Constify Fn* traits

Author: oli-obk

compiler/rustc_hir_typeck/src/upvar.rs

@@ -529,7 +529,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // process any deferred resolutions.
         let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
         for deferred_call_resolution in deferred_call_resolutions {
-            deferred_call_resolution.resolve(self);
+            deferred_call_resolution.resolve(&mut FnCtxt::new(
+                self,
+                self.param_env,
+                closure_def_id,
+            ));
         }
     }
 

compiler/rustc_trait_selection/src/traits/effects.rs

@@ -1,7 +1,8 @@
 use rustc_hir::{self as hir, LangItem};
 use rustc_infer::infer::{BoundRegionConversionTime, DefineOpaqueTypes};
 use rustc_infer::traits::{
-    ImplDerivedHostCause, ImplSource, Obligation, ObligationCauseCode, PredicateObligation,
+    ImplDerivedHostCause, ImplSource, Obligation, ObligationCause, ObligationCauseCode,
+    PredicateObligation,
 };
 use rustc_middle::span_bug;
 use rustc_middle::traits::query::NoSolution;
@@ -303,6 +304,9 @@ fn evaluate_host_effect_from_builtin_impls<'tcx>(
 ) -> Result<ThinVec<PredicateObligation<'tcx>>, EvaluationFailure> {
     match selcx.tcx().as_lang_item(obligation.predicate.def_id()) {
         Some(LangItem::Destruct) => evaluate_host_effect_for_destruct_goal(selcx, obligation),
+        Some(LangItem::Fn | LangItem::FnMut | LangItem::FnOnce) => {
+            evaluate_host_effect_for_fn_goal(selcx, obligation)
+        }
         _ => Err(EvaluationFailure::NoSolution),
     }
 }
@@ -398,6 +402,54 @@ fn evaluate_host_effect_for_destruct_goal<'tcx>(
         .collect())
 }
 
+// NOTE: Keep this in sync with `extract_fn_def_from_const_callable` in the new solver.
+fn evaluate_host_effect_for_fn_goal<'tcx>(
+    selcx: &mut SelectionContext<'_, 'tcx>,
+    obligation: &HostEffectObligation<'tcx>,
+) -> Result<ThinVec<PredicateObligation<'tcx>>, EvaluationFailure> {
+    let tcx = selcx.tcx();
+    let self_ty = obligation.predicate.self_ty();
+
+    let (def, args) = match *self_ty.kind() {
+        ty::FnDef(def, args) => (def, args),
+
+        // We may support function pointers at some point in the future
+        ty::FnPtr(..) => return Err(EvaluationFailure::NoSolution),
+
+        // Coroutines could implement `[const] Fn`,
+        // but they don't really need to right now.
+        ty::Closure(..)
+        | ty::CoroutineClosure(_, _)
+        | ty::Coroutine(_, _)
+        | ty::CoroutineWitness(_, _) => {
+            return Err(EvaluationFailure::NoSolution);
+        }
+
+        // Everything else needs explicit impls or cannot have an impl
+        _ => return Err(EvaluationFailure::NoSolution),
+    };
+
+    match tcx.constness(def) {
+        hir::Constness::Const => Ok(tcx
+            .const_conditions(def)
+            .instantiate(tcx, args)
+            .into_iter()
+            .map(|(c, span)| {
+                let code = ObligationCauseCode::WhereClause(def, span);
+                let cause =
+                    ObligationCause::new(obligation.cause.span, obligation.cause.body_id, code);
+                Obligation::new(
+                    tcx,
+                    cause,
+                    obligation.param_env,
+                    c.to_host_effect_clause(tcx, obligation.predicate.constness),
+                )
+            })
+            .collect()),
+        hir::Constness::NotConst => Err(EvaluationFailure::NoSolution),
+    }
+}
+
 fn evaluate_host_effect_from_selection_candidate<'tcx>(
     selcx: &mut SelectionContext<'_, 'tcx>,
     obligation: &HostEffectObligation<'tcx>,

library/core/src/ops/function.rs

@@ -72,7 +72,8 @@ use crate::marker::Tuple;
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
-// FIXME(const_trait_impl) #[const_trait]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait Fn<Args: Tuple>: FnMut<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -159,7 +160,8 @@ pub trait Fn<Args: Tuple>: FnMut<Args> {
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
-// FIXME(const_trait_impl) #[const_trait]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait FnMut<Args: Tuple>: FnOnce<Args> {
     /// Performs the call operation.
     #[unstable(feature = "fn_traits", issue = "29625")]
@@ -238,7 +240,8 @@ pub trait FnMut<Args: Tuple>: FnOnce<Args> {
 )]
 #[fundamental] // so that regex can rely that `&str: !FnMut`
 #[must_use = "closures are lazy and do nothing unless called"]
-// FIXME(const_trait_impl) #[const_trait]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait FnOnce<Args: Tuple> {
     /// The returned type after the call operator is used.
     #[lang = "fn_once_output"]
@@ -254,29 +257,32 @@ mod impls {
     use crate::marker::Tuple;
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: Tuple, F: ?Sized> Fn<A> for &F
+    #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+    impl<A: Tuple, F: ?Sized> const Fn<A> for &F
     where
-        F: Fn<A>,
+        F: ~const Fn<A>,
     {
         extern "rust-call" fn call(&self, args: A) -> F::Output {
             (**self).call(args)
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: Tuple, F: ?Sized> FnMut<A> for &F
+    #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+    impl<A: Tuple, F: ?Sized> const FnMut<A> for &F
     where
-        F: Fn<A>,
+        F: ~const Fn<A>,
     {
         extern "rust-call" fn call_mut(&mut self, args: A) -> F::Output {
             (**self).call(args)
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: Tuple, F: ?Sized> FnOnce<A> for &F
+    #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+    impl<A: Tuple, F: ?Sized> const FnOnce<A> for &F
     where
-        F: Fn<A>,
+        F: ~const Fn<A>,
     {
         type Output = F::Output;
 
@@ -286,19 +292,21 @@ mod impls {
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: Tuple, F: ?Sized> FnMut<A> for &mut F
+    #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+    impl<A: Tuple, F: ?Sized> const FnMut<A> for &mut F
     where
-        F: FnMut<A>,
+        F: ~const FnMut<A>,
     {
         extern "rust-call" fn call_mut(&mut self, args: A) -> F::Output {
             (*self).call_mut(args)
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: Tuple, F: ?Sized> FnOnce<A> for &mut F
+    #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+    impl<A: Tuple, F: ?Sized> const FnOnce<A> for &mut F
     where
-        F: FnMut<A>,
+        F: ~const FnMut<A>,
     {
         type Output = F::Output;
         extern "rust-call" fn call_once(self, args: A) -> F::Output {

tests/ui/consts/fn_trait_refs.stderr

@@ -4,151 +4,6 @@ error[E0635]: unknown feature `const_fn_trait_ref_impls`
 LL | #![feature(const_fn_trait_ref_impls)]
    |            ^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:14:8
-   |
-LL |     T: [const] Fn<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `Fn`
-   |
-note: `Fn` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:14:8
-   |
-LL |     T: [const] Fn<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `Fn`
-   |
-note: `Fn` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:14:8
-   |
-LL |     T: [const] Fn<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `Fn`
-   |
-note: `Fn` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:21:8
-   |
-LL |     T: [const] FnMut<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `FnMut`
-   |
-note: `FnMut` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:21:8
-   |
-LL |     T: [const] FnMut<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `FnMut`
-   |
-note: `FnMut` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:21:8
-   |
-LL |     T: [const] FnMut<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `FnMut`
-   |
-note: `FnMut` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:28:8
-   |
-LL |     T: [const] FnOnce<()>,
-   |        ^^^^^^^ can't be applied to `FnOnce`
-   |
-note: `FnOnce` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:28:8
-   |
-LL |     T: [const] FnOnce<()>,
-   |        ^^^^^^^ can't be applied to `FnOnce`
-   |
-note: `FnOnce` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:28:8
-   |
-LL |     T: [const] FnOnce<()>,
-   |        ^^^^^^^ can't be applied to `FnOnce`
-   |
-note: `FnOnce` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:35:8
-   |
-LL |     T: [const] Fn<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `Fn`
-   |
-note: `Fn` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:35:8
-   |
-LL |     T: [const] Fn<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `Fn`
-   |
-note: `Fn` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:35:8
-   |
-LL |     T: [const] Fn<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `Fn`
-   |
-note: `Fn` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:49:8
-   |
-LL |     T: [const] FnMut<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `FnMut`
-   |
-note: `FnMut` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:49:8
-   |
-LL |     T: [const] FnMut<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `FnMut`
-   |
-note: `FnMut` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: `[const]` can only be applied to `#[const_trait]` traits
-  --> $DIR/fn_trait_refs.rs:49:8
-   |
-LL |     T: [const] FnMut<()> + [const] Destruct,
-   |        ^^^^^^^ can't be applied to `FnMut`
-   |
-note: `FnMut` can't be used with `[const]` because it isn't annotated with `#[const_trait]`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
 error[E0277]: the trait bound `(i32, i32, i32): const PartialEq` is not satisfied
   --> $DIR/fn_trait_refs.rs:71:17
    |
@@ -161,31 +16,7 @@ error[E0277]: the trait bound `(i32, i32): const PartialEq` is not satisfied
 LL |         assert!(test_two == (2, 2));
    |                 ^^^^^^^^^^^^^^^^^^
 
-error[E0015]: cannot call non-const closure in constant functions
-  --> $DIR/fn_trait_refs.rs:16:5
-   |
-LL |     f()
-   |     ^^^
-   |
-   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
-
-error[E0015]: cannot call non-const closure in constant functions
-  --> $DIR/fn_trait_refs.rs:23:5
-   |
-LL |     f()
-   |     ^^^
-   |
-   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
-
-error[E0015]: cannot call non-const closure in constant functions
-  --> $DIR/fn_trait_refs.rs:30:5
-   |
-LL |     f()
-   |     ^^^
-   |
-   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
-
-error: aborting due to 21 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0015, E0277, E0635.
-For more information about an error, try `rustc --explain E0015`.
+Some errors have detailed explanations: E0277, E0635.
+For more information about an error, try `rustc --explain E0277`.