Auto merge of #67874 - Dylan-DPC:rollup-xy6bkoe, r=Dylan-DPC

Rollup of 4 pull requests

Successful merges:

 - #67137 (libstd uses `core::panic::Location` where possible.)
 - #67709 (Introduce an option for disabling deduplication of diagnostics)
 - #67775 (Make "use $crate" a hard error)
 - #67812 (Tweak and extend internal BTreeMap documentation, including debug asserts.)

Failed merges:

r? @ghost

35 files changed, 211 insertions, 197 deletions

diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs
index fa8aae04011..302c2bcd5e4 100644
--- a/src/liballoc/collections/btree/map.rs
+++ b/src/liballoc/collections/btree/map.rs
@@ -493,7 +493,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
         BTreeMap { root: node::Root::shared_empty_root(), length: 0 }
     }
 
-    /// Clears the map, removing all values.
+    /// Clears the map, removing all elements.
     ///
     /// # Examples
     ///
@@ -2605,7 +2605,7 @@ impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
 
         // Handle underflow
         let mut cur_node = small_leaf.forget_type();
-        while cur_node.len() < node::CAPACITY / 2 {
+        while cur_node.len() < node::MIN_LEN {
             match handle_underfull_node(cur_node) {
                 AtRoot => break,
                 EmptyParent(_) => unreachable!(),
diff --git a/src/liballoc/collections/btree/node.rs b/src/liballoc/collections/btree/node.rs
index 0a2849f6e39..260e51d635d 100644
--- a/src/liballoc/collections/btree/node.rs
+++ b/src/liballoc/collections/btree/node.rs
@@ -308,15 +308,15 @@ impl<K, V> Root<K, V> {
 ///   `Leaf`, the `NodeRef` points to a leaf node, when this is `Internal` the
 ///   `NodeRef` points to an internal node, and when this is `LeafOrInternal` the
 ///   `NodeRef` could be pointing to either type of node.
-///   Note that in case of a leaf node, this might still be the shared root!  Only turn
-///   this into a `LeafNode` reference if you know it is not a root!  Shared references
-///   must be dereferencable *for the entire size of their pointee*, so `&InternalNode`
-///   pointing to the shared root is UB.
-///   Turning this into a `NodeHeader` is always safe.
+///   Note that in case of a leaf node, this might still be the shared root!
+///   Only turn this into a `LeafNode` reference if you know it is not the shared root!
+///   Shared references must be dereferencable *for the entire size of their pointee*,
+///   so '&LeafNode` or `&InternalNode` pointing to the shared root is undefined behavior.
+///   Turning this into a `NodeHeader` reference is always safe.
 pub struct NodeRef<BorrowType, K, V, Type> {
     height: usize,
     node: NonNull<LeafNode<K, V>>,
-    // This is null unless the borrow type is `Mut`
+    // `root` is null unless the borrow type is `Mut`
     root: *const Root<K, V>,
     _marker: PhantomData<(BorrowType, Type)>,
 }
@@ -370,8 +370,13 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
         NodeRef { height: self.height, node: self.node, root: self.root, _marker: PhantomData }
     }
 
-    /// Assert that this is indeed a proper leaf node, and not the shared root.
+    /// Exposes the leaf "portion" of any leaf or internal node that is not the shared root.
+    /// If the node is a leaf, this function simply opens up its data.
+    /// If the node is an internal node, so not a leaf, it does have all the data a leaf has
+    /// (header, keys and values), and this function exposes that.
+    /// See `NodeRef` on why the node may not be a shared root.
     unsafe fn as_leaf(&self) -> &LeafNode<K, V> {
+        debug_assert!(!self.is_shared_root());
         self.node.as_ref()
     }
 
@@ -379,14 +384,19 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
         unsafe { &*(self.node.as_ptr() as *const NodeHeader<K, V>) }
     }
 
+    /// Returns whether the node is the shared, empty root.
     pub fn is_shared_root(&self) -> bool {
         self.as_header().is_shared_root()
     }
 
+    /// Borrows a view into the keys stored in the node.
+    /// Works on all possible nodes, including the shared root.
     pub fn keys(&self) -> &[K] {
         self.reborrow().into_key_slice()
     }
 
+    /// Borrows a view into the values stored in the node.
+    /// The caller must ensure that the node is not the shared root.
     fn vals(&self) -> &[V] {
         self.reborrow().into_val_slice()
     }
@@ -491,16 +501,24 @@ impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
         NodeRef { height: self.height, node: self.node, root: self.root, _marker: PhantomData }
     }
 
+    /// Exposes the leaf "portion" of any leaf or internal node for writing.
+    /// If the node is a leaf, this function simply opens up its data.
+    /// If the node is an internal node, so not a leaf, it does have all the data a leaf has
+    /// (header, keys and values), and this function exposes that.
+    ///
     /// Returns a raw ptr to avoid asserting exclusive access to the entire node.
+    /// This also implies you can invoke this member on the shared root, but the resulting pointer
+    /// might not be properly aligned and definitely would not allow accessing keys and values.
     fn as_leaf_mut(&mut self) -> *mut LeafNode<K, V> {
-        // We are mutable, so we cannot be the shared root, so accessing this as a leaf is okay.
         self.node.as_ptr()
     }
 
+    /// The caller must ensure that the node is not the shared root.
     fn keys_mut(&mut self) -> &mut [K] {
         unsafe { self.reborrow_mut().into_key_slice_mut() }
     }
 
+    /// The caller must ensure that the node is not the shared root.
     fn vals_mut(&mut self) -> &mut [V] {
         unsafe { self.reborrow_mut().into_val_slice_mut() }
     }
@@ -551,9 +569,10 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
         }
     }
 
+    /// The caller must ensure that the node is not the shared root.
     fn into_val_slice(self) -> &'a [V] {
         debug_assert!(!self.is_shared_root());
-        // We cannot be the shared root, so `as_leaf` is okay
+        // We cannot be the shared root, so `as_leaf` is okay.
         unsafe { slice::from_raw_parts(MaybeUninit::first_ptr(&self.as_leaf().vals), self.len()) }
     }
 
@@ -587,6 +606,7 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
         }
     }
 
+    /// The caller must ensure that the node is not the shared root.
     fn into_val_slice_mut(mut self) -> &'a mut [V] {
         debug_assert!(!self.is_shared_root());
         unsafe {
@@ -597,6 +617,7 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
         }
     }
 
+    /// The caller must ensure that the node is not the shared root.
     fn into_slices_mut(mut self) -> (&'a mut [K], &'a mut [V]) {
         debug_assert!(!self.is_shared_root());
         // We cannot use the getters here, because calling the second one
@@ -655,6 +676,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
         // Necessary for correctness, but this is an internal module
         debug_assert!(edge.height == self.height - 1);
         debug_assert!(self.len() < CAPACITY);
+        debug_assert!(!self.is_shared_root());
 
         let idx = self.len();
 
@@ -686,6 +708,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
         // Necessary for correctness, but this is an internal module
         debug_assert!(edge.height == self.height - 1);
         debug_assert!(self.len() < CAPACITY);
+        debug_assert!(!self.is_shared_root());
 
         unsafe {
             slice_insert(self.keys_mut(), 0, key);
@@ -773,6 +796,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
         }
     }
 
+    /// The caller must ensure that the node is not the shared root.
     fn into_kv_pointers_mut(mut self) -> (*mut K, *mut V) {
         (self.keys_mut().as_mut_ptr(), self.vals_mut().as_mut_ptr())
     }
@@ -1116,8 +1140,8 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV>
         }
     }
 
-    /// Removes the key/value pair pointed to by this handle, returning the edge between the
-    /// now adjacent key/value pairs to the left and right of this handle.
+    /// Removes the key/value pair pointed to by this handle and returns it, along with the edge
+    /// between the now adjacent key/value pairs (if any) to the left and right of this handle.
     pub fn remove(
         mut self,
     ) -> (Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>, K, V) {
@@ -1260,7 +1284,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         }
     }
 
-    /// This removes a key/value pair from the left child and replaces it with the key/value pair
+    /// This removes a key/value pair from the left child and places it in the key/value storage
     /// pointed to by this handle while pushing the old key/value pair of this handle into the right
     /// child.
     pub fn steal_left(&mut self) {
@@ -1277,7 +1301,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         }
     }
 
-    /// This removes a key/value pair from the right child and replaces it with the key/value pair
+    /// This removes a key/value pair from the right child and places it in the key/value storage
     /// pointed to by this handle while pushing the old key/value pair of this handle into the left
     /// child.
     pub fn steal_right(&mut self) {
diff --git a/src/libcore/macros/mod.rs b/src/libcore/macros/mod.rs
index 9a52823a454..0eb9e194236 100644
--- a/src/libcore/macros/mod.rs
+++ b/src/libcore/macros/mod.rs
@@ -1,19 +1,13 @@
 #[doc(include = "panic.md")]
 #[macro_export]
-#[allow_internal_unstable(core_panic,
-    // FIXME(anp, eddyb) `core_intrinsics` is used here to allow calling
-    // the `caller_location` intrinsic, but once  `#[track_caller]` is implemented,
-    // `panicking::{panic, panic_fmt}` can use that instead of a `Location` argument.
-    core_intrinsics,
-    const_caller_location,
-)]
+#[allow_internal_unstable(core_panic, track_caller)]
 #[stable(feature = "core", since = "1.6.0")]
 macro_rules! panic {
     () => (
         $crate::panic!("explicit panic")
     );
     ($msg:expr) => (
-        $crate::panicking::panic($msg, $crate::intrinsics::caller_location())
+        $crate::panicking::panic($msg)
     );
     ($msg:expr,) => (
         $crate::panic!($msg)
@@ -21,7 +15,7 @@ macro_rules! panic {
     ($fmt:expr, $($arg:tt)+) => (
         $crate::panicking::panic_fmt(
             $crate::format_args!($fmt, $($arg)+),
-            $crate::intrinsics::caller_location(),
+            $crate::panic::Location::caller(),
         )
     );
 }
diff --git a/src/libcore/panicking.rs b/src/libcore/panicking.rs
index 7ebb72e3ce7..61b764f2d62 100644
--- a/src/libcore/panicking.rs
+++ b/src/libcore/panicking.rs
@@ -36,8 +36,9 @@ use crate::panic::{Location, PanicInfo};
 // never inline unless panic_immediate_abort to avoid code
 // bloat at the call sites as much as possible
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
+#[track_caller]
 #[lang = "panic"] // needed by codegen for panic on overflow and other `Assert` MIR terminators
-pub fn panic(expr: &str, location: &Location<'_>) -> ! {
+pub fn panic(expr: &str) -> ! {
     if cfg!(feature = "panic_immediate_abort") {
         unsafe { super::intrinsics::abort() }
     }
@@ -48,7 +49,7 @@ pub fn panic(expr: &str, location: &Location<'_>) -> ! {
     // truncation and padding (even though none is used here). Using
     // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
     // output binary, saving up to a few kilobytes.
-    panic_fmt(fmt::Arguments::new_v1(&[expr], &[]), location)
+    panic_fmt(fmt::Arguments::new_v1(&[expr], &[]), Location::caller())
 }
 
 #[cold]
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index aa2865a75f9..2279ed85954 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -329,6 +329,8 @@ pub struct HandlerFlags {
     /// show macro backtraces even for non-local macros.
     /// (rustc: see `-Z external-macro-backtrace`)
     pub external_macro_backtrace: bool,
+    /// If true, identical diagnostics are reported only once.
+    pub deduplicate_diagnostics: bool,
 }
 
 impl Drop for HandlerInner {
@@ -736,16 +738,17 @@ impl HandlerInner {
             self.emitted_diagnostic_codes.insert(code.clone());
         }
 
-        let diagnostic_hash = {
+        let already_emitted = |this: &mut Self| {
             use std::hash::Hash;
             let mut hasher = StableHasher::new();
             diagnostic.hash(&mut hasher);
-            hasher.finish()
+            let diagnostic_hash = hasher.finish();
+            !this.emitted_diagnostics.insert(diagnostic_hash)
         };
 
-        // Only emit the diagnostic if we haven't already emitted an equivalent
-        // one:
-        if self.emitted_diagnostics.insert(diagnostic_hash) {
+        // Only emit the diagnostic if we've been asked to deduplicate and
+        // haven't already emitted an equivalent diagnostic.
+        if !(self.flags.deduplicate_diagnostics && already_emitted(self)) {
             self.emitter.emit_diagnostic(diagnostic);
             if diagnostic.is_error() {
                 self.deduplicated_err_count += 1;
diff --git a/src/librustc_expand/build.rs b/src/librustc_expand/build.rs
index 799781a8963..11f94ab2e62 100644
--- a/src/librustc_expand/build.rs
+++ b/src/librustc_expand/build.rs
@@ -6,7 +6,7 @@ use syntax::ast::{self, AttrVec, BlockCheckMode, Expr, Ident, PatKind, UnOp};
 use syntax::attr;
 use syntax::ptr::P;
 
-use rustc_span::{Pos, Span};
+use rustc_span::Span;
 
 impl<'a> ExtCtxt<'a> {
     pub fn path(&self, span: Span, strs: Vec<ast::Ident>) -> ast::Path {
@@ -350,16 +350,10 @@ impl<'a> ExtCtxt<'a> {
     }
 
     pub fn expr_fail(&self, span: Span, msg: Symbol) -> P<ast::Expr> {
-        let loc = self.source_map().lookup_char_pos(span.lo());
-        let expr_file = self.expr_str(span, Symbol::intern(&loc.file.name.to_string()));
-        let expr_line = self.expr_u32(span, loc.line as u32);
-        let expr_col = self.expr_u32(span, loc.col.to_usize() as u32 + 1);
-        let expr_loc_tuple = self.expr_tuple(span, vec![expr_file, expr_line, expr_col]);
-        let expr_loc_ptr = self.expr_addr_of(span, expr_loc_tuple);
         self.expr_call_global(
             span,
             [sym::std, sym::rt, sym::begin_panic].iter().map(|s| Ident::new(*s, span)).collect(),
-            vec![self.expr_str(span, msg), expr_loc_ptr],
+            vec![self.expr_str(span, msg)],
         )
     }
 
diff --git a/src/librustc_mir/const_eval/machine.rs b/src/librustc_mir/const_eval/machine.rs
index d4556919652..b39a61c5e0d 100644
--- a/src/librustc_mir/const_eval/machine.rs
+++ b/src/librustc_mir/const_eval/machine.rs
@@ -177,6 +177,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
 
     fn find_mir_or_eval_fn(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        span: Span,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx>],
         ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
@@ -199,7 +200,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
                 // Some functions we support even if they are non-const -- but avoid testing
                 // that for const fn!  We certainly do *not* want to actually call the fn
                 // though, so be sure we return here.
-                return if ecx.hook_panic_fn(instance, args, ret)? {
+                return if ecx.hook_panic_fn(span, instance, args)? {
                     Ok(None)
                 } else {
                     throw_unsup_format!("calling non-const function `{}`", instance)
diff --git a/src/librustc_mir/interpret/intrinsics.rs b/src/librustc_mir/interpret/intrinsics.rs
index cc38cbbac8d..b075e8ea383 100644
--- a/src/librustc_mir/interpret/intrinsics.rs
+++ b/src/librustc_mir/interpret/intrinsics.rs
@@ -366,47 +366,21 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// Returns `true` if an intercept happened.
     pub fn hook_panic_fn(
         &mut self,
+        span: Span,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx, M::PointerTag>],
-        _ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
     ) -> InterpResult<'tcx, bool> {
         let def_id = instance.def_id();
-        if Some(def_id) == self.tcx.lang_items().panic_fn() {
-            // &'static str, &core::panic::Location { &'static str, u32, u32 }
-            assert!(args.len() == 2);
+        if Some(def_id) == self.tcx.lang_items().panic_fn()
+            || Some(def_id) == self.tcx.lang_items().begin_panic_fn()
+        {
+            // &'static str
+            assert!(args.len() == 1);
 
             let msg_place = self.deref_operand(args[0])?;
             let msg = Symbol::intern(self.read_str(msg_place)?);
-
-            let location = self.deref_operand(args[1])?;
-            let (file, line, col) = (
-                self.mplace_field(location, 0)?,
-                self.mplace_field(location, 1)?,
-                self.mplace_field(location, 2)?,
-            );
-
-            let file_place = self.deref_operand(file.into())?;
-            let file = Symbol::intern(self.read_str(file_place)?);
-            let line = self.read_scalar(line.into())?.to_u32()?;
-            let col = self.read_scalar(col.into())?.to_u32()?;
-            throw_panic!(Panic { msg, file, line, col })
-        } else if Some(def_id) == self.tcx.lang_items().begin_panic_fn() {
-            assert!(args.len() == 2);
-            // &'static str, &(&'static str, u32, u32)
-            let msg = args[0];
-            let place = self.deref_operand(args[1])?;
-            let (file, line, col) = (
-                self.mplace_field(place, 0)?,
-                self.mplace_field(place, 1)?,
-                self.mplace_field(place, 2)?,
-            );
-
-            let msg_place = self.deref_operand(msg.into())?;
-            let msg = Symbol::intern(self.read_str(msg_place)?);
-            let file_place = self.deref_operand(file.into())?;
-            let file = Symbol::intern(self.read_str(file_place)?);
-            let line = self.read_scalar(line.into())?.to_u32()?;
-            let col = self.read_scalar(col.into())?.to_u32()?;
+            let span = self.find_closest_untracked_caller_location().unwrap_or(span);
+            let (file, line, col) = self.location_triple_for_span(span);
             throw_panic!(Panic { msg, file, line, col })
         } else {
             return Ok(false);
diff --git a/src/librustc_mir/interpret/intrinsics/caller_location.rs b/src/librustc_mir/interpret/intrinsics/caller_location.rs
index da0a9fb4f1b..0525108d2d1 100644
--- a/src/librustc_mir/interpret/intrinsics/caller_location.rs
+++ b/src/librustc_mir/interpret/intrinsics/caller_location.rs
@@ -9,8 +9,9 @@ use crate::interpret::{
 };
 
 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
-    /// Walks up the callstack from the intrinsic's callsite, searching for the first frame which is
-    /// not `#[track_caller]`.
+    /// Walks up the callstack from the intrinsic's callsite, searching for the first callsite in a
+    /// frame which is not `#[track_caller]`. If the first frame found lacks `#[track_caller]`, then
+    /// `None` is returned and the callsite of the function invocation itself should be used.
     crate fn find_closest_untracked_caller_location(&self) -> Option<Span> {
         let mut caller_span = None;
         for next_caller in self.stack.iter().rev() {
@@ -54,9 +55,14 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     }
 
     pub fn alloc_caller_location_for_span(&mut self, span: Span) -> MPlaceTy<'tcx, M::PointerTag> {
+        let (file, line, column) = self.location_triple_for_span(span);
+        self.alloc_caller_location(file, line, column)
+    }
+
+    pub(super) fn location_triple_for_span(&self, span: Span) -> (Symbol, u32, u32) {
         let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
         let caller = self.tcx.sess.source_map().lookup_char_pos(topmost.lo());
-        self.alloc_caller_location(
+        (
             Symbol::intern(&caller.file.name.to_string()),
             caller.line as u32,
             caller.col_display as u32 + 1,
diff --git a/src/librustc_mir/interpret/machine.rs b/src/librustc_mir/interpret/machine.rs
index 3b444ac46ef..3dc572d256d 100644
--- a/src/librustc_mir/interpret/machine.rs
+++ b/src/librustc_mir/interpret/machine.rs
@@ -139,6 +139,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
     /// was used.
     fn find_mir_or_eval_fn(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        span: Span,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx, Self::PointerTag>],
         ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
diff --git a/src/librustc_mir/interpret/terminator.rs b/src/librustc_mir/interpret/terminator.rs
index e4af3037055..032062d6360 100644
--- a/src/librustc_mir/interpret/terminator.rs
+++ b/src/librustc_mir/interpret/terminator.rs
@@ -238,7 +238,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             | ty::InstanceDef::CloneShim(..)
             | ty::InstanceDef::Item(_) => {
                 // We need MIR for this fn
-                let body = match M::find_mir_or_eval_fn(self, instance, args, ret, unwind)? {
+                let body = match M::find_mir_or_eval_fn(self, span, instance, args, ret, unwind)? {
                     Some(body) => body,
                     None => return Ok(()),
                 };
diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
index 958239b76e4..31c3a2c7ebc 100644
--- a/src/librustc_mir/transform/const_prop.rs
+++ b/src/librustc_mir/transform/const_prop.rs
@@ -125,6 +125,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine {
 
     fn find_mir_or_eval_fn(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
+        _span: Span,
         _instance: ty::Instance<'tcx>,
         _args: &[OpTy<'tcx>],
         _ret: Option<(PlaceTy<'tcx>, BasicBlock)>,
diff --git a/src/librustc_resolve/build_reduced_graph.rs b/src/librustc_resolve/build_reduced_graph.rs
index 5304aced69f..3521ae0faf5 100644
--- a/src/librustc_resolve/build_reduced_graph.rs
+++ b/src/librustc_resolve/build_reduced_graph.rs
@@ -472,11 +472,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
 
                         self.r
                             .session
-                            .struct_span_warn(item.span, "`$crate` may not be imported")
-                            .note(
-                                "`use $crate;` was erroneously allowed and \
-                                   will become a hard error in a future release",
-                            )
+                            .struct_span_err(item.span, "`$crate` may not be imported")
                             .emit();
                     }
                 }
diff --git a/src/librustc_session/config.rs b/src/librustc_session/config.rs
index 164803d92b1..b6b22e298ca 100644
--- a/src/librustc_session/config.rs
+++ b/src/librustc_session/config.rs
@@ -20,7 +20,7 @@ use rustc_span::source_map::{FileName, FilePathMapping};
 use rustc_span::symbol::{sym, Symbol};
 
 use rustc_errors::emitter::HumanReadableErrorType;
-use rustc_errors::{ColorConfig, FatalError, Handler};
+use rustc_errors::{ColorConfig, FatalError, Handler, HandlerFlags};
 
 use getopts;
 
@@ -597,6 +597,17 @@ impl DebuggingOptions {
     pub fn ui_testing(&self) -> bool {
         self.ui_testing.unwrap_or(false)
     }
+
+    pub fn diagnostic_handler_flags(&self, can_emit_warnings: bool) -> HandlerFlags {
+        HandlerFlags {
+            can_emit_warnings,
+            treat_err_as_bug: self.treat_err_as_bug,
+            dont_buffer_diagnostics: self.dont_buffer_diagnostics,
+            report_delayed_bugs: self.report_delayed_bugs,
+            external_macro_backtrace: self.external_macro_backtrace,
+            deduplicate_diagnostics: self.deduplicate_diagnostics.unwrap_or(true),
+        }
+    }
 }
 
 // The type of entry function, so users can have their own entry functions
diff --git a/src/librustc_session/options.rs b/src/librustc_session/options.rs
index 7e44ef7d4a4..656c1b019b2 100644
--- a/src/librustc_session/options.rs
+++ b/src/librustc_session/options.rs
@@ -946,4 +946,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
     insert_sideeffect: bool = (false, parse_bool, [TRACKED],
         "fix undefined behavior when a thread doesn't eventually make progress \
          (such as entering an empty infinite loop) by inserting llvm.sideeffect"),
+    deduplicate_diagnostics: Option<bool> = (None, parse_opt_bool, [UNTRACKED],
+        "deduplicate identical diagnostics"),
 }
diff --git a/src/librustc_session/session.rs b/src/librustc_session/session.rs
index 28acbd5713f..15911db46fe 100644
--- a/src/librustc_session/session.rs
+++ b/src/librustc_session/session.rs
@@ -941,15 +941,8 @@ pub fn build_session_with_source_map(
         .last()
         .unwrap_or(false);
     let cap_lints_allow = sopts.lint_cap.map_or(false, |cap| cap == lint::Allow);
-
     let can_emit_warnings = !(warnings_allow || cap_lints_allow);
 
-    let treat_err_as_bug = sopts.debugging_opts.treat_err_as_bug;
-    let dont_buffer_diagnostics = sopts.debugging_opts.dont_buffer_diagnostics;
-    let report_delayed_bugs = sopts.debugging_opts.report_delayed_bugs;
-
-    let external_macro_backtrace = sopts.debugging_opts.external_macro_backtrace;
-
     let write_dest = match diagnostics_output {
         DiagnosticOutput::Default => None,
         DiagnosticOutput::Raw(write) => Some(write),
@@ -958,14 +951,7 @@ pub fn build_session_with_source_map(
 
     let diagnostic_handler = rustc_errors::Handler::with_emitter_and_flags(
         emitter,
-        rustc_errors::HandlerFlags {
-            can_emit_warnings,
-            treat_err_as_bug,
-            report_delayed_bugs,
-            dont_buffer_diagnostics,
-            external_macro_backtrace,
-            ..Default::default()
-        },
+        sopts.debugging_opts.diagnostic_handler_flags(can_emit_warnings),
     );
 
     build_session_(sopts, local_crate_source_file, diagnostic_handler, source_map, lint_caps)
diff --git a/src/librustdoc/config.rs b/src/librustdoc/config.rs
index 4a65a9f431a..0af25efc042 100644
--- a/src/librustdoc/config.rs
+++ b/src/librustdoc/config.rs
@@ -269,12 +269,7 @@ impl Options {
         let codegen_options = build_codegen_options(matches, error_format);
         let debugging_options = build_debugging_options(matches, error_format);
 
-        let diag = new_handler(
-            error_format,
-            None,
-            debugging_options.treat_err_as_bug,
-            debugging_options.ui_testing(),
-        );
+        let diag = new_handler(error_format, None, &debugging_options);
 
         // check for deprecated options
         check_deprecated_options(&matches, &diag);
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index cb22039327e..f53f3a75e09 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -35,7 +35,7 @@ use crate::html::render::RenderInfo;
 
 use crate::passes;
 
-pub use rustc::session::config::{CodegenOptions, Input, Options};
+pub use rustc::session::config::{CodegenOptions, DebuggingOptions, Input, Options};
 pub use rustc::session::search_paths::SearchPath;
 
 pub type ExternalPaths = FxHashMap<DefId, (Vec<String>, clean::TypeKind)>;
@@ -170,12 +170,8 @@ impl<'tcx> DocContext<'tcx> {
 pub fn new_handler(
     error_format: ErrorOutputType,
     source_map: Option<Lrc<source_map::SourceMap>>,
-    treat_err_as_bug: Option<usize>,
-    ui_testing: bool,
+    debugging_opts: &DebuggingOptions,
 ) -> errors::Handler {
-    // rustdoc doesn't override (or allow to override) anything from this that is relevant here, so
-    // stick to the defaults
-    let sessopts = Options::default();
     let emitter: Box<dyn Emitter + sync::Send> = match error_format {
         ErrorOutputType::HumanReadable(kind) => {
             let (short, color_config) = kind.unzip();
@@ -184,34 +180,25 @@ pub fn new_handler(
                     color_config,
                     source_map.map(|cm| cm as _),
                     short,
-                    sessopts.debugging_opts.teach,
-                    sessopts.debugging_opts.terminal_width,
+                    debugging_opts.teach,
+                    debugging_opts.terminal_width,
                     false,
                 )
-                .ui_testing(ui_testing),
+                .ui_testing(debugging_opts.ui_testing()),
             )
         }
         ErrorOutputType::Json { pretty, json_rendered } => {
             let source_map = source_map.unwrap_or_else(|| {
-                Lrc::new(source_map::SourceMap::new(sessopts.file_path_mapping()))
+                Lrc::new(source_map::SourceMap::new(source_map::FilePathMapping::empty()))
             });
             Box::new(
                 JsonEmitter::stderr(None, source_map, pretty, json_rendered, false)
-                    .ui_testing(ui_testing),
+                    .ui_testing(debugging_opts.ui_testing()),
             )
         }
     };
 
-    errors::Handler::with_emitter_and_flags(
-        emitter,
-        errors::HandlerFlags {
-            can_emit_warnings: true,
-            treat_err_as_bug,
-            report_delayed_bugs: false,
-            external_macro_backtrace: false,
-            ..Default::default()
-        },
-    )
+    errors::Handler::with_emitter_and_flags(emitter, debugging_opts.diagnostic_handler_flags(true))
 }
 
 pub fn run_core(options: RustdocOptions) -> (clean::Crate, RenderInfo, RenderOptions) {
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index 998b28b8807..c8a32306194 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -445,12 +445,7 @@ fn main_args(args: &[String]) -> i32 {
 }
 
 fn main_options(options: config::Options) -> i32 {
-    let diag = core::new_handler(
-        options.error_format,
-        None,
-        options.debugging_options.treat_err_as_bug,
-        options.debugging_options.ui_testing(),
-    );
+    let diag = core::new_handler(options.error_format, None, &options.debugging_options);
 
     match (options.should_test, options.markdown_input()) {
         (true, true) => return markdown::test(options, &diag),
@@ -463,12 +458,7 @@ fn main_options(options: config::Options) -> i32 {
 
     // need to move these items separately because we lose them by the time the closure is called,
     // but we can't crates the Handler ahead of time because it's not Send
-    let diag_opts = (
-        options.error_format,
-        options.debugging_options.treat_err_as_bug,
-        options.debugging_options.ui_testing(),
-        options.edition,
-    );
+    let diag_opts = (options.error_format, options.edition, options.debugging_options.clone());
     let show_coverage = options.show_coverage;
     rust_input(options, move |out| {
         if show_coverage {
@@ -479,8 +469,8 @@ fn main_options(options: config::Options) -> i32 {
 
         let Output { krate, renderinfo, renderopts } = out;
         info!("going to format");
-        let (error_format, treat_err_as_bug, ui_testing, edition) = diag_opts;
-        let diag = core::new_handler(error_format, None, treat_err_as_bug, ui_testing);
+        let (error_format, edition, debugging_options) = diag_opts;
+        let diag = core::new_handler(error_format, None, &debugging_options);
         match html::render::run(krate, renderopts, renderinfo, &diag, edition) {
             Ok(_) => rustc_driver::EXIT_SUCCESS,
             Err(e) => {
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 4b15c9ba4f3..f90647472c6 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -305,6 +305,7 @@
 #![feature(thread_local)]
 #![feature(toowned_clone_into)]
 #![feature(trace_macros)]
+#![feature(track_caller)]
 #![feature(try_reserve)]
 #![feature(unboxed_closures)]
 #![feature(untagged_unions)]
diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index 11850a1b5fc..18fb0f87688 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -4,6 +4,7 @@
 //! library. Each macro is available for use when linking against the standard
 //! library.
 
+#[cfg(bootstrap)]
 #[doc(include = "../libcore/macros/panic.md")]
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -19,8 +20,21 @@ macro_rules! panic {
         $crate::panic!($msg)
     });
     ($fmt:expr, $($arg:tt)+) => ({
-        $crate::rt::begin_panic_fmt(&$crate::format_args!($fmt, $($arg)+),
-                                    &($crate::file!(), $crate::line!(), $crate::column!()))
+        $crate::rt::begin_panic_fmt(&$crate::format_args!($fmt, $($arg)+))
+    });
+}
+
+#[cfg(not(bootstrap))]
+#[doc(include = "../libcore/macros/panic.md")]
+#[macro_export]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[allow_internal_unstable(libstd_sys_internals)]
+macro_rules! panic {
+    () => ({ $crate::panic!("explicit panic") });
+    ($msg:expr) => ({ $crate::rt::begin_panic($msg) });
+    ($msg:expr,) => ({ $crate::panic!($msg) });
+    ($fmt:expr, $($arg:tt)+) => ({
+        $crate::rt::begin_panic_fmt(&$crate::format_args!($fmt, $($arg)+))
     });
 }
 
diff --git a/src/libstd/panicking.rs b/src/libstd/panicking.rs
index 43230d7a2c7..599ccc809be 100644
--- a/src/libstd/panicking.rs
+++ b/src/libstd/panicking.rs
@@ -313,17 +313,15 @@ pub fn panicking() -> bool {
 #[cold]
 // If panic_immediate_abort, inline the abort call,
 // otherwise avoid inlining because of it is cold path.
+#[cfg_attr(not(feature = "panic_immediate_abort"), track_caller)]
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
 #[cfg_attr(feature = "panic_immediate_abort", inline)]
-pub fn begin_panic_fmt(msg: &fmt::Arguments<'_>, file_line_col: &(&'static str, u32, u32)) -> ! {
+pub fn begin_panic_fmt(msg: &fmt::Arguments<'_>) -> ! {
     if cfg!(feature = "panic_immediate_abort") {
         unsafe { intrinsics::abort() }
     }
 
-    // Just package everything into a `PanicInfo` and continue like libcore panics.
-    let (file, line, col) = *file_line_col;
-    let location = Location::internal_constructor(file, line, col);
-    let info = PanicInfo::internal_constructor(Some(msg), &location);
+    let info = PanicInfo::internal_constructor(Some(msg), Location::caller());
     begin_panic_handler(&info)
 }
 
@@ -356,6 +354,9 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
 
     unsafe impl<'a> BoxMeUp for PanicPayload<'a> {
         fn take_box(&mut self) -> *mut (dyn Any + Send) {
+            // We do two allocations here, unfortunately. But (a) they're required with the current
+            // scheme, and (b) we don't handle panic + OOM properly anyway (see comment in
+            // begin_panic below).
             let contents = mem::take(self.fill());
             Box::into_raw(Box::new(contents))
         }
@@ -365,15 +366,9 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
         }
     }
 
-    // We do two allocations here, unfortunately. But (a) they're
-    // required with the current scheme, and (b) we don't handle
-    // panic + OOM properly anyway (see comment in begin_panic
-    // below).
-
     let loc = info.location().unwrap(); // The current implementation always returns Some
     let msg = info.message().unwrap(); // The current implementation always returns Some
-    let file_line_col = (loc.file(), loc.line(), loc.column());
-    rust_panic_with_hook(&mut PanicPayload::new(msg), info.message(), &file_line_col);
+    rust_panic_with_hook(&mut PanicPayload::new(msg), info.message(), loc);
 }
 
 /// This is the entry point of panicking for the non-format-string variants of
@@ -386,19 +381,13 @@ pub fn begin_panic_handler(info: &PanicInfo<'_>) -> ! {
 // bloat at the call sites as much as possible
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
 #[cold]
-pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
+#[track_caller]
+pub fn begin_panic<M: Any + Send>(msg: M, #[cfg(bootstrap)] _: &(&str, u32, u32)) -> ! {
     if cfg!(feature = "panic_immediate_abort") {
         unsafe { intrinsics::abort() }
     }
 
-    // Note that this should be the only allocation performed in this code path.
-    // Currently this means that panic!() on OOM will invoke this code path,
-    // but then again we're not really ready for panic on OOM anyway. If
-    // we do start doing this, then we should propagate this allocation to
-    // be performed in the parent of this thread instead of the thread that's
-    // panicking.
-
-    rust_panic_with_hook(&mut PanicPayload::new(msg), None, file_line_col);
+    rust_panic_with_hook(&mut PanicPayload::new(msg), None, Location::caller());
 
     struct PanicPayload<A> {
         inner: Option<A>,
@@ -412,6 +401,11 @@ pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u3
 
     unsafe impl<A: Send + 'static> BoxMeUp for PanicPayload<A> {
         fn take_box(&mut self) -> *mut (dyn Any + Send) {
+            // Note that this should be the only allocation performed in this code path. Currently
+            // this means that panic!() on OOM will invoke this code path, but then again we're not
+            // really ready for panic on OOM anyway. If we do start doing this, then we should
+            // propagate this allocation to be performed in the parent of this thread instead of the
+            // thread that's panicking.
             let data = match self.inner.take() {
                 Some(a) => Box::new(a) as Box<dyn Any + Send>,
                 None => process::abort(),
@@ -436,10 +430,8 @@ pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u3
 fn rust_panic_with_hook(
     payload: &mut dyn BoxMeUp,
     message: Option<&fmt::Arguments<'_>>,
-    file_line_col: &(&str, u32, u32),
+    location: &Location<'_>,
 ) -> ! {
-    let (file, line, col) = *file_line_col;
-
     let panics = update_panic_count(1);
 
     // If this is the third nested call (e.g., panics == 2, this is 0-indexed),
@@ -456,8 +448,7 @@ fn rust_panic_with_hook(
     }
 
     unsafe {
-        let location = Location::internal_constructor(file, line, col);
-        let mut info = PanicInfo::internal_constructor(message, &location);
+        let mut info = PanicInfo::internal_constructor(message, location);
         HOOK_LOCK.read();
         match HOOK {
             // Some platforms (like wasm) know that printing to stderr won't ever actually
diff --git a/src/test/mir-opt/retain-never-const.rs b/src/test/mir-opt/retain-never-const.rs
index 04394dcdf13..8e9bae8569f 100644
--- a/src/test/mir-opt/retain-never-const.rs
+++ b/src/test/mir-opt/retain-never-const.rs
@@ -6,6 +6,7 @@
 
 #![feature(const_panic)]
 #![feature(never_type)]
+#![warn(const_err)]
 
 struct PrintName<T>(T);
 
diff --git a/src/test/ui/consts/miri_unleashed/mutable_const2.stderr b/src/test/ui/consts/miri_unleashed/mutable_const2.stderr
index 2212b7d75d2..3493b7c54c4 100644
--- a/src/test/ui/consts/miri_unleashed/mutable_const2.stderr
+++ b/src/test/ui/consts/miri_unleashed/mutable_const2.stderr
@@ -10,7 +10,7 @@ error: internal compiler error: mutable allocation in constant
 LL | const MUTABLE_BEHIND_RAW: *mut i32 = &UnsafeCell::new(42) as *const _ as *mut _;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:345:17
+thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:347:17
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
 
 error: internal compiler error: unexpected panic
diff --git a/src/test/ui/deduplicate-diagnostics.deduplicate.stderr b/src/test/ui/deduplicate-diagnostics.deduplicate.stderr
new file mode 100644
index 00000000000..1acfce50622
--- /dev/null
+++ b/src/test/ui/deduplicate-diagnostics.deduplicate.stderr
@@ -0,0 +1,8 @@
+error: cannot find derive macro `Unresolved` in this scope
+  --> $DIR/deduplicate-diagnostics.rs:4:10
+   |
+LL | #[derive(Unresolved)]
+   |          ^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/deduplicate-diagnostics.duplicate.stderr b/src/test/ui/deduplicate-diagnostics.duplicate.stderr
new file mode 100644
index 00000000000..325da3b5d91
--- /dev/null
+++ b/src/test/ui/deduplicate-diagnostics.duplicate.stderr
@@ -0,0 +1,14 @@
+error: cannot find derive macro `Unresolved` in this scope
+  --> $DIR/deduplicate-diagnostics.rs:4:10
+   |
+LL | #[derive(Unresolved)]
+   |          ^^^^^^^^^^
+
+error: cannot find derive macro `Unresolved` in this scope
+  --> $DIR/deduplicate-diagnostics.rs:4:10
+   |
+LL | #[derive(Unresolved)]
+   |          ^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/deduplicate-diagnostics.rs b/src/test/ui/deduplicate-diagnostics.rs
new file mode 100644
index 00000000000..4a1f503d757
--- /dev/null
+++ b/src/test/ui/deduplicate-diagnostics.rs
@@ -0,0 +1,8 @@
+// revisions: duplicate deduplicate
+//[duplicate] compile-flags: -Z deduplicate-diagnostics=no
+
+#[derive(Unresolved)] //~ ERROR cannot find derive macro `Unresolved` in this scope
+                      //[duplicate]~| ERROR cannot find derive macro `Unresolved` in this scope
+struct S;
+
+fn main() {}
diff --git a/src/test/ui/dollar-crate/dollar-crate-is-keyword.rs b/src/test/ui/dollar-crate/dollar-crate-is-keyword.rs
index 6deaeb81179..d625163dc7e 100644
--- a/src/test/ui/dollar-crate/dollar-crate-is-keyword.rs
+++ b/src/test/ui/dollar-crate/dollar-crate-is-keyword.rs
@@ -6,10 +6,9 @@ macro_rules! m {
             struct $crate {} //~ ERROR expected identifier, found reserved identifier `$crate`
         }
 
-        use $crate; // OK
-                    //~^ WARN `$crate` may not be imported
+        use $crate; //~ ERROR `$crate` may not be imported
         use $crate as $crate; //~ ERROR expected identifier, found reserved identifier `$crate`
-                              //~^ WARN `$crate` may not be imported
+        //~^ ERROR `$crate` may not be imported
     }
 }
 
diff --git a/src/test/ui/dollar-crate/dollar-crate-is-keyword.stderr b/src/test/ui/dollar-crate/dollar-crate-is-keyword.stderr
index 5d4f39086ce..f5a5f13f912 100644
--- a/src/test/ui/dollar-crate/dollar-crate-is-keyword.stderr
+++ b/src/test/ui/dollar-crate/dollar-crate-is-keyword.stderr
@@ -8,7 +8,7 @@ LL | m!();
    | ----- in this macro invocation
 
 error: expected identifier, found reserved identifier `$crate`
-  --> $DIR/dollar-crate-is-keyword.rs:11:23
+  --> $DIR/dollar-crate-is-keyword.rs:10:23
    |
 LL |         use $crate as $crate;
    |                       ^^^^^^ expected identifier, found reserved identifier
@@ -16,27 +16,23 @@ LL |         use $crate as $crate;
 LL | m!();
    | ----- in this macro invocation
 
-warning: `$crate` may not be imported
+error: `$crate` may not be imported
   --> $DIR/dollar-crate-is-keyword.rs:9:9
    |
-LL |         use $crate; // OK
+LL |         use $crate;
    |         ^^^^^^^^^^^
 ...
 LL | m!();
    | ----- in this macro invocation
-   |
-   = note: `use $crate;` was erroneously allowed and will become a hard error in a future release
 
-warning: `$crate` may not be imported
-  --> $DIR/dollar-crate-is-keyword.rs:11:9
+error: `$crate` may not be imported
+  --> $DIR/dollar-crate-is-keyword.rs:10:9
    |
 LL |         use $crate as $crate;
    |         ^^^^^^^^^^^^^^^^^^^^^
 ...
 LL | m!();
    | ----- in this macro invocation
-   |
-   = note: `use $crate;` was erroneously allowed and will become a hard error in a future release
 
-error: aborting due to 2 previous errors
+error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/extern/issue-64655-allow-unwind-when-calling-panic-directly.rs b/src/test/ui/extern/issue-64655-allow-unwind-when-calling-panic-directly.rs
index 8727c9d1ca6..74c6e501c91 100644
--- a/src/test/ui/extern/issue-64655-allow-unwind-when-calling-panic-directly.rs
+++ b/src/test/ui/extern/issue-64655-allow-unwind-when-calling-panic-directly.rs
@@ -22,7 +22,7 @@
 //[thin]compile-flags: -C lto=thin
 //[fat]compile-flags: -C lto=fat
 
-#![feature(core_panic, panic_internals)]
+#![feature(core_panic)]
 
 // (For some reason, reproducing the LTO issue requires pulling in std
 // explicitly this way.)
@@ -50,9 +50,7 @@ fn main() {
         }
 
         let _guard = Droppable;
-        let s = "issue-64655-allow-unwind-when-calling-panic-directly.rs";
-        let location = core::panic::Location::internal_constructor(s, 17, 4);
-        core::panicking::panic("???", &location);
+        core::panicking::panic("???");
     });
 
     let wait = handle.join();
diff --git a/src/test/ui/imports/import-crate-var.rs b/src/test/ui/imports/import-crate-var.rs
index b9d146d3735..aac5a15d3e6 100644
--- a/src/test/ui/imports/import-crate-var.rs
+++ b/src/test/ui/imports/import-crate-var.rs
@@ -1,10 +1,8 @@
-// check-pass
 // aux-build:import_crate_var.rs
 
 #[macro_use] extern crate import_crate_var;
 
 fn main() {
     m!();
-    //~^ WARN `$crate` may not be imported
-    //~| NOTE `use $crate;` was erroneously allowed and will become a hard error
+    //~^ ERROR `$crate` may not be imported
 }
diff --git a/src/test/ui/imports/import-crate-var.stderr b/src/test/ui/imports/import-crate-var.stderr
index 2f8c845156a..85f15ad4648 100644
--- a/src/test/ui/imports/import-crate-var.stderr
+++ b/src/test/ui/imports/import-crate-var.stderr
@@ -1,9 +1,10 @@
-warning: `$crate` may not be imported
-  --> $DIR/import-crate-var.rs:7:5
+error: `$crate` may not be imported
+  --> $DIR/import-crate-var.rs:6:5
    |
 LL |     m!();
    |     ^^^^^
    |
-   = note: `use $crate;` was erroneously allowed and will become a hard error in a future release
-   = note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+
+error: aborting due to previous error
 
diff --git a/src/test/ui/rfc-2091-track-caller/caller-location-intrinsic.rs b/src/test/ui/rfc-2091-track-caller/caller-location-intrinsic.rs
index 0a79aea376f..090e912c1d0 100644
--- a/src/test/ui/rfc-2091-track-caller/caller-location-intrinsic.rs
+++ b/src/test/ui/rfc-2091-track-caller/caller-location-intrinsic.rs
@@ -4,16 +4,16 @@
 
 #[inline(never)]
 #[track_caller]
-fn defeat_const_prop() -> &'static core::panic::Location<'static> {
+fn codegen_caller_loc() -> &'static core::panic::Location<'static> {
     core::panic::Location::caller()
 }
 
 macro_rules! caller_location_from_macro {
-    () => (defeat_const_prop());
+    () => (codegen_caller_loc());
 }
 
 fn main() {
-    let loc = defeat_const_prop();
+    let loc = codegen_caller_loc();
     assert_eq!(loc.file(), file!());
     assert_eq!(loc.line(), 16);
     assert_eq!(loc.column(), 15);
diff --git a/src/test/ui/rfc-2091-track-caller/diverging-caller-location.rs b/src/test/ui/rfc-2091-track-caller/diverging-caller-location.rs
new file mode 100644
index 00000000000..1fb75ef35ff
--- /dev/null
+++ b/src/test/ui/rfc-2091-track-caller/diverging-caller-location.rs
@@ -0,0 +1,19 @@
+// run-fail
+
+//! This test ensures that `#[track_caller]` can be applied directly to diverging functions, as
+//! the tracking issue says: https://github.com/rust-lang/rust/issues/47809#issue-292138490.
+//! Because the annotated function must diverge and a panic keeps that faster than an infinite loop,
+//! we don't inspect the location returned -- it would be difficult to distinguish between the
+//! explicit panic and a failed assertion. That it compiles and runs is enough for this one.
+
+#![feature(track_caller)]
+
+#[track_caller]
+fn doesnt_return() -> ! {
+    let _location = core::panic::Location::caller();
+    panic!("huzzah");
+}
+
+fn main() {
+    doesnt_return();
+}
diff --git a/src/test/ui/rfc-2091-track-caller/track-caller-attribute.rs b/src/test/ui/rfc-2091-track-caller/track-caller-attribute.rs
index 8436ee510a5..76a380ed3e3 100644
--- a/src/test/ui/rfc-2091-track-caller/track-caller-attribute.rs
+++ b/src/test/ui/rfc-2091-track-caller/track-caller-attribute.rs
@@ -1,6 +1,6 @@
 // run-pass
 
-#![feature(const_fn, track_caller)]
+#![feature(track_caller)]
 
 use std::panic::Location;