Rollup of 5 pull requests

compiler/rustc_ast_lowering/src/lib.rs

@@ -142,13 +142,9 @@ struct LoweringContext<'a, 'hir: 'a> {
     /// indicate whether or not we're in a place where new lifetimes will result
     /// in in-band lifetime definitions, such a function or an impl header,
     /// including implicit lifetimes from `impl_header_lifetime_elision`.
-    is_collecting_in_band_lifetimes: bool,
+    is_collecting_anonymous_lifetimes: bool,
 
     /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
-    /// When `is_collecting_in_band_lifetimes` is true, each lifetime is checked
-    /// against this list to see if it is already in-scope, or if a definition
-    /// needs to be created for it.
-    ///
     /// We always store a `normalize_to_macros_2_0()` version of the param-name in this
     /// vector.
     in_scope_lifetimes: Vec<ParamName>,
@@ -377,7 +373,7 @@ pub fn lower_crate<'a, 'hir>(
         task_context: None,
         current_item: None,
         lifetimes_to_define: Vec::new(),
-        is_collecting_in_band_lifetimes: false,
+        is_collecting_anonymous_lifetimes: false,
         in_scope_lifetimes: Vec::new(),
         allow_try_trait: Some([sym::try_trait_v2][..].into()),
         allow_gen_future: Some([sym::gen_future][..].into()),
@@ -724,13 +720,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         &mut self,
         f: impl FnOnce(&mut Self) -> T,
     ) -> (Vec<(Span, ParamName)>, T) {
-        let was_collecting = std::mem::replace(&mut self.is_collecting_in_band_lifetimes, true);
+        let was_collecting = std::mem::replace(&mut self.is_collecting_anonymous_lifetimes, true);
         let len = self.lifetimes_to_define.len();
 
         let res = f(self);
 
         let lifetimes_to_define = self.lifetimes_to_define.split_off(len);
-        self.is_collecting_in_band_lifetimes = was_collecting;
+        self.is_collecting_anonymous_lifetimes = was_collecting;
         (lifetimes_to_define, res)
     }
 
@@ -747,7 +743,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // that collisions are ok here and this shouldn't
         // really show up for end-user.
         let (str_name, kind) = match hir_name {
-            ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
+            ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::Explicit),
             ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
             ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
         };
@@ -771,38 +767,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         }
     }
 
-    /// When there is a reference to some lifetime `'a`, and in-band
-    /// lifetimes are enabled, then we want to push that lifetime into
-    /// the vector of names to define later. In that case, it will get
-    /// added to the appropriate generics.
-    fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
-        if !self.is_collecting_in_band_lifetimes {
-            return;
-        }
-
-        if !self.sess.features_untracked().in_band_lifetimes {
-            return;
-        }
-
-        if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) {
-            return;
-        }
-
-        let hir_name = ParamName::Plain(ident);
-
-        if self.lifetimes_to_define.iter().any(|(_, lt_name)| {
-            lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0()
-        }) {
-            return;
-        }
-
-        self.lifetimes_to_define.push((ident.span, hir_name));
-    }
-
     /// When we have either an elided or `'_` lifetime in an impl
     /// header, we convert it to an in-band lifetime.
-    fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
-        assert!(self.is_collecting_in_band_lifetimes);
+    fn collect_fresh_anonymous_lifetime(&mut self, span: Span) -> ParamName {
+        assert!(self.is_collecting_anonymous_lifetimes);
         let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
         let hir_name = ParamName::Fresh(index);
         self.lifetimes_to_define.push((span, hir_name));
@@ -1944,7 +1912,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             }
             ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
                 AnonymousLifetimeMode::CreateParameter => {
-                    let fresh_name = self.collect_fresh_in_band_lifetime(span);
+                    let fresh_name = self.collect_fresh_anonymous_lifetime(span);
                     self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
                 }
 
@@ -1955,7 +1923,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
             },
             ident => {
-                self.maybe_collect_in_band_lifetime(ident);
                 let param_name = ParamName::Plain(self.lower_ident(ident));
                 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
             }
@@ -1999,8 +1966,8 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
         let (name, kind) = match param.kind {
             GenericParamKind::Lifetime => {
-                let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
-                self.is_collecting_in_band_lifetimes = false;
+                let was_collecting_in_band = self.is_collecting_anonymous_lifetimes;
+                self.is_collecting_anonymous_lifetimes = false;
 
                 let lt = self
                     .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
@@ -2023,7 +1990,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 let kind =
                     hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
 
-                self.is_collecting_in_band_lifetimes = was_collecting_in_band;
+                self.is_collecting_anonymous_lifetimes = was_collecting_in_band;
 
                 (param_name, kind)
             }
@@ -2382,7 +2349,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
             // `'f`.
             AnonymousLifetimeMode::CreateParameter => {
-                let fresh_name = self.collect_fresh_in_band_lifetime(span);
+                let fresh_name = self.collect_fresh_anonymous_lifetime(span);
                 hir::Lifetime {
                     hir_id: self.next_id(),
                     span: self.lower_span(span),

compiler/rustc_attr/src/builtin.rs

@@ -8,6 +8,7 @@ use rustc_errors::{struct_span_err, Applicability};
 use rustc_feature::{find_gated_cfg, is_builtin_attr_name, Features, GatedCfg};
 use rustc_macros::HashStable_Generic;
 use rustc_session::lint::builtin::UNEXPECTED_CFGS;
+use rustc_session::lint::BuiltinLintDiagnostics;
 use rustc_session::parse::{feature_err, ParseSess};
 use rustc_session::Session;
 use rustc_span::hygiene::Transparency;
@@ -461,29 +462,37 @@ pub fn cfg_matches(cfg: &ast::MetaItem, sess: &ParseSess, features: Option<&Feat
                 true
             }
             MetaItemKind::NameValue(..) | MetaItemKind::Word => {
-                let name = cfg.ident().expect("multi-segment cfg predicate").name;
+                let ident = cfg.ident().expect("multi-segment cfg predicate");
+                let name = ident.name;
                 let value = cfg.value_str();
-                if sess.check_config.names_checked && !sess.check_config.names_valid.contains(&name)
-                {
-                    sess.buffer_lint(
-                        UNEXPECTED_CFGS,
-                        cfg.span,
-                        CRATE_NODE_ID,
-                        "unexpected `cfg` condition name",
-                    );
-                }
-                if let Some(val) = value {
-                    if sess.check_config.values_checked.contains(&name)
-                        && !sess.check_config.values_valid.contains(&(name, val))
-                    {
-                        sess.buffer_lint(
+                if let Some(names_valid) = &sess.check_config.names_valid {
+                    if !names_valid.contains(&name) {
+                        sess.buffer_lint_with_diagnostic(
                             UNEXPECTED_CFGS,
                             cfg.span,
                             CRATE_NODE_ID,
-                            "unexpected `cfg` condition value",
+                            "unexpected `cfg` condition name",
+                            BuiltinLintDiagnostics::UnexpectedCfg(ident.span, name, None),
                         );
                     }
                 }
+                if let Some(value) = value {
+                    if let Some(values) = &sess.check_config.values_valid.get(&name) {
+                        if !values.contains(&value) {
+                            sess.buffer_lint_with_diagnostic(
+                                UNEXPECTED_CFGS,
+                                cfg.span,
+                                CRATE_NODE_ID,
+                                "unexpected `cfg` condition value",
+                                BuiltinLintDiagnostics::UnexpectedCfg(
+                                    cfg.name_value_literal_span().unwrap(),
+                                    name,
+                                    Some(value),
+                                ),
+                            );
+                        }
+                    }
+                }
                 sess.config.contains(&(name, value))
             }
         }

compiler/rustc_codegen_cranelift/src/main_shim.rs

@@ -51,7 +51,10 @@ pub(crate) fn maybe_create_entry_wrapper(
         // late-bound regions, since late-bound
         // regions must appear in the argument
         // listing.
-        let main_ret_ty = tcx.erase_regions(main_ret_ty.no_bound_vars().unwrap());
+        let main_ret_ty = tcx.normalize_erasing_regions(
+            ty::ParamEnv::reveal_all(),
+            main_ret_ty.no_bound_vars().unwrap(),
+        );
 
         let cmain_sig = Signature {
             params: vec![

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -449,7 +449,10 @@ fn pointer_or_reference_metadata<'ll, 'tcx>(
             // This is a thin pointer. Create a regular pointer type and give it the correct name.
             debug_assert_eq!(
                 (thin_pointer_size, thin_pointer_align),
-                cx.size_and_align_of(ptr_type)
+                cx.size_and_align_of(ptr_type),
+                "ptr_type={}, pointee_type={}",
+                ptr_type,
+                pointee_type,
             );
 
             unsafe {

compiler/rustc_codegen_llvm/src/debuginfo/utils.rs

@@ -4,9 +4,9 @@ use super::namespace::item_namespace;
 use super::CrateDebugContext;
 
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::layout::LayoutOf;
+use rustc_middle::ty::layout::{HasParamEnv, LayoutOf};
 use rustc_middle::ty::{self, DefIdTree, Ty};
-use rustc_target::abi::Variants;
+use tracing::trace;
 
 use crate::common::CodegenCx;
 use crate::llvm;
@@ -63,38 +63,37 @@ pub(crate) fn fat_pointer_kind<'ll, 'tcx>(
     cx: &CodegenCx<'ll, 'tcx>,
     pointee_ty: Ty<'tcx>,
 ) -> Option<FatPtrKind> {
-    let layout = cx.layout_of(pointee_ty);
+    let pointee_tail_ty = cx.tcx.struct_tail_erasing_lifetimes(pointee_ty, cx.param_env());
+    let layout = cx.layout_of(pointee_tail_ty);
+    trace!(
+        "fat_pointer_kind: {:?} has layout {:?} (is_unsized? {})",
+        pointee_tail_ty,
+        layout,
+        layout.is_unsized()
+    );
 
     if !layout.is_unsized() {
         return None;
     }
 
-    match *pointee_ty.kind() {
+    match *pointee_tail_ty.kind() {
         ty::Str | ty::Slice(_) => Some(FatPtrKind::Slice),
         ty::Dynamic(..) => Some(FatPtrKind::Dyn),
-        ty::Adt(..) | ty::Tuple(..) if matches!(layout.variants, Variants::Single { .. }) => {
-            let last_field_index = layout.fields.count() - 1;
-            debug_assert!(
-                (0..last_field_index)
-                    .all(|field_index| { !layout.field(cx, field_index).is_unsized() })
-            );
-
-            let unsized_field = layout.field(cx, last_field_index);
-            debug_assert!(unsized_field.is_unsized());
-            fat_pointer_kind(cx, unsized_field.ty)
-        }
         ty::Foreign(_) => {
             // Assert that pointers to foreign types really are thin:
             debug_assert_eq!(
-                cx.size_of(cx.tcx.mk_imm_ptr(pointee_ty)),
+                cx.size_of(cx.tcx.mk_imm_ptr(pointee_tail_ty)),
                 cx.size_of(cx.tcx.mk_imm_ptr(cx.tcx.types.u8))
             );
             None
         }
         _ => {
             // For all other pointee types we should already have returned None
             // at the beginning of the function.
-            panic!("fat_pointer_kind() - Encountered unexpected `pointee_ty`: {:?}", pointee_ty)
+            panic!(
+                "fat_pointer_kind() - Encountered unexpected `pointee_tail_ty`: {:?}",
+                pointee_tail_ty
+            )
         }
     }
 }

compiler/rustc_codegen_ssa/src/base.rs

@@ -407,7 +407,10 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         // late-bound regions, since late-bound
         // regions must appear in the argument
         // listing.
-        let main_ret_ty = cx.tcx().erase_regions(main_ret_ty.no_bound_vars().unwrap());
+        let main_ret_ty = cx.tcx().normalize_erasing_regions(
+            ty::ParamEnv::reveal_all(),
+            main_ret_ty.no_bound_vars().unwrap(),
+        );
 
         let Some(llfn) = cx.declare_c_main(llfty) else {
             // FIXME: We should be smart and show a better diagnostic here.

compiler/rustc_error_codes/src/error_codes/E0687.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 In-band lifetimes cannot be used in `fn`/`Fn` syntax.
 
 Erroneous code examples:
 
-```compile_fail,E0687
+```ignore (feature got removed)
 #![feature(in_band_lifetimes)]
 
 fn foo(x: fn(&'a u32)) {} // error!

compiler/rustc_error_codes/src/error_codes/E0688.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 In-band lifetimes were mixed with explicit lifetime binders.
 
 Erroneous code example:
 
-```compile_fail,E0688
+```ignore (feature got removed)
 #![feature(in_band_lifetimes)]
 
 fn foo<'a>(x: &'a u32, y: &'b u32) {}   // error!

compiler/rustc_feature/src/active.rs

@@ -400,8 +400,6 @@ declare_features! (
     (active, if_let_guard, "1.47.0", Some(51114), None),
     /// Allows using imported `main` function
     (active, imported_main, "1.53.0", Some(28937), None),
-    /// Allows in-band quantification of lifetime bindings (e.g., `fn foo(x: &'a u8) -> &'a u8`).
-    (active, in_band_lifetimes, "1.23.0", Some(44524), None),
     /// Allows inferring `'static` outlives requirements (RFC 2093).
     (active, infer_static_outlives_requirements, "1.26.0", Some(54185), None),
     /// Allows associated types in inherent impls.

compiler/rustc_feature/src/removed.rs

@@ -104,6 +104,9 @@ declare_features! (
     (removed, impl_trait_in_bindings, "1.55.0", Some(63065), None,
      Some("the implementation was not maintainable, the feature may get reintroduced once the current refactorings are done")),
     (removed, import_shadowing, "1.0.0", None, None, None),
+    /// Allows in-band quantification of lifetime bindings (e.g., `fn foo(x: &'a u8) -> &'a u8`).
+    (removed, in_band_lifetimes, "1.23.0", Some(44524), None,
+     Some("removed due to unsolved ergonomic questions and added lifetime resolution complexity")),
     /// Lazily evaluate constants. This allows constants to depend on type parameters.
     (removed, lazy_normalization_consts, "1.46.0", Some(72219), None, Some("superseded by `generic_const_exprs`")),
     /// Allows using the `#[link_args]` attribute.

compiler/rustc_hir/src/hir.rs

@@ -470,11 +470,6 @@ pub enum LifetimeParamKind {
     // `fn foo<'a>(x: &'a u8) -> &'a u8 { x }`).
     Explicit,
 
-    // Indicates that the lifetime definition was synthetically added
-    // as a result of an in-band lifetime usage (e.g., in
-    // `fn foo(x: &'a u8) -> &'a u8 { x }`).
-    InBand,
-
     // Indication that the lifetime was elided (e.g., in both cases in
     // `fn foo(x: &u8) -> &'_ u8 { x }`).
     Elided,