RegionNameCollector::new();
         value.visit_with(&mut collector);
+        self.used_region_names = collector.used_region_names;
         self.region_index = 0;
     }
 }
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 258fb2e2f9f..f4f4bb37c1a 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -85,6 +85,17 @@ impl BoundRegionKind {
             _ => false,
         }
     }
+
+    pub fn get_name(&self) -> Option<Symbol> {
+        if self.is_named() {
+            match *self {
+                BoundRegionKind::BrNamed(_, name) => return Some(name),
+                _ => unreachable!(),
+            }
+        }
+
+        None
+    }
 }
 
 pub trait Article {
@@ -1445,6 +1456,23 @@ impl<'tcx> Region<'tcx> {
         *self.0.0
     }
 
+    pub fn get_name(self) -> Option<Symbol> {
+        if self.has_name() {
+            let name = match *self {
+                ty::ReEarlyBound(ebr) => Some(ebr.name),
+                ty::ReLateBound(_, br) => br.kind.get_name(),
+                ty::ReFree(fr) => fr.bound_region.get_name(),
+                ty::ReStatic => Some(kw::StaticLifetime),
+                ty::RePlaceholder(placeholder) => placeholder.name.get_name(),
+                _ => None,
+            };
+
+            return name;
+        }
+
+        None
+    }
+
     /// Is this region named by the user?
     pub fn has_name(self) -> bool {
         match *self {
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 0a81cde93be..ccdffb8ce07 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -745,6 +745,14 @@ pub(crate) struct UseEqInstead {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(parser::use_empty_block_not_semi)]
+pub(crate) struct UseEmptyBlockNotSemi {
+    #[primary_span]
+    #[suggestion_hidden(applicability = "machine-applicable", code = "{{}}")]
+    pub span: Span,
+}
+
 // SnapshotParser is used to create a snapshot of the parser
 // without causing duplicate errors being emitted when the `Parser`
 // is dropped.
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index e385ac44113..34f25bd0716 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -1,4 +1,4 @@
-use super::diagnostics::{dummy_arg, ConsumeClosingDelim, Error};
+use super::diagnostics::{dummy_arg, ConsumeClosingDelim, Error, UseEmptyBlockNotSemi};
 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
 use super::{AttrWrapper, FollowedByType, ForceCollect, Parser, PathStyle, TrailingToken};
 
@@ -664,6 +664,14 @@ impl<'a> Parser<'a> {
         mut parse_item: impl FnMut(&mut Parser<'a>) -> PResult<'a, Option<Option<T>>>,
     ) -> PResult<'a, Vec<T>> {
         let open_brace_span = self.token.span;
+
+        // Recover `impl Ty;` instead of `impl Ty {}`
+        if self.token == TokenKind::Semi {
+            self.sess.emit_err(UseEmptyBlockNotSemi { span: self.token.span });
+            self.bump();
+            return Ok(vec![]);
+        }
+
         self.expect(&token::OpenDelim(Delimiter::Brace))?;
         attrs.extend(self.parse_inner_attributes()?);
 
@@ -1305,12 +1313,19 @@ impl<'a> Parser<'a> {
         let mut generics = self.parse_generics()?;
         generics.where_clause = self.parse_where_clause()?;
 
-        let (variants, _) = self
-            .parse_delim_comma_seq(Delimiter::Brace, |p| p.parse_enum_variant())
-            .map_err(|e| {
-                self.recover_stmt();
-                e
-            })?;
+        // Possibly recover `enum Foo;` instead of `enum Foo {}`
+        let (variants, _) = if self.token == TokenKind::Semi {
+            self.sess.emit_err(UseEmptyBlockNotSemi { span: self.token.span });
+            self.bump();
+            (vec![], false)
+        } else {
+            self.parse_delim_comma_seq(Delimiter::Brace, |p| p.parse_enum_variant()).map_err(
+                |e| {
+                    self.recover_stmt();
+                    e
+                },
+            )?
+        };
 
         let enum_definition = EnumDef { variants: variants.into_iter().flatten().collect() };
         Ok((id, ItemKind::Enum(enum_definition, generics)))
diff --git a/compiler/rustc_typeck/src/coherence/builtin.rs b/compiler/rustc_typeck/src/coherence/builtin.rs
index d08c0d4dbb7..d4eb826f0b4 100644
--- a/compiler/rustc_typeck/src/coherence/builtin.rs
+++ b/compiler/rustc_typeck/src/coherence/builtin.rs
@@ -70,23 +70,21 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
     let self_type = tcx.type_of(impl_did);
     debug!("visit_implementation_of_copy: self_type={:?} (bound)", self_type);
 
-    let span = tcx.hir().span(impl_hir_id);
     let param_env = tcx.param_env(impl_did);
     assert!(!self_type.has_escaping_bound_vars());
 
     debug!("visit_implementation_of_copy: self_type={:?} (free)", self_type);
 
+    let span = match tcx.hir().expect_item(impl_did).kind {
+        ItemKind::Impl(hir::Impl { polarity: hir::ImplPolarity::Negative(_), .. }) => return,
+        ItemKind::Impl(impl_) => impl_.self_ty.span,
+        _ => bug!("expected Copy impl item"),
+    };
+
     let cause = traits::ObligationCause::misc(span, impl_hir_id);
     match can_type_implement_copy(tcx, param_env, self_type, cause) {
         Ok(()) => {}
         Err(CopyImplementationError::InfrigingFields(fields)) => {
-            let item = tcx.hir().expect_item(impl_did);
-            let span = if let ItemKind::Impl(hir::Impl { of_trait: Some(ref tr), .. }) = item.kind {
-                tr.path.span
-            } else {
-                span
-            };
-
             let mut err = struct_span_err!(
                 tcx.sess,
                 span,
@@ -166,10 +164,6 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
             err.emit();
         }
         Err(CopyImplementationError::NotAnAdt) => {
-            let item = tcx.hir().expect_item(impl_did);
-            let span =
-                if let ItemKind::Impl(ref impl_) = item.kind { impl_.self_ty.span } else { span };
-
             tcx.sess.emit_err(CopyImplOnNonAdt { span });
         }
         Err(CopyImplementationError::HasDestructor) => {