Auto merge of #79903 - Mark-Simulacrum:beta-next, r=Mark-Simulacrum

[beta] backports

* Revert #77534 fixing #77713 on beta, principled fix landed on master
* fix soundness issue in `make_contiguous` #79814
* Fix exhaustiveness in case a byte string literal is used at slice type #79072

Author: bors

compiler/rustc_lint/src/levels.rs

@@ -10,7 +10,6 @@ use rustc_hir as hir;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc_hir::{intravisit, HirId};
 use rustc_middle::hir::map::Map;
-use rustc_middle::lint::LevelSource;
 use rustc_middle::lint::LintDiagnosticBuilder;
 use rustc_middle::lint::{struct_lint_level, LintLevelMap, LintLevelSets, LintSet, LintSource};
 use rustc_middle::ty::query::Providers;
@@ -97,44 +96,6 @@ impl<'s> LintLevelsBuilder<'s> {
         self.sets.list.push(LintSet::CommandLine { specs });
     }
 
-    /// Attempts to insert the `id` to `level_src` map entry. If unsuccessful
-    /// (e.g. if a forbid was already inserted on the same scope), then emits a
-    /// diagnostic with no change to `specs`.
-    fn insert_spec(
-        &mut self,
-        specs: &mut FxHashMap<LintId, LevelSource>,
-        id: LintId,
-        (level, src): LevelSource,
-    ) {
-        if let Some((old_level, old_src)) = specs.get(&id) {
-            if old_level == &Level::Forbid && level != Level::Forbid {
-                let mut diag_builder = struct_span_err!(
-                    self.sess,
-                    src.span(),
-                    E0453,
-                    "{}({}) incompatible with previous forbid in same scope",
-                    level.as_str(),
-                    src.name(),
-                );
-                match *old_src {
-                    LintSource::Default => {}
-                    LintSource::Node(_, forbid_source_span, reason) => {
-                        diag_builder.span_label(forbid_source_span, "`forbid` level set here");
-                        if let Some(rationale) = reason {
-                            diag_builder.note(&rationale.as_str());
-                        }
-                    }
-                    LintSource::CommandLine(_, _) => {
-                        diag_builder.note("`forbid` lint level was set on command line");
-                    }
-                }
-                diag_builder.emit();
-                return;
-            }
-        }
-        specs.insert(id, (level, src));
-    }
-
     /// Pushes a list of AST lint attributes onto this context.
     ///
     /// This function will return a `BuilderPush` object which should be passed
@@ -149,7 +110,7 @@ impl<'s> LintLevelsBuilder<'s> {
     ///   `#[allow]`
     ///
     /// Don't forget to call `pop`!
-    pub(crate) fn push(
+    pub fn push(
         &mut self,
         attrs: &[ast::Attribute],
         store: &LintStore,
@@ -261,7 +222,7 @@ impl<'s> LintLevelsBuilder<'s> {
                         let src = LintSource::Node(name, li.span(), reason);
                         for &id in ids {
                             self.check_gated_lint(id, attr.span);
-                            self.insert_spec(&mut specs, id, (level, src));
+                            specs.insert(id, (level, src));
                         }
                     }
 
@@ -275,7 +236,7 @@ impl<'s> LintLevelsBuilder<'s> {
                                     reason,
                                 );
                                 for id in ids {
-                                    self.insert_spec(&mut specs, *id, (level, src));
+                                    specs.insert(*id, (level, src));
                                 }
                             }
                             Err((Some(ids), new_lint_name)) => {
@@ -312,7 +273,7 @@ impl<'s> LintLevelsBuilder<'s> {
                                     reason,
                                 );
                                 for id in ids {
-                                    self.insert_spec(&mut specs, *id, (level, src));
+                                    specs.insert(*id, (level, src));
                                 }
                             }
                             Err((None, _)) => {

compiler/rustc_middle/src/lint.rs

@@ -9,7 +9,7 @@ use rustc_session::lint::{builtin, Level, Lint, LintId};
 use rustc_session::{DiagnosticMessageId, Session};
 use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::{DesugaringKind, ExpnKind, MultiSpan};
-use rustc_span::{symbol, Span, Symbol, DUMMY_SP};
+use rustc_span::{Span, Symbol};
 
 /// How a lint level was set.
 #[derive(Clone, Copy, PartialEq, Eq, HashStable)]
@@ -27,24 +27,6 @@ pub enum LintSource {
     CommandLine(Symbol, Level),
 }
 
-impl LintSource {
-    pub fn name(&self) -> Symbol {
-        match *self {
-            LintSource::Default => symbol::kw::Default,
-            LintSource::Node(name, _, _) => name,
-            LintSource::CommandLine(name, _) => name,
-        }
-    }
-
-    pub fn span(&self) -> Span {
-        match *self {
-            LintSource::Default => DUMMY_SP,
-            LintSource::Node(_, span, _) => span,
-            LintSource::CommandLine(_, _) => DUMMY_SP,
-        }
-    }
-}
-
 pub type LevelSource = (Level, LintSource);
 
 pub struct LintLevelSets {

compiler/rustc_middle/src/ty/context.rs

@@ -418,6 +418,12 @@ pub struct TypeckResults<'tcx> {
     /// Stores the type, expression, span and optional scope span of all types
     /// that are live across the yield of this generator (if a generator).
     pub generator_interior_types: Vec<GeneratorInteriorTypeCause<'tcx>>,
+
+    /// We sometimes treat byte string literals (which are of type `&[u8; N]`)
+    /// as `&[u8]`, depending on the pattern  in which they are used.
+    /// This hashset records all instances where we behave
+    /// like this to allow `const_to_pat` to reliably handle this situation.
+    pub treat_byte_string_as_slice: ItemLocalSet,
 }
 
 impl<'tcx> TypeckResults<'tcx> {
@@ -443,6 +449,7 @@ impl<'tcx> TypeckResults<'tcx> {
             concrete_opaque_types: Default::default(),
             closure_captures: Default::default(),
             generator_interior_types: Default::default(),
+            treat_byte_string_as_slice: Default::default(),
         }
     }
 
@@ -677,6 +684,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for TypeckResults<'tcx> {
             ref concrete_opaque_types,
             ref closure_captures,
             ref generator_interior_types,
+            ref treat_byte_string_as_slice,
         } = *self;
 
         hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
@@ -710,6 +718,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for TypeckResults<'tcx> {
             concrete_opaque_types.hash_stable(hcx, hasher);
             closure_captures.hash_stable(hcx, hasher);
             generator_interior_types.hash_stable(hcx, hasher);
+            treat_byte_string_as_slice.hash_stable(hcx, hasher);
         })
     }
 }

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -18,22 +18,20 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
     /// Converts an evaluated constant to a pattern (if possible).
     /// This means aggregate values (like structs and enums) are converted
     /// to a pattern that matches the value (as if you'd compared via structural equality).
+    #[instrument(skip(self))]
     pub(super) fn const_to_pat(
         &self,
         cv: &'tcx ty::Const<'tcx>,
         id: hir::HirId,
         span: Span,
         mir_structural_match_violation: bool,
     ) -> Pat<'tcx> {
-        debug!("const_to_pat: cv={:#?} id={:?}", cv, id);
-        debug!("const_to_pat: cv.ty={:?} span={:?}", cv.ty, span);
-
         let pat = self.tcx.infer_ctxt().enter(|infcx| {
             let mut convert = ConstToPat::new(self, id, span, infcx);
             convert.to_pat(cv, mir_structural_match_violation)
         });
 
-        debug!("const_to_pat: pat={:?}", pat);
+        debug!(?pat);
         pat
     }
 }
@@ -61,6 +59,8 @@ struct ConstToPat<'a, 'tcx> {
     infcx: InferCtxt<'a, 'tcx>,
 
     include_lint_checks: bool,
+
+    treat_byte_string_as_slice: bool,
 }
 
 mod fallback_to_const_ref {
@@ -88,6 +88,7 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
         span: Span,
         infcx: InferCtxt<'a, 'tcx>,
     ) -> Self {
+        trace!(?pat_ctxt.typeck_results.hir_owner);
         ConstToPat {
             id,
             span,
@@ -97,6 +98,10 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
             saw_const_match_error: Cell::new(false),
             saw_const_match_lint: Cell::new(false),
             behind_reference: Cell::new(false),
+            treat_byte_string_as_slice: pat_ctxt
+                .typeck_results
+                .treat_byte_string_as_slice
+                .contains(&id.local_id),
         }
     }
 
@@ -153,6 +158,7 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
         cv: &'tcx ty::Const<'tcx>,
         mir_structural_match_violation: bool,
     ) -> Pat<'tcx> {
+        trace!(self.treat_byte_string_as_slice);
         // This method is just a wrapper handling a validity check; the heavy lifting is
         // performed by the recursive `recur` method, which is not meant to be
         // invoked except by this method.
@@ -384,7 +390,7 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                     }
                     PatKind::Wild
                 }
-                // `&str` and `&[u8]` are represented as `ConstValue::Slice`, let's keep using this
+                // `&str` is represented as `ConstValue::Slice`, let's keep using this
                 // optimization for now.
                 ty::Str => PatKind::Constant { value: cv },
                 // `b"foo"` produces a `&[u8; 3]`, but you can't use constants of array type when
@@ -393,11 +399,33 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                 // as slices. This means we turn `&[T; N]` constants into slice patterns, which
                 // has no negative effects on pattern matching, even if we're actually matching on
                 // arrays.
-                ty::Array(..) |
+                ty::Array(..) if !self.treat_byte_string_as_slice => {
+                    let old = self.behind_reference.replace(true);
+                    let array = tcx.deref_const(self.param_env.and(cv));
+                    let val = PatKind::Deref {
+                        subpattern: Pat {
+                            kind: Box::new(PatKind::Array {
+                                prefix: tcx
+                                    .destructure_const(param_env.and(array))
+                                    .fields
+                                    .iter()
+                                    .map(|val| self.recur(val, false))
+                                    .collect::<Result<_, _>>()?,
+                                slice: None,
+                                suffix: vec![],
+                            }),
+                            span,
+                            ty: pointee_ty,
+                        },
+                    };
+                    self.behind_reference.set(old);
+                    val
+                }
+                ty::Array(elem_ty, _) |
                 // Cannot merge this with the catch all branch below, because the `const_deref`
                 // changes the type from slice to array, we need to keep the original type in the
                 // pattern.
-                ty::Slice(..) => {
+                ty::Slice(elem_ty) => {
                     let old = self.behind_reference.replace(true);
                     let array = tcx.deref_const(self.param_env.and(cv));
                     let val = PatKind::Deref {
@@ -413,7 +441,7 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                                 suffix: vec![],
                             }),
                             span,
-                            ty: pointee_ty,
+                            ty: tcx.mk_slice(elem_ty),
                         },
                     };
                     self.behind_reference.set(old);

compiler/rustc_typeck/src/check/pat.rs

@@ -149,15 +149,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ///
     /// Outside of this module, `check_pat_top` should always be used.
     /// Conversely, inside this module, `check_pat_top` should never be used.
+    #[instrument(skip(self, ti))]
     fn check_pat(
         &self,
         pat: &'tcx Pat<'tcx>,
         expected: Ty<'tcx>,
         def_bm: BindingMode,
         ti: TopInfo<'tcx>,
     ) {
-        debug!("check_pat(pat={:?},expected={:?},def_bm={:?})", pat, expected, def_bm);
-
         let path_res = match &pat.kind {
             PatKind::Path(qpath) => Some(self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span)),
             _ => None,
@@ -398,6 +397,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if let ty::Ref(_, inner_ty, _) = expected.kind() {
                 if matches!(inner_ty.kind(), ty::Slice(_)) {
                     let tcx = self.tcx;
+                    trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
+                    self.typeck_results
+                        .borrow_mut()
+                        .treat_byte_string_as_slice
+                        .insert(lt.hir_id.local_id);
                     pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
                 }
             }

compiler/rustc_typeck/src/check/writeback.rs

@@ -70,6 +70,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         debug!("used_trait_imports({:?}) = {:?}", item_def_id, used_trait_imports);
         wbcx.typeck_results.used_trait_imports = used_trait_imports;
 
+        wbcx.typeck_results.treat_byte_string_as_slice =
+            mem::take(&mut self.typeck_results.borrow_mut().treat_byte_string_as_slice);
+
         wbcx.typeck_results.closure_captures =
             mem::take(&mut self.typeck_results.borrow_mut().closure_captures);
 

library/alloc/src/collections/vec_deque.rs

@@ -1507,6 +1507,8 @@ impl<T> VecDeque<T> {
 
     #[inline]
     fn is_contiguous(&self) -> bool {
+        // FIXME: Should we consider `head == 0` to mean
+        // that `self` is contiguous?
         self.tail <= self.head
     }
 
@@ -2236,7 +2238,7 @@ impl<T> VecDeque<T> {
         if self.is_contiguous() {
             let tail = self.tail;
             let head = self.head;
-            return unsafe { &mut self.buffer_as_mut_slice()[tail..head] };
+            return unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 };
         }
 
         let buf = self.buf.ptr();
@@ -2262,7 +2264,13 @@ impl<T> VecDeque<T> {
                 self.tail = 0;
                 self.head = len;
             }
-        } else if free >= self.head {
+        } else if free > self.head {
+            // FIXME: We currently do not consider ....ABCDEFGH
+            // to be contiguous because `head` would be `0` in this
+            // case. While we probably want to change this it
+            // isn't trivial as a few places expect `is_contiguous`
+            // to mean that we can just slice using `buf[tail..head]`.
+
             // there is enough free space to copy the head in one go,
             // this means that we first shift the tail forwards, and then
             // copy the head to the correct position.
@@ -2276,7 +2284,7 @@ impl<T> VecDeque<T> {
                 // ...ABCDEFGH.
 
                 self.tail = self.head;
-                self.head = self.tail + len;
+                self.head = self.wrap_add(self.tail, len);
             }
         } else {
             // free is smaller than both head and tail,
@@ -2316,7 +2324,7 @@ impl<T> VecDeque<T> {
 
         let tail = self.tail;
         let head = self.head;
-        unsafe { &mut self.buffer_as_mut_slice()[tail..head] }
+        unsafe { RingSlices::ring_slices(self.buffer_as_mut_slice(), head, tail).0 }
     }
 
     /// Rotates the double-ended queue `mid` places to the left.
@@ -3282,7 +3290,7 @@ impl<T> From<VecDeque<T>> for Vec<T> {
             let len = other.len();
             let cap = other.cap();
 
-            if other.head != 0 {
+            if other.tail != 0 {
                 ptr::copy(buf.add(other.tail), buf, len);
             }
             Vec::from_raw_parts(buf, len, cap)

library/alloc/src/collections/vec_deque/tests.rs

@@ -210,6 +210,20 @@ fn make_contiguous_small_free() {
     );
 }
 
+#[test]
+fn make_contiguous_head_to_end() {
+    let mut dq = VecDeque::with_capacity(3);
+    dq.push_front('B');
+    dq.push_front('A');
+    dq.push_back('C');
+    dq.make_contiguous();
+    let expected_tail = 0;
+    let expected_head = 3;
+    assert_eq!(expected_tail, dq.tail);
+    assert_eq!(expected_head, dq.head);
+    assert_eq!((&['A', 'B', 'C'] as &[_], &[] as &[_]), dq.as_slices());
+}
+
 #[test]
 fn test_remove() {
     // This test checks that every single combination of tail position, length, and