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

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!(),

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)>,
 }
@@ -370,23 +370,33 @@ 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()
     }
 
     fn as_header(&self) -> &NodeHeader<K, V> {
         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) {

src/libcore/macros/mod.rs

@@ -1,27 +1,21 @@
 #[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)
     );
     ($fmt:expr, $($arg:tt)+) => (
         $crate::panicking::panic_fmt(
             $crate::format_args!($fmt, $($arg)+),
-            $crate::intrinsics::caller_location(),
+            $crate::panic::Location::caller(),
         )
     );
 }

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]

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;

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)],
         )
     }
 

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)

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);

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,