Implement the Fn trait for bare fn pointers in the compiler rather than doing it using hard-coded impls. This means that it works also for more complex fn types involving bound regions. Fixes #19126.

Author: nikomatsakis

src/libcore/ops.rs

@@ -833,48 +833,52 @@ impl<F,A,R> FnOnce<A,R> for F
     }
 }
 
-
-impl<Result> Fn<(),Result> for extern "Rust" fn() -> Result {
-    #[allow(non_snake_case)]
-    extern "rust-call" fn call(&self, _args: ()) -> Result {
-        (*self)()
+#[cfg(stage0)]
+mod fn_impls {
+    use super::Fn;
+
+    impl<Result> Fn<(),Result> for extern "Rust" fn() -> Result {
+        #[allow(non_snake_case)]
+        extern "rust-call" fn call(&self, _args: ()) -> Result {
+            (*self)()
+        }
     }
-}
 
-impl<Result,A0> Fn<(A0,),Result> for extern "Rust" fn(A0) -> Result {
-    #[allow(non_snake_case)]
-    extern "rust-call" fn call(&self, args: (A0,)) -> Result {
-        let (a0,) = args;
-        (*self)(a0)
+    impl<Result,A0> Fn<(A0,),Result> for extern "Rust" fn(A0) -> Result {
+        #[allow(non_snake_case)]
+        extern "rust-call" fn call(&self, args: (A0,)) -> Result {
+            let (a0,) = args;
+            (*self)(a0)
+        }
     }
-}
 
-macro_rules! def_fn(
-    ($($args:ident)*) => (
-        impl<Result$(,$args)*>
-        Fn<($($args,)*),Result>
-        for extern "Rust" fn($($args: $args,)*) -> Result {
-            #[allow(non_snake_case)]
-            extern "rust-call" fn call(&self, args: ($($args,)*)) -> Result {
-                let ($($args,)*) = args;
-                (*self)($($args,)*)
+    macro_rules! def_fn(
+        ($($args:ident)*) => (
+            impl<Result$(,$args)*>
+            Fn<($($args,)*),Result>
+            for extern "Rust" fn($($args: $args,)*) -> Result {
+                #[allow(non_snake_case)]
+                extern "rust-call" fn call(&self, args: ($($args,)*)) -> Result {
+                    let ($($args,)*) = args;
+                    (*self)($($args,)*)
+                }
             }
-        }
+        )
     )
-)
 
-def_fn!(A0 A1)
-def_fn!(A0 A1 A2)
-def_fn!(A0 A1 A2 A3)
-def_fn!(A0 A1 A2 A3 A4)
-def_fn!(A0 A1 A2 A3 A4 A5)
-def_fn!(A0 A1 A2 A3 A4 A5 A6)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14)
-def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15)
+    def_fn!(A0 A1)
+    def_fn!(A0 A1 A2)
+    def_fn!(A0 A1 A2 A3)
+    def_fn!(A0 A1 A2 A3 A4)
+    def_fn!(A0 A1 A2 A3 A4 A5)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14)
+    def_fn!(A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15)
+}

src/librustc/middle/traits/mod.rs

@@ -167,18 +167,21 @@ pub enum Vtable<'tcx, N> {
     /// Vtable identifying a particular impl.
     VtableImpl(VtableImplData<'tcx, N>),
 
-    /// Vtable automatically generated for an unboxed closure. The def
-    /// ID is the ID of the closure expression. This is a `VtableImpl`
-    /// in spirit, but the impl is generated by the compiler and does
-    /// not appear in the source.
-    VtableUnboxedClosure(ast::DefId, subst::Substs<'tcx>),
-
     /// Successful resolution to an obligation provided by the caller
     /// for some type parameter.
     VtableParam(VtableParamData<'tcx>),
 
     /// Successful resolution for a builtin trait.
     VtableBuiltin(VtableBuiltinData<N>),
+
+    /// Vtable automatically generated for an unboxed closure. The def
+    /// ID is the ID of the closure expression. This is a `VtableImpl`
+    /// in spirit, but the impl is generated by the compiler and does
+    /// not appear in the source.
+    VtableUnboxedClosure(ast::DefId, subst::Substs<'tcx>),
+
+    /// Same as above, but for a fn pointer type with the given signature.
+    VtableFnPointer(ty::Ty<'tcx>),
 }
 
 /// Identifies a particular impl in the source, along with a set of
@@ -322,6 +325,7 @@ impl<'tcx, N> Vtable<'tcx, N> {
     pub fn iter_nested(&self) -> Items<N> {
         match *self {
             VtableImpl(ref i) => i.iter_nested(),
+            VtableFnPointer(..) => (&[]).iter(),
             VtableUnboxedClosure(..) => (&[]).iter(),
             VtableParam(_) => (&[]).iter(),
             VtableBuiltin(ref i) => i.iter_nested(),
@@ -331,6 +335,7 @@ impl<'tcx, N> Vtable<'tcx, N> {
     pub fn map_nested<M>(&self, op: |&N| -> M) -> Vtable<'tcx, M> {
         match *self {
             VtableImpl(ref i) => VtableImpl(i.map_nested(op)),
+            VtableFnPointer(ref sig) => VtableFnPointer((*sig).clone()),
             VtableUnboxedClosure(d, ref s) => VtableUnboxedClosure(d, s.clone()),
             VtableParam(ref p) => VtableParam((*p).clone()),
             VtableBuiltin(ref i) => VtableBuiltin(i.map_nested(op)),
@@ -340,6 +345,7 @@ impl<'tcx, N> Vtable<'tcx, N> {
     pub fn map_move_nested<M>(self, op: |N| -> M) -> Vtable<'tcx, M> {
         match self {
             VtableImpl(i) => VtableImpl(i.map_move_nested(op)),
+            VtableFnPointer(sig) => VtableFnPointer(sig),
             VtableUnboxedClosure(d, s) => VtableUnboxedClosure(d, s),
             VtableParam(p) => VtableParam(p),
             VtableBuiltin(i) => VtableBuiltin(i.map_move_nested(op)),

src/librustc/middle/traits/select.rs

@@ -22,7 +22,7 @@ use super::{SelectionError, Unimplemented, Overflow,
             OutputTypeParameterMismatch};
 use super::{Selection};
 use super::{SelectionResult};
-use super::{VtableBuiltin, VtableImpl, VtableParam, VtableUnboxedClosure};
+use super::{VtableBuiltin, VtableImpl, VtableParam, VtableUnboxedClosure, VtableFnPointer};
 use super::{VtableImplData, VtableParamData, VtableBuiltinData};
 use super::{util};
 
@@ -36,7 +36,7 @@ use middle::ty_fold::TypeFoldable;
 use std::cell::RefCell;
 use std::collections::hash_map::HashMap;
 use std::rc::Rc;
-use syntax::ast;
+use syntax::{abi, ast};
 use util::common::ErrorReported;
 use util::ppaux::Repr;
 
@@ -131,7 +131,15 @@ enum Candidate<'tcx> {
     BuiltinCandidate(ty::BuiltinBound),
     ParamCandidate(VtableParamData<'tcx>),
     ImplCandidate(ast::DefId),
+
+    /// Implementation of a `Fn`-family trait by one of the
+    /// anonymous types generated for a `||` expression.
     UnboxedClosureCandidate(/* closure */ ast::DefId, Substs<'tcx>),
+
+    /// Implementation of a `Fn`-family trait by one of the anonymous
+    /// types generated for a fn pointer type (e.g., `fn(int)->int`)
+    FnPointerCandidate,
+
     ErrorCandidate,
 }
 
@@ -917,7 +925,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             None => {
                 // For the time being, we ignore user-defined impls for builtin-bounds.
                 // (And unboxed candidates only apply to the Fn/FnMut/etc traits.)
-                try!(self.assemble_unboxed_candidates(obligation, &mut candidates));
+                try!(self.assemble_unboxed_closure_candidates(obligation, &mut candidates));
+                try!(self.assemble_fn_pointer_candidates(obligation, &mut candidates));
                 try!(self.assemble_candidates_from_impls(obligation, &mut candidates));
             }
         }
@@ -968,20 +977,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// Note: the type parameters on an unboxed closure candidate are modeled as *output* type
     /// parameters and hence do not affect whether this trait is a match or not. They will be
     /// unified during the confirmation step.
-    fn assemble_unboxed_candidates(&mut self,
-                                   obligation: &Obligation<'tcx>,
-                                   candidates: &mut CandidateSet<'tcx>)
-                                   -> Result<(),SelectionError<'tcx>>
+    fn assemble_unboxed_closure_candidates(&mut self,
+                                           obligation: &Obligation<'tcx>,
+                                           candidates: &mut CandidateSet<'tcx>)
+                                           -> Result<(),SelectionError<'tcx>>
     {
-        let tcx = self.tcx();
-        let kind = if Some(obligation.trait_ref.def_id) == tcx.lang_items.fn_trait() {
-            ty::FnUnboxedClosureKind
-        } else if Some(obligation.trait_ref.def_id) == tcx.lang_items.fn_mut_trait() {
-            ty::FnMutUnboxedClosureKind
-        } else if Some(obligation.trait_ref.def_id) == tcx.lang_items.fn_once_trait() {
-            ty::FnOnceUnboxedClosureKind
-        } else {
-            return Ok(()); // not a fn trait, ignore
+        let kind = match self.fn_family_trait_kind(obligation.trait_ref.def_id) {
+            Some(k) => k,
+            None => { return Ok(()); }
         };
 
         let self_ty = self.infcx.shallow_resolve(obligation.self_ty());
@@ -1015,6 +1018,42 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         Ok(())
     }
 
+    /// Implement one of the `Fn()` family for a fn pointer.
+    fn assemble_fn_pointer_candidates(&mut self,
+                                      obligation: &Obligation<'tcx>,
+                                      candidates: &mut CandidateSet<'tcx>)
+                                      -> Result<(),SelectionError<'tcx>>
+    {
+        // We provide a `Fn` impl for fn pointers (but not e.g. `FnMut`).
+        if Some(obligation.trait_ref.def_id) != self.tcx().lang_items.fn_trait() {
+            return Ok(());
+        }
+
+        let self_ty = self.infcx.shallow_resolve(obligation.self_ty());
+        match self_ty.sty {
+            ty::ty_infer(..) => {
+                candidates.ambiguous = true; // could wind up being a fn() type
+            }
+
+            // provide an impl, but only for suitable `fn` pointers
+            ty::ty_bare_fn(ty::BareFnTy {
+                fn_style: ast::NormalFn,
+                abi: abi::Rust,
+                sig: ty::FnSig {
+                    inputs: _,
+                    output: ty::FnConverging(_),
+                    variadic: false
+                }
+            }) => {
+                candidates.vec.push(FnPointerCandidate);
+            }
+
+            _ => { }
+        }
+
+        Ok(())
+    }
+
     /// Search for impls that might apply to `obligation`.
     fn assemble_candidates_from_impls(&mut self,
                                       obligation: &Obligation<'tcx>,
@@ -1551,6 +1590,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 try!(self.confirm_unboxed_closure_candidate(obligation, closure_def_id, &substs));
                 Ok(VtableUnboxedClosure(closure_def_id, substs))
             }
+
+            FnPointerCandidate => {
+                let fn_type =
+                    try!(self.confirm_fn_pointer_candidate(obligation));
+                Ok(VtableFnPointer(fn_type))
+            }
         }
     }
 
@@ -1646,6 +1691,51 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                          nested: impl_obligations }
     }
 
+    fn confirm_fn_pointer_candidate(&mut self,
+                                    obligation: &Obligation<'tcx>)
+                                    -> Result<ty::Ty<'tcx>,SelectionError<'tcx>>
+    {
+        debug!("confirm_fn_pointer_candidate({})",
+               obligation.repr(self.tcx()));
+
+        let self_ty = self.infcx.shallow_resolve(obligation.self_ty());
+        let sig = match self_ty.sty {
+            ty::ty_bare_fn(ty::BareFnTy {
+                fn_style: ast::NormalFn,
+                abi: abi::Rust,
+                ref sig
+            }) => {
+                (*sig).clone()
+            }
+            _ => {
+                self.tcx().sess.span_bug(
+                    obligation.cause.span,
+                    format!("Fn pointer candidate for inappropriate self type: {}",
+                            self_ty.repr(self.tcx())).as_slice());
+            }
+        };
+
+        let arguments_tuple = ty::mk_tup(self.tcx(), sig.inputs.to_vec());
+        let output_type = sig.output.unwrap();
+        let substs =
+            Substs::new_trait(
+                vec![arguments_tuple, output_type],
+                vec![],
+                vec![],
+                self_ty);
+        let trait_ref = Rc::new(ty::TraitRef {
+            def_id: obligation.trait_ref.def_id,
+            substs: substs,
+        });
+
+        let () =
+            try!(self.confirm(obligation.cause,
+                              obligation.trait_ref.clone(),
+                              trait_ref));
+
+        Ok(self_ty)
+    }
+
     fn confirm_unboxed_closure_candidate(&mut self,
                                          obligation: &Obligation<'tcx>,
                                          closure_def_id: ast::DefId,
@@ -1964,6 +2054,22 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         util::obligations_for_generics(self.tcx(), cause, recursion_depth,
                                        &bounds, &impl_substs.types)
     }
+
+    fn fn_family_trait_kind(&self,
+                            trait_def_id: ast::DefId)
+                            -> Option<ty::UnboxedClosureKind>
+    {
+        let tcx = self.tcx();
+        if Some(trait_def_id) == tcx.lang_items.fn_trait() {
+            Some(ty::FnUnboxedClosureKind)
+        } else if Some(trait_def_id) == tcx.lang_items.fn_mut_trait() {
+            Some(ty::FnMutUnboxedClosureKind)
+        } else if Some(trait_def_id) == tcx.lang_items.fn_once_trait() {
+            Some(ty::FnOnceUnboxedClosureKind)
+        } else {
+            None
+        }
+    }
 }
 
 impl<'tcx> Repr<'tcx> for Candidate<'tcx> {
@@ -1972,7 +2078,10 @@ impl<'tcx> Repr<'tcx> for Candidate<'tcx> {
             ErrorCandidate => format!("ErrorCandidate"),
             BuiltinCandidate(b) => format!("BuiltinCandidate({})", b),
             UnboxedClosureCandidate(c, ref s) => {
-                format!("MatchedUnboxedClosureCandidate({},{})", c, s.repr(tcx))
+                format!("UnboxedClosureCandidate({},{})", c, s.repr(tcx))
+            }
+            FnPointerCandidate => {
+                format!("FnPointerCandidate")
             }
             ParamCandidate(ref a) => format!("ParamCandidate({})", a.repr(tcx)),
             ImplCandidate(a) => format!("ImplCandidate({})", a.repr(tcx)),

src/librustc/middle/traits/util.rs

@@ -302,6 +302,10 @@ impl<'tcx, N:Repr<'tcx>> Repr<'tcx> for super::Vtable<'tcx, N> {
                         d.repr(tcx),
                         s.repr(tcx)),
 
+            super::VtableFnPointer(ref d) =>
+                format!("VtableFnPointer({})",
+                        d.repr(tcx)),
+
             super::VtableParam(ref v) =>
                 format!("VtableParam({})", v.repr(tcx)),
 

src/librustc/middle/ty_fold.rs

@@ -466,6 +466,9 @@ impl<'tcx, N: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::Vtable<'tcx, N>
             traits::VtableUnboxedClosure(d, ref s) => {
                 traits::VtableUnboxedClosure(d, s.fold_with(folder))
             }
+            traits::VtableFnPointer(ref d) => {
+                traits::VtableFnPointer(d.fold_with(folder))
+            }
             traits::VtableParam(ref p) => traits::VtableParam(p.fold_with(folder)),
             traits::VtableBuiltin(ref d) => traits::VtableBuiltin(d.fold_with(folder)),
         }