Auto merge of #65196 - Centril:rollup-q06lcxm, r=Centril

Rollup of 8 pull requests

Successful merges:

 - #64726 (rewrite documentation for unimplemented! to clarify use)
 - #65040 (syntax: more cleanups in item and function signature parsing)
 - #65046 (Make `Cell::new` method come first in documentation)
 - #65098 (Add long error explanation for E0561)
 - #65150 (Suggest dereferencing boolean reference when used in 'if' or 'while')
 - #65154 (Fix const generic arguments not displaying in types mismatch diagnostic)
 - #65181 (fix bug in folding for constants)
 - #65187 (use 'invalid argument' for vxWorks)

Failed merges:

 - #65179 (Add long error explanation for E0567)

r? @ghost

src/libcore/cell.rs

@@ -229,52 +229,6 @@ pub struct Cell<T: ?Sized> {
     value: UnsafeCell<T>,
 }
 
-impl<T:Copy> Cell<T> {
-    /// Returns a copy of the contained value.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::cell::Cell;
-    ///
-    /// let c = Cell::new(5);
-    ///
-    /// let five = c.get();
-    /// ```
-    #[inline]
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn get(&self) -> T {
-        unsafe{ *self.value.get() }
-    }
-
-    /// Updates the contained value using a function and returns the new value.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(cell_update)]
-    ///
-    /// use std::cell::Cell;
-    ///
-    /// let c = Cell::new(5);
-    /// let new = c.update(|x| x + 1);
-    ///
-    /// assert_eq!(new, 6);
-    /// assert_eq!(c.get(), 6);
-    /// ```
-    #[inline]
-    #[unstable(feature = "cell_update", issue = "50186")]
-    pub fn update<F>(&self, f: F) -> T
-    where
-        F: FnOnce(T) -> T,
-    {
-        let old = self.get();
-        let new = f(old);
-        self.set(new);
-        new
-    }
-}
-
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: ?Sized> Send for Cell<T> where T: Send {}
 
@@ -448,6 +402,52 @@ impl<T> Cell<T> {
     }
 }
 
+impl<T:Copy> Cell<T> {
+    /// Returns a copy of the contained value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::cell::Cell;
+    ///
+    /// let c = Cell::new(5);
+    ///
+    /// let five = c.get();
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn get(&self) -> T {
+        unsafe{ *self.value.get() }
+    }
+
+    /// Updates the contained value using a function and returns the new value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cell_update)]
+    ///
+    /// use std::cell::Cell;
+    ///
+    /// let c = Cell::new(5);
+    /// let new = c.update(|x| x + 1);
+    ///
+    /// assert_eq!(new, 6);
+    /// assert_eq!(c.get(), 6);
+    /// ```
+    #[inline]
+    #[unstable(feature = "cell_update", issue = "50186")]
+    pub fn update<F>(&self, f: F) -> T
+    where
+        F: FnOnce(T) -> T,
+    {
+        let old = self.get();
+        let new = f(old);
+        self.set(new);
+        new
+    }
+}
+
 impl<T: ?Sized> Cell<T> {
     /// Returns a raw pointer to the underlying data in this cell.
     ///

src/libcore/macros.rs

@@ -520,18 +520,20 @@ macro_rules! unreachable {
     });
 }
 
-/// Indicates unfinished code.
+/// Indicates unfinished code by panicking with a message of "not yet implemented".
 ///
-/// This can be useful if you are prototyping and are just looking to have your
+/// This allows the your code to type-check, which is useful if you are prototyping or
-/// code type-check, or if you're implementing a trait that requires multiple
+/// implementing a trait that requires multiple methods which you don't plan of using all of.
-/// methods, and you're only planning on using one of them.
 ///
 /// There is no difference between `unimplemented!` and `todo!` apart from the
 /// name.
 ///
 /// # Panics
 ///
-/// This will always [panic!](macro.panic.html)
+/// This will always [panic!](macro.panic.html) because `unimplemented!` is just a
+/// shorthand for `panic!` with a fixed, specific message.
+///
+/// Like `panic!`, this macro has a second form for displaying custom values.
 ///
 /// # Examples
 ///
@@ -539,38 +541,53 @@ macro_rules! unreachable {
 ///
 /// ```
 /// trait Foo {
-///     fn bar(&self);
+///     fn bar(&self) -> u8;
 ///     fn baz(&self);
+///     fn qux(&self) -> Result<u64, ()>;
 /// }
 /// ```
 ///
-/// We want to implement `Foo` on one of our types, but we also want to work on
+/// We want to implement `Foo` for 'MyStruct', but so far we only know how to
-/// just `bar()` first. In order for our code to compile, we need to implement
+/// implement the `bar()` function. `baz()` and `qux()` will still need to be defined
-/// `baz()`, so we can use `unimplemented!`:
+/// in our implementation of `Foo`, but we can use `unimplemented!` in their definitions
+/// to allow our code to compile.
+///
+/// In the meantime, we want to have our program stop running once these
+/// unimplemented functions are reached.
 ///
 /// ```
 /// # trait Foo {
-/// #     fn bar(&self);
+/// #     fn bar(&self) -> u8;
 /// #     fn baz(&self);
+/// #     fn qux(&self) -> Result<u64, ()>;
 /// # }
 /// struct MyStruct;
 ///
 /// impl Foo for MyStruct {
-///     fn bar(&self) {
+///     fn bar(&self) -> u8 {
-///         // implementation goes here
+///         1 + 1
 ///     }
 ///
 ///     fn baz(&self) {
-///         // let's not worry about implementing baz() for now
+///         // We aren't sure how to even start writing baz yet,
+///         // so we have no logic here at all.
+///         // This will display "thread 'main' panicked at 'not yet implemented'".
 ///         unimplemented!();
 ///     }
+///
+///     fn qux(&self) -> Result<u64, ()> {
+///         let n = self.bar();
+///         // We have some logic here,
+///         // so we can use unimplemented! to display what we have so far.
+///         // This will display:
+///         // "thread 'main' panicked at 'not yet implemented: we need to divide by 2'".
+///         unimplemented!("we need to divide by {}", n);
+///     }
 /// }
 ///
 /// fn main() {
 ///     let s = MyStruct;
 ///     s.bar();
-///
-///     // we aren't even using baz() yet, so this is fine.
 /// }
 /// ```
 #[macro_export]

src/librustc/infer/error_reporting/mod.rs

@@ -935,6 +935,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         .filter(|(a, b)| a == b)
                         .count();
                     let len = sub1.len() - common_default_params;
+                    let consts_offset = len - sub1.consts().count();
 
                     // Only draw `<...>` if there're lifetime/type arguments.
                     if len > 0 {
@@ -981,7 +982,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     //         ^ elided type as this type argument was the same in both sides
                     let type_arguments = sub1.types().zip(sub2.types());
                     let regions_len = sub1.regions().count();
-                    for (i, (ta1, ta2)) in type_arguments.take(len).enumerate() {
+                    let num_display_types = consts_offset - regions_len;
+                    for (i, (ta1, ta2)) in type_arguments.take(num_display_types).enumerate() {
                         let i = i + regions_len;
                         if ta1 == ta2 {
                             values.0.push_normal("_");
@@ -994,6 +996,21 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         self.push_comma(&mut values.0, &mut values.1, len, i);
                     }
 
+                    // Do the same for const arguments, if they are equal, do not highlight and
+                    // elide them from the output.
+                    let const_arguments = sub1.consts().zip(sub2.consts());
+                    for (i, (ca1, ca2)) in const_arguments.enumerate() {
+                        let i = i + consts_offset;
+                        if ca1 == ca2 {
+                            values.0.push_normal("_");
+                            values.1.push_normal("_");
+                        } else {
+                            values.0.push_highlighted(ca1.to_string());
+                            values.1.push_highlighted(ca2.to_string());
+                        }
+                        self.push_comma(&mut values.0, &mut values.1, len, i);
+                    }
+
                     // Close the type argument bracket.
                     // Only draw `<...>` if there're lifetime/type arguments.
                     if len > 0 {

src/librustc/ty/flags.rs

@@ -250,7 +250,9 @@ impl FlagComputation {
             ConstValue::Placeholder(_) => {
                 self.add_flags(TypeFlags::HAS_FREE_REGIONS | TypeFlags::HAS_CT_PLACEHOLDER);
             }
-            _ => {},
+            ConstValue::Scalar(_) => { }
+            ConstValue::Slice { data: _, start: _, end: _ } => { }
+            ConstValue::ByRef { alloc: _, offset: _ } => { }
         }
     }
 

src/librustc/ty/fold.rs

@@ -911,13 +911,15 @@ impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
     }
 
     fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> bool {
-        if let ty::Const {
+        // we don't have a `visit_infer_const` callback, so we have to
-            val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, _)),
+        // hook in here to catch this case (annoying...), but
-            ..
+        // otherwise we do want to remember to visit the rest of the
-        } = *ct {
+        // const, as it has types/regions embedded in a lot of other
-            debruijn >= self.outer_index
+        // places.
-        } else {
+        match ct.val {
-            false
+            ConstValue::Infer(ty::InferConst::Canonical(debruijn, _))
+                if debruijn >= self.outer_index => true,
+            _ => ct.super_visit_with(self),
         }
     }
 }

src/librustc/ty/print/pretty.rs

@@ -689,7 +689,7 @@ pub trait PrettyPrinter<'tcx>:
                 if self.tcx().sess.verbose() {
                     p!(write(
                         " closure_kind_ty={:?} closure_sig_ty={:?}",
-                        substs.as_closure().kind(did, self.tcx()),
+                        substs.as_closure().kind_ty(did, self.tcx()),
                         substs.as_closure().sig_ty(did, self.tcx())
                     ));
                 }
@@ -698,7 +698,9 @@ pub trait PrettyPrinter<'tcx>:
             },
             ty::Array(ty, sz) => {
                 p!(write("["), print(ty), write("; "));
-                if let ConstValue::Unevaluated(..) = sz.val {
+                if self.tcx().sess.verbose() {
+                    p!(write("{:?}", sz));
+                } else if let ConstValue::Unevaluated(..) = sz.val {
                     // do not try to evalute unevaluated constants. If we are const evaluating an
                     // array length anon const, rustc will (with debug assertions) print the
                     // constant's path. Which will end up here again.
@@ -855,6 +857,11 @@ pub trait PrettyPrinter<'tcx>:
     ) -> Result<Self::Const, Self::Error> {
         define_scoped_cx!(self);
 
+        if self.tcx().sess.verbose() {
+            p!(write("Const({:?}: {:?})", ct.val, ct.ty));
+            return Ok(self);
+        }
+
         let u8 = self.tcx().types.u8;
         if let ty::FnDef(did, substs) = ct.ty.kind {
             p!(print_value_path(did, substs));

src/librustc/ty/sty.rs

@@ -2203,7 +2203,9 @@ impl<'tcx> TyS<'tcx> {
                 _ => bug!("cannot convert type `{:?}` to a closure kind", self),
             },
 
-            Infer(_) => None,
+            // "Bound" types appear in canonical queries when the
+            // closure type is not yet known
+            Bound(..) | Infer(_) => None,
 
             Error => Some(ty::ClosureKind::Fn),
 

src/librustc_passes/error_codes.rs

@@ -286,6 +286,34 @@ fn main() {
 ```
 "##,
 
+E0561: r##"
+A non-ident or non-wildcard pattern has been used as a parameter of a function
+pointer type.
+
+Erroneous code example:
+
+```compile_fail,E0561
+type A1 = fn(mut param: u8); // error!
+type A2 = fn(&param: u32); // error!
+```
+
+When using an alias over a function type, you cannot e.g. denote a parameter as
+being mutable.
+
+To fix the issue, remove patterns (`_` is allowed though). Example:
+
+```
+type A1 = fn(param: u8); // ok!
+type A2 = fn(_: u32); // ok!
+```
+
+You can also omit the parameter name:
+
+```
+type A3 = fn(i16); // ok!
+```
+"##,
+
 E0571: r##"
 A `break` statement with an argument appeared in a non-`loop` loop.
 
@@ -503,7 +531,6 @@ Switch to the Rust 2018 edition to use `async fn`.
 ;
     E0226, // only a single explicit lifetime bound is permitted
     E0472, // asm! is unsupported on this target
-    E0561, // patterns aren't allowed in function pointer types
     E0567, // auto traits can not have generic parameters
     E0568, // auto traits can not have super traits
     E0666, // nested `impl Trait` is illegal

src/librustc_traits/evaluate_obligation.rs

@@ -17,10 +17,12 @@ fn evaluate_obligation<'tcx>(
     tcx: TyCtxt<'tcx>,
     canonical_goal: CanonicalPredicateGoal<'tcx>,
 ) -> Result<EvaluationResult, OverflowError> {
+    debug!("evaluate_obligation(canonical_goal={:#?})", canonical_goal);
     tcx.infer_ctxt().enter_with_canonical(
         DUMMY_SP,
         &canonical_goal,
         |ref infcx, goal, _canonical_inference_vars| {
+            debug!("evaluate_obligation: goal={:#?}", goal);
             let ParamEnvAnd {
                 param_env,
                 value: predicate,

src/librustc_typeck/check/demand.rs

@@ -349,7 +349,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // If the span is from a macro, then it's hard to extract the text
         // and make a good suggestion, so don't bother.
-        let is_macro = sp.from_expansion();
+        let is_desugaring = match sp.desugaring_kind() {
+            Some(k) => sp.is_desugaring(k),
+            None => false
+        };
+        let is_macro = sp.from_expansion() && !is_desugaring;
 
         match (&expr.kind, &expected.kind, &checked_ty.kind) {
             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {

src/librustc_typeck/check/expr.rs

@@ -87,6 +87,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
+            self.suggest_ref_or_into(&mut err, expr, expected_ty, ty);
+
             let expr = match &expr.kind {
                 ExprKind::DropTemps(expr) => expr,
                 _ => expr,

src/libstd/fs.rs

@@ -3112,8 +3112,10 @@ mod tests {
 
         #[cfg(windows)]
         let invalid_options = 87; // ERROR_INVALID_PARAMETER
-        #[cfg(unix)]
+        #[cfg(all(unix, not(target_os = "vxworks")))]
         let invalid_options = "Invalid argument";
+        #[cfg(target_os = "vxworks")]
+        let invalid_options = "invalid argument";
 
         // Test various combinations of creation modes and access modes.
         //

src/libsyntax/parse/parser.rs

@@ -11,7 +11,7 @@ mod stmt;
 mod generics;
 
 use crate::ast::{
-    self, DUMMY_NODE_ID, AttrStyle, Attribute, BindingMode, CrateSugar, FnDecl, Ident,
+    self, DUMMY_NODE_ID, AttrStyle, Attribute, BindingMode, CrateSugar, Ident,
     IsAsync, MacDelimiter, Mutability, Param, StrStyle, SelfKind, TyKind, Visibility,
     VisibilityKind, Unsafety,
 };
@@ -56,6 +56,17 @@ crate enum BlockMode {
     Ignore,
 }
 
+/// The parsing configuration used to parse a parameter list (see `parse_fn_params`).
+struct ParamCfg {
+    /// Is `self` is allowed as the first parameter?
+    is_self_allowed: bool,
+    /// Is `...` allowed as the tail of the parameter list?
+    allow_c_variadic: bool,
+    /// `is_name_required` decides if, per-parameter,
+    /// the parameter must have a pattern or just a type.
+    is_name_required: fn(&token::Token) -> bool,
+}
+
 /// Like `maybe_whole_expr`, but for things other than expressions.
 #[macro_export]
 macro_rules! maybe_whole {
@@ -1094,26 +1105,18 @@ impl<'a> Parser<'a> {
         res
     }
 
-    fn parse_fn_params(
+    /// Parses the parameter list of a function, including the `(` and `)` delimiters.
-        &mut self,
+    fn parse_fn_params(&mut self, mut cfg: ParamCfg) -> PResult<'a, Vec<Param>> {
-        named_params: bool,
-        allow_c_variadic: bool,
-    ) -> PResult<'a, Vec<Param>> {
         let sp = self.token.span;
-        let do_not_enforce_named_params_for_c_variadic = |token: &token::Token| {
+        let is_trait_item = cfg.is_self_allowed;
-            match token.kind {
-                token::DotDotDot => false,
-                _ => named_params,
-            }
-        };
         let mut c_variadic = false;
+        // Parse the arguments, starting out with `self` being possibly allowed...
         let (params, _) = self.parse_paren_comma_seq(|p| {
-            match p.parse_param_general(
+            let param = p.parse_param_general(&cfg, is_trait_item);
-                false,
+            // ...now that we've parsed the first argument, `self` is no longer allowed.
-                false,
+            cfg.is_self_allowed = false;
-                allow_c_variadic,
+
-                do_not_enforce_named_params_for_c_variadic,
+            match param {
-            ) {
                 Ok(param) => Ok(
                     if let TyKind::CVarArgs = param.ty.kind {
                         c_variadic = true;
@@ -1144,7 +1147,10 @@ impl<'a> Parser<'a> {
             }
         })?;
 
-        let params: Vec<_> = params.into_iter().filter_map(|x| x).collect();
+        let mut params: Vec<_> = params.into_iter().filter_map(|x| x).collect();
+
+        // Replace duplicated recovered params with `_` pattern to avoid unecessary errors.
+        self.deduplicate_recovered_params_names(&mut params);
 
         if c_variadic && params.len() <= 1 {
             self.span_err(
@@ -1156,79 +1162,53 @@ impl<'a> Parser<'a> {
         Ok(params)
     }
 
-    /// Parses the parameter list and result type of a function that may have a `self` parameter.
-    fn parse_fn_decl_with_self(
-        &mut self,
-        is_name_required: impl Copy + Fn(&token::Token) -> bool,
-    ) -> PResult<'a, P<FnDecl>> {
-        // Parse the arguments, starting out with `self` being allowed...
-        let mut is_self_allowed = true;
-        let (mut inputs, _): (Vec<_>, _) = self.parse_paren_comma_seq(|p| {
-            let res = p.parse_param_general(is_self_allowed, true, false, is_name_required);
-            // ...but now that we've parsed the first argument, `self` is no longer allowed.
-            is_self_allowed = false;
-            res
-        })?;
-
-        // Replace duplicated recovered params with `_` pattern to avoid unecessary errors.
-        self.deduplicate_recovered_params_names(&mut inputs);
-
-        Ok(P(FnDecl {
-            inputs,
-            output: self.parse_ret_ty(true)?,
-        }))
-    }
-
     /// Skips unexpected attributes and doc comments in this position and emits an appropriate
     /// error.
     /// This version of parse param doesn't necessarily require identifier names.
-    fn parse_param_general(
+    fn parse_param_general(&mut self, cfg: &ParamCfg, is_trait_item: bool) -> PResult<'a, Param> {
-        &mut self,
-        is_self_allowed: bool,
-        is_trait_item: bool,
-        allow_c_variadic: bool,
-        is_name_required: impl Fn(&token::Token) -> bool,
-    ) -> PResult<'a, Param> {
         let lo = self.token.span;
         let attrs = self.parse_outer_attributes()?;
 
         // Possibly parse `self`. Recover if we parsed it and it wasn't allowed here.
         if let Some(mut param) = self.parse_self_param()? {
             param.attrs = attrs.into();
-            return if is_self_allowed {
+            return if cfg.is_self_allowed {
                 Ok(param)
             } else {
                 self.recover_bad_self_param(param, is_trait_item)
             };
         }
 
-        let is_name_required = is_name_required(&self.token);
+        let is_name_required = match self.token.kind {
+            token::DotDotDot => false,
+            _ => (cfg.is_name_required)(&self.token),
+        };
         let (pat, ty) = if is_name_required || self.is_named_param() {
             debug!("parse_param_general parse_pat (is_name_required:{})", is_name_required);
 
             let pat = self.parse_fn_param_pat()?;
             if let Err(mut err) = self.expect(&token::Colon) {
-                if let Some(ident) = self.parameter_without_type(
+                return if let Some(ident) = self.parameter_without_type(
                     &mut err,
                     pat,
                     is_name_required,
-                    is_self_allowed,
+                    cfg.is_self_allowed,
                     is_trait_item,
                 ) {
                     err.emit();
-                    return Ok(dummy_arg(ident));
+                    Ok(dummy_arg(ident))
                 } else {
-                    return Err(err);
+                    Err(err)
-                }
+                };
             }
 
             self.eat_incorrect_doc_comment_for_param_type();
-            (pat, self.parse_ty_common(true, true, allow_c_variadic)?)
+            (pat, self.parse_ty_common(true, true, cfg.allow_c_variadic)?)
         } else {
             debug!("parse_param_general ident_to_pat");
             let parser_snapshot_before_ty = self.clone();
             self.eat_incorrect_doc_comment_for_param_type();
-            let mut ty = self.parse_ty_common(true, true, allow_c_variadic);
+            let mut ty = self.parse_ty_common(true, true, cfg.allow_c_variadic);
             if ty.is_ok() && self.token != token::Comma &&
                self.token != token::CloseDelim(token::Paren) {
                 // This wasn't actually a type, but a pattern looking like a type,

src/libsyntax/parse/parser/item.rs

@@ -1,10 +1,10 @@
-use super::{Parser, PResult, PathStyle, SemiColonMode, BlockMode};
+use super::{Parser, PResult, PathStyle, SemiColonMode, BlockMode, ParamCfg};
 
 use crate::maybe_whole;
 use crate::ptr::P;
 use crate::ast::{
     self, DUMMY_NODE_ID, Ident, Attribute, AttrStyle,
-    Item, ItemKind, ImplItem, TraitItem, TraitItemKind,
+    Item, ItemKind, ImplItem, ImplItemKind, TraitItem, TraitItemKind,
     UseTree, UseTreeKind, PathSegment,
     IsAuto, Constness, IsAsync, Unsafety, Defaultness,
     Visibility, VisibilityKind, Mutability, FnDecl, FnHeader, MethodSig, Block,
@@ -98,7 +98,7 @@ impl<'a> Parser<'a> {
 
         let lo = self.token.span;
 
-        let visibility = self.parse_visibility(false)?;
+        let vis = self.parse_visibility(false)?;
 
         if self.eat_keyword(kw::Use) {
             // USE ITEM
@@ -106,15 +106,14 @@ impl<'a> Parser<'a> {
             self.expect(&token::Semi)?;
 
             let span = lo.to(self.prev_span);
-            let item =
+            let item = self.mk_item(span, Ident::invalid(), item_, vis, attrs);
-                self.mk_item(span, Ident::invalid(), item_, visibility, attrs);
             return Ok(Some(item));
         }
 
         if self.eat_keyword(kw::Extern) {
             let extern_sp = self.prev_span;
             if self.eat_keyword(kw::Crate) {
-                return Ok(Some(self.parse_item_extern_crate(lo, visibility, attrs)?));
+                return Ok(Some(self.parse_item_extern_crate(lo, vis, attrs)?));
             }
 
             let opt_abi = self.parse_opt_abi()?;
@@ -128,10 +127,10 @@ impl<'a> Parser<'a> {
                     constness: respan(fn_span, Constness::NotConst),
                     abi: opt_abi.unwrap_or(Abi::C),
                 };
-                return self.parse_item_fn(lo, visibility, attrs, header);
+                return self.parse_item_fn(lo, vis, attrs, header);
             } else if self.check(&token::OpenDelim(token::Brace)) {
                 return Ok(Some(
-                    self.parse_item_foreign_mod(lo, opt_abi, visibility, attrs, extern_sp)?,
+                    self.parse_item_foreign_mod(lo, opt_abi, vis, attrs, extern_sp)?,
                 ));
             }
 
@@ -142,16 +141,14 @@ impl<'a> Parser<'a> {
             self.bump();
             // STATIC ITEM
             let m = self.parse_mutability();
-            let (ident, item_, extra_attrs) = self.parse_item_const(Some(m))?;
+            let info = self.parse_item_const(Some(m))?;
-            let span = lo.to(self.prev_span);
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            let attrs = maybe_append(attrs, extra_attrs);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
+
         if self.eat_keyword(kw::Const) {
             let const_span = self.prev_span;
             if [kw::Fn, kw::Unsafe, kw::Extern].iter().any(|k| self.check_keyword(*k)) {
                 // CONST FUNCTION ITEM
-
                 let unsafety = self.parse_unsafety();
 
                 if self.check_keyword(kw::Extern) {
@@ -160,7 +157,7 @@ impl<'a> Parser<'a> {
                     );
                 }
                 let abi = self.parse_extern_abi()?;
-                self.bump(); // 'fn'
+                self.bump(); // `fn`
 
                 let header = FnHeader {
                     unsafety,
@@ -168,7 +165,7 @@ impl<'a> Parser<'a> {
                     constness: respan(const_span, Constness::Const),
                     abi,
                 };
-                return self.parse_item_fn(lo, visibility, attrs, header);
+                return self.parse_item_fn(lo, vis, attrs, header);
             }
 
             // CONST ITEM
@@ -184,10 +181,9 @@ impl<'a> Parser<'a> {
                     )
                     .emit();
             }
-            let (ident, item_, extra_attrs) = self.parse_item_const(None)?;
+
-            let span = lo.to(self.prev_span);
+            let info = self.parse_item_const(None)?;
-            let attrs = maybe_append(attrs, extra_attrs);
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
 
         // Parses `async unsafe? fn`.
@@ -212,40 +208,33 @@ impl<'a> Parser<'a> {
                     constness: respan(fn_span, Constness::NotConst),
                     abi: Abi::Rust,
                 };
-                return self.parse_item_fn(lo, visibility, attrs, header);
+                return self.parse_item_fn(lo, vis, attrs, header);
             }
         }
+
         if self.check_keyword(kw::Unsafe) &&
             self.is_keyword_ahead(1, &[kw::Trait, kw::Auto])
         {
             // UNSAFE TRAIT ITEM
             self.bump(); // `unsafe`
-            let is_auto = if self.eat_keyword(kw::Trait) {
+            let info = self.parse_item_trait(Unsafety::Unsafe)?;
-                IsAuto::No
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            } else {
-                self.expect_keyword(kw::Auto)?;
-                self.expect_keyword(kw::Trait)?;
-                IsAuto::Yes
-            };
-            let (ident, item_, extra_attrs) = self.parse_item_trait(is_auto, Unsafety::Unsafe)?;
-            let span = lo.to(self.prev_span);
-            let attrs = maybe_append(attrs, extra_attrs);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
+
         if self.check_keyword(kw::Impl) ||
            self.check_keyword(kw::Unsafe) &&
                 self.is_keyword_ahead(1, &[kw::Impl]) ||
            self.check_keyword(kw::Default) &&
-                self.is_keyword_ahead(1, &[kw::Impl, kw::Unsafe]) {
+                self.is_keyword_ahead(1, &[kw::Impl, kw::Unsafe])
+        {
             // IMPL ITEM
             let defaultness = self.parse_defaultness();
             let unsafety = self.parse_unsafety();
             self.expect_keyword(kw::Impl)?;
-            let (ident, item_, extra_attrs) = self.parse_item_impl(unsafety, defaultness)?;
+            let info = self.parse_item_impl(unsafety, defaultness)?;
-            let span = lo.to(self.prev_span);
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            let attrs = maybe_append(attrs, extra_attrs);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
+
         if self.check_keyword(kw::Fn) {
             // FUNCTION ITEM
             self.bump();
@@ -256,10 +245,12 @@ impl<'a> Parser<'a> {
                 constness: respan(fn_span, Constness::NotConst),
                 abi: Abi::Rust,
             };
-            return self.parse_item_fn(lo, visibility, attrs, header);
+            return self.parse_item_fn(lo, vis, attrs, header);
         }
+
         if self.check_keyword(kw::Unsafe)
-            && self.look_ahead(1, |t| *t != token::OpenDelim(token::Brace)) {
+            && self.look_ahead(1, |t| *t != token::OpenDelim(token::Brace))
+        {
             // UNSAFE FUNCTION ITEM
             self.bump(); // `unsafe`
             // `{` is also expected after `unsafe`; in case of error, include it in the diagnostic.
@@ -273,15 +264,15 @@ impl<'a> Parser<'a> {
                 constness: respan(fn_span, Constness::NotConst),
                 abi,
             };
-            return self.parse_item_fn(lo, visibility, attrs, header);
+            return self.parse_item_fn(lo, vis, attrs, header);
         }
+
         if self.eat_keyword(kw::Mod) {
             // MODULE ITEM
-            let (ident, item_, extra_attrs) = self.parse_item_mod(&attrs[..])?;
+            let info = self.parse_item_mod(&attrs[..])?;
-            let span = lo.to(self.prev_span);
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            let attrs = maybe_append(attrs, extra_attrs);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
+
         if let Some(type_) = self.eat_type() {
             let (ident, alias, generics) = type_?;
             // TYPE ITEM
@@ -290,54 +281,44 @@ impl<'a> Parser<'a> {
                 AliasKind::OpaqueTy(bounds) => ItemKind::OpaqueTy(bounds, generics),
             };
             let span = lo.to(self.prev_span);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
+            return Ok(Some(self.mk_item(span, ident, item_, vis, attrs)));
         }
+
         if self.eat_keyword(kw::Enum) {
             // ENUM ITEM
-            let (ident, item_, extra_attrs) = self.parse_item_enum()?;
+            let info = self.parse_item_enum()?;
-            let span = lo.to(self.prev_span);
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            let attrs = maybe_append(attrs, extra_attrs);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
+
         if self.check_keyword(kw::Trait)
             || (self.check_keyword(kw::Auto)
                 && self.is_keyword_ahead(1, &[kw::Trait]))
         {
-            let is_auto = if self.eat_keyword(kw::Trait) {
-                IsAuto::No
-            } else {
-                self.expect_keyword(kw::Auto)?;
-                self.expect_keyword(kw::Trait)?;
-                IsAuto::Yes
-            };
             // TRAIT ITEM
-            let (ident, item_, extra_attrs) = self.parse_item_trait(is_auto, Unsafety::Normal)?;
+            let info = self.parse_item_trait(Unsafety::Normal)?;
-            let span = lo.to(self.prev_span);
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            let attrs = maybe_append(attrs, extra_attrs);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
+
         if self.eat_keyword(kw::Struct) {
             // STRUCT ITEM
-            let (ident, item_, extra_attrs) = self.parse_item_struct()?;
+            let info = self.parse_item_struct()?;
-            let span = lo.to(self.prev_span);
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            let attrs = maybe_append(attrs, extra_attrs);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
+
         if self.is_union_item() {
             // UNION ITEM
             self.bump();
-            let (ident, item_, extra_attrs) = self.parse_item_union()?;
+            let info = self.parse_item_union()?;
-            let span = lo.to(self.prev_span);
+            return self.mk_item_with_info(attrs, lo, vis, info);
-            let attrs = maybe_append(attrs, extra_attrs);
-            return Ok(Some(self.mk_item(span, ident, item_, visibility, attrs)));
         }
-        if let Some(macro_def) = self.eat_macro_def(&attrs, &visibility, lo)? {
+
+        if let Some(macro_def) = self.eat_macro_def(&attrs, &vis, lo)? {
             return Ok(Some(macro_def));
         }
 
         // Verify whether we have encountered a struct or method definition where the user forgot to
         // add the `struct` or `fn` keyword after writing `pub`: `pub S {}`
-        if visibility.node.is_pub() &&
+        if vis.node.is_pub() &&
             self.check_ident() &&
             self.look_ahead(1, |t| *t != token::Not)
         {
@@ -428,7 +409,20 @@ impl<'a> Parser<'a> {
                 return Err(err);
             }
         }
-        self.parse_macro_use_or_failure(attrs, macros_allowed, attributes_allowed, lo, visibility)
+        self.parse_macro_use_or_failure(attrs, macros_allowed, attributes_allowed, lo, vis)
+    }
+
+    fn mk_item_with_info(
+        &self,
+        attrs: Vec<Attribute>,
+        lo: Span,
+        vis: Visibility,
+        info: ItemInfo,
+    ) -> PResult<'a, Option<P<Item>>> {
+        let (ident, item, extra_attrs) = info;
+        let span = lo.to(self.prev_span);
+        let attrs = maybe_append(attrs, extra_attrs);
+        Ok(Some(self.mk_item(span, ident, item, vis, attrs)))
     }
 
     fn recover_first_param(&mut self) -> &'static str {
@@ -727,16 +721,7 @@ impl<'a> Parser<'a> {
             };
             (name, kind, generics)
         } else if self.is_const_item() {
-            // This parses the grammar:
+            self.parse_impl_const()?
-            //     ImplItemConst = "const" Ident ":" Ty "=" Expr ";"
-            self.expect_keyword(kw::Const)?;
-            let name = self.parse_ident()?;
-            self.expect(&token::Colon)?;
-            let typ = self.parse_ty()?;
-            self.expect(&token::Eq)?;
-            let expr = self.parse_expr()?;
-            self.expect(&token::Semi)?;
-            (name, ast::ImplItemKind::Const(typ, expr), Generics::default())
         } else {
             let (name, inner_attrs, generics, kind) = self.parse_impl_method(&vis, at_end)?;
             attrs.extend(inner_attrs);
@@ -785,12 +770,25 @@ impl<'a> Parser<'a> {
             !self.is_keyword_ahead(1, &[kw::Fn, kw::Unsafe])
     }
 
+    /// This parses the grammar:
+    ///     ImplItemConst = "const" Ident ":" Ty "=" Expr ";"
+    fn parse_impl_const(&mut self) -> PResult<'a, (Ident, ImplItemKind, Generics)> {
+        self.expect_keyword(kw::Const)?;
+        let name = self.parse_ident()?;
+        self.expect(&token::Colon)?;
+        let typ = self.parse_ty()?;
+        self.expect(&token::Eq)?;
+        let expr = self.parse_expr()?;
+        self.expect(&token::Semi)?;
+        Ok((name, ImplItemKind::Const(typ, expr), Generics::default()))
+    }
+
     /// Parses a method or a macro invocation in a trait impl.
     fn parse_impl_method(
         &mut self,
         vis: &Visibility,
         at_end: &mut bool
-    ) -> PResult<'a, (Ident, Vec<Attribute>, Generics, ast::ImplItemKind)> {
+    ) -> PResult<'a, (Ident, Vec<Attribute>, Generics, ImplItemKind)> {
         // FIXME: code copied from `parse_macro_use_or_failure` -- use abstraction!
         if let Some(mac) = self.parse_assoc_macro_invoc("impl", Some(vis), at_end)? {
             // method macro
@@ -807,14 +805,15 @@ impl<'a> Parser<'a> {
     /// of a method. The body is not parsed as that differs between `trait`s and `impl`s.
     fn parse_method_sig(
         &mut self,
-        is_name_required: impl Copy + Fn(&token::Token) -> bool,
+        is_name_required: fn(&token::Token) -> bool,
     ) -> PResult<'a, (Ident, MethodSig, Generics)> {
         let header = self.parse_fn_front_matter()?;
-        let (ident, mut generics) = self.parse_fn_header()?;
+        let (ident, decl, generics) = self.parse_fn_sig(ParamCfg {
-        let decl = self.parse_fn_decl_with_self(is_name_required)?;
+            is_self_allowed: true,
-        let sig = MethodSig { header, decl };
+            allow_c_variadic: false,
-        generics.where_clause = self.parse_where_clause()?;
+            is_name_required,
-        Ok((ident, sig, generics))
+        })?;
+        Ok((ident, MethodSig { header, decl }, generics))
     }
 
     /// Parses all the "front matter" for a `fn` declaration, up to
@@ -849,8 +848,16 @@ impl<'a> Parser<'a> {
         Ok(FnHeader { constness, unsafety, asyncness, abi })
     }
 
-    /// Parses `trait Foo { ... }` or `trait Foo = Bar;`.
+    /// Parses `auto? trait Foo { ... }` or `trait Foo = Bar;`.
-    fn parse_item_trait(&mut self, is_auto: IsAuto, unsafety: Unsafety) -> PResult<'a, ItemInfo> {
+    fn parse_item_trait(&mut self, unsafety: Unsafety) -> PResult<'a, ItemInfo> {
+        // Parse optional `auto` prefix.
+        let is_auto = if self.eat_keyword(kw::Auto) {
+            IsAuto::Yes
+        } else {
+            IsAuto::No
+        };
+
+        self.expect_keyword(kw::Trait)?;
         let ident = self.parse_ident()?;
         let mut tps = self.parse_generics()?;
 
@@ -935,30 +942,20 @@ impl<'a> Parser<'a> {
         Ok(item)
     }
 
-    fn parse_trait_item_(&mut self,
+    fn parse_trait_item_(
-                         at_end: &mut bool,
+        &mut self,
-                         mut attrs: Vec<Attribute>) -> PResult<'a, TraitItem> {
+        at_end: &mut bool,
+        mut attrs: Vec<Attribute>,
+    ) -> PResult<'a, TraitItem> {
         let lo = self.token.span;
         self.eat_bad_pub();
         let (name, kind, generics) = if self.eat_keyword(kw::Type) {
             self.parse_trait_item_assoc_ty()?
         } else if self.is_const_item() {
-            self.expect_keyword(kw::Const)?;
+            self.parse_trait_item_const()?
-            let ident = self.parse_ident()?;
-            self.expect(&token::Colon)?;
-            let ty = self.parse_ty()?;
-            let default = if self.eat(&token::Eq) {
-                let expr = self.parse_expr()?;
-                self.expect(&token::Semi)?;
-                Some(expr)
-            } else {
-                self.expect(&token::Semi)?;
-                None
-            };
-            (ident, TraitItemKind::Const(ty, default), Generics::default())
         } else if let Some(mac) = self.parse_assoc_macro_invoc("trait", None, &mut false)? {
             // trait item macro.
-            (Ident::invalid(), ast::TraitItemKind::Macro(mac), Generics::default())
+            (Ident::invalid(), TraitItemKind::Macro(mac), Generics::default())
         } else {
             // This is somewhat dubious; We don't want to allow
             // argument names to be left off if there is a definition...
@@ -966,7 +963,7 @@ impl<'a> Parser<'a> {
             // We don't allow argument names to be left off in edition 2018.
             let (ident, sig, generics) = self.parse_method_sig(|t| t.span.rust_2018())?;
             let body = self.parse_trait_method_body(at_end, &mut attrs)?;
-            (ident, ast::TraitItemKind::Method(sig, body), generics)
+            (ident, TraitItemKind::Method(sig, body), generics)
         };
 
         Ok(TraitItem {
@@ -980,6 +977,20 @@ impl<'a> Parser<'a> {
         })
     }
 
+    fn parse_trait_item_const(&mut self) -> PResult<'a, (Ident, TraitItemKind, Generics)> {
+        self.expect_keyword(kw::Const)?;
+        let ident = self.parse_ident()?;
+        self.expect(&token::Colon)?;
+        let ty = self.parse_ty()?;
+        let default = if self.eat(&token::Eq) {
+            Some(self.parse_expr()?)
+        } else {
+            None
+        };
+        self.expect(&token::Semi)?;
+        Ok((ident, TraitItemKind::Const(ty, default), Generics::default()))
+    }
+
     /// Parse the "body" of a method in a trait item definition.
     /// This can either be `;` when there's no body,
     /// or e.g. a block when the method is a provided one.
@@ -1020,8 +1031,7 @@ impl<'a> Parser<'a> {
     /// Parses the following grammar:
     ///
     ///     TraitItemAssocTy = Ident ["<"...">"] [":" [GenericBounds]] ["where" ...] ["=" Ty]
-    fn parse_trait_item_assoc_ty(&mut self)
+    fn parse_trait_item_assoc_ty(&mut self) -> PResult<'a, (Ident, TraitItemKind, Generics)> {
-        -> PResult<'a, (Ident, TraitItemKind, Generics)> {
         let ident = self.parse_ident()?;
         let mut generics = self.parse_generics()?;
 
@@ -1067,21 +1077,13 @@ impl<'a> Parser<'a> {
                 );
             }
 
-            if self.eat(&token::BinOp(token::Star)) {
+            self.parse_use_tree_glob_or_nested()?
-                UseTreeKind::Glob
-            } else {
-                UseTreeKind::Nested(self.parse_use_tree_list()?)
-            }
         } else {
             // `use path::*;` or `use path::{...};` or `use path;` or `use path as bar;`
             prefix = self.parse_path(PathStyle::Mod)?;
 
             if self.eat(&token::ModSep) {
-                if self.eat(&token::BinOp(token::Star)) {
+                self.parse_use_tree_glob_or_nested()?
-                    UseTreeKind::Glob
-                } else {
-                    UseTreeKind::Nested(self.parse_use_tree_list()?)
-                }
             } else {
                 UseTreeKind::Simple(self.parse_rename()?, DUMMY_NODE_ID, DUMMY_NODE_ID)
             }
@@ -1090,6 +1092,15 @@ impl<'a> Parser<'a> {
         Ok(UseTree { prefix, kind, span: lo.to(self.prev_span) })
     }
 
+    /// Parses `*` or `{...}`.
+    fn parse_use_tree_glob_or_nested(&mut self) -> PResult<'a, UseTreeKind> {
+        Ok(if self.eat(&token::BinOp(token::Star)) {
+            UseTreeKind::Glob
+        } else {
+            UseTreeKind::Nested(self.parse_use_tree_list()?)
+        })
+    }
+
     /// Parses a `UseTreeKind::Nested(list)`.
     ///
     /// ```
@@ -1191,38 +1202,34 @@ impl<'a> Parser<'a> {
         attrs: Vec<Attribute>,
         header: FnHeader,
     ) -> PResult<'a, Option<P<Item>>> {
-        let allow_c_variadic = header.abi == Abi::C && header.unsafety == Unsafety::Unsafe;
+        let (ident, decl, generics) = self.parse_fn_sig(ParamCfg {
-        let (ident, decl, generics) = self.parse_fn_sig(allow_c_variadic)?;
+            is_self_allowed: false,
+            allow_c_variadic: header.abi == Abi::C && header.unsafety == Unsafety::Unsafe,
+            is_name_required: |_| true,
+        })?;
         let (inner_attrs, body) = self.parse_inner_attrs_and_block()?;
-        let span = lo.to(self.prev_span);
         let kind = ItemKind::Fn(decl, header, generics, body);
-        let attrs = maybe_append(attrs, Some(inner_attrs));
+        self.mk_item_with_info(attrs, lo, vis, (ident, kind, Some(inner_attrs)))
-        Ok(Some(self.mk_item(span, ident, kind, vis, attrs)))
     }
 
     /// Parse the "signature", including the identifier, parameters, and generics of a function.
-    fn parse_fn_sig(
+    fn parse_fn_sig(&mut self, cfg: ParamCfg) -> PResult<'a, (Ident, P<FnDecl>, Generics)> {
-        &mut self,
+        let ident = self.parse_ident()?;
-        allow_c_variadic: bool,
+        let mut generics = self.parse_generics()?;
-    ) -> PResult<'a, (Ident, P<FnDecl>, Generics)> {
+        let decl = self.parse_fn_decl(cfg, true)?;
-        let (ident, mut generics) = self.parse_fn_header()?;
-        let decl = self.parse_fn_decl(allow_c_variadic)?;
         generics.where_clause = self.parse_where_clause()?;
         Ok((ident, decl, generics))
     }
 
-    /// Parses the name and optional generic types of a function header.
-    fn parse_fn_header(&mut self) -> PResult<'a, (Ident, Generics)> {
-        let id = self.parse_ident()?;
-        let generics = self.parse_generics()?;
-        Ok((id, generics))
-    }
-
     /// Parses the parameter list and result type of a function declaration.
-    fn parse_fn_decl(&mut self, allow_c_variadic: bool) -> PResult<'a, P<FnDecl>> {
+    pub(super) fn parse_fn_decl(
+        &mut self,
+        cfg: ParamCfg,
+        ret_allow_plus: bool,
+    ) -> PResult<'a, P<FnDecl>> {
         Ok(P(FnDecl {
-            inputs: self.parse_fn_params(true, allow_c_variadic)?,
+            inputs: self.parse_fn_params(cfg)?,
-            output: self.parse_ret_ty(true)?,
+            output: self.parse_ret_ty(ret_allow_plus)?,
         }))
     }
 
@@ -1346,7 +1353,11 @@ impl<'a> Parser<'a> {
         extern_sp: Span,
     ) -> PResult<'a, ForeignItem> {
         self.expect_keyword(kw::Fn)?;
-        let (ident, decl, generics) = self.parse_fn_sig(true)?;
+        let (ident, decl, generics) = self.parse_fn_sig(super::ParamCfg {
+            is_self_allowed: false,
+            allow_c_variadic: true,
+            is_name_required: |_| true,
+        })?;
         let span = lo.to(self.token.span);
         self.parse_semi_or_incorrect_foreign_fn_body(&ident, extern_sp)?;
         Ok(ast::ForeignItem {

src/libsyntax/parse/parser/ty.rs

@@ -4,13 +4,11 @@ use crate::{maybe_whole, maybe_recover_from_interpolated_ty_qpath};
 use crate::ptr::P;
 use crate::ast::{self, Ty, TyKind, MutTy, BareFnTy, FunctionRetTy, GenericParam, Lifetime, Ident};
 use crate::ast::{TraitBoundModifier, TraitObjectSyntax, GenericBound, GenericBounds, PolyTraitRef};
-use crate::ast::{Mutability, AnonConst, FnDecl, Mac};
+use crate::ast::{Mutability, AnonConst, Mac};
 use crate::parse::token::{self, Token};
 use crate::source_map::Span;
 use crate::symbol::{kw};
 
-use rustc_target::spec::abi::Abi;
-
 use errors::{Applicability, pluralise};
 
 /// Returns `true` if `IDENT t` can start a type -- `IDENT::a::b`, `IDENT<u8, u8>`,
@@ -281,19 +279,14 @@ impl<'a> Parser<'a> {
         */
 
         let unsafety = self.parse_unsafety();
-        let abi = if self.eat_keyword(kw::Extern) {
+        let abi = self.parse_extern_abi()?;
-            self.parse_opt_abi()?.unwrap_or(Abi::C)
-        } else {
-            Abi::Rust
-        };
-
         self.expect_keyword(kw::Fn)?;
-        let inputs = self.parse_fn_params(false, true)?;
+        let cfg = super::ParamCfg {
-        let ret_ty = self.parse_ret_ty(false)?;
+            is_self_allowed: false,
-        let decl = P(FnDecl {
+            allow_c_variadic: true,
-            inputs,
+            is_name_required: |_| false,
-            output: ret_ty,
+        };
-        });
+        let decl = self.parse_fn_decl(cfg, false)?;
         Ok(TyKind::BareFn(P(BareFnTy {
             abi,
             unsafety,

src/test/ui/const-generics/slice-const-param-mismatch.stderr

@@ -12,8 +12,8 @@ error[E0308]: mismatched types
 LL |     let _: ConstString<"Hello"> = ConstString::<"World">;
    |                                   ^^^^^^^^^^^^^^^^^^^^^^ expected `"Hello"`, found `"World"`
    |
-   = note: expected type `ConstString<>`
+   = note: expected type `ConstString<"Hello">`
-              found type `ConstString<>`
+              found type `ConstString<"World">`
 
 error[E0308]: mismatched types
   --> $DIR/slice-const-param-mismatch.rs:11:33
@@ -21,8 +21,8 @@ error[E0308]: mismatched types
 LL |     let _: ConstString<"ℇ㇈↦"> = ConstString::<"ℇ㇈↥">;
    |                                  ^^^^^^^^^^^^^^^^^^^^^ expected `"ℇ㇈↦"`, found `"ℇ㇈↥"`
    |
-   = note: expected type `ConstString<>`
+   = note: expected type `ConstString<"ℇ㇈↦">`
-              found type `ConstString<>`
+              found type `ConstString<"ℇ㇈↥">`
 
 error[E0308]: mismatched types
   --> $DIR/slice-const-param-mismatch.rs:13:33
@@ -30,8 +30,8 @@ error[E0308]: mismatched types
 LL |     let _: ConstBytes<b"AAA"> = ConstBytes::<b"BBB">;
    |                                 ^^^^^^^^^^^^^^^^^^^^ expected `b"AAA"`, found `b"BBB"`
    |
-   = note: expected type `ConstBytes<>`
+   = note: expected type `ConstBytes<b"AAA">`
-              found type `ConstBytes<>`
+              found type `ConstBytes<b"BBB">`
 
 error: aborting due to 3 previous errors
 

src/test/ui/const-generics/types-mismatch-const-args.rs

@@ -0,0 +1,19 @@
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+// tests the diagnostic output of type mismatches for types that have const generics arguments.
+
+use std::marker::PhantomData;
+
+struct A<'a, T, const X: u32, const Y: u32> {
+    data: PhantomData<&'a T>
+}
+
+fn a<'a, 'b>() {
+    let _: A<'a, u32, {2u32}, {3u32}> = A::<'a, u32, {4u32}, {3u32}> { data: PhantomData };
+    //~^ ERROR mismatched types
+    let _: A<'a, u16, {2u32}, {3u32}> = A::<'b, u32, {2u32}, {3u32}> { data: PhantomData };
+    //~^ ERROR mismatched types
+}
+
+pub fn main() {}

src/test/ui/const-generics/types-mismatch-const-args.stderr

@@ -0,0 +1,29 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/types-mismatch-const-args.rs:1:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0308]: mismatched types
+  --> $DIR/types-mismatch-const-args.rs:13:41
+   |
+LL |     let _: A<'a, u32, {2u32}, {3u32}> = A::<'a, u32, {4u32}, {3u32}> { data: PhantomData };
+   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `2u32`, found `4u32`
+   |
+   = note: expected type `A<'_, _, 2u32, _>`
+              found type `A<'_, _, 4u32, _>`
+
+error[E0308]: mismatched types
+  --> $DIR/types-mismatch-const-args.rs:15:41
+   |
+LL |     let _: A<'a, u16, {2u32}, {3u32}> = A::<'b, u32, {2u32}, {3u32}> { data: PhantomData };
+   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected u16, found u32
+   |
+   = note: expected type `A<'a, u16, _, _>`
+              found type `A<'b, u32, _, _>`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/if/if-no-match-bindings.stderr

@@ -2,7 +2,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:18:8
    |
 LL |     if b_ref() {}
-   |        ^^^^^^^ expected bool, found &bool
+   |        ^^^^^^^
+   |        |
+   |        expected bool, found &bool
+   |        help: consider dereferencing the borrow: `*b_ref()`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -11,7 +14,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:19:8
    |
 LL |     if b_mut_ref() {}
-   |        ^^^^^^^^^^^ expected bool, found &mut bool
+   |        ^^^^^^^^^^^
+   |        |
+   |        expected bool, found &mut bool
+   |        help: consider dereferencing the borrow: `*b_mut_ref()`
    |
    = note: expected type `bool`
               found type `&mut bool`
@@ -20,7 +26,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:20:8
    |
 LL |     if &true {}
-   |        ^^^^^ expected bool, found &bool
+   |        ^^^^^
+   |        |
+   |        expected bool, found &bool
+   |        help: consider dereferencing the borrow: `*&true`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -29,7 +38,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:21:8
    |
 LL |     if &mut true {}
-   |        ^^^^^^^^^ expected bool, found &mut bool
+   |        ^^^^^^^^^
+   |        |
+   |        expected bool, found &mut bool
+   |        help: consider dereferencing the borrow: `*&mut true`
    |
    = note: expected type `bool`
               found type `&mut bool`
@@ -38,7 +50,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:24:11
    |
 LL |     while b_ref() {}
-   |           ^^^^^^^ expected bool, found &bool
+   |           ^^^^^^^
+   |           |
+   |           expected bool, found &bool
+   |           help: consider dereferencing the borrow: `*b_ref()`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -47,7 +62,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:25:11
    |
 LL |     while b_mut_ref() {}
-   |           ^^^^^^^^^^^ expected bool, found &mut bool
+   |           ^^^^^^^^^^^
+   |           |
+   |           expected bool, found &mut bool
+   |           help: consider dereferencing the borrow: `*b_mut_ref()`
    |
    = note: expected type `bool`
               found type `&mut bool`
@@ -56,7 +74,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:26:11
    |
 LL |     while &true {}
-   |           ^^^^^ expected bool, found &bool
+   |           ^^^^^
+   |           |
+   |           expected bool, found &bool
+   |           help: consider dereferencing the borrow: `*&true`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -65,7 +86,10 @@ error[E0308]: mismatched types
   --> $DIR/if-no-match-bindings.rs:27:11
    |
 LL |     while &mut true {}
-   |           ^^^^^^^^^ expected bool, found &mut bool
+   |           ^^^^^^^^^
+   |           |
+   |           expected bool, found &mut bool
+   |           help: consider dereferencing the borrow: `*&mut true`
    |
    = note: expected type `bool`
               found type `&mut bool`

src/test/ui/no-patterns-in-args-macro.stderr

@@ -18,5 +18,5 @@ LL |     m!((bad, pat));
 
 error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0130, E0642.
+Some errors have detailed explanations: E0130, E0561, E0642.
 For more information about an error, try `rustc --explain E0130`.

src/test/ui/no-patterns-in-args.stderr

@@ -30,4 +30,5 @@ LL | type A2 = fn(&arg: u8);
 
 error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0130`.
+Some errors have detailed explanations: E0130, E0561.
+For more information about an error, try `rustc --explain E0130`.

src/test/ui/parser/issue-33413.rs

@@ -3,6 +3,7 @@ struct S;
 impl S {
     fn f(*, a: u8) -> u8 {}
     //~^ ERROR expected parameter name, found `*`
+    //~| ERROR mismatched types
 }
 
 fn main() {}

src/test/ui/parser/issue-33413.stderr

@@ -4,5 +4,17 @@ error: expected parameter name, found `*`
 LL |     fn f(*, a: u8) -> u8 {}
    |          ^ expected parameter name
 
-error: aborting due to previous error
+error[E0308]: mismatched types
+  --> $DIR/issue-33413.rs:4:23
+   |
+LL |     fn f(*, a: u8) -> u8 {}
+   |        -              ^^ expected u8, found ()
+   |        |
+   |        implicitly returns `()` as its body has no tail or `return` expression
+   |
+   = note: expected type `u8`
+              found type `()`
 
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr

@@ -517,7 +517,10 @@ error[E0308]: mismatched types
   --> $DIR/disallowed-positions.rs:32:8
    |
 LL |     if &let 0 = 0 {}
-   |        ^^^^^^^^^^ expected bool, found &bool
+   |        ^^^^^^^^^^
+   |        |
+   |        expected bool, found &bool
+   |        help: consider dereferencing the borrow: `*&let 0 = 0`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -702,7 +705,10 @@ error[E0308]: mismatched types
   --> $DIR/disallowed-positions.rs:96:11
    |
 LL |     while &let 0 = 0 {}
-   |           ^^^^^^^^^^ expected bool, found &bool
+   |           ^^^^^^^^^^
+   |           |
+   |           expected bool, found &bool
+   |           help: consider dereferencing the borrow: `*&let 0 = 0`
    |
    = note: expected type `bool`
               found type `&bool`