Auto merge of #132940 - matthiaskrgr:rollup-f0czmkq, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #132487 (Provide placeholder generics for traits in "no method found for type parameter" suggestions)
 - #132627 (cleanup: Remove outdated comment of `thir_body`)
 - #132653 (Don't use `maybe_unwrap_block` when checking for macro calls in a block expr)
 - #132793 (Update mdbook to 0.4.42)
 - #132847 (elem_offset / subslice_range: use addr() instead of 'as usize')
 - #132869 (split up the first paragraph of doc comments for better summaries)
 - #132929 (Check for null in the `alloc_zeroed` example)
 - #132933 (Make sure that we suggest turbofishing the right type arg for never suggestion)

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

27 files changed, 770 insertions, 86 deletions

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 997c44cffff..5f71fb97d76 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -1194,7 +1194,7 @@ impl Expr {
     ///
     /// Does not ensure that the path resolves to a const param, the caller should check this.
     pub fn is_potential_trivial_const_arg(&self, strip_identity_block: bool) -> bool {
-        let this = if strip_identity_block { self.maybe_unwrap_block().1 } else { self };
+        let this = if strip_identity_block { self.maybe_unwrap_block() } else { self };
 
         if let ExprKind::Path(None, path) = &this.kind
             && path.is_potential_trivial_const_arg()
@@ -1206,14 +1206,41 @@ impl Expr {
     }
 
     /// Returns an expression with (when possible) *one* outter brace removed
-    pub fn maybe_unwrap_block(&self) -> (bool, &Expr) {
+    pub fn maybe_unwrap_block(&self) -> &Expr {
         if let ExprKind::Block(block, None) = &self.kind
             && let [stmt] = block.stmts.as_slice()
             && let StmtKind::Expr(expr) = &stmt.kind
         {
-            (true, expr)
+            expr
         } else {
-            (false, self)
+            self
+        }
+    }
+
+    /// Determines whether this expression is a macro call optionally wrapped in braces . If
+    /// `already_stripped_block` is set then we do not attempt to peel off a layer of braces.
+    ///
+    /// Returns the [`NodeId`] of the macro call and whether a layer of braces has been peeled
+    /// either before, or part of, this function.
+    pub fn optionally_braced_mac_call(
+        &self,
+        already_stripped_block: bool,
+    ) -> Option<(bool, NodeId)> {
+        match &self.kind {
+            ExprKind::Block(block, None)
+                if let [stmt] = &*block.stmts
+                    && !already_stripped_block =>
+            {
+                match &stmt.kind {
+                    StmtKind::MacCall(_) => Some((true, stmt.id)),
+                    StmtKind::Expr(expr) if let ExprKind::MacCall(_) = &expr.kind => {
+                        Some((true, expr.id))
+                    }
+                    _ => None,
+                }
+            }
+            ExprKind::MacCall(_) => Some((already_stripped_block, self.id)),
+            _ => None,
         }
     }
 
diff --git a/compiler/rustc_hir_typeck/src/fallback.rs b/compiler/rustc_hir_typeck/src/fallback.rs
index 97f3807c252..7719facccc7 100644
--- a/compiler/rustc_hir_typeck/src/fallback.rs
+++ b/compiler/rustc_hir_typeck/src/fallback.rs
@@ -621,7 +621,11 @@ impl<'tcx> AnnotateUnitFallbackVisitor<'_, 'tcx> {
                 .iter()
                 .filter(|arg| matches!(arg.unpack(), ty::GenericArgKind::Type(_)))
                 .count();
-            for (idx, arg) in args.iter().enumerate() {
+            for (idx, arg) in args
+                .iter()
+                .filter(|arg| matches!(arg.unpack(), ty::GenericArgKind::Type(_)))
+                .enumerate()
+            {
                 if let Some(ty) = arg.as_type()
                     && let Some(vid) = self.fcx.root_vid(ty)
                     && self.reachable_vids.contains(&vid)
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
index f5987a11fa5..63dccf8b0ce 100644
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@@ -4,6 +4,7 @@
 #![feature(array_windows)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
+#![feature(iter_intersperse)]
 #![feature(let_chains)]
 #![feature(never_type)]
 #![feature(try_blocks)]
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index cb20a1d7c7b..8772599e316 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -3874,22 +3874,52 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 param.name.ident(),
                             ));
                             let bounds_span = hir_generics.bounds_span_for_suggestions(def_id);
+                            let mut applicability = Applicability::MaybeIncorrect;
+                            // Format the path of each suggested candidate, providing placeholders
+                            // for any generic arguments without defaults.
+                            let candidate_strs: Vec<_> = candidates
+                                .iter()
+                                .map(|cand| {
+                                    let cand_path = self.tcx.def_path_str(cand.def_id);
+                                    let cand_params = &self.tcx.generics_of(cand.def_id).own_params;
+                                    let cand_args: String = cand_params
+                                        .iter()
+                                        .skip(1)
+                                        .filter_map(|param| match param.kind {
+                                            ty::GenericParamDefKind::Type {
+                                                has_default: true,
+                                                ..
+                                            }
+                                            | ty::GenericParamDefKind::Const {
+                                                has_default: true,
+                                                ..
+                                            } => None,
+                                            _ => Some(param.name.as_str()),
+                                        })
+                                        .intersperse(", ")
+                                        .collect();
+                                    if cand_args.is_empty() {
+                                        cand_path
+                                    } else {
+                                        applicability = Applicability::HasPlaceholders;
+                                        format!("{cand_path}</* {cand_args} */>")
+                                    }
+                                })
+                                .collect();
+
                             if rcvr_ty.is_ref()
                                 && param.is_impl_trait()
                                 && let Some((bounds_span, _)) = bounds_span
                             {
                                 err.multipart_suggestions(
                                     msg,
-                                    candidates.iter().map(|t| {
+                                    candidate_strs.iter().map(|cand| {
                                         vec![
                                             (param.span.shrink_to_lo(), "(".to_string()),
-                                            (
-                                                bounds_span,
-                                                format!(" + {})", self.tcx.def_path_str(t.def_id)),
-                                            ),
+                                            (bounds_span, format!(" + {cand})")),
                                         ]
                                     }),
-                                    Applicability::MaybeIncorrect,
+                                    applicability,
                                 );
                                 return;
                             }
@@ -3905,16 +3935,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                     (param.span.shrink_to_hi(), Introducer::Colon, None)
                                 };
 
-                            let all_suggs = candidates.iter().map(|cand| {
-                                let suggestion = format!(
-                                    "{} {}",
-                                    match introducer {
-                                        Introducer::Plus => " +",
-                                        Introducer::Colon => ":",
-                                        Introducer::Nothing => "",
-                                    },
-                                    self.tcx.def_path_str(cand.def_id)
-                                );
+                            let all_suggs = candidate_strs.iter().map(|cand| {
+                                let suggestion = format!("{} {cand}", match introducer {
+                                    Introducer::Plus => " +",
+                                    Introducer::Colon => ":",
+                                    Introducer::Nothing => "",
+                                },);
 
                                 let mut suggs = vec![];
 
@@ -3928,11 +3954,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 suggs
                             });
 
-                            err.multipart_suggestions(
-                                msg,
-                                all_suggs,
-                                Applicability::MaybeIncorrect,
-                            );
+                            err.multipart_suggestions(msg, all_suggs, applicability);
 
                             return;
                         }
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 54ead9a7a75..b25ed1c44e1 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -463,7 +463,7 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    /// Fetch the THIR for a given body. If typeck for that body failed, returns an empty `Thir`.
+    /// Fetch the THIR for a given body.
     query thir_body(key: LocalDefId) -> Result<(&'tcx Steal<thir::Thir<'tcx>>, thir::ExprId), ErrorGuaranteed> {
         // Perf tests revealed that hashing THIR is inefficient (see #85729).
         no_hash
diff --git a/compiler/rustc_mir_build/src/check_unsafety.rs b/compiler/rustc_mir_build/src/check_unsafety.rs
index f3e6301d9d1..33e194fa246 100644
--- a/compiler/rustc_mir_build/src/check_unsafety.rs
+++ b/compiler/rustc_mir_build/src/check_unsafety.rs
@@ -1005,10 +1005,6 @@ pub(crate) fn check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
     // Runs all other queries that depend on THIR.
     tcx.ensure_with_value().mir_built(def);
     let thir = &thir.steal();
-    // If `thir` is empty, a type error occurred, skip this body.
-    if thir.exprs.is_empty() {
-        return;
-    }
 
     let hir_id = tcx.local_def_id_to_hir_id(def);
     let safety_context = tcx.hir().fn_sig_by_hir_id(hir_id).map_or(SafetyContext::Safe, |fn_sig| {
diff --git a/compiler/rustc_resolve/src/def_collector.rs b/compiler/rustc_resolve/src/def_collector.rs
index a825458dc89..bf27b767a49 100644
--- a/compiler/rustc_resolve/src/def_collector.rs
+++ b/compiler/rustc_resolve/src/def_collector.rs
@@ -130,18 +130,16 @@ impl<'a, 'ra, 'tcx> DefCollector<'a, 'ra, 'tcx> {
         &self,
         anon_const: &'a AnonConst,
     ) -> Option<(PendingAnonConstInfo, NodeId)> {
-        let (block_was_stripped, expr) = anon_const.value.maybe_unwrap_block();
-        match expr {
-            Expr { kind: ExprKind::MacCall(..), id, .. } => Some((
+        anon_const.value.optionally_braced_mac_call(false).map(|(block_was_stripped, id)| {
+            (
                 PendingAnonConstInfo {
                     id: anon_const.id,
                     span: anon_const.value.span,
                     block_was_stripped,
                 },
-                *id,
-            )),
-            _ => None,
-        }
+                id,
+            )
+        })
     }
 
     /// Determines whether the expression `const_arg_sub_expr` is a simple macro call, sometimes
@@ -161,18 +159,11 @@ impl<'a, 'ra, 'tcx> DefCollector<'a, 'ra, 'tcx> {
             panic!("Checking expr is trivial macro call without having entered anon const: `{const_arg_sub_expr:?}`"),
         );
 
-        let (block_was_stripped, expr) = if pending_anon.block_was_stripped {
-            (true, const_arg_sub_expr)
-        } else {
-            const_arg_sub_expr.maybe_unwrap_block()
-        };
-
-        match expr {
-            Expr { kind: ExprKind::MacCall(..), id, .. } => {
-                Some((PendingAnonConstInfo { block_was_stripped, ..pending_anon }, *id))
-            }
-            _ => None,
-        }
+        const_arg_sub_expr.optionally_braced_mac_call(pending_anon.block_was_stripped).map(
+            |(block_was_stripped, id)| {
+                (PendingAnonConstInfo { block_was_stripped, ..pending_anon }, id)
+            },
+        )
     }
 }
 
diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
index a91659b6de5..98402a46201 100644
--- a/library/alloc/src/alloc.rs
+++ b/library/alloc/src/alloc.rs
@@ -155,11 +155,14 @@ pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8
 /// # Examples
 ///
 /// ```
-/// use std::alloc::{alloc_zeroed, dealloc, Layout};
+/// use std::alloc::{alloc_zeroed, dealloc, handle_alloc_error, Layout};
 ///
 /// unsafe {
 ///     let layout = Layout::new::<u16>();
 ///     let ptr = alloc_zeroed(layout);
+///     if ptr.is_null() {
+///         handle_alloc_error(layout);
+///     }
 ///
 ///     assert_eq!(*(ptr as *mut u16), 0);
 ///
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index a68aaec5f70..4718264e685 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -2932,7 +2932,9 @@ impl<T, I: iter::TrustedLen<Item = T>> ToRcSlice<T> for I {
 }
 
 /// `Weak` is a version of [`Rc`] that holds a non-owning reference to the
-/// managed allocation. The allocation is accessed by calling [`upgrade`] on the `Weak`
+/// managed allocation.
+///
+/// The allocation is accessed by calling [`upgrade`] on the `Weak`
 /// pointer, which returns an <code>[Option]<[Rc]\<T>></code>.
 ///
 /// Since a `Weak` reference does not count towards ownership, it will not
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index c78a4db95ff..8520c3c196b 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -291,7 +291,9 @@ impl<T: ?Sized, A: Allocator> Arc<T, A> {
 }
 
 /// `Weak` is a version of [`Arc`] that holds a non-owning reference to the
-/// managed allocation. The allocation is accessed by calling [`upgrade`] on the `Weak`
+/// managed allocation.
+///
+/// The allocation is accessed by calling [`upgrade`] on the `Weak`
 /// pointer, which returns an <code>[Option]<[Arc]\<T>></code>.
 ///
 /// Since a `Weak` reference does not count towards ownership, it will not
diff --git a/library/alloc/src/task.rs b/library/alloc/src/task.rs
index 27589aed2f9..0f8e74300a4 100644
--- a/library/alloc/src/task.rs
+++ b/library/alloc/src/task.rs
@@ -176,9 +176,11 @@ fn raw_waker<W: Wake + Send + Sync + 'static>(waker: Arc<W>) -> RawWaker {
     )
 }
 
-/// An analogous trait to `Wake` but used to construct a `LocalWaker`. This API
-/// works in exactly the same way as `Wake`, except that it uses an `Rc` instead
-/// of an `Arc`, and the result is a `LocalWaker` instead of a `Waker`.
+/// An analogous trait to `Wake` but used to construct a `LocalWaker`.
+///
+/// This API works in exactly the same way as `Wake`,
+/// except that it uses an `Rc` instead of an `Arc`,
+/// and the result is a `LocalWaker` instead of a `Waker`.
 ///
 /// The benefits of using `LocalWaker` over `Waker` are that it allows the local waker
 /// to hold data that does not implement `Send` and `Sync`. Additionally, it saves calls
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 52d2179b04d..ce9d04d01d7 100644
--- a/library/core/src/slice/mod.rs
+++ b/library/core/src/slice/mod.rs
@@ -4578,8 +4578,8 @@ impl<T> [T] {
             panic!("elements are zero-sized");
         }
 
-        let self_start = self.as_ptr() as usize;
-        let elem_start = element as *const T as usize;
+        let self_start = self.as_ptr().addr();
+        let elem_start = ptr::from_ref(element).addr();
 
         let byte_offset = elem_start.wrapping_sub(self_start);
 
@@ -4631,8 +4631,8 @@ impl<T> [T] {
             panic!("elements are zero-sized");
         }
 
-        let self_start = self.as_ptr() as usize;
-        let subslice_start = subslice.as_ptr() as usize;
+        let self_start = self.as_ptr().addr();
+        let subslice_start = subslice.as_ptr().addr();
 
         let byte_start = subslice_start.wrapping_sub(self_start);
 
diff --git a/library/std/src/sync/mpmc/mod.rs b/library/std/src/sync/mpmc/mod.rs
index 44e146a89ba..0cf4902d6d5 100644
--- a/library/std/src/sync/mpmc/mod.rs
+++ b/library/std/src/sync/mpmc/mod.rs
@@ -153,6 +153,7 @@ use crate::panic::{RefUnwindSafe, UnwindSafe};
 use crate::time::{Duration, Instant};
 
 /// Creates a new asynchronous channel, returning the sender/receiver halves.
+///
 /// All data sent on the [`Sender`] will become available on the [`Receiver`] in
 /// the same order as it was sent, and no [`send`] will block the calling thread
 /// (this channel has an "infinite buffer", unlike [`sync_channel`], which will
@@ -201,6 +202,7 @@ pub fn channel<T>() -> (Sender<T>, Receiver<T>) {
 }
 
 /// Creates a new synchronous, bounded channel.
+///
 /// All data sent on the [`Sender`] will become available on the [`Receiver`]
 /// in the same order as it was sent. Like asynchronous [`channel`]s, the
 /// [`Receiver`] will block until a message becomes available. `sync_channel`
diff --git a/library/std/src/sync/mpsc/mod.rs b/library/std/src/sync/mpsc/mod.rs
index 83a93a06369..c86b546e011 100644
--- a/library/std/src/sync/mpsc/mod.rs
+++ b/library/std/src/sync/mpsc/mod.rs
@@ -483,6 +483,7 @@ pub enum TrySendError<T> {
 }
 
 /// Creates a new asynchronous channel, returning the sender/receiver halves.
+///
 /// All data sent on the [`Sender`] will become available on the [`Receiver`] in
 /// the same order as it was sent, and no [`send`] will block the calling thread
 /// (this channel has an "infinite buffer", unlike [`sync_channel`], which will
@@ -527,6 +528,7 @@ pub fn channel<T>() -> (Sender<T>, Receiver<T>) {
 }
 
 /// Creates a new synchronous, bounded channel.
+///
 /// All data sent on the [`SyncSender`] will become available on the [`Receiver`]
 /// in the same order as it was sent. Like asynchronous [`channel`]s, the
 /// [`Receiver`] will block until a message becomes available. `sync_channel`
diff --git a/src/doc/rust-by-example b/src/doc/rust-by-example
-Subproject 9db78608b17d5f4a6c033b8a3038466b87d6320
+Subproject e1d1f2cdcee4d52b9a01ff7c448be4372a377b7
diff --git a/src/tools/rustbook/.gitignore b/src/tools/rustbook/.gitignore
new file mode 100644
index 00000000000..ea8c4bf7f35
--- /dev/null
+++ b/src/tools/rustbook/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/src/tools/rustbook/Cargo.lock b/src/tools/rustbook/Cargo.lock
index 27ccb205b50..914b03c8679 100644
--- a/src/tools/rustbook/Cargo.lock
+++ b/src/tools/rustbook/Cargo.lock
@@ -441,11 +441,12 @@ dependencies = [
 
 [[package]]
 name = "handlebars"
-version = "5.1.2"
+version = "6.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d08485b96a0e6393e9e4d1b8d48cf74ad6c063cd905eb33f42c1ce3f0377539b"
+checksum = "fd4ccde012831f9a071a637b0d4e31df31c0f6c525784b35ae76a9ac6bc1e315"
 dependencies = [
  "log",
+ "num-order",
  "pest",
  "pest_derive",
  "serde",
@@ -645,9 +646,9 @@ dependencies = [
 
 [[package]]
 name = "mdbook"
-version = "0.4.40"
+version = "0.4.42"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b45a38e19bd200220ef07c892b0157ad3d2365e5b5a267ca01ad12182491eea5"
+checksum = "7624879735513024d323e7267a0b3a7176aceb0db537939beb4ee31d9e8945e3"
 dependencies = [
  "ammonia",
  "anyhow",
@@ -763,6 +764,21 @@ dependencies = [
 ]
 
 [[package]]
+name = "num-modular"
+version = "0.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "17bb261bf36fa7d83f4c294f834e91256769097b3cb505d44831e0a179ac647f"
+
+[[package]]
+name = "num-order"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "537b596b97c40fcf8056d153049eb22f481c17ebce72a513ec9286e4986d1bb6"
+dependencies = [
+ "num-modular",
+]
+
+[[package]]
 name = "num-traits"
 version = "0.2.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/tests/crashes/131915.rs b/tests/crashes/131915.rs
deleted file mode 100644
index 58d45adcb3b..00000000000
--- a/tests/crashes/131915.rs
+++ /dev/null
@@ -1,13 +0,0 @@
-//@ known-bug: #131915
-
-macro_rules! y {
-    ( $($matcher:tt)*) => {
-        x
-    };
-}
-
-const _: A<
-    {
-        y! { test.tou8 }
-    },
->;
diff --git a/tests/ui/const-generics/early/const_arg_trivial_macro_expansion-2.rs b/tests/ui/const-generics/early/const_arg_trivial_macro_expansion-2.rs
new file mode 100644
index 00000000000..bce7ac5708a
--- /dev/null
+++ b/tests/ui/const-generics/early/const_arg_trivial_macro_expansion-2.rs
@@ -0,0 +1,20 @@
+// Regression test for #131915 where we did not handle macro calls as
+// statements correctly when determining if a const argument should
+// have a `DefId` created or not.
+
+macro_rules! y {
+    ( $($matcher:tt)*) => {
+        x
+        //~^ ERROR: cannot find value `x` in this scope
+    };
+}
+
+const _: A<
+    //~^ ERROR: free constant item without body
+    //~| ERROR: cannot find type `A` in this scope
+    {
+        y! { test.tou8 }
+    },
+>;
+
+fn main() {}
diff --git a/tests/ui/const-generics/early/const_arg_trivial_macro_expansion-2.stderr b/tests/ui/const-generics/early/const_arg_trivial_macro_expansion-2.stderr
new file mode 100644
index 00000000000..a3211b77623
--- /dev/null
+++ b/tests/ui/const-generics/early/const_arg_trivial_macro_expansion-2.stderr
@@ -0,0 +1,39 @@
+error: free constant item without body
+  --> $DIR/const_arg_trivial_macro_expansion-2.rs:12:1
+   |
+LL | / const _: A<
+LL | |
+LL | |
+LL | |     {
+LL | |         y! { test.tou8 }
+LL | |     },
+LL | | >;
+   | |  ^ help: provide a definition for the constant: `= <expr>;`
+   | |__|
+   |
+
+error[E0412]: cannot find type `A` in this scope
+  --> $DIR/const_arg_trivial_macro_expansion-2.rs:12:10
+   |
+LL | const _: A<
+   |          ^ not found in this scope
+
+error[E0425]: cannot find value `x` in this scope
+  --> $DIR/const_arg_trivial_macro_expansion-2.rs:7:9
+   |
+LL |         x
+   |         ^ not found in this scope
+...
+LL |         y! { test.tou8 }
+   |         ---------------- in this macro invocation
+   |
+   = note: this error originates in the macro `y` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: you might be missing a const parameter
+   |
+LL | const _<const x: /* Type */>: A<
+   |        +++++++++++++++++++++
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0412, E0425.
+For more information about an error, try `rustc --explain E0412`.
diff --git a/tests/ui/const-generics/early/const_arg_trivial_macro_expansion.rs b/tests/ui/const-generics/early/const_arg_trivial_macro_expansion.rs
new file mode 100644
index 00000000000..2fdd703ab6f
--- /dev/null
+++ b/tests/ui/const-generics/early/const_arg_trivial_macro_expansion.rs
@@ -0,0 +1,366 @@
+//@ known-bug: #132647
+//@ dont-check-compiler-stderr
+#![allow(unused_braces)]
+
+// FIXME(bootstrap): This isn't a known bug, we just don't want to write any error annotations.
+// this is hard because macro expansion errors have their span be inside the *definition* of the
+// macro rather than the line *invoking* it. This means we would wind up with hundreds of error
+// annotations on the macro definitions below rather than on any of the actual lines
+// that act as a "test".
+//
+// It's also made more complicated by the fact that compiletest generates "extra" expected
+// notes to give an assertable macro backtrace as otherwise there would *nothing* to annotate
+// on the actual test lines. All of these extra notes result in needing to write hundreds of
+// unnecessary notes on almost every line in this file.
+//
+// Even though this is marked `known-bug` it should still fail if this test starts ICEing which
+// is "enough" in this case.
+
+// Test that we correctly create definitions for anon consts even when
+// the trivial-ness of the expression is obscured by macro expansions.
+//
+// Acts as a regression test for: #131915 130321 128016
+
+// macros expanding to idents
+
+macro_rules! unbraced_ident {
+    () => {
+        ident
+    };
+}
+
+macro_rules! braced_ident {
+    () => {{ ident }};
+}
+
+macro_rules! unbraced_unbraced_ident {
+    () => {
+        unbraced_ident!()
+    };
+}
+
+macro_rules! braced_unbraced_ident {
+    () => {{ unbraced_ident!() }};
+}
+
+macro_rules! unbraced_braced_ident {
+    () => {
+        braced_ident!()
+    };
+}
+
+macro_rules! braced_braced_ident {
+    () => {{ braced_ident!() }};
+}
+
+// macros expanding to complex expr
+
+macro_rules! unbraced_expr {
+    () => {
+        ident.other
+    };
+}
+
+macro_rules! braced_expr {
+    () => {{ ident.otherent }};
+}
+
+macro_rules! unbraced_unbraced_expr {
+    () => {
+        unbraced_expr!()
+    };
+}
+
+macro_rules! braced_unbraced_expr {
+    () => {{ unbraced_expr!() }};
+}
+
+macro_rules! unbraced_braced_expr {
+    () => {
+        braced_expr!()
+    };
+}
+
+macro_rules! braced_braced_expr {
+    () => {{ braced_expr!() }};
+}
+
+#[rustfmt::skip]
+mod array_paren_call {
+    // Arrays where the expanded result is a `Res::Err`
+    fn array_0() -> [(); unbraced_unbraced_ident!()] { loop {} }
+    fn array_1() -> [(); braced_unbraced_ident!()] { loop {} }
+    fn array_2() -> [(); unbraced_braced_ident!()] { loop {} }
+    fn array_3() -> [(); braced_braced_ident!()] { loop {} }
+    fn array_4() -> [(); { unbraced_unbraced_ident!() }] { loop {} }
+    fn array_5() -> [(); { braced_unbraced_ident!() }] { loop {} }
+    fn array_6() -> [(); { unbraced_braced_ident!() }] { loop {} }
+    fn array_7() -> [(); { braced_braced_ident!() }] { loop {} }
+    fn array_8() -> [(); unbraced_ident!()] { loop {} }
+    fn array_9() -> [(); braced_ident!()] { loop {} }
+    fn array_10() -> [(); { unbraced_ident!() }] { loop {} }
+    fn array_11() -> [(); { braced_ident!() }] { loop {} }
+
+    // Arrays where the expanded result is a `Res::ConstParam`
+    fn array_12<const ident: usize>() -> [(); unbraced_unbraced_ident!()] { loop {} }
+    fn array_13<const ident: usize>() -> [(); braced_unbraced_ident!()] { loop {} }
+    fn array_14<const ident: usize>() -> [(); unbraced_braced_ident!()] { loop {} }
+    fn array_15<const ident: usize>() -> [(); braced_braced_ident!()] { loop {} }
+    fn array_16<const ident: usize>() -> [(); { unbraced_unbraced_ident!() }] { loop {} }
+    fn array_17<const ident: usize>() -> [(); { braced_unbraced_ident!() }] { loop {} }
+    fn array_18<const ident: usize>() -> [(); { unbraced_braced_ident!() }] { loop {} }
+    fn array_19<const ident: usize>() -> [(); { braced_braced_ident!() }] { loop {} }
+    fn array_20<const ident: usize>() -> [(); unbraced_ident!()] { loop {} }
+    fn array_21<const ident: usize>() -> [(); braced_ident!()] { loop {} }
+    fn array_22<const ident: usize>() -> [(); { unbraced_ident!() }] { loop {} }
+    fn array_23<const ident: usize>() -> [(); { braced_ident!() }] { loop {} }
+
+    // Arrays where the expanded result is a complex expr
+    fn array_24() -> [(); unbraced_unbraced_expr!()] { loop {} }
+    fn array_25() -> [(); braced_unbraced_expr!()] { loop {} }
+    fn array_26() -> [(); unbraced_braced_expr!()] { loop {} }
+    fn array_27() -> [(); braced_braced_expr!()] { loop {} }
+    fn array_28() -> [(); { unbraced_unbraced_expr!() }] { loop {} }
+    fn array_29() -> [(); { braced_unbraced_expr!() }] { loop {} }
+    fn array_30() -> [(); { unbraced_braced_expr!() }] { loop {} }
+    fn array_31() -> [(); { braced_braced_expr!() }] { loop {} }
+    fn array_32() -> [(); unbraced_expr!()] { loop {} }
+    fn array_33() -> [(); braced_expr!()] { loop {} }
+    fn array_34() -> [(); { unbraced_expr!() }] { loop {} }
+    fn array_35() -> [(); { braced_expr!() }] { loop {} }
+}
+
+#[rustfmt::skip]
+mod array_brace_call {
+    // Arrays where the expanded result is a `Res::Err`
+    fn array_0() -> [(); unbraced_unbraced_ident!{}] { loop {} }
+    fn array_1() -> [(); braced_unbraced_ident!{}] { loop {} }
+    fn array_2() -> [(); unbraced_braced_ident!{}] { loop {} }
+    fn array_3() -> [(); braced_braced_ident!{}] { loop {} }
+    fn array_4() -> [(); { unbraced_unbraced_ident!{} }] { loop {} }
+    fn array_5() -> [(); { braced_unbraced_ident!{} }] { loop {} }
+    fn array_6() -> [(); { unbraced_braced_ident!{} }] { loop {} }
+    fn array_7() -> [(); { braced_braced_ident!{} }] { loop {} }
+    fn array_8() -> [(); unbraced_ident!{}] { loop {} }
+    fn array_9() -> [(); braced_ident!{}] { loop {} }
+    fn array_10() -> [(); { unbraced_ident!{} }] { loop {} }
+    fn array_11() -> [(); { braced_ident!{} }] { loop {} }
+
+    // Arrays where the expanded result is a `Res::ConstParam`
+    fn array_12<const ident: usize>() -> [(); unbraced_unbraced_ident!{}] { loop {} }
+    fn array_13<const ident: usize>() -> [(); braced_unbraced_ident!{}] { loop {} }
+    fn array_14<const ident: usize>() -> [(); unbraced_braced_ident!{}] { loop {} }
+    fn array_15<const ident: usize>() -> [(); braced_braced_ident!{}] { loop {} }
+    fn array_16<const ident: usize>() -> [(); { unbraced_unbraced_ident!{} }] { loop {} }
+    fn array_17<const ident: usize>() -> [(); { braced_unbraced_ident!{} }] { loop {} }
+    fn array_18<const ident: usize>() -> [(); { unbraced_braced_ident!{} }] { loop {} }
+    fn array_19<const ident: usize>() -> [(); { braced_braced_ident!{} }] { loop {} }
+    fn array_20<const ident: usize>() -> [(); unbraced_ident!{}] { loop {} }
+    fn array_21<const ident: usize>() -> [(); braced_ident!{}] { loop {} }
+    fn array_22<const ident: usize>() -> [(); { unbraced_ident!{} }] { loop {} }
+    fn array_23<const ident: usize>() -> [(); { braced_ident!{} }] { loop {} }
+
+    // Arrays where the expanded result is a complex expr
+    fn array_24() -> [(); unbraced_unbraced_expr!{}] { loop {} }
+    fn array_25() -> [(); braced_unbraced_expr!{}] { loop {} }
+    fn array_26() -> [(); unbraced_braced_expr!{}] { loop {} }
+    fn array_27() -> [(); braced_braced_expr!{}] { loop {} }
+    fn array_28() -> [(); { unbraced_unbraced_expr!{} }] { loop {} }
+    fn array_29() -> [(); { braced_unbraced_expr!{} }] { loop {} }
+    fn array_30() -> [(); { unbraced_braced_expr!{} }] { loop {} }
+    fn array_31() -> [(); { braced_braced_expr!{} }] { loop {} }
+    fn array_32() -> [(); unbraced_expr!{}] { loop {} }
+    fn array_33() -> [(); braced_expr!{}] { loop {} }
+    fn array_34() -> [(); { unbraced_expr!{} }] { loop {} }
+    fn array_35() -> [(); { braced_expr!{} }] { loop {} }
+}
+
+#[rustfmt::skip]
+mod array_square_call {
+    // Arrays where the expanded result is a `Res::Err`
+    fn array_0() -> [(); unbraced_unbraced_ident![]] { loop {} }
+    fn array_1() -> [(); braced_unbraced_ident![]] { loop {} }
+    fn array_2() -> [(); unbraced_braced_ident![]] { loop {} }
+    fn array_3() -> [(); braced_braced_ident![]] { loop {} }
+    fn array_4() -> [(); { unbraced_unbraced_ident![] }] { loop {} }
+    fn array_5() -> [(); { braced_unbraced_ident![] }] { loop {} }
+    fn array_6() -> [(); { unbraced_braced_ident![] }] { loop {} }
+    fn array_7() -> [(); { braced_braced_ident![] }] { loop {} }
+    fn array_8() -> [(); unbraced_ident![]] { loop {} }
+    fn array_9() -> [(); braced_ident![]] { loop {} }
+    fn array_10() -> [(); { unbraced_ident![] }] { loop {} }
+    fn array_11() -> [(); { braced_ident![] }] { loop {} }
+
+    // Arrays where the expanded result is a `Res::ConstParam`
+    fn array_12<const ident: usize>() -> [(); unbraced_unbraced_ident![]] { loop {} }
+    fn array_13<const ident: usize>() -> [(); braced_unbraced_ident![]] { loop {} }
+    fn array_14<const ident: usize>() -> [(); unbraced_braced_ident![]] { loop {} }
+    fn array_15<const ident: usize>() -> [(); braced_braced_ident![]] { loop {} }
+    fn array_16<const ident: usize>() -> [(); { unbraced_unbraced_ident![] }] { loop {} }
+    fn array_17<const ident: usize>() -> [(); { braced_unbraced_ident![] }] { loop {} }
+    fn array_18<const ident: usize>() -> [(); { unbraced_braced_ident![] }] { loop {} }
+    fn array_19<const ident: usize>() -> [(); { braced_braced_ident![] }] { loop {} }
+    fn array_20<const ident: usize>() -> [(); unbraced_ident![]] { loop {} }
+    fn array_21<const ident: usize>() -> [(); braced_ident![]] { loop {} }
+    fn array_22<const ident: usize>() -> [(); { unbraced_ident![] }] { loop {} }
+    fn array_23<const ident: usize>() -> [(); { braced_ident![] }] { loop {} }
+
+    // Arrays where the expanded result is a complex expr
+    fn array_24() -> [(); unbraced_unbraced_expr![]] { loop {} }
+    fn array_25() -> [(); braced_unbraced_expr![]] { loop {} }
+    fn array_26() -> [(); unbraced_braced_expr![]] { loop {} }
+    fn array_27() -> [(); braced_braced_expr![]] { loop {} }
+    fn array_28() -> [(); { unbraced_unbraced_expr![] }] { loop {} }
+    fn array_29() -> [(); { braced_unbraced_expr![] }] { loop {} }
+    fn array_30() -> [(); { unbraced_braced_expr![] }] { loop {} }
+    fn array_31() -> [(); { braced_braced_expr![] }] { loop {} }
+    fn array_32() -> [(); unbraced_expr![]] { loop {} }
+    fn array_33() -> [(); braced_expr![]] { loop {} }
+    fn array_34() -> [(); { unbraced_expr![] }] { loop {} }
+    fn array_35() -> [(); { braced_expr![] }] { loop {} }
+}
+
+struct Foo<const N: usize>;
+
+#[rustfmt::skip]
+mod adt_paren_call {
+    use super::Foo;
+
+    // An ADT where the expanded result is a `Res::Err`
+    fn adt_0() -> Foo<unbraced_unbraced_ident!()> { loop {} }
+    fn adt_1() -> Foo<braced_unbraced_ident!()> { loop {} }
+    fn adt_2() -> Foo<unbraced_braced_ident!()> { loop {} }
+    fn adt_3() -> Foo<braced_braced_ident!()> { loop {} }
+    fn adt_4() -> Foo<{ unbraced_unbraced_ident!() }> { loop {} }
+    fn adt_5() -> Foo<{ braced_unbraced_ident!() }> { loop {} }
+    fn adt_6() -> Foo<{ unbraced_braced_ident!() }> { loop {} }
+    fn adt_7() -> Foo<{ braced_braced_ident!() }> { loop {} }
+    fn adt_8() -> Foo<unbraced_ident!()> { loop {} }
+    fn adt_9() -> Foo<braced_ident!()> { loop {} }
+    fn adt_10() -> Foo<{ unbraced_ident!() }> { loop {} }
+    fn adt_11() -> Foo<{ braced_ident!() }> { loop {} }
+
+    // An ADT where the expanded result is a `Res::ConstParam`
+    fn adt_12<const ident: usize>() -> Foo<unbraced_unbraced_ident!()> { loop {} }
+    fn adt_13<const ident: usize>() -> Foo<braced_unbraced_ident!()> { loop {} }
+    fn adt_14<const ident: usize>() -> Foo<unbraced_braced_ident!()> { loop {} }
+    fn adt_15<const ident: usize>() -> Foo<braced_braced_ident!()> { loop {} }
+    fn adt_16<const ident: usize>() -> Foo<{ unbraced_unbraced_ident!() }> { loop {} }
+    fn adt_17<const ident: usize>() -> Foo<{ braced_unbraced_ident!() }> { loop {} }
+    fn adt_18<const ident: usize>() -> Foo<{ unbraced_braced_ident!() }> { loop {} }
+    fn adt_19<const ident: usize>() -> Foo<{ braced_braced_ident!() }> { loop {} }
+    fn adt_20<const ident: usize>() -> Foo<unbraced_ident!()> { loop {} }
+    fn adt_21<const ident: usize>() -> Foo<braced_ident!()> { loop {} }
+    fn adt_22<const ident: usize>() -> Foo<{ unbraced_ident!() }> { loop {} }
+    fn adt_23<const ident: usize>() -> Foo<{ braced_ident!() }> { loop {} }
+
+    // An ADT where the expanded result is a complex expr
+    fn array_24() -> Foo<unbraced_unbraced_expr!()> { loop {} }
+    fn array_25() -> Foo<braced_unbraced_expr!()> { loop {} }
+    fn array_26() -> Foo<unbraced_braced_expr!()> { loop {} }
+    fn array_27() -> Foo<braced_braced_expr!()> { loop {} }
+    fn array_28() -> Foo<{ unbraced_unbraced_expr!() }> { loop {} }
+    fn array_29() -> Foo<{ braced_unbraced_expr!() }> { loop {} }
+    fn array_30() -> Foo<{ unbraced_braced_expr!() }> { loop {} }
+    fn array_31() -> Foo<{ braced_braced_expr!() }> { loop {} }
+    fn array_32() -> Foo<unbraced_expr!()> { loop {} }
+    fn array_33() -> Foo<braced_expr!()> { loop {} }
+    fn array_34() -> Foo<{ unbraced_expr!() }> { loop {} }
+    fn array_35() -> Foo<{ braced_expr!() }> { loop {} }
+}
+
+#[rustfmt::skip]
+mod adt_brace_call {
+    use super::Foo;
+
+    // An ADT where the expanded result is a `Res::Err`
+    fn adt_0() -> Foo<unbraced_unbraced_ident!{}> { loop {} }
+    fn adt_1() -> Foo<braced_unbraced_ident!{}> { loop {} }
+    fn adt_2() -> Foo<unbraced_braced_ident!{}> { loop {} }
+    fn adt_3() -> Foo<braced_braced_ident!{}> { loop {} }
+    fn adt_4() -> Foo<{ unbraced_unbraced_ident!{} }> { loop {} }
+    fn adt_5() -> Foo<{ braced_unbraced_ident!{} }> { loop {} }
+    fn adt_6() -> Foo<{ unbraced_braced_ident!{} }> { loop {} }
+    fn adt_7() -> Foo<{ braced_braced_ident!{} }> { loop {} }
+    fn adt_8() -> Foo<unbraced_ident!{}> { loop {} }
+    fn adt_9() -> Foo<braced_ident!{}> { loop {} }
+    fn adt_10() -> Foo<{ unbraced_ident!{} }> { loop {} }
+    fn adt_11() -> Foo<{ braced_ident!{} }> { loop {} }
+
+    // An ADT where the expanded result is a `Res::ConstParam`
+    fn adt_12<const ident: usize>() -> Foo<unbraced_unbraced_ident!{}> { loop {} }
+    fn adt_13<const ident: usize>() -> Foo<braced_unbraced_ident!{}> { loop {} }
+    fn adt_14<const ident: usize>() -> Foo<unbraced_braced_ident!{}> { loop {} }
+    fn adt_15<const ident: usize>() -> Foo<braced_braced_ident!{}> { loop {} }
+    fn adt_16<const ident: usize>() -> Foo<{ unbraced_unbraced_ident!{} }> { loop {} }
+    fn adt_17<const ident: usize>() -> Foo<{ braced_unbraced_ident!{} }> { loop {} }
+    fn adt_18<const ident: usize>() -> Foo<{ unbraced_braced_ident!{} }> { loop {} }
+    fn adt_19<const ident: usize>() -> Foo<{ braced_braced_ident!{} }> { loop {} }
+    fn adt_20<const ident: usize>() -> Foo<unbraced_ident!{}> { loop {} }
+    fn adt_21<const ident: usize>() -> Foo<braced_ident!{}> { loop {} }
+    fn adt_22<const ident: usize>() -> Foo<{ unbraced_ident!{} }> { loop {} }
+    fn adt_23<const ident: usize>() -> Foo<{ braced_ident!{} }> { loop {} }
+
+    // An ADT where the expanded result is a complex expr
+    fn array_24() -> Foo<unbraced_unbraced_expr!{}> { loop {} }
+    fn array_25() -> Foo<braced_unbraced_expr!{}> { loop {} }
+    fn array_26() -> Foo<unbraced_braced_expr!{}> { loop {} }
+    fn array_27() -> Foo<braced_braced_expr!{}> { loop {} }
+    fn array_28() -> Foo<{ unbraced_unbraced_expr!{} }> { loop {} }
+    fn array_29() -> Foo<{ braced_unbraced_expr!{} }> { loop {} }
+    fn array_30() -> Foo<{ unbraced_braced_expr!{} }> { loop {} }
+    fn array_31() -> Foo<{ braced_braced_expr!{} }> { loop {} }
+    fn array_32() -> Foo<unbraced_expr!{}> { loop {} }
+    fn array_33() -> Foo<braced_expr!{}> { loop {} }
+    fn array_34() -> Foo<{ unbraced_expr!{} }> { loop {} }
+    fn array_35() -> Foo<{ braced_expr!{} }> { loop {} }
+}
+
+#[rustfmt::skip]
+mod adt_square_call {
+    use super::Foo;
+
+    // An ADT where the expanded result is a `Res::Err`
+    fn adt_0() -> Foo<unbraced_unbraced_ident![]> { loop {} }
+    fn adt_1() -> Foo<braced_unbraced_ident![]> { loop {} }
+    fn adt_2() -> Foo<unbraced_braced_ident![]> { loop {} }
+    fn adt_3() -> Foo<braced_braced_ident![]> { loop {} }
+    fn adt_4() -> Foo<{ unbraced_unbraced_ident![] }> { loop {} }
+    fn adt_5() -> Foo<{ braced_unbraced_ident![] }> { loop {} }
+    fn adt_6() -> Foo<{ unbraced_braced_ident![] }> { loop {} }
+    fn adt_7() -> Foo<{ braced_braced_ident![] }> { loop {} }
+    fn adt_8() -> Foo<unbraced_ident![]> { loop {} }
+    fn adt_9() -> Foo<braced_ident![]> { loop {} }
+    fn adt_10() -> Foo<{ unbraced_ident![] }> { loop {} }
+    fn adt_11() -> Foo<{ braced_ident![] }> { loop {} }
+
+    // An ADT where the expanded result is a `Res::ConstParam`
+    fn adt_12<const ident: usize>() -> Foo<unbraced_unbraced_ident![]> { loop {} }
+    fn adt_13<const ident: usize>() -> Foo<braced_unbraced_ident![]> { loop {} }
+    fn adt_14<const ident: usize>() -> Foo<unbraced_braced_ident![]> { loop {} }
+    fn adt_15<const ident: usize>() -> Foo<braced_braced_ident![]> { loop {} }
+    fn adt_16<const ident: usize>() -> Foo<{ unbraced_unbraced_ident![] }> { loop {} }
+    fn adt_17<const ident: usize>() -> Foo<{ braced_unbraced_ident![] }> { loop {} }
+    fn adt_18<const ident: usize>() -> Foo<{ unbraced_braced_ident![] }> { loop {} }
+    fn adt_19<const ident: usize>() -> Foo<{ braced_braced_ident![] }> { loop {} }
+    fn adt_20<const ident: usize>() -> Foo<unbraced_ident![]> { loop {} }
+    fn adt_21<const ident: usize>() -> Foo<braced_ident![]> { loop {} }
+    fn adt_22<const ident: usize>() -> Foo<{ unbraced_ident![] }> { loop {} }
+    fn adt_23<const ident: usize>() -> Foo<{ braced_ident![] }> { loop {} }
+
+    // An ADT where the expanded result is a complex expr
+    fn array_24() -> Foo<unbraced_unbraced_expr![]> { loop {} }
+    fn array_25() -> Foo<braced_unbraced_expr![]> { loop {} }
+    fn array_26() -> Foo<unbraced_braced_expr![]> { loop {} }
+    fn array_27() -> Foo<braced_braced_expr![]> { loop {} }
+    fn array_28() -> Foo<{ unbraced_unbraced_expr![] }> { loop {} }
+    fn array_29() -> Foo<{ braced_unbraced_expr![] }> { loop {} }
+    fn array_30() -> Foo<{ unbraced_braced_expr![] }> { loop {} }
+    fn array_31() -> Foo<{ braced_braced_expr![] }> { loop {} }
+    fn array_32() -> Foo<unbraced_expr![]> { loop {} }
+    fn array_33() -> Foo<braced_expr![]> { loop {} }
+    fn array_34() -> Foo<{ unbraced_expr![] }> { loop {} }
+    fn array_35() -> Foo<{ braced_expr![] }> { loop {} }
+}
+
+fn main() {}
diff --git a/tests/ui/editions/never-type-fallback-breaking.e2021.fixed b/tests/ui/editions/never-type-fallback-breaking.e2021.fixed
new file mode 100644
index 00000000000..3fed16f0ee7
--- /dev/null
+++ b/tests/ui/editions/never-type-fallback-breaking.e2021.fixed
@@ -0,0 +1,52 @@
+//@ revisions: e2021 e2024
+//
+//@[e2021] edition: 2021
+//@[e2024] edition: 2024
+//@[e2024] compile-flags: -Zunstable-options
+//
+//@[e2021] run-pass
+//@[e2021] run-rustfix
+//@[e2024] check-fail
+
+fn main() {
+    m();
+    q();
+    let _ = meow();
+}
+
+fn m() {
+    //[e2021]~^ this function depends on never type fallback being `()`
+    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    let x: () = match true {
+        true => Default::default(),
+        //[e2024]~^ error: the trait bound `!: Default` is not satisfied
+        false => panic!("..."),
+    };
+
+    dbg!(x);
+}
+
+fn q() -> Option<()> {
+    //[e2021]~^ this function depends on never type fallback being `()`
+    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    fn deserialize<T: Default>() -> Option<T> {
+        Some(T::default())
+    }
+
+    deserialize::<()>()?;
+    //[e2024]~^ error: the trait bound `!: Default` is not satisfied
+
+    None
+}
+
+// Make sure we turbofish the right argument
+fn help<'a: 'a, T: Into<()>, U>(_: U) -> Result<T, ()> {
+    Err(())
+}
+fn meow() -> Result<(), ()> {
+    //[e2021]~^ this function depends on never type fallback being `()`
+    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    help::<(), _>(1)?;
+    //[e2024]~^ error: the trait bound `(): From<!>` is not satisfied
+    Ok(())
+}
diff --git a/tests/ui/editions/never-type-fallback-breaking.e2021.stderr b/tests/ui/editions/never-type-fallback-breaking.e2021.stderr
index 79eee2a3def..fdc97e54d4e 100644
--- a/tests/ui/editions/never-type-fallback-breaking.e2021.stderr
+++ b/tests/ui/editions/never-type-fallback-breaking.e2021.stderr
@@ -1,5 +1,5 @@
 warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:15:1
+  --> $DIR/never-type-fallback-breaking.rs:17:1
    |
 LL | fn m() {
    | ^^^^^^
@@ -8,7 +8,7 @@ LL | fn m() {
    = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:19:17
+  --> $DIR/never-type-fallback-breaking.rs:21:17
    |
 LL |         true => Default::default(),
    |                 ^^^^^^^^^^^^^^^^^^
@@ -19,7 +19,7 @@ LL |     let x: () = match true {
    |          ++++
 
 warning: this function depends on never type fallback being `()`
-  --> $DIR/never-type-fallback-breaking.rs:27:1
+  --> $DIR/never-type-fallback-breaking.rs:29:1
    |
 LL | fn q() -> Option<()> {
    | ^^^^^^^^^^^^^^^^^^^^
@@ -28,7 +28,7 @@ LL | fn q() -> Option<()> {
    = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
    = help: specify the types explicitly
 note: in edition 2024, the requirement `!: Default` will fail
-  --> $DIR/never-type-fallback-breaking.rs:34:5
+  --> $DIR/never-type-fallback-breaking.rs:36:5
    |
 LL |     deserialize()?;
    |     ^^^^^^^^^^^^^
@@ -37,5 +37,24 @@ help: use `()` annotations to avoid fallback changes
 LL |     deserialize::<()>()?;
    |                ++++++
 
-warning: 2 warnings emitted
+warning: this function depends on never type fallback being `()`
+  --> $DIR/never-type-fallback-breaking.rs:46:1
+   |
+LL | fn meow() -> Result<(), ()> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #123748 <https://github.com/rust-lang/rust/issues/123748>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `(): From<!>` will fail
+  --> $DIR/never-type-fallback-breaking.rs:49:5
+   |
+LL |     help(1)?;
+   |     ^^^^^^^
+help: use `()` annotations to avoid fallback changes
+   |
+LL |     help::<(), _>(1)?;
+   |         +++++++++
+
+warning: 3 warnings emitted
 
diff --git a/tests/ui/editions/never-type-fallback-breaking.e2024.stderr b/tests/ui/editions/never-type-fallback-breaking.e2024.stderr
index 461e4ae0bdf..6258247f8b2 100644
--- a/tests/ui/editions/never-type-fallback-breaking.e2024.stderr
+++ b/tests/ui/editions/never-type-fallback-breaking.e2024.stderr
@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `!: Default` is not satisfied
-  --> $DIR/never-type-fallback-breaking.rs:19:17
+  --> $DIR/never-type-fallback-breaking.rs:21:17
    |
 LL |         true => Default::default(),
    |                 ^^^^^^^^^^^^^^^^^^ the trait `Default` is not implemented for `!`
@@ -8,7 +8,7 @@ LL |         true => Default::default(),
    = help: did you intend to use the type `()` here instead?
 
 error[E0277]: the trait bound `!: Default` is not satisfied
-  --> $DIR/never-type-fallback-breaking.rs:34:5
+  --> $DIR/never-type-fallback-breaking.rs:36:5
    |
 LL |     deserialize()?;
    |     ^^^^^^^^^^^^^ the trait `Default` is not implemented for `!`
@@ -16,11 +16,34 @@ LL |     deserialize()?;
    = note: this error might have been caused by changes to Rust's type-inference algorithm (see issue #48950 <https://github.com/rust-lang/rust/issues/48950> for more information)
    = help: did you intend to use the type `()` here instead?
 note: required by a bound in `deserialize`
-  --> $DIR/never-type-fallback-breaking.rs:30:23
+  --> $DIR/never-type-fallback-breaking.rs:32:23
    |
 LL |     fn deserialize<T: Default>() -> Option<T> {
    |                       ^^^^^^^ required by this bound in `deserialize`
 
-error: aborting due to 2 previous errors
+error[E0277]: the trait bound `(): From<!>` is not satisfied
+  --> $DIR/never-type-fallback-breaking.rs:49:5
+   |
+LL |     help(1)?;
+   |     ^^^^^^^ the trait `From<!>` is not implemented for `()`
+   |
+   = help: the following other types implement trait `From<T>`:
+             `(T, T)` implements `From<[T; 2]>`
+             `(T, T, T)` implements `From<[T; 3]>`
+             `(T, T, T, T)` implements `From<[T; 4]>`
+             `(T, T, T, T, T)` implements `From<[T; 5]>`
+             `(T, T, T, T, T, T)` implements `From<[T; 6]>`
+             `(T, T, T, T, T, T, T)` implements `From<[T; 7]>`
+             `(T, T, T, T, T, T, T, T)` implements `From<[T; 8]>`
+             `(T, T, T, T, T, T, T, T, T)` implements `From<[T; 9]>`
+           and 4 others
+   = note: required for `!` to implement `Into<()>`
+note: required by a bound in `help`
+  --> $DIR/never-type-fallback-breaking.rs:43:20
+   |
+LL | fn help<'a: 'a, T: Into<()>, U>(_: U) -> Result<T, ()> {
+   |                    ^^^^^^^^ required by this bound in `help`
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/editions/never-type-fallback-breaking.rs b/tests/ui/editions/never-type-fallback-breaking.rs
index 7b4a1b1de04..71d36f3a2d9 100644
--- a/tests/ui/editions/never-type-fallback-breaking.rs
+++ b/tests/ui/editions/never-type-fallback-breaking.rs
@@ -5,11 +5,13 @@
 //@[e2024] compile-flags: -Zunstable-options
 //
 //@[e2021] run-pass
+//@[e2021] run-rustfix
 //@[e2024] check-fail
 
 fn main() {
     m();
     q();
+    let _ = meow();
 }
 
 fn m() {
@@ -36,3 +38,15 @@ fn q() -> Option<()> {
 
     None
 }
+
+// Make sure we turbofish the right argument
+fn help<'a: 'a, T: Into<()>, U>(_: U) -> Result<T, ()> {
+    Err(())
+}
+fn meow() -> Result<(), ()> {
+    //[e2021]~^ this function depends on never type fallback being `()`
+    //[e2021]~| this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    help(1)?;
+    //[e2024]~^ error: the trait bound `(): From<!>` is not satisfied
+    Ok(())
+}
diff --git a/tests/ui/suggestions/no-method-found-suggest-trait-args.rs b/tests/ui/suggestions/no-method-found-suggest-trait-args.rs
new file mode 100644
index 00000000000..d51f86b29e8
--- /dev/null
+++ b/tests/ui/suggestions/no-method-found-suggest-trait-args.rs
@@ -0,0 +1,30 @@
+/// Tests that suggestions to add trait bounds that would enable using a method include appropriate
+/// placeholder arguments for that trait.
+
+trait Trait<I> {
+    fn method(&self) {}
+}
+
+trait Trait2<'a, A, const B: u8, C = (), const D: u8 = 0> {
+    fn method2(&self) {}
+}
+
+fn foo<T>(value: T) {
+    //~^ SUGGESTION : Trait</* I */>
+    //~| SUGGESTION : Trait2</* 'a, A, B */>
+    value.method();
+    //~^ ERROR no method named `method` found for type parameter `T` in the current scope [E0599]
+    value.method2();
+    //~^ ERROR no method named `method2` found for type parameter `T` in the current scope [E0599]
+}
+
+fn bar(value: impl Copy) {
+    //~^ SUGGESTION + Trait</* I */>
+    //~| SUGGESTION + Trait2</* 'a, A, B */>
+    value.method();
+    //~^ ERROR no method named `method` found for type parameter `impl Copy` in the current scope [E0599]
+    value.method2();
+    //~^ ERROR no method named `method2` found for type parameter `impl Copy` in the current scope [E0599]
+}
+
+fn main() {}
diff --git a/tests/ui/suggestions/no-method-found-suggest-trait-args.stderr b/tests/ui/suggestions/no-method-found-suggest-trait-args.stderr
new file mode 100644
index 00000000000..3dcd4667fa0
--- /dev/null
+++ b/tests/ui/suggestions/no-method-found-suggest-trait-args.stderr
@@ -0,0 +1,63 @@
+error[E0599]: no method named `method` found for type parameter `T` in the current scope
+  --> $DIR/no-method-found-suggest-trait-args.rs:15:11
+   |
+LL | fn foo<T>(value: T) {
+   |        - method `method` not found for this type parameter
+...
+LL |     value.method();
+   |           ^^^^^^ method not found in `T`
+   |
+   = help: items from traits can only be used if the type parameter is bounded by the trait
+help: the following trait defines an item `method`, perhaps you need to restrict type parameter `T` with it:
+   |
+LL | fn foo<T: Trait</* I */>>(value: T) {
+   |         ++++++++++++++++
+
+error[E0599]: no method named `method2` found for type parameter `T` in the current scope
+  --> $DIR/no-method-found-suggest-trait-args.rs:17:11
+   |
+LL | fn foo<T>(value: T) {
+   |        - method `method2` not found for this type parameter
+...
+LL |     value.method2();
+   |           ^^^^^^^ method not found in `T`
+   |
+   = help: items from traits can only be used if the type parameter is bounded by the trait
+help: the following trait defines an item `method2`, perhaps you need to restrict type parameter `T` with it:
+   |
+LL | fn foo<T: Trait2</* 'a, A, B */>>(value: T) {
+   |         ++++++++++++++++++++++++
+
+error[E0599]: no method named `method` found for type parameter `impl Copy` in the current scope
+  --> $DIR/no-method-found-suggest-trait-args.rs:24:11
+   |
+LL | fn bar(value: impl Copy) {
+   |               --------- method `method` not found for this type parameter
+...
+LL |     value.method();
+   |           ^^^^^^ method not found in `impl Copy`
+   |
+   = help: items from traits can only be used if the type parameter is bounded by the trait
+help: the following trait defines an item `method`, perhaps you need to restrict type parameter `impl Copy` with it:
+   |
+LL | fn bar(value: impl Copy + Trait</* I */>) {
+   |                         ++++++++++++++++
+
+error[E0599]: no method named `method2` found for type parameter `impl Copy` in the current scope
+  --> $DIR/no-method-found-suggest-trait-args.rs:26:11
+   |
+LL | fn bar(value: impl Copy) {
+   |               --------- method `method2` not found for this type parameter
+...
+LL |     value.method2();
+   |           ^^^^^^^ method not found in `impl Copy`
+   |
+   = help: items from traits can only be used if the type parameter is bounded by the trait
+help: the following trait defines an item `method2`, perhaps you need to restrict type parameter `impl Copy` with it:
+   |
+LL | fn bar(value: impl Copy + Trait2</* 'a, A, B */>) {
+   |                         ++++++++++++++++++++++++
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0599`.