Rollup of 5 pull requests

src/librustc_error_codes/error_codes/E0493.md

@@ -1,5 +1,4 @@
-A type with a `Drop` implementation was destructured when trying to initialize
-a static item.
+A value with a custom `Drop` implementation may be dropped during const-eval.
 
 Erroneous code example:
 
@@ -16,13 +15,14 @@ struct Foo {
     field1: DropType,
 }
 
-static FOO: Foo = Foo { ..Foo { field1: DropType::A } }; // error!
+static FOO: Foo = Foo { field1: (DropType::A, DropType::A).1 }; // error!
 ```
 
 The problem here is that if the given type or one of its fields implements the
-`Drop` trait, this `Drop` implementation cannot be called during the static
-type initialization which might cause a memory leak. To prevent this issue,
-you need to instantiate all the static type's fields by hand.
+`Drop` trait, this `Drop` implementation cannot be called within a const
+context since it may run arbitrary, non-const-checked code. To prevent this
+issue, ensure all values with custom a custom `Drop` implementation escape the
+initializer.
 
 ```
 enum DropType {

src/librustc_errors/diagnostic.rs

@@ -296,6 +296,29 @@ impl Diagnostic {
         self
     }
 
+    pub fn multipart_suggestions(
+        &mut self,
+        msg: &str,
+        suggestions: Vec<Vec<(Span, String)>>,
+        applicability: Applicability,
+    ) -> &mut Self {
+        self.suggestions.push(CodeSuggestion {
+            substitutions: suggestions
+                .into_iter()
+                .map(|suggestion| Substitution {
+                    parts: suggestion
+                        .into_iter()
+                        .map(|(span, snippet)| SubstitutionPart { snippet, span })
+                        .collect(),
+                })
+                .collect(),
+            msg: msg.to_owned(),
+            style: SuggestionStyle::ShowCode,
+            applicability,
+        });
+        self
+    }
+
     /// Prints out a message with for a multipart suggestion without showing the suggested code.
     ///
     /// This is intended to be used for suggestions that are obvious in what the changes need to

src/librustc_errors/diagnostic_builder.rs

@@ -260,6 +260,19 @@ impl<'a> DiagnosticBuilder<'a> {
         self
     }
 
+    pub fn multipart_suggestions(
+        &mut self,
+        msg: &str,
+        suggestions: Vec<Vec<(Span, String)>>,
+        applicability: Applicability,
+    ) -> &mut Self {
+        if !self.0.allow_suggestions {
+            return self;
+        }
+        self.0.diagnostic.multipart_suggestions(msg, suggestions, applicability);
+        self
+    }
+
     pub fn tool_only_multipart_suggestion(
         &mut self,
         msg: &str,

src/librustc_feature/active.rs

@@ -577,6 +577,9 @@ declare_features! (
     /// Allows `extern "avr-interrupt" fn()` and `extern "avr-non-blocking-interrupt" fn()`.
     (active, abi_avr_interrupt, "1.45.0", Some(69664), None),
 
+    /// Be more precise when looking for live drops in a const context.
+    (active, const_precise_live_drops, "1.46.0", Some(73255), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

src/librustc_interface/passes.rs

@@ -847,7 +847,11 @@ fn analysis(tcx: TyCtxt<'_>, cnum: CrateNum) -> Result<()> {
 
     sess.time("MIR_effect_checking", || {
         for def_id in tcx.body_owners() {
-            mir::transform::check_unsafety::check_unsafety(tcx, def_id)
+            mir::transform::check_unsafety::check_unsafety(tcx, def_id);
+
+            if tcx.hir().body_const_context(def_id).is_some() {
+                tcx.ensure().mir_drops_elaborated_and_const_checked(def_id);
+            }
         }
     });
 

src/librustc_lint/types.rs

@@ -927,22 +927,33 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
     fn check_for_opaque_ty(&mut self, sp: Span, ty: Ty<'tcx>) -> bool {
         use rustc_middle::ty::TypeFoldable;
 
-        struct ProhibitOpaqueTypes<'tcx> {
+        struct ProhibitOpaqueTypes<'a, 'tcx> {
+            cx: &'a LateContext<'a, 'tcx>,
             ty: Option<Ty<'tcx>>,
         };
 
-        impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'tcx> {
+        impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
             fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
-                if let ty::Opaque(..) = ty.kind {
-                    self.ty = Some(ty);
-                    true
-                } else {
-                    ty.super_visit_with(self)
+                match ty.kind {
+                    ty::Opaque(..) => {
+                        self.ty = Some(ty);
+                        true
+                    }
+                    // Consider opaque types within projections FFI-safe if they do not normalize
+                    // to more opaque types.
+                    ty::Projection(..) => {
+                        let ty = self.cx.tcx.normalize_erasing_regions(self.cx.param_env, ty);
+
+                        // If `ty` is a opaque type directly then `super_visit_with` won't invoke
+                        // this function again.
+                        if ty.has_opaque_types() { self.visit_ty(ty) } else { false }
+                    }
+                    _ => ty.super_visit_with(self),
                 }
             }
         }
 
-        let mut visitor = ProhibitOpaqueTypes { ty: None };
+        let mut visitor = ProhibitOpaqueTypes { cx: self.cx, ty: None };
         ty.visit_with(&mut visitor);
         if let Some(ty) = visitor.ty {
             self.emit_ffi_unsafe_type_lint(ty, sp, "opaque types have no C equivalent", None);

src/librustc_middle/mir/mod.rs

@@ -76,7 +76,8 @@ pub enum MirPhase {
     Build = 0,
     Const = 1,
     Validated = 2,
-    Optimized = 3,
+    DropElab = 3,
+    Optimized = 4,
 }
 
 impl MirPhase {

src/librustc_middle/query/mod.rs

@@ -190,6 +190,12 @@ rustc_queries! {
             no_hash
         }
 
+        query mir_drops_elaborated_and_const_checked(key: LocalDefId) -> Steal<mir::Body<'tcx>> {
+            storage(ArenaCacheSelector<'tcx>)
+            no_hash
+            desc { |tcx| "elaborating drops for `{}`", tcx.def_path_str(key.to_def_id()) }
+        }
+
         query mir_validated(key: LocalDefId) ->
             (
                 Steal<mir::Body<'tcx>>,

src/librustc_middle/ty/util.rs

@@ -878,7 +878,15 @@ impl<'tcx> ty::TyS<'tcx> {
                     // Find non representable fields with their spans
                     fold_repr(def.all_fields().map(|field| {
                         let ty = field.ty(tcx, substs);
-                        let span = tcx.hir().span_if_local(field.did).unwrap_or(sp);
+                        let span = match field
+                            .did
+                            .as_local()
+                            .map(|id| tcx.hir().as_local_hir_id(id))
+                            .and_then(|id| tcx.hir().find(id))
+                        {
+                            Some(hir::Node::Field(field)) => field.ty.span,
+                            _ => sp,
+                        };
                         match is_type_structurally_recursive(
                             tcx,
                             span,

src/librustc_mir/transform/check_consts/mod.rs

@@ -12,6 +12,7 @@ use rustc_middle::ty::{self, TyCtxt};
 pub use self::qualifs::Qualif;
 
 mod ops;
+pub mod post_drop_elaboration;
 pub mod qualifs;
 mod resolver;
 pub mod validation;

src/librustc_mir/transform/check_consts/ops.rs

@@ -10,6 +10,22 @@ use rustc_span::{Span, Symbol};
 
 use super::ConstCx;
 
+/// Emits an error if `op` is not allowed in the given const context.
+pub fn non_const<O: NonConstOp>(ccx: &ConstCx<'_, '_>, op: O, span: Span) {
+    debug!("illegal_op: op={:?}", op);
+
+    if op.is_allowed_in_item(ccx) {
+        return;
+    }
+
+    if ccx.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
+        ccx.tcx.sess.miri_unleashed_feature(span, O::feature_gate());
+        return;
+    }
+
+    op.emit_error(ccx, span);
+}
+
 /// An operation that is not *always* allowed in a const context.
 pub trait NonConstOp: std::fmt::Debug {
     /// Returns the `Symbol` corresponding to the feature gate that would enable this operation,

src/librustc_mir/transform/check_consts/post_drop_elaboration.rs

@@ -0,0 +1,119 @@
+use rustc_hir::def_id::LocalDefId;
+use rustc_middle::mir::visit::Visitor;
+use rustc_middle::mir::{self, BasicBlock, Location};
+use rustc_middle::ty::TyCtxt;
+use rustc_span::Span;
+
+use super::ops;
+use super::qualifs::{NeedsDrop, Qualif};
+use super::validation::Qualifs;
+use super::ConstCx;
+
+/// Returns `true` if we should use the more precise live drop checker that runs after drop
+/// elaboration.
+pub fn checking_enabled(tcx: TyCtxt<'tcx>) -> bool {
+    tcx.features().const_precise_live_drops
+}
+
+/// Look for live drops in a const context.
+///
+/// This is separate from the rest of the const checking logic because it must run after drop
+/// elaboration.
+pub fn check_live_drops(tcx: TyCtxt<'tcx>, def_id: LocalDefId, body: &mir::Body<'tcx>) {
+    let const_kind = tcx.hir().body_const_context(def_id);
+    if const_kind.is_none() {
+        return;
+    }
+
+    if !checking_enabled(tcx) {
+        return;
+    }
+
+    let ccx = ConstCx {
+        body,
+        tcx,
+        def_id: def_id.to_def_id(),
+        const_kind,
+        param_env: tcx.param_env(def_id),
+    };
+
+    let mut visitor = CheckLiveDrops { ccx: &ccx, qualifs: Qualifs::default() };
+
+    visitor.visit_body(body);
+}
+
+struct CheckLiveDrops<'mir, 'tcx> {
+    ccx: &'mir ConstCx<'mir, 'tcx>,
+    qualifs: Qualifs<'mir, 'tcx>,
+}
+
+// So we can access `body` and `tcx`.
+impl std::ops::Deref for CheckLiveDrops<'mir, 'tcx> {
+    type Target = ConstCx<'mir, 'tcx>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.ccx
+    }
+}
+
+impl CheckLiveDrops<'mir, 'tcx> {
+    fn check_live_drop(&self, span: Span) {
+        ops::non_const(self.ccx, ops::LiveDrop, span);
+    }
+}
+
+impl Visitor<'tcx> for CheckLiveDrops<'mir, 'tcx> {
+    fn visit_basic_block_data(&mut self, bb: BasicBlock, block: &mir::BasicBlockData<'tcx>) {
+        trace!("visit_basic_block_data: bb={:?} is_cleanup={:?}", bb, block.is_cleanup);
+
+        // Ignore drop terminators in cleanup blocks.
+        if block.is_cleanup {
+            return;
+        }
+
+        self.super_basic_block_data(bb, block);
+    }
+
+    fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
+        trace!("visit_terminator: terminator={:?} location={:?}", terminator, location);
+
+        match &terminator.kind {
+            mir::TerminatorKind::Drop { location: dropped_place, .. } => {
+                let dropped_ty = dropped_place.ty(self.body, self.tcx).ty;
+                if !NeedsDrop::in_any_value_of_ty(self.ccx, dropped_ty) {
+                    return;
+                }
+
+                if dropped_place.is_indirect() {
+                    self.check_live_drop(terminator.source_info.span);
+                    return;
+                }
+
+                if self.qualifs.needs_drop(self.ccx, dropped_place.local, location) {
+                    // Use the span where the dropped local was declared for the error.
+                    let span = self.body.local_decls[dropped_place.local].source_info.span;
+                    self.check_live_drop(span);
+                }
+            }
+
+            mir::TerminatorKind::DropAndReplace { .. } => span_bug!(
+                terminator.source_info.span,
+                "`DropAndReplace` should be removed by drop elaboration",
+            ),
+
+            mir::TerminatorKind::Abort
+            | mir::TerminatorKind::Call { .. }
+            | mir::TerminatorKind::Assert { .. }
+            | mir::TerminatorKind::FalseEdge { .. }
+            | mir::TerminatorKind::FalseUnwind { .. }
+            | mir::TerminatorKind::GeneratorDrop
+            | mir::TerminatorKind::Goto { .. }
+            | mir::TerminatorKind::InlineAsm { .. }
+            | mir::TerminatorKind::Resume
+            | mir::TerminatorKind::Return
+            | mir::TerminatorKind::SwitchInt { .. }
+            | mir::TerminatorKind::Unreachable
+            | mir::TerminatorKind::Yield { .. } => {}
+        }
+    }
+}