Rollup of 6 pull requests

compiler/rustc_ast_lowering/src/expr.rs

@@ -442,18 +442,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
         then: &Block,
         else_opt: Option<&Expr>,
     ) -> hir::ExprKind<'hir> {
-        macro_rules! make_if {
-            ($opt:expr) => {{
-                let cond = self.lower_expr(cond);
-                let then_expr = self.lower_block_expr(then);
-                hir::ExprKind::If(cond, self.arena.alloc(then_expr), $opt)
-            }};
-        }
-        if let Some(rslt) = else_opt {
-            make_if!(Some(self.lower_expr(rslt)))
-        } else {
-            make_if!(None)
-        }
+        let cond = self.lower_expr(cond);
+        let then = self.arena.alloc(self.lower_block_expr(then));
+        let els = else_opt.map(|els| self.lower_expr(els));
+        hir::ExprKind::If(cond, then, els)
     }
 
     fn lower_expr_if_let(

compiler/rustc_feature/src/active.rs

@@ -687,6 +687,9 @@ declare_features! (
     /// Trait upcasting is casting, e.g., `dyn Foo -> dyn Bar` where `Foo: Bar`.
     (incomplete, trait_upcasting, "1.56.0", Some(65991), None),
 
+    /// Allows explicit generic arguments specification with `impl Trait` present.
+    (active, explicit_generic_args_with_impl_trait, "1.56.0", Some(83701), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -71,7 +71,7 @@ use rustc_middle::ty::{
     subst::{GenericArgKind, Subst, SubstsRef},
     Region, Ty, TyCtxt, TypeFoldable,
 };
-use rustc_span::{sym, BytePos, DesugaringKind, Pos, Span};
+use rustc_span::{sym, BytePos, DesugaringKind, MultiSpan, Pos, Span};
 use rustc_target::spec::abi;
 use std::ops::ControlFlow;
 use std::{cmp, fmt, iter};
@@ -1485,31 +1485,49 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     let count = values.len();
                     let kind = key.descr();
                     let mut returned_async_output_error = false;
-                    for sp in values {
-                        err.span_label(
-                            *sp,
-                            format!(
-                                "{}{}{} {}{}",
-                                if sp.is_desugaring(DesugaringKind::Async)
-                                    && !returned_async_output_error
-                                {
-                                    "checked the `Output` of this `async fn`, "
-                                } else if count == 1 {
-                                    "the "
-                                } else {
-                                    ""
-                                },
-                                if count > 1 { "one of the " } else { "" },
-                                target,
-                                kind,
-                                pluralize!(count),
-                            ),
-                        );
-                        if sp.is_desugaring(DesugaringKind::Async)
-                            && returned_async_output_error == false
-                        {
-                            err.note("while checking the return type of the `async fn`");
+                    for &sp in values {
+                        if sp.is_desugaring(DesugaringKind::Async) && !returned_async_output_error {
+                            if &[sp] != err.span.primary_spans() {
+                                let mut span: MultiSpan = sp.into();
+                                span.push_span_label(
+                                    sp,
+                                    format!(
+                                        "checked the `Output` of this `async fn`, {}{} {}{}",
+                                        if count > 1 { "one of the " } else { "" },
+                                        target,
+                                        kind,
+                                        pluralize!(count),
+                                    ),
+                                );
+                                err.span_note(
+                                    span,
+                                    "while checking the return type of the `async fn`",
+                                );
+                            } else {
+                                err.span_label(
+                                    sp,
+                                    format!(
+                                        "checked the `Output` of this `async fn`, {}{} {}{}",
+                                        if count > 1 { "one of the " } else { "" },
+                                        target,
+                                        kind,
+                                        pluralize!(count),
+                                    ),
+                                );
+                                err.note("while checking the return type of the `async fn`");
+                            }
                             returned_async_output_error = true;
+                        } else {
+                            err.span_label(
+                                sp,
+                                format!(
+                                    "{}{} {}{}",
+                                    if count == 1 { "the " } else { "one of the " },
+                                    target,
+                                    kind,
+                                    pluralize!(count),
+                                ),
+                            );
                         }
                     }
                 }

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -769,7 +769,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 
                 // (#83606): Do not emit a suggestion if the parent has an `impl Trait`
                 // as an argument otherwise it will cause the E0282 error.
-                if !has_impl_trait {
+                if !has_impl_trait || self.tcx.features().explicit_generic_args_with_impl_trait {
                     err.span_suggestion_verbose(
                         span,
                         "consider specifying the const argument",

compiler/rustc_parse/src/lexer/unescape_error_reporting.rs

@@ -153,16 +153,37 @@ pub(crate) fn emit_unescape_error(
         EscapeError::NonAsciiCharInByte => {
             assert!(mode.is_bytes());
             let (c, span) = last_char();
-            handler
-                .struct_span_err(span, "non-ASCII character in byte constant")
-                .span_label(span, "byte constant must be ASCII")
-                .span_suggestion(
+            let mut err = handler.struct_span_err(span, "non-ASCII character in byte constant");
+            err.span_label(span, "byte constant must be ASCII");
+            if (c as u32) <= 0xFF {
+                err.span_suggestion(
                     span,
-                    "use a \\xHH escape for a non-ASCII byte",
+                    &format!(
+                        "if you meant to use the unicode code point for '{}', use a \\xHH escape",
+                        c
+                    ),
                     format!("\\x{:X}", c as u32),
-                    Applicability::MachineApplicable,
-                )
-                .emit();
+                    Applicability::MaybeIncorrect,
+                );
+            } else if matches!(mode, Mode::Byte) {
+                err.span_label(span, "this multibyte character does not fit into a single byte");
+            } else if matches!(mode, Mode::ByteStr) {
+                let mut utf8 = String::new();
+                utf8.push(c);
+                err.span_suggestion(
+                    span,
+                    &format!(
+                        "if you meant to use the UTF-8 encoding of '{}', use \\xHH escapes",
+                        c
+                    ),
+                    utf8.as_bytes()
+                        .iter()
+                        .map(|b: &u8| format!("\\x{:X}", *b))
+                        .fold("".to_string(), |a, c| a + &c),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            err.emit();
         }
         EscapeError::NonAsciiCharInByteString => {
             assert!(mode.is_bytes());

compiler/rustc_span/src/symbol.rs

@@ -554,6 +554,7 @@ symbols! {
         expected,
         expf32,
         expf64,
+        explicit_generic_args_with_impl_trait,
         export_name,
         expr,
         extended_key_value_attributes,

compiler/rustc_typeck/src/astconv/generics.rs

@@ -459,7 +459,32 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let default_counts = gen_params.own_defaults();
         let param_counts = gen_params.own_counts();
-        let named_type_param_count = param_counts.types - has_self as usize;
+
+        // Subtracting from param count to ensure type params synthesized from `impl Trait`
+        // cannot be explictly specified even with `explicit_generic_args_with_impl_trait`
+        // feature enabled.
+        let synth_type_param_count = if tcx.features().explicit_generic_args_with_impl_trait {
+            gen_params
+                .params
+                .iter()
+                .filter(|param| {
+                    matches!(
+                        param.kind,
+                        ty::GenericParamDefKind::Type {
+                            synthetic: Some(
+                                hir::SyntheticTyParamKind::ImplTrait
+                                    | hir::SyntheticTyParamKind::FromAttr
+                            ),
+                            ..
+                        }
+                    )
+                })
+                .count()
+        } else {
+            0
+        };
+        let named_type_param_count =
+            param_counts.types - has_self as usize - synth_type_param_count;
         let infer_lifetimes =
             gen_pos != GenericArgPosition::Type && !gen_args.has_lifetime_params();
 
@@ -588,6 +613,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 param_counts.consts + named_type_param_count
                     - default_counts.types
                     - default_counts.consts
+                    - synth_type_param_count
             };
             debug!("expected_min: {:?}", expected_min);
             debug!("arg_counts.lifetimes: {:?}", gen_args.num_lifetime_params());
@@ -617,7 +643,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         seg: &hir::PathSegment<'_>,
         generics: &ty::Generics,
     ) -> bool {
-        let explicit = !seg.infer_args;
+        if seg.infer_args || tcx.features().explicit_generic_args_with_impl_trait {
+            return false;
+        }
+
         let impl_trait = generics.params.iter().any(|param| {
             matches!(
                 param.kind,
@@ -630,7 +659,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             )
         });
 
-        if explicit && impl_trait {
+        if impl_trait {
             let spans = seg
                 .args()
                 .args

compiler/rustc_typeck/src/check/_match.rs

@@ -13,41 +13,6 @@ use rustc_trait_selection::traits::{
     StatementAsExpression,
 };
 
-macro_rules! create_maybe_get_coercion_reason {
-    ($fn_name:ident, $node:expr) => {
-        pub(crate) fn $fn_name(&self, hir_id: hir::HirId, sp: Span) -> Option<(Span, String)> {
-            let node = $node(self.tcx.hir(), hir_id);
-            if let hir::Node::Block(block) = node {
-                // check that the body's parent is an fn
-                let parent = self.tcx.hir().get(
-                    self.tcx.hir().get_parent_node(self.tcx.hir().get_parent_node(block.hir_id)),
-                );
-                if let (
-                    Some(expr),
-                    hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(..), .. }),
-                ) = (&block.expr, parent)
-                {
-                    // check that the `if` expr without `else` is the fn body's expr
-                    if expr.span == sp {
-                        return self.get_fn_decl(hir_id).and_then(|(fn_decl, _)| {
-                            let span = fn_decl.output.span();
-                            let snippet = self.tcx.sess.source_map().span_to_snippet(span).ok()?;
-                            Some((
-                                span,
-                                format!("expected `{}` because of this return type", snippet),
-                            ))
-                        });
-                    }
-                }
-            }
-            if let hir::Node::Local(hir::Local { ty: Some(_), pat, .. }) = node {
-                return Some((pat.span, "expected because of this assignment".to_string()));
-            }
-            None
-        }
-    };
-}
-
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     pub fn check_match(
         &self,
@@ -154,7 +119,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     expr.span,
                     &arms[0].body,
                     &mut coercion,
-                    |hir_id, span| self.maybe_get_coercion_reason(hir_id, span),
+                    |hir_id, span| self.coercion_reason_match(hir_id, span),
                 ) {
                 tcx.ty_error()
             } else {
@@ -373,23 +338,56 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         error
     }
 
-    create_maybe_get_coercion_reason!(
-        maybe_get_coercion_reason,
-        |hir: rustc_middle::hir::map::Map<'a>, id| {
-            let arm_id = hir.get_parent_node(id);
-            let match_id = hir.get_parent_node(arm_id);
-            let containing_id = hir.get_parent_node(match_id);
-            hir.get(containing_id)
-        }
-    );
+    pub(crate) fn coercion_reason_if(
+        &self,
+        hir_id: hir::HirId,
+        span: Span,
+    ) -> Option<(Span, String)> {
+        self.coercion_reason_inner(hir_id, span, 1)
+    }
 
-    create_maybe_get_coercion_reason!(
-        maybe_get_coercion_reason_if,
-        |hir: rustc_middle::hir::map::Map<'a>, id| {
-            let rslt = hir.get_parent_node(hir.get_parent_node(id));
-            hir.get(rslt)
+    pub(crate) fn coercion_reason_match(
+        &self,
+        hir_id: hir::HirId,
+        span: Span,
+    ) -> Option<(Span, String)> {
+        self.coercion_reason_inner(hir_id, span, 2)
+    }
+
+    fn coercion_reason_inner(
+        &self,
+        hir_id: hir::HirId,
+        span: Span,
+        parent_index: usize,
+    ) -> Option<(Span, String)> {
+        let hir = self.tcx.hir();
+        let mut parent_iter = hir.parent_iter(hir_id);
+        let (_, node) = parent_iter.nth(parent_index)?;
+        match node {
+            hir::Node::Block(block) => {
+                let expr = block.expr?;
+                // check that the body's parent is an fn
+                let (_, parent) = parent_iter.nth(1)?;
+                if let hir::Node::Item(hir::Item { kind: hir::ItemKind::Fn(..), .. }) = parent {
+                    // check that the `if` expr without `else` is the fn body's expr
+                    if expr.span == span {
+                        let (fn_decl, _) = self.get_fn_decl(hir_id)?;
+                        let span = fn_decl.output.span();
+                        let snippet = self.tcx.sess.source_map().span_to_snippet(span).ok()?;
+                        return Some((
+                            span,
+                            format!("expected `{}` because of this return type", snippet),
+                        ));
+                    }
+                }
+                None
+            }
+            hir::Node::Local(hir::Local { ty: Some(_), pat, .. }) => {
+                Some((pat.span, "expected because of this assignment".to_string()))
+            }
+            _ => None,
         }
-    );
+    }
 
     pub(crate) fn if_cause(
         &self,

compiler/rustc_typeck/src/check/expr.rs

@@ -838,7 +838,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.diverges.set(cond_diverges | then_diverges & else_diverges);
         } else {
             self.if_fallback_coercion(sp, then_expr, &mut coerce, |hir_id, span| {
-                self.maybe_get_coercion_reason_if(hir_id, span)
+                self.coercion_reason_if(hir_id, span)
             });
 
             // If the condition is false we can't diverge.

library/core/src/option.rs

@@ -285,6 +285,19 @@
 //! assert_eq!(res, ["error!", "error!", "foo", "error!", "bar"]);
 //! ```
 //!
+//! ## Comparison operators
+//!
+//! If `T` implements [`PartialOrd`] then [`Option<T>`] will derive its
+//! [`PartialOrd`] implementation.  With this order, [`None`] compares as
+//! less than any [`Some`], and two [`Some`] compare the same way as their
+//! contained values would in `T`.  If `T` also implements
+//! [`Ord`], then so does [`Option<T>`].
+//!
+//! ```
+//! assert!(None < Some(0));
+//! assert!(Some(0) < Some(1));
+//! ```
+//!
 //! ## Iterating over `Option`
 //!
 //! An [`Option`] can be iterated over. This can be helpful if you need an