Rollup of 6 pull requests

.mailmap

@@ -49,6 +49,7 @@ Carol (Nichols || Goulding) <carol.nichols@gmail.com> <193874+carols10cents@user
 Carol (Nichols || Goulding) <carol.nichols@gmail.com> <carol.nichols@gmail.com>
 Carol (Nichols || Goulding) <carol.nichols@gmail.com> <cnichols@thinkthroughmath.com>
 Carol Willing <carolcode@willingconsulting.com>
+Charles Lew <crlf0710@gmail.com> CrLF0710 <crlf0710@gmail.com>
 Chris C Cerami <chrisccerami@users.noreply.github.com> Chris C Cerami <chrisccerami@gmail.com>
 Chris Pressey <cpressey@gmail.com>
 Chris Thorn <chris@thorn.co> Chris Thorn <thorn@thoughtbot.com>

src/librustc_attr/build.rs

@@ -1,4 +1,5 @@
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
-    println!("cargo:rerun-if-env-changed=CFG_VERSION");
+    println!("cargo:rerun-if-env-changed=CFG_RELEASE");
+    println!("cargo:rerun-if-env-changed=CFG_RELEASE_CHANNEL");
 }

src/librustc_attr/builtin.rs

@@ -652,9 +652,12 @@ pub fn eval_condition(
                     return false;
                 }
             };
-            let version = Version::parse(env!("CFG_VERSION")).unwrap();
+            let channel = env!("CFG_RELEASE_CHANNEL");
+            let nightly = channel == "nightly" || channel == "dev";
+            let rustc_version = Version::parse(env!("CFG_RELEASE")).unwrap();
 
-            version >= min_version
+            // See https://github.com/rust-lang/rust/issues/64796#issuecomment-625474439 for details
+            if nightly { rustc_version > min_version } else { rustc_version >= min_version }
         }
         ast::MetaItemKind::List(ref mis) => {
             for mi in mis.iter() {

src/librustc_hir/hir.rs

@@ -1291,6 +1291,53 @@ impl BodyOwnerKind {
     }
 }
 
+/// The kind of an item that requires const-checking.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum ConstContext {
+    /// A `const fn`.
+    ConstFn,
+
+    /// A `static` or `static mut`.
+    Static(Mutability),
+
+    /// A `const`, associated `const`, or other const context.
+    ///
+    /// Other contexts include:
+    /// - Array length expressions
+    /// - Enum discriminants
+    /// - Const generics
+    ///
+    /// For the most part, other contexts are treated just like a regular `const`, so they are
+    /// lumped into the same category.
+    Const,
+}
+
+impl ConstContext {
+    /// A description of this const context that can appear between backticks in an error message.
+    ///
+    /// E.g. `const` or `static mut`.
+    pub fn keyword_name(self) -> &'static str {
+        match self {
+            Self::Const => "const",
+            Self::Static(Mutability::Not) => "static",
+            Self::Static(Mutability::Mut) => "static mut",
+            Self::ConstFn => "const fn",
+        }
+    }
+}
+
+/// A colloquial, trivially pluralizable description of this const context for use in error
+/// messages.
+impl fmt::Display for ConstContext {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Self::Const => write!(f, "constant"),
+            Self::Static(_) => write!(f, "static"),
+            Self::ConstFn => write!(f, "constant function"),
+        }
+    }
+}
+
 /// A literal.
 pub type Lit = Spanned<LitKind>;
 

src/librustc_middle/hir/map/mod.rs

@@ -408,6 +408,9 @@ impl<'hir> Map<'hir> {
         })
     }
 
+    /// Returns the `BodyOwnerKind` of this `LocalDefId`.
+    ///
+    /// Panics if `LocalDefId` does not have an associated body.
     pub fn body_owner_kind(&self, id: HirId) -> BodyOwnerKind {
         match self.get(id) {
             Node::Item(&Item { kind: ItemKind::Const(..), .. })
@@ -424,6 +427,23 @@ impl<'hir> Map<'hir> {
         }
     }
 
+    /// Returns the `ConstContext` of the body associated with this `LocalDefId`.
+    ///
+    /// Panics if `LocalDefId` does not have an associated body.
+    pub fn body_const_context(&self, did: LocalDefId) -> Option<ConstContext> {
+        let hir_id = self.local_def_id_to_hir_id(did);
+        let ccx = match self.body_owner_kind(hir_id) {
+            BodyOwnerKind::Const => ConstContext::Const,
+            BodyOwnerKind::Static(mt) => ConstContext::Static(mt),
+
+            BodyOwnerKind::Fn if self.tcx.is_constructor(did.to_def_id()) => return None,
+            BodyOwnerKind::Fn if self.tcx.is_const_fn_raw(did.to_def_id()) => ConstContext::ConstFn,
+            BodyOwnerKind::Fn | BodyOwnerKind::Closure => return None,
+        };
+
+        Some(ccx)
+    }
+
     pub fn ty_param_owner(&self, id: HirId) -> HirId {
         match self.get(id) {
             Node::Item(&Item { kind: ItemKind::Trait(..) | ItemKind::TraitAlias(..), .. }) => id,

src/librustc_mir/borrow_check/def_use.rs

@@ -0,0 +1,78 @@
+use rustc_middle::mir::visit::{
+    MutatingUseContext, NonMutatingUseContext, NonUseContext, PlaceContext,
+};
+
+#[derive(Eq, PartialEq, Clone)]
+pub enum DefUse {
+    Def,
+    Use,
+    Drop,
+}
+
+pub fn categorize(context: PlaceContext) -> Option<DefUse> {
+    match context {
+        ///////////////////////////////////////////////////////////////////////////
+        // DEFS
+
+        PlaceContext::MutatingUse(MutatingUseContext::Store) |
+
+        // This is potentially both a def and a use...
+        PlaceContext::MutatingUse(MutatingUseContext::AsmOutput) |
+
+        // We let Call define the result in both the success and
+        // unwind cases. This is not really correct, however it
+        // does not seem to be observable due to the way that we
+        // generate MIR. To do things properly, we would apply
+        // the def in call only to the input from the success
+        // path and not the unwind path. -nmatsakis
+        PlaceContext::MutatingUse(MutatingUseContext::Call) |
+        PlaceContext::MutatingUse(MutatingUseContext::Yield) |
+
+        // Storage live and storage dead aren't proper defines, but we can ignore
+        // values that come before them.
+        PlaceContext::NonUse(NonUseContext::StorageLive) |
+        PlaceContext::NonUse(NonUseContext::StorageDead) => Some(DefUse::Def),
+
+        ///////////////////////////////////////////////////////////////////////////
+        // REGULAR USES
+        //
+        // These are uses that occur *outside* of a drop. For the
+        // purposes of NLL, these are special in that **all** the
+        // lifetimes appearing in the variable must be live for each regular use.
+
+        PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection) |
+        PlaceContext::MutatingUse(MutatingUseContext::Projection) |
+
+        // Borrows only consider their local used at the point of the borrow.
+        // This won't affect the results since we use this analysis for generators
+        // and we only care about the result at suspension points. Borrows cannot
+        // cross suspension points so this behavior is unproblematic.
+        PlaceContext::MutatingUse(MutatingUseContext::Borrow) |
+        PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow) |
+        PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow) |
+        PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow) |
+
+        PlaceContext::MutatingUse(MutatingUseContext::AddressOf) |
+        PlaceContext::NonMutatingUse(NonMutatingUseContext::AddressOf) |
+        PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect) |
+        PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) |
+        PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) |
+        PlaceContext::NonUse(NonUseContext::AscribeUserTy) |
+        PlaceContext::MutatingUse(MutatingUseContext::Retag) =>
+            Some(DefUse::Use),
+
+        ///////////////////////////////////////////////////////////////////////////
+        // DROP USES
+        //
+        // These are uses that occur in a DROP (a MIR drop, not a
+        // call to `std::mem::drop()`). For the purposes of NLL,
+        // uses in drop are special because `#[may_dangle]`
+        // attributes can affect whether lifetimes must be live.
+
+        PlaceContext::MutatingUse(MutatingUseContext::Drop) =>
+            Some(DefUse::Drop),
+
+        // Debug info is neither def nor use.
+        PlaceContext::NonUse(NonUseContext::VarDebugInfo) => None,
+    }
+}

src/librustc_mir/borrow_check/diagnostics/find_use.rs

@@ -2,10 +2,10 @@ use std::collections::VecDeque;
 use std::rc::Rc;
 
 use crate::borrow_check::{
+    def_use::{self, DefUse},
     nll::ToRegionVid,
     region_infer::{Cause, RegionInferenceContext},
 };
-use crate::util::liveness::{self, DefUse};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::mir::visit::{MirVisitable, PlaceContext, Visitor};
 use rustc_middle::mir::{Body, Local, Location};
@@ -117,7 +117,7 @@ impl<'cx, 'tcx> Visitor<'tcx> for DefUseVisitor<'cx, 'tcx> {
         });
 
         if found_it {
-            self.def_use_result = match liveness::categorize(context) {
+            self.def_use_result = match def_use::categorize(context) {
                 Some(DefUse::Def) => Some(DefUseResult::Def),
                 Some(DefUse::Use) => Some(DefUseResult::UseLive { local }),
                 Some(DefUse::Drop) => Some(DefUseResult::UseDrop { local }),

src/librustc_mir/borrow_check/mod.rs

@@ -51,6 +51,7 @@ use self::path_utils::*;
 mod borrow_set;
 mod constraint_generation;
 mod constraints;
+mod def_use;
 mod diagnostics;
 mod facts;
 mod invalidation;

src/librustc_mir/borrow_check/type_check/liveness/local_use_map.rs

@@ -3,8 +3,7 @@ use rustc_index::vec::IndexVec;
 use rustc_middle::mir::visit::{PlaceContext, Visitor};
 use rustc_middle::mir::{Body, Local, Location};
 
-use crate::util::liveness::{categorize, DefUse};
-
+use crate::borrow_check::def_use::{self, DefUse};
 use crate::borrow_check::region_infer::values::{PointIndex, RegionValueElements};
 
 /// A map that cross references each local with the locations where it
@@ -160,7 +159,7 @@ impl LocalUseMapBuild<'_> {
 impl Visitor<'tcx> for LocalUseMapBuild<'_> {
     fn visit_local(&mut self, &local: &Local, context: PlaceContext, location: Location) {
         if self.locals_with_use_data[local] {
-            match categorize(context) {
+            match def_use::categorize(context) {
                 Some(DefUse::Def) => self.insert_def(local, location),
                 Some(DefUse::Use) => self.insert_use(local, location),
                 Some(DefUse::Drop) => self.insert_drop(local, location),

src/librustc_mir/borrow_check/type_check/liveness/polonius.rs

@@ -1,7 +1,7 @@
+use crate::borrow_check::def_use::{self, DefUse};
 use crate::borrow_check::location::{LocationIndex, LocationTable};
 use crate::dataflow::indexes::MovePathIndex;
 use crate::dataflow::move_paths::{LookupResult, MoveData};
-use crate::util::liveness::{categorize, DefUse};
 use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::{Body, Local, Location, Place};
 use rustc_middle::ty::subst::GenericArg;
@@ -56,7 +56,7 @@ impl UseFactsExtractor<'_> {
 
 impl Visitor<'tcx> for UseFactsExtractor<'_> {
     fn visit_local(&mut self, &local: &Local, context: PlaceContext, location: Location) {
-        match categorize(context) {
+        match def_use::categorize(context) {
             Some(DefUse::Def) => self.insert_def(local, location),
             Some(DefUse::Use) => self.insert_use(local, location),
             Some(DefUse::Drop) => self.insert_drop_use(local, location),

src/librustc_mir/dataflow/impls/liveness.rs

@@ -6,6 +6,13 @@ use crate::dataflow::{AnalysisDomain, Backward, BottomValue, GenKill, GenKillAna
 
 /// A [live-variable dataflow analysis][liveness].
 ///
+/// This analysis considers references as being used only at the point of the
+/// borrow. In other words, this analysis does not track uses because of references that already
+/// exist. See [this `mir-datalow` test][flow-test] for an example. You almost never want to use
+/// this analysis without also looking at the results of [`MaybeBorrowedLocals`].
+///
+/// [`MaybeBorrowedLocals`]: ../struct.MaybeBorrowedLocals.html
+/// [flow-test]: https://github.com/rust-lang/rust/blob/a08c47310c7d49cbdc5d7afb38408ba519967ecd/src/test/ui/mir-dataflow/liveness-ptr.rs
 /// [liveness]: https://en.wikipedia.org/wiki/Live_variable_analysis
 pub struct MaybeLiveLocals;
 

src/librustc_mir/transform/check_consts/mod.rs

@@ -9,8 +9,6 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::mir;
 use rustc_middle::ty::{self, TyCtxt};
 
-use std::fmt;
-
 pub use self::qualifs::Qualif;
 
 mod ops;
@@ -25,7 +23,7 @@ pub struct ConstCx<'mir, 'tcx> {
     pub tcx: TyCtxt<'tcx>,
     pub def_id: DefId,
     pub param_env: ty::ParamEnv<'tcx>,
-    pub const_kind: Option<ConstKind>,
+    pub const_kind: Option<hir::ConstContext>,
 }
 
 impl ConstCx<'mir, 'tcx> {
@@ -40,78 +38,18 @@ impl ConstCx<'mir, 'tcx> {
         body: &'mir mir::Body<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> Self {
-        let const_kind = ConstKind::for_item(tcx, def_id);
-
+        let const_kind = tcx.hir().body_const_context(def_id);
         ConstCx { body, tcx, def_id: def_id.to_def_id(), param_env, const_kind }
     }
 
     /// Returns the kind of const context this `Item` represents (`const`, `static`, etc.).
     ///
     /// Panics if this `Item` is not const.
-    pub fn const_kind(&self) -> ConstKind {
+    pub fn const_kind(&self) -> hir::ConstContext {
         self.const_kind.expect("`const_kind` must not be called on a non-const fn")
     }
 }
 
-/// The kinds of items which require compile-time evaluation.
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub enum ConstKind {
-    /// A `static` item.
-    Static,
-    /// A `static mut` item.
-    StaticMut,
-    /// A `const fn` item.
-    ConstFn,
-    /// A `const` item or an anonymous constant (e.g. in array lengths).
-    Const,
-}
-
-impl ConstKind {
-    /// Returns the validation mode for the item with the given `DefId`, or `None` if this item
-    /// does not require validation (e.g. a non-const `fn`).
-    pub fn for_item(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Option<Self> {
-        use hir::BodyOwnerKind as HirKind;
-
-        let hir_id = tcx.hir().as_local_hir_id(def_id);
-
-        let mode = match tcx.hir().body_owner_kind(hir_id) {
-            HirKind::Closure => return None,
-
-            // Note: this is deliberately checking for `is_const_fn_raw`, as the `is_const_fn`
-            // checks take into account the `rustc_const_unstable` attribute combined with enabled
-            // feature gates. Otherwise, const qualification would _not check_ whether this
-            // function body follows the `const fn` rules, as an unstable `const fn` would
-            // be considered "not const". More details are available in issue #67053.
-            HirKind::Fn if tcx.is_const_fn_raw(def_id) => ConstKind::ConstFn,
-            HirKind::Fn => return None,
-
-            HirKind::Const => ConstKind::Const,
-
-            HirKind::Static(hir::Mutability::Not) => ConstKind::Static,
-            HirKind::Static(hir::Mutability::Mut) => ConstKind::StaticMut,
-        };
-
-        Some(mode)
-    }
-
-    pub fn is_static(self) -> bool {
-        match self {
-            ConstKind::Static | ConstKind::StaticMut => true,
-            ConstKind::ConstFn | ConstKind::Const => false,
-        }
-    }
-}
-
-impl fmt::Display for ConstKind {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            ConstKind::Const => write!(f, "constant"),
-            ConstKind::Static | ConstKind::StaticMut => write!(f, "static"),
-            ConstKind::ConstFn => write!(f, "constant function"),
-        }
-    }
-}
-
 /// Returns `true` if this `DefId` points to one of the official `panic` lang items.
 pub fn is_lang_panic_fn(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
     Some(def_id) == tcx.lang_items().panic_fn() || Some(def_id) == tcx.lang_items().begin_panic_fn()