Rollup of 10 pull requests

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1357,9 +1357,7 @@ impl<'a> State<'a> {
                 self.bclose(item.span, empty);
             }
             ast::ItemKind::TraitAlias(ref generics, ref bounds) => {
-                self.head("");
-                self.print_visibility(&item.vis);
-                self.word_nbsp("trait");
+                self.head(visibility_qualified(&item.vis, "trait"));
                 self.print_ident(item.ident);
                 self.print_generic_params(&generics.params);
                 let mut real_bounds = Vec::with_capacity(bounds.len());
@@ -1377,6 +1375,8 @@ impl<'a> State<'a> {
                 self.print_type_bounds("=", &real_bounds);
                 self.print_where_clause(&generics.where_clause);
                 self.word(";");
+                self.end(); // end inner head-block
+                self.end(); // end outer head-block
             }
             ast::ItemKind::MacCall(ref mac) => {
                 self.print_mac(mac);

compiler/rustc_feature/src/builtin_attrs.rs

@@ -623,6 +623,11 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         lang, Normal, template!(NameValueStr: "name"), DuplicatesOk, lang_items,
         "language items are subject to change",
     ),
+    rustc_attr!(
+        rustc_pass_by_value, Normal,
+        template!(Word), WarnFollowing,
+        "#[rustc_pass_by_value] is used to mark types that must be passed by value instead of reference."
+    ),
     BuiltinAttribute {
         name: sym::rustc_diagnostic_item,
         type_: Normal,

compiler/rustc_hir_pretty/src/lib.rs

@@ -705,9 +705,7 @@ impl<'a> State<'a> {
                 self.bclose(item.span);
             }
             hir::ItemKind::TraitAlias(ref generics, ref bounds) => {
-                self.head("");
-                self.print_visibility(&item.vis);
-                self.word_nbsp("trait");
+                self.head(visibility_qualified(&item.vis, "trait"));
                 self.print_ident(item.ident);
                 self.print_generic_params(&generics.params);
                 let mut real_bounds = Vec::with_capacity(bounds.len());
@@ -725,6 +723,8 @@ impl<'a> State<'a> {
                 self.print_bounds("=", real_bounds);
                 self.print_where_clause(&generics.where_clause);
                 self.word(";");
+                self.end(); // end inner head-block
+                self.end(); // end outer head-block
             }
         }
         self.ann.post(self, AnnNode::Item(item))

compiler/rustc_index/src/lib.rs

@@ -9,7 +9,3 @@
 pub mod bit_set;
 pub mod interval;
 pub mod vec;
-
-// FIXME(#56935): Work around ICEs during cross-compilation.
-#[allow(unused)]
-extern crate rustc_macros;

compiler/rustc_infer/src/infer/outlives/obligations.rs

@@ -164,7 +164,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
             "cannot process registered region obligations in a snapshot"
         );
 
-        debug!("process_registered_region_obligations()");
+        debug!(?param_env, "process_registered_region_obligations()");
 
         let my_region_obligations = self.take_registered_region_obligations();
 
@@ -356,6 +356,8 @@ where
         let trait_bounds: Vec<_> =
             self.verify_bound.projection_declared_bounds_from_trait(projection_ty).collect();
 
+        debug!(?trait_bounds);
+
         // Compute the bounds we can derive from the environment. This
         // is an "approximate" match -- in some cases, these bounds
         // may not apply.

compiler/rustc_infer/src/traits/util.rs

@@ -241,10 +241,19 @@ impl<'tcx> Elaborator<'tcx> {
 
                             Component::UnresolvedInferenceVariable(_) => None,
 
-                            Component::Projection(_) | Component::EscapingProjection(_) => {
-                                // We can probably do more here. This
-                                // corresponds to a case like `<T as
-                                // Foo<'a>>::U: 'b`.
+                            Component::Projection(projection) => {
+                                // We might end up here if we have `Foo<<Bar as Baz>::Assoc>: 'a`.
+                                // With this, we can deduce that `<Bar as Baz>::Assoc: 'a`.
+                                let ty =
+                                    tcx.mk_projection(projection.item_def_id, projection.substs);
+                                Some(ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(
+                                    ty, r_min,
+                                )))
+                            }
+
+                            Component::EscapingProjection(_) => {
+                                // We might be able to do more here, but we don't
+                                // want to deal with escaping vars right now.
                                 None
                             }
                         })

compiler/rustc_lint/src/internal.rs

@@ -5,10 +5,7 @@ use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext}
 use rustc_ast as ast;
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
-use rustc_hir::{
-    GenericArg, HirId, Item, ItemKind, MutTy, Mutability, Node, Path, PathSegment, QPath, Ty,
-    TyKind,
-};
+use rustc_hir::{GenericArg, HirId, Item, ItemKind, Node, Path, PathSegment, QPath, Ty, TyKind};
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::hygiene::{ExpnKind, MacroKind};
@@ -58,13 +55,6 @@ declare_tool_lint! {
     report_in_external_macro: true
 }
 
-declare_tool_lint! {
-    pub rustc::TY_PASS_BY_REFERENCE,
-    Allow,
-    "passing `Ty` or `TyCtxt` by reference",
-    report_in_external_macro: true
-}
-
 declare_tool_lint! {
     pub rustc::USAGE_OF_QUALIFIED_TY,
     Allow,
@@ -74,7 +64,6 @@ declare_tool_lint! {
 
 declare_lint_pass!(TyTyKind => [
     USAGE_OF_TY_TYKIND,
-    TY_PASS_BY_REFERENCE,
     USAGE_OF_QUALIFIED_TY,
 ]);
 
@@ -131,26 +120,6 @@ impl<'tcx> LateLintPass<'tcx> for TyTyKind {
                     }
                 }
             }
-            TyKind::Rptr(_, MutTy { ty: inner_ty, mutbl: Mutability::Not }) => {
-                if let Some(impl_did) = cx.tcx.impl_of_method(ty.hir_id.owner.to_def_id()) {
-                    if cx.tcx.impl_trait_ref(impl_did).is_some() {
-                        return;
-                    }
-                }
-                if let Some(t) = is_ty_or_ty_ctxt(cx, &inner_ty) {
-                    cx.struct_span_lint(TY_PASS_BY_REFERENCE, ty.span, |lint| {
-                        lint.build(&format!("passing `{}` by reference", t))
-                            .span_suggestion(
-                                ty.span,
-                                "try passing by value",
-                                t,
-                                // Changing type of function argument
-                                Applicability::MaybeIncorrect,
-                            )
-                            .emit();
-                    })
-                }
-            }
             _ => {}
         }
     }

compiler/rustc_lint/src/lib.rs

@@ -56,6 +56,7 @@ mod non_ascii_idents;
 mod non_fmt_panic;
 mod nonstandard_style;
 mod noop_method_call;
+mod pass_by_value;
 mod passes;
 mod redundant_semicolon;
 mod traits;
@@ -85,6 +86,7 @@ use non_ascii_idents::*;
 use non_fmt_panic::NonPanicFmt;
 use nonstandard_style::*;
 use noop_method_call::*;
+use pass_by_value::*;
 use redundant_semicolon::*;
 use traits::*;
 use types::*;
@@ -490,15 +492,17 @@ fn register_internals(store: &mut LintStore) {
     store.register_late_pass(|| Box::new(ExistingDocKeyword));
     store.register_lints(&TyTyKind::get_lints());
     store.register_late_pass(|| Box::new(TyTyKind));
+    store.register_lints(&PassByValue::get_lints());
+    store.register_late_pass(|| Box::new(PassByValue));
     store.register_group(
         false,
         "rustc::internal",
         None,
         vec![
             LintId::of(DEFAULT_HASH_TYPES),
             LintId::of(USAGE_OF_TY_TYKIND),
+            LintId::of(PASS_BY_VALUE),
             LintId::of(LINT_PASS_IMPL_WITHOUT_MACRO),
-            LintId::of(TY_PASS_BY_REFERENCE),
             LintId::of(USAGE_OF_QUALIFIED_TY),
             LintId::of(EXISTING_DOC_KEYWORD),
         ],

compiler/rustc_lint/src/pass_by_value.rs

@@ -0,0 +1,94 @@
+use crate::{LateContext, LateLintPass, LintContext};
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_hir::def::Res;
+use rustc_hir::{GenericArg, PathSegment, QPath, TyKind};
+use rustc_middle::ty;
+use rustc_span::symbol::sym;
+
+declare_tool_lint! {
+    /// The `rustc_pass_by_value` lint marks a type with `#[rustc_pass_by_value]` requiring it to always be passed by value.
+    /// This is usually used for types that are thin wrappers around references, so there is no benefit to an extra
+    /// layer of indirection. (Example: `Ty` which is a reference to a `TyS`)
+    pub rustc::PASS_BY_VALUE,
+    Warn,
+    "pass by reference of a type flagged as `#[rustc_pass_by_value]`",
+    report_in_external_macro: true
+}
+
+declare_lint_pass!(PassByValue => [PASS_BY_VALUE]);
+
+impl<'tcx> LateLintPass<'tcx> for PassByValue {
+    fn check_ty(&mut self, cx: &LateContext<'_>, ty: &'tcx hir::Ty<'tcx>) {
+        match &ty.kind {
+            TyKind::Rptr(_, hir::MutTy { ty: inner_ty, mutbl: hir::Mutability::Not }) => {
+                if let Some(impl_did) = cx.tcx.impl_of_method(ty.hir_id.owner.to_def_id()) {
+                    if cx.tcx.impl_trait_ref(impl_did).is_some() {
+                        return;
+                    }
+                }
+                if let Some(t) = path_for_pass_by_value(cx, &inner_ty) {
+                    cx.struct_span_lint(PASS_BY_VALUE, ty.span, |lint| {
+                        lint.build(&format!("passing `{}` by reference", t))
+                            .span_suggestion(
+                                ty.span,
+                                "try passing by value",
+                                t,
+                                // Changing type of function argument
+                                Applicability::MaybeIncorrect,
+                            )
+                            .emit();
+                    })
+                }
+            }
+            _ => {}
+        }
+    }
+}
+
+fn path_for_pass_by_value(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> Option<String> {
+    if let TyKind::Path(QPath::Resolved(_, path)) = &ty.kind {
+        match path.res {
+            Res::Def(_, def_id) if cx.tcx.has_attr(def_id, sym::rustc_pass_by_value) => {
+                let name = cx.tcx.item_name(def_id).to_ident_string();
+                let path_segment = path.segments.last().unwrap();
+                return Some(format!("{}{}", name, gen_args(cx, path_segment)));
+            }
+            Res::SelfTy(None, Some((did, _))) => {
+                if let ty::Adt(adt, substs) = cx.tcx.type_of(did).kind() {
+                    if cx.tcx.has_attr(adt.did, sym::rustc_pass_by_value) {
+                        return Some(cx.tcx.def_path_str_with_substs(adt.did, substs));
+                    }
+                }
+            }
+            _ => (),
+        }
+    }
+
+    None
+}
+
+fn gen_args(cx: &LateContext<'_>, segment: &PathSegment<'_>) -> String {
+    if let Some(args) = &segment.args {
+        let params = args
+            .args
+            .iter()
+            .map(|arg| match arg {
+                GenericArg::Lifetime(lt) => lt.name.ident().to_string(),
+                GenericArg::Type(ty) => {
+                    cx.tcx.sess.source_map().span_to_snippet(ty.span).unwrap_or_default()
+                }
+                GenericArg::Const(c) => {
+                    cx.tcx.sess.source_map().span_to_snippet(c.span).unwrap_or_default()
+                }
+                GenericArg::Infer(_) => String::from("_"),
+            })
+            .collect::<Vec<_>>();
+
+        if !params.is_empty() {
+            return format!("<{}>", params.join(", "));
+        }
+    }
+
+    String::new()
+}

compiler/rustc_middle/src/ty/context.rs

@@ -961,6 +961,7 @@ pub struct FreeRegionInfo {
 /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/ty.html
 #[derive(Copy, Clone)]
 #[rustc_diagnostic_item = "TyCtxt"]
+#[cfg_attr(not(bootstrap), rustc_pass_by_value)]
 pub struct TyCtxt<'tcx> {
     gcx: &'tcx GlobalCtxt<'tcx>,
 }

compiler/rustc_middle/src/ty/mod.rs

@@ -464,6 +464,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for TyS<'tcx> {
 }
 
 #[rustc_diagnostic_item = "Ty"]
+#[cfg_attr(not(bootstrap), rustc_pass_by_value)]
 pub type Ty<'tcx> = &'tcx TyS<'tcx>;
 
 impl ty::EarlyBoundRegion {

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1,5 +1,5 @@
 use super::pat::Expected;
-use super::ty::AllowPlus;
+use super::ty::{AllowPlus, IsAsCast};
 use super::{
     BlockMode, Parser, PathStyle, RecoverColon, RecoverComma, Restrictions, SemiColonMode, SeqSep,
     TokenExpectType, TokenType,
@@ -1032,6 +1032,34 @@ impl<'a> Parser<'a> {
         }
     }
 
+    /// Swift lets users write `Ty?` to mean `Option<Ty>`. Parse the construct and recover from it.
+    pub(super) fn maybe_recover_from_question_mark(
+        &mut self,
+        ty: P<Ty>,
+        is_as_cast: IsAsCast,
+    ) -> P<Ty> {
+        if let IsAsCast::Yes = is_as_cast {
+            return ty;
+        }
+        if self.token == token::Question {
+            self.bump();
+            self.struct_span_err(self.prev_token.span, "invalid `?` in type")
+                .span_label(self.prev_token.span, "`?` is only allowed on expressions, not types")
+                .multipart_suggestion(
+                    "if you meant to express that the type might not contain a value, use the `Option` wrapper type",
+                    vec![
+                        (ty.span.shrink_to_lo(), "Option<".to_string()),
+                        (self.prev_token.span, ">".to_string()),
+                    ],
+                    Applicability::MachineApplicable,
+                )
+                .emit();
+            self.mk_ty(ty.span.to(self.prev_token.span), TyKind::Err)
+        } else {
+            ty
+        }
+    }
+
     pub(super) fn maybe_recover_from_bad_type_plus(
         &mut self,
         allow_plus: AllowPlus,

compiler/rustc_parse/src/parser/expr.rs

@@ -682,7 +682,7 @@ impl<'a> Parser<'a> {
         // Save the state of the parser before parsing type normally, in case there is a
         // LessThan comparison after this cast.
         let parser_snapshot_before_type = self.clone();
-        let cast_expr = match self.parse_ty_no_plus() {
+        let cast_expr = match self.parse_as_cast_ty() {
             Ok(rhs) => mk_expr(self, lhs, rhs),
             Err(mut type_err) => {
                 // Rewind to before attempting to parse the type with generics, to recover
@@ -808,7 +808,7 @@ impl<'a> Parser<'a> {
                 "casts cannot be followed by {}",
                 match with_postfix.kind {
                     ExprKind::Index(_, _) => "indexing",
-                    ExprKind::Try(_) => "?",
+                    ExprKind::Try(_) => "`?`",
                     ExprKind::Field(_, _) => "a field access",
                     ExprKind::MethodCall(_, _, _) => "a method call",
                     ExprKind::Call(_, _) => "a function call",