Auto merge of #54424 - RalfJung:sync-promote, r=<try>

WIP: do not borrow non-Sync data in constants

We cannot share that data across threads. non-Sync is as bad as non-Freeze in that regard.

This is currently WIP because it ignores a test that is broken by #54419. But it is good enough ti get crater going.

Fixes #49206.

Cc @eddyb @nikomatsakis

src/librustc/dep_graph/dep_node.rs

@@ -538,6 +538,7 @@ define_dep_nodes!( <'tcx>
     [] IsCopy { param_env: ParamEnvAnd<'tcx, Ty<'tcx>> },
     [] IsSized { param_env: ParamEnvAnd<'tcx, Ty<'tcx>> },
     [] IsFreeze { param_env: ParamEnvAnd<'tcx, Ty<'tcx>> },
+    [] IsSync { param_env: ParamEnvAnd<'tcx, Ty<'tcx>> },
     [] NeedsDrop { param_env: ParamEnvAnd<'tcx, Ty<'tcx>> },
     [] Layout { param_env: ParamEnvAnd<'tcx, Ty<'tcx>> },
 

src/librustc/ty/query/config.rs

@@ -179,6 +179,12 @@ impl<'tcx> QueryDescription<'tcx> for queries::is_freeze_raw<'tcx> {
     }
 }
 
+impl<'tcx> QueryDescription<'tcx> for queries::is_sync_raw<'tcx> {
+    fn describe(_tcx: TyCtxt, env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> String {
+        format!("computing whether `{}` is `Sync`", env.value)
+    }
+}
+
 impl<'tcx> QueryDescription<'tcx> for queries::needs_drop_raw<'tcx> {
     fn describe(_tcx: TyCtxt, env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> String {
         format!("computing whether `{}` needs drop", env.value)

src/librustc/ty/query/mod.rs

@@ -366,6 +366,7 @@ define_queries! { <'tcx>
         [] fn is_copy_raw: is_copy_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
         [] fn is_sized_raw: is_sized_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
         [] fn is_freeze_raw: is_freeze_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
+        [] fn is_sync_raw: is_sync_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
         [] fn needs_drop_raw: needs_drop_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool,
         [] fn layout_raw: layout_dep_node(ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
                                     -> Result<&'tcx ty::layout::LayoutDetails,
@@ -767,6 +768,10 @@ fn is_freeze_dep_node<'tcx>(param_env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> DepCo
     DepConstructor::IsFreeze { param_env }
 }
 
+fn is_sync_dep_node<'tcx>(param_env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> DepConstructor<'tcx> {
+    DepConstructor::IsSync { param_env }
+}
+
 fn needs_drop_dep_node<'tcx>(param_env: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> DepConstructor<'tcx> {
     DepConstructor::NeedsDrop { param_env }
 }

src/librustc/ty/query/plumbing.rs

@@ -1057,6 +1057,7 @@ pub fn force_from_dep_node<'a, 'gcx, 'lcx>(tcx: TyCtxt<'a, 'gcx, 'lcx>,
         DepKind::IsCopy |
         DepKind::IsSized |
         DepKind::IsFreeze |
+        DepKind::IsSync |
         DepKind::NeedsDrop |
         DepKind::Layout |
         DepKind::ConstEval |

src/librustc/ty/util.rs

@@ -655,6 +655,14 @@ impl<'a, 'tcx> ty::TyS<'tcx> {
         tcx.at(span).is_freeze_raw(param_env.and(self))
     }
 
+    pub fn is_sync(&'tcx self,
+                     tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                     param_env: ty::ParamEnv<'tcx>,
+                     span: Span)-> bool
+    {
+        tcx.at(span).is_sync_raw(param_env.and(self))
+    }
+
     /// If `ty.needs_drop(...)` returns `true`, then `ty` is definitely
     /// non-copy and *might* have a destructor attached; if it returns
     /// `false`, then `ty` definitely has no destructor (i.e. no drop glue).
@@ -897,6 +905,20 @@ fn is_freeze_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                                        DUMMY_SP))
 }
 
+fn is_sync_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+                           query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
+                           -> bool
+{
+    let (param_env, ty) = query.into_parts();
+    let trait_def_id = tcx.require_lang_item(lang_items::SyncTraitLangItem);
+    tcx.infer_ctxt()
+       .enter(|infcx| traits::type_known_to_meet_bound(&infcx,
+                                                       param_env,
+                                                       ty,
+                                                       trait_def_id,
+                                                       DUMMY_SP))
+}
+
 fn needs_drop_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                             query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>)
                             -> bool
@@ -1044,6 +1066,7 @@ pub fn provide(providers: &mut ty::query::Providers) {
         is_copy_raw,
         is_sized_raw,
         is_freeze_raw,
+        is_sync_raw,
         needs_drop_raw,
         ..*providers
     };

src/librustc_mir/transform/qualify_consts.rs

@@ -46,8 +46,10 @@ bitflags! {
     // they have none of these qualifications, with
     // the exception of `STATIC_REF` (in statics only).
     struct Qualif: u8 {
-        // Constant containing interior mutability (UnsafeCell).
-        const MUTABLE_INTERIOR  = 1 << 0;
+        // Constant containing interior mutability (UnsafeCell) or non-Sync data.
+        // Both of these prevent sound re-use of the same global static memory for
+        // the same data across multiple threads.
+        const UNSHAREABLE_INTERIOR  = 1 << 0;
 
         // Constant containing an ADT that implements Drop.
         const NEEDS_DROP        = 1 << 1;
@@ -63,9 +65,9 @@ bitflags! {
         // promote_consts decided they weren't simple enough.
         const NOT_PROMOTABLE    = 1 << 4;
 
-        // Const items can only have MUTABLE_INTERIOR
+        // Const items can only have UNSHAREABLE_INTERIOR
         // and NOT_PROMOTABLE without producing an error.
-        const CONST_ERROR       = !Qualif::MUTABLE_INTERIOR.bits &
+        const CONST_ERROR       = !Qualif::UNSHAREABLE_INTERIOR.bits &
                                   !Qualif::NOT_PROMOTABLE.bits;
     }
 }
@@ -75,8 +77,8 @@ impl<'a, 'tcx> Qualif {
     fn restrict(&mut self, ty: Ty<'tcx>,
                 tcx: TyCtxt<'a, 'tcx, 'tcx>,
                 param_env: ty::ParamEnv<'tcx>) {
-        if ty.is_freeze(tcx, param_env, DUMMY_SP) {
-            *self = *self - Qualif::MUTABLE_INTERIOR;
+        if ty.is_freeze(tcx, param_env, DUMMY_SP) && ty.is_sync(tcx, param_env, DUMMY_SP) {
+            *self = *self - Qualif::UNSHAREABLE_INTERIOR;
         }
         if !ty.needs_drop(tcx, param_env) {
             *self = *self - Qualif::NEEDS_DROP;
@@ -206,7 +208,7 @@ impl<'a, 'tcx> Qualifier<'a, 'tcx, 'tcx> {
 
     /// Add the given type's qualification to self.qualif.
     fn add_type(&mut self, ty: Ty<'tcx>) {
-        self.add(Qualif::MUTABLE_INTERIOR | Qualif::NEEDS_DROP);
+        self.add(Qualif::UNSHAREABLE_INTERIOR | Qualif::NEEDS_DROP);
         self.qualif.restrict(ty, self.tcx, self.param_env);
     }
 
@@ -679,18 +681,19 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
                     // Constants cannot be borrowed if they contain interior mutability as
                     // it means that our "silent insertion of statics" could change
                     // initializer values (very bad).
-                    if self.qualif.contains(Qualif::MUTABLE_INTERIOR) {
-                        // A reference of a MUTABLE_INTERIOR place is instead
+                    if self.qualif.contains(Qualif::UNSHAREABLE_INTERIOR) {
+                        // A reference of a UNSHAREABLE_INTERIOR place is instead
                         // NOT_CONST (see `if forbidden_mut` below), to avoid
                         // duplicate errors (from reborrowing, for example).
-                        self.qualif = self.qualif - Qualif::MUTABLE_INTERIOR;
+                        self.qualif = self.qualif - Qualif::UNSHAREABLE_INTERIOR;
                         if self.mode != Mode::Fn {
                             span_err!(self.tcx.sess, self.span, E0492,
                                       "cannot borrow a constant which may contain \
-                                       interior mutability, create a static instead");
+                                       interior mutability or non-`Sync` data. If your \
+                                       data is `Sync`, create a static instead");
                         }
                     } else {
-                        // We allow immutable borrows of frozen data.
+                        // We allow immutable borrows of frozen non-Sync data.
                         forbidden_mut = false;
                     }
                 }
@@ -712,11 +715,11 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
                         if self.mir.local_kind(local) == LocalKind::Temp {
                             if let Some(qualif) = self.local_qualif[local] {
                                 // `forbidden_mut` is false, so we can safely ignore
-                                // `MUTABLE_INTERIOR` from the local's qualifications.
+                                // `UNSHAREABLE_INTERIOR` from the local's qualifications.
                                 // This allows borrowing fields which don't have
-                                // `MUTABLE_INTERIOR`, from a type that does, e.g.:
+                                // `UNSHAREABLE_INTERIOR`, from a type that does, e.g.:
                                 // `let _: &'static _ = &(Cell::new(1), 2).1;`
-                                if (qualif - Qualif::MUTABLE_INTERIOR).is_empty() {
+                                if (qualif - Qualif::UNSHAREABLE_INTERIOR).is_empty() {
                                     self.promotion_candidates.push(candidate);
                                 }
                             }
@@ -794,10 +797,17 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
                         self.add(Qualif::NEEDS_DROP);
                     }
 
-                    if Some(def.did) == self.tcx.lang_items().unsafe_cell_type() {
-                        let ty = rvalue.ty(self.mir, self.tcx);
-                        self.add_type(ty);
-                        assert!(self.qualif.contains(Qualif::MUTABLE_INTERIOR));
+                    // We are looking at a concrete type constructor, and we know
+                    // the only way to construct "fresh" non-Freeze data is `UnsafeCell`.
+                    // So we can check for that instead of `Freeze`.
+                    // There is no similar shortcut for Sync, though.
+                    let ty = rvalue.ty(self.mir, self.tcx);
+                    let freeze = Some(def.did) != self.tcx.lang_items().unsafe_cell_type();
+                    let sync = ty.is_sync(self.tcx, self.param_env, DUMMY_SP);
+                    if !(freeze && sync)
+                    {
+                        // Not freeze and sync? Be careful.
+                        self.add(Qualif::UNSHAREABLE_INTERIOR);
                     }
                 }
             }
@@ -1247,6 +1257,7 @@ impl MirPass for QualifyAndPromoteConstants {
                 }
             }
             let ty = mir.return_ty();
+            // Not using ty.is_sync() to get the right kind of error message
             tcx.infer_ctxt().enter(|infcx| {
                 let param_env = ty::ParamEnv::empty();
                 let cause = traits::ObligationCause::new(mir.span, id, traits::SharedStatic);

src/librustc_passes/rvalue_promotion.rs

@@ -153,6 +153,7 @@ impl<'a, 'gcx> CheckCrateVisitor<'a, 'gcx> {
         debug!("type_promotability({})", ty);
 
         if ty.is_freeze(self.tcx, self.param_env, DUMMY_SP) &&
+            ty.is_sync(self.tcx, self.param_env, DUMMY_SP) &&
             !ty.needs_drop(self.tcx, self.param_env) {
             Promotable
         } else {
@@ -289,6 +290,11 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
         let mut outer = check_expr_kind(self, ex, node_ty);
         outer &= check_adjustments(self, ex);
 
+        // Avoid non-Sync types
+        if !self.tables.expr_ty(ex).is_sync(self.tcx, self.param_env, DUMMY_SP) {
+            outer = NotPromotable;
+        }
+
         // Handle borrows on (or inside the autorefs of) this expression.
         if self.mut_rvalue_borrows.remove(&ex.id) {
             outer = NotPromotable

src/test/ui/consts/const-eval/dont_promote_non_sync.rs

@@ -0,0 +1,29 @@
+#![feature(optin_builtin_traits)]
+
+struct Foo;
+impl !Sync for Foo {}
+
+struct Bar(i32);
+impl !Sync for Bar {}
+
+struct Baz { field: i32 }
+impl !Sync for Baz {}
+
+enum Bla { T(i32), S { field: i32 } }
+impl !Sync for Bla {}
+
+// Known values of the given types
+fn mk_foo() -> &'static Foo { &Foo } //~ ERROR does not live long enough
+fn mk_bar() -> &'static Bar { &Bar(0) } //~ ERROR does not live long enough
+fn mk_baz() -> &'static Baz { &Baz { field: 0 } } //~ ERROR does not live long enough
+fn mk_bla_t() -> &'static Bla { &Bla::T(0) } //~ ERROR does not live long enough
+fn mk_bla_s() -> &'static Bla { &Bla::S { field: 0 } } //~ ERROR does not live long enough
+
+// Unknown values of the given types (test a ZST and a non-ZST)
+trait FooT { const C: Foo; }
+fn mk_foo2<T: FooT>() -> &'static Foo { &T::C } //~ ERROR does not live long enough
+
+trait BarT { const C: Bar; }
+fn mk_bar2<T: BarT>() -> &'static Bar { &T::C } //~ ERROR does not live long enough
+
+fn main() {}

src/test/ui/consts/const-eval/dont_promote_non_sync.stderr

@@ -0,0 +1,73 @@
+error[E0597]: borrowed value does not live long enough
+  --> $DIR/dont_promote_non_sync.rs:16:32
+   |
+LL | fn mk_foo() -> &'static Foo { &Foo } //~ ERROR does not live long enough
+   |                                ^^^ - temporary value only lives until here
+   |                                |
+   |                                temporary value does not live long enough
+   |
+   = note: borrowed value must be valid for the static lifetime...
+
+error[E0597]: borrowed value does not live long enough
+  --> $DIR/dont_promote_non_sync.rs:17:32
+   |
+LL | fn mk_bar() -> &'static Bar { &Bar(0) } //~ ERROR does not live long enough
+   |                                ^^^^^^ - temporary value only lives until here
+   |                                |
+   |                                temporary value does not live long enough
+   |
+   = note: borrowed value must be valid for the static lifetime...
+
+error[E0597]: borrowed value does not live long enough
+  --> $DIR/dont_promote_non_sync.rs:18:32
+   |
+LL | fn mk_baz() -> &'static Baz { &Baz { field: 0 } } //~ ERROR does not live long enough
+   |                                ^^^^^^^^^^^^^^^^ - temporary value only lives until here
+   |                                |
+   |                                temporary value does not live long enough
+   |
+   = note: borrowed value must be valid for the static lifetime...
+
+error[E0597]: borrowed value does not live long enough
+  --> $DIR/dont_promote_non_sync.rs:19:34
+   |
+LL | fn mk_bla_t() -> &'static Bla { &Bla::T(0) } //~ ERROR does not live long enough
+   |                                  ^^^^^^^^^ - temporary value only lives until here
+   |                                  |
+   |                                  temporary value does not live long enough
+   |
+   = note: borrowed value must be valid for the static lifetime...
+
+error[E0597]: borrowed value does not live long enough
+  --> $DIR/dont_promote_non_sync.rs:20:34
+   |
+LL | fn mk_bla_s() -> &'static Bla { &Bla::S { field: 0 } } //~ ERROR does not live long enough
+   |                                  ^^^^^^^^^^^^^^^^^^^ - temporary value only lives until here
+   |                                  |
+   |                                  temporary value does not live long enough
+   |
+   = note: borrowed value must be valid for the static lifetime...
+
+error[E0597]: borrowed value does not live long enough
+  --> $DIR/dont_promote_non_sync.rs:24:42
+   |
+LL | fn mk_foo2<T: FooT>() -> &'static Foo { &T::C } //~ ERROR does not live long enough
+   |                                          ^^^^ - temporary value only lives until here
+   |                                          |
+   |                                          temporary value does not live long enough
+   |
+   = note: borrowed value must be valid for the static lifetime...
+
+error[E0597]: borrowed value does not live long enough
+  --> $DIR/dont_promote_non_sync.rs:27:42
+   |
+LL | fn mk_bar2<T: BarT>() -> &'static Bar { &T::C } //~ ERROR does not live long enough
+   |                                          ^^^^ - temporary value only lives until here
+   |                                          |
+   |                                          temporary value does not live long enough
+   |
+   = note: borrowed value must be valid for the static lifetime...
+
+error: aborting due to 7 previous errors
+
+For more information about this error, try `rustc --explain E0597`.

src/test/ui/consts/const-eval/non_sync_const.rs

@@ -0,0 +1,19 @@
+#![feature(optin_builtin_traits)]
+
+struct Foo;
+impl !Sync for Foo {}
+
+struct Bar(i32);
+impl !Sync for Bar {}
+
+const FOO : &Foo = &Foo; //~ ERROR cannot borrow
+const FOO2 : Option<&Foo> = Some(&Foo); //~ ERROR cannot borrow
+//~^ ERROR borrowed value does not live long enough
+const FOO3 : &Option<Foo> = &Some(Foo); //~ ERROR cannot borrow
+
+const BAR : &Bar = &Bar(42); //~ ERROR cannot borrow
+const BAR2 : Option<&Bar> = Some(&Bar(42)); //~ ERROR cannot borrow
+//~^ ERROR borrowed value does not live long enough
+const BAR3 : &Option<Bar> = &Some(Bar(42)); //~ ERROR cannot borrow
+
+fn main() {}