Rollup merge of rust-lang#73783 - estebank:impl-dyn-trait-static-lifetime, r=nikomatsakis

Detect when `'static` obligation might come from an `impl`

Partly address rust-lang#71341.

Author: Manishearth

src/librustc_error_codes/error_codes.rs

@@ -632,4 +632,5 @@ E0770: include_str!("./error_codes/E0770.md"),
     E0755, // `#[ffi_pure]` is only allowed on foreign functions
     E0756, // `#[ffi_const]` is only allowed on foreign functions
     E0757, // `#[ffi_const]` functions cannot be `#[ffi_pure]`
+    E0767, // `'static' obligation coming from `impl dyn Trait {}` or `impl Foo for dyn Bar {}`.
 }

src/librustc_hir/hir.rs

@@ -2198,7 +2198,17 @@ pub enum IsAsync {
     NotAsync,
 }
 
-#[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, HashStable_Generic)]
+#[derive(
+    Copy,
+    Clone,
+    PartialEq,
+    RustcEncodable,
+    RustcDecodable,
+    Debug,
+    HashStable_Generic,
+    Eq,
+    Hash
+)]
 pub enum Defaultness {
     Default { has_value: bool },
     Final,

src/librustc_infer/infer/combine.rs

@@ -36,12 +36,13 @@ use crate::traits::{Obligation, PredicateObligations};
 
 use rustc_ast::ast;
 use rustc_hir::def_id::DefId;
+use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, InferConst, ToPredicate, Ty, TyCtxt, TypeFoldable};
 use rustc_middle::ty::{IntType, UintType};
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::DUMMY_SP;
 
 #[derive(Clone)]
 pub struct CombineFields<'infcx, 'tcx> {
@@ -367,10 +368,11 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
         };
 
         debug!("generalize: for_universe = {:?}", for_universe);
+        debug!("generalize: trace = {:?}", self.trace);
 
         let mut generalize = Generalizer {
             infcx: self.infcx,
-            span: self.trace.cause.span,
+            cause: &self.trace.cause,
             for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables().sub_root_var(for_vid),
             for_universe,
             ambient_variance,
@@ -414,7 +416,7 @@ struct Generalizer<'cx, 'tcx> {
     infcx: &'cx InferCtxt<'cx, 'tcx>,
 
     /// The span, used when creating new type variables and things.
-    span: Span,
+    cause: &'cx ObligationCause<'tcx>,
 
     /// The vid of the type variable that is in the process of being
     /// instantiated; if we find this within the type we are folding,
@@ -639,7 +641,7 @@ impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
 
         // FIXME: This is non-ideal because we don't give a
         // very descriptive origin for this region variable.
-        Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.span), self.for_universe))
+        Ok(self.infcx.next_region_var_in_universe(MiscVariable(self.cause.span), self.for_universe))
     }
 
     fn consts(

src/librustc_infer/infer/error_reporting/mod.rs

@@ -2007,7 +2007,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             infer::MiscVariable(_) => String::new(),
             infer::PatternRegion(_) => " for pattern".to_string(),
             infer::AddrOfRegion(_) => " for borrow expression".to_string(),
-            infer::Autoref(_) => " for autoref".to_string(),
+            infer::Autoref(_, _) => " for autoref".to_string(),
             infer::Coercion(_) => " for automatic coercion".to_string(),
             infer::LateBoundRegion(_, br, infer::FnCall) => {
                 format!(" for lifetime parameter {}in function call", br_string(br))

src/librustc_infer/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -7,20 +7,18 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_middle::ty::{self, DefIdTree, Region, Ty};
 use rustc_span::Span;
 
-// The struct contains the information about the anonymous region
-// we are searching for.
+/// Information about the anonymous region we are searching for.
 #[derive(Debug)]
 pub(super) struct AnonymousParamInfo<'tcx> {
-    // the parameter corresponding to the anonymous region
+    /// The parameter corresponding to the anonymous region.
     pub param: &'tcx hir::Param<'tcx>,
-    // the type corresponding to the anonymopus region parameter
+    /// The type corresponding to the anonymous region parameter.
     pub param_ty: Ty<'tcx>,
-    // the ty::BoundRegion corresponding to the anonymous region
+    /// The ty::BoundRegion corresponding to the anonymous region.
     pub bound_region: ty::BoundRegion,
-    // param_ty_span contains span of parameter type
+    /// The `Span` of the parameter type.
     pub param_ty_span: Span,
-    // corresponds to id the argument is the first parameter
-    // in the declaration
+    /// Signals that the argument is the first parameter in the declaration.
     pub is_first: bool,
 }
 

src/librustc_infer/infer/error_reporting/nice_region_error/util.rs

@@ -463,7 +463,7 @@ pub enum RegionVariableOrigin {
     AddrOfRegion(Span),
 
     /// Regions created as part of an autoref of a method receiver
-    Autoref(Span),
+    Autoref(Span, ty::AssocItem),
 
     /// Regions created as part of an automatic coercion
     Coercion(Span),
@@ -1798,15 +1798,15 @@ impl<'tcx> SubregionOrigin<'tcx> {
 impl RegionVariableOrigin {
     pub fn span(&self) -> Span {
         match *self {
-            MiscVariable(a) => a,
-            PatternRegion(a) => a,
-            AddrOfRegion(a) => a,
-            Autoref(a) => a,
-            Coercion(a) => a,
-            EarlyBoundRegion(a, ..) => a,
-            LateBoundRegion(a, ..) => a,
+            MiscVariable(a)
+            | PatternRegion(a)
+            | AddrOfRegion(a)
+            | Autoref(a, _)
+            | Coercion(a)
+            | EarlyBoundRegion(a, ..)
+            | LateBoundRegion(a, ..)
+            | UpvarRegion(_, a) => a,
             BoundRegionInCoherence(_) => rustc_span::DUMMY_SP,
-            UpvarRegion(_, a) => a,
             NLL(..) => bug!("NLL variable used with `span`"),
         }
     }

src/librustc_infer/infer/mod.rs

@@ -13,6 +13,7 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
+#![feature(bindings_after_at)]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]

src/librustc_infer/lib.rs

@@ -169,6 +169,13 @@ impl<'tcx> ObligationCause<'tcx> {
     }
 }
 
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub struct UnifyReceiverContext<'tcx> {
+    pub assoc_item: ty::AssocItem,
+    pub param_env: ty::ParamEnv<'tcx>,
+    pub substs: SubstsRef<'tcx>,
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub enum ObligationCauseCode<'tcx> {
     /// Not well classified or should be obvious from the span.
@@ -300,6 +307,8 @@ pub enum ObligationCauseCode<'tcx> {
     /// Method receiver
     MethodReceiver,
 
+    UnifyReceiver(Box<UnifyReceiverContext<'tcx>>),
+
     /// `return` with no expression
     ReturnNoExpression,
 

src/librustc_middle/traits/mod.rs

@@ -213,12 +213,26 @@ impl<'a, 'tcx> Lift<'tcx> for traits::ObligationCauseCode<'a> {
             super::StartFunctionType => Some(super::StartFunctionType),
             super::IntrinsicType => Some(super::IntrinsicType),
             super::MethodReceiver => Some(super::MethodReceiver),
+            super::UnifyReceiver(ref ctxt) => tcx.lift(ctxt).map(|ctxt| super::UnifyReceiver(ctxt)),
             super::BlockTailExpression(id) => Some(super::BlockTailExpression(id)),
             super::TrivialBound => Some(super::TrivialBound),
         }
     }
 }
 
+impl<'a, 'tcx> Lift<'tcx> for traits::UnifyReceiverContext<'a> {
+    type Lifted = traits::UnifyReceiverContext<'tcx>;
+    fn lift_to_tcx(&self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
+        tcx.lift(&self.param_env).and_then(|param_env| {
+            tcx.lift(&self.substs).map(|substs| traits::UnifyReceiverContext {
+                assoc_item: self.assoc_item,
+                param_env,
+                substs,
+            })
+        })
+    }
+}
+
 impl<'a, 'tcx> Lift<'tcx> for traits::DerivedObligationCause<'a> {
     type Lifted = traits::DerivedObligationCause<'tcx>;
     fn lift_to_tcx(&self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {

src/librustc_middle/traits/structural_impls.rs

@@ -136,7 +136,7 @@ pub struct ResolverOutputs {
     pub extern_prelude: FxHashMap<Symbol, bool>,
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug, HashStable)]
+#[derive(Clone, Copy, PartialEq, Eq, Debug, HashStable, Hash)]
 pub enum AssocItemContainer {
     TraitContainer(DefId),
     ImplContainer(DefId),
@@ -184,7 +184,7 @@ pub enum ImplPolarity {
     Reservation,
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, HashStable)]
+#[derive(Copy, Clone, Debug, PartialEq, HashStable, Eq, Hash)]
 pub struct AssocItem {
     pub def_id: DefId,
     #[stable_hasher(project(name))]
@@ -199,7 +199,7 @@ pub struct AssocItem {
     pub fn_has_self_parameter: bool,
 }
 
-#[derive(Copy, Clone, PartialEq, Debug, HashStable)]
+#[derive(Copy, Clone, PartialEq, Debug, HashStable, Eq, Hash)]
 pub enum AssocKind {
     Const,
     Fn,
@@ -316,7 +316,7 @@ impl<'tcx> AssociatedItems<'tcx> {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Eq, Copy, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, Debug, PartialEq, Eq, Copy, RustcEncodable, RustcDecodable, HashStable, Hash)]
 pub enum Visibility {
     /// Visible everywhere (including in other crates).
     Public,

src/librustc_middle/ty/mod.rs

@@ -6,6 +6,7 @@
 use crate::infer::{InferCtxt, TyCtxtInferExt};
 use crate::traits::{
     FulfillmentContext, ImplSource, Obligation, ObligationCause, SelectionContext, TraitEngine,
+    Unimplemented,
 };
 use rustc_errors::ErrorReported;
 use rustc_middle::ty::fold::TypeFoldable;
@@ -58,6 +59,18 @@ pub fn codegen_fulfill_obligation<'tcx>(
                 );
                 return Err(ErrorReported);
             }
+            Err(Unimplemented) => {
+                // This can trigger when we probe for the source of a `'static` lifetime requirement
+                // on a trait object: `impl Foo for dyn Trait {}` has an implicit `'static` bound.
+                infcx.tcx.sess.delay_span_bug(
+                    rustc_span::DUMMY_SP,
+                    &format!(
+                        "Encountered error `Unimplemented` selecting `{:?}` during codegen",
+                        trait_ref
+                    ),
+                );
+                return Err(ErrorReported);
+            }
             Err(e) => {
                 bug!("Encountered error `{:?}` selecting `{:?}` during codegen", e, trait_ref)
             }

src/librustc_trait_selection/traits/codegen/mod.rs

@@ -1706,6 +1706,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             | ObligationCauseCode::IntrinsicType
             | ObligationCauseCode::MethodReceiver
             | ObligationCauseCode::ReturnNoExpression
+            | ObligationCauseCode::UnifyReceiver(..)
             | ObligationCauseCode::MiscObligation => {}
             ObligationCauseCode::SliceOrArrayElem => {
                 err.note("slice and array elements must have `Sized` type");

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -6,6 +6,7 @@ use crate::hir::def_id::DefId;
 use crate::hir::GenericArg;
 use rustc_hir as hir;
 use rustc_infer::infer::{self, InferOk};
+use rustc_middle::traits::{ObligationCauseCode, UnifyReceiverContext};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCast};
 use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::fold::TypeFoldable;
@@ -91,7 +92,11 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         // signature (which is also done during probing).
         let method_sig_rcvr =
             self.normalize_associated_types_in(self.span, &method_sig.inputs()[0]);
-        self.unify_receivers(self_ty, method_sig_rcvr);
+        debug!(
+            "confirm: self_ty={:?} method_sig_rcvr={:?} method_sig={:?} method_predicates={:?}",
+            self_ty, method_sig_rcvr, method_sig, method_predicates
+        );
+        self.unify_receivers(self_ty, method_sig_rcvr, &pick, all_substs);
 
         let (method_sig, method_predicates) =
             self.normalize_associated_types_in(self.span, &(method_sig, method_predicates));
@@ -150,7 +155,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
             self.structurally_resolved_type(autoderef.span(), autoderef.final_ty(false));
 
         if let Some(mutbl) = pick.autoref {
-            let region = self.next_region_var(infer::Autoref(self.span));
+            let region = self.next_region_var(infer::Autoref(self.span, pick.item));
             target = self.tcx.mk_ref(region, ty::TypeAndMut { mutbl, ty: target });
             let mutbl = match mutbl {
                 hir::Mutability::Not => AutoBorrowMutability::Not,
@@ -334,8 +339,26 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         )
     }
 
-    fn unify_receivers(&mut self, self_ty: Ty<'tcx>, method_self_ty: Ty<'tcx>) {
-        match self.at(&self.misc(self.span), self.param_env).sup(method_self_ty, self_ty) {
+    fn unify_receivers(
+        &mut self,
+        self_ty: Ty<'tcx>,
+        method_self_ty: Ty<'tcx>,
+        pick: &probe::Pick<'tcx>,
+        substs: SubstsRef<'tcx>,
+    ) {
+        debug!(
+            "unify_receivers: self_ty={:?} method_self_ty={:?} span={:?} pick={:?}",
+            self_ty, method_self_ty, self.span, pick
+        );
+        let cause = self.cause(
+            self.span,
+            ObligationCauseCode::UnifyReceiver(Box::new(UnifyReceiverContext {
+                assoc_item: pick.item,
+                param_env: self.param_env,
+                substs,
+            })),
+        );
+        match self.at(&cause, self.param_env).sup(method_self_ty, self_ty) {
             Ok(InferOk { obligations, value: () }) => {
                 self.register_predicates(obligations);
             }

src/librustc_typeck/check/method/confirm.rs

@@ -35,7 +35,7 @@ fn baz<'a,'b>(x: &'a u32, y: &'b u32) -> (&'a u32, &'b u32) {
 
 #[cfg(transmute)] // one instantiations: BAD
 fn baz<'a,'b>(x: &'a u32) -> &'static u32 {
-   bar(foo, x) //[transmute]~ ERROR E0495
+   bar(foo, x) //[transmute]~ ERROR E0759
 }
 
 #[cfg(krisskross)] // two instantiations, mixing and matching: BAD

src/test/ui/associated-types/cache/project-fn-ret-contravariant.rs

@@ -1,26 +1,11 @@
-error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
+error[E0759]: `x` has lifetime `'a` but it needs to satisfy a `'static` lifetime requirement
   --> $DIR/project-fn-ret-contravariant.rs:38:8
    |
-LL |    bar(foo, x)
-   |        ^^^
-   |
-note: first, the lifetime cannot outlive the lifetime `'a` as defined on the function body at 37:8...
-  --> $DIR/project-fn-ret-contravariant.rs:37:8
-   |
 LL | fn baz<'a,'b>(x: &'a u32) -> &'static u32 {
-   |        ^^
-note: ...so that reference does not outlive borrowed content
-  --> $DIR/project-fn-ret-contravariant.rs:38:13
-   |
-LL |    bar(foo, x)
-   |             ^
-   = note: but, the lifetime must be valid for the static lifetime...
-note: ...so that reference does not outlive borrowed content
-  --> $DIR/project-fn-ret-contravariant.rs:38:4
-   |
+   |                  ------- this data with lifetime `'a`...
 LL |    bar(foo, x)
-   |    ^^^^^^^^^^^
+   |    ----^^^---- ...is captured and required to live as long as `'static` here
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0495`.
+For more information about this error, try `rustc --explain E0759`.

src/test/ui/associated-types/cache/project-fn-ret-contravariant.transmute.stderr

@@ -46,7 +46,7 @@ fn baz<'a, 'b>(x: Type<'a>) -> Type<'static> {
     // Cannot instantiate `foo` with any lifetime other than `'a`,
     // since it is provided as input.
 
-    bar(foo, x) //[transmute]~ ERROR E0495
+    bar(foo, x) //[transmute]~ ERROR E0759
 }
 
 #[cfg(krisskross)] // two instantiations, mixing and matching: BAD