Auto merge of #42417 - eddyb:separate-fn-sig, r=nikomatsakis

Don't drag function signatures along function item types.

This PR separates the signature of a function from the "function item type" (`TyFnDef`), leaving only the `DefId` and parameter `Substs`, making them even more like (captureless) closure types.

The motivation for this change is reducing typesystem complexity, and its consequences:
* operating on the signature instead of just the parameters was less efficient
  * specifically, signatures can easily add several levels of depth on top of the parameter types
  * and the signatured were always substituted and normalized, so typically even more complex
* it was *the only* type that was *both* nominal (identity) and structural (signature)
  * harder to model in Chalk than either a purely nominal or structural type
  * subtyping worked on the signature but parameters were always invariant
  * call type-checking was transforming signatures but keeping the nominal half intact
  * the signature could therefore get out of sync during type inference in several ways

That last point comes with a `[breaking-change]`, because functions with `'static` in their return types will now *not* be as usable as if they were using lifetime parameters instead:
```rust
// Will cause lifetime mismatch in main after this PR.
fn bar() -> &'static str { "bar" }
// Will continue to work fine, as every use can choose its own lifetime.
fn bar<'a>() -> &'a str { "bar" }

fn main() {
    let s = String::from("foo");
    Some(&s[..]).unwrap_or_else(bar);
}
```

r? @nikomatsakis

src/librustc/ich/impls_ty.rs

@@ -524,10 +524,9 @@ for ty::TypeVariants<'tcx>
                 region.hash_stable(hcx, hasher);
                 pointee_ty.hash_stable(hcx, hasher);
             }
-            TyFnDef(def_id, substs, ref sig) => {
+            TyFnDef(def_id, substs) => {
                 def_id.hash_stable(hcx, hasher);
                 substs.hash_stable(hcx, hasher);
-                sig.hash_stable(hcx, hasher);
             }
             TyFnPtr(ref sig) => {
                 sig.hash_stable(hcx, hasher);

src/librustc/infer/mod.rs

@@ -1369,7 +1369,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         Some(self.tcx.closure_kind(def_id))
     }
 
-    pub fn closure_type(&self, def_id: DefId) -> ty::PolyFnSig<'tcx> {
+    /// Obtain the signature of a function or closure.
+    /// For closures, unlike `tcx.fn_sig(def_id)`, this method will
+    /// work during the type-checking of the enclosing function and
+    /// return the closure signature in its partially inferred state.
+    pub fn fn_sig(&self, def_id: DefId) -> ty::PolyFnSig<'tcx> {
         if let Some(tables) = self.in_progress_tables {
             if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
                 if let Some(&ty) = tables.borrow().closure_tys.get(&id) {
@@ -1378,7 +1382,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             }
         }
 
-        self.tcx.closure_type(def_id)
+        self.tcx.fn_sig(def_id)
     }
 }
 

src/librustc/middle/effect.rs

@@ -12,7 +12,7 @@
 //! `unsafe`.
 use self::RootUnsafeContext::*;
 
-use ty::{self, Ty, TyCtxt};
+use ty::{self, TyCtxt};
 use lint;
 
 use syntax::ast;
@@ -40,14 +40,6 @@ enum RootUnsafeContext {
     UnsafeBlock(ast::NodeId),
 }
 
-fn type_is_unsafe_function(ty: Ty) -> bool {
-    match ty.sty {
-        ty::TyFnDef(.., f) |
-        ty::TyFnPtr(f) => f.unsafety() == hir::Unsafety::Unsafe,
-        _ => false,
-    }
-}
-
 struct EffectCheckVisitor<'a, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     tables: &'a ty::TypeckTables<'tcx>,
@@ -174,10 +166,11 @@ impl<'a, 'tcx> Visitor<'tcx> for EffectCheckVisitor<'a, 'tcx> {
         match expr.node {
             hir::ExprMethodCall(..) => {
                 let def_id = self.tables.type_dependent_defs[&expr.id].def_id();
-                let base_type = self.tcx.type_of(def_id);
-                debug!("effect: method call case, base type is {:?}",
-                        base_type);
-                if type_is_unsafe_function(base_type) {
+                let sig = self.tcx.fn_sig(def_id);
+                debug!("effect: method call case, signature is {:?}",
+                        sig);
+
+                if sig.0.unsafety == hir::Unsafety::Unsafe {
                     self.require_unsafe(expr.span,
                                         "invocation of unsafe method")
                 }
@@ -186,8 +179,13 @@ impl<'a, 'tcx> Visitor<'tcx> for EffectCheckVisitor<'a, 'tcx> {
                 let base_type = self.tables.expr_ty_adjusted(base);
                 debug!("effect: call case, base type is {:?}",
                         base_type);
-                if type_is_unsafe_function(base_type) {
-                    self.require_unsafe(expr.span, "call to unsafe function")
+                match base_type.sty {
+                    ty::TyFnDef(..) | ty::TyFnPtr(_) => {
+                        if base_type.fn_sig(self.tcx).unsafety() == hir::Unsafety::Unsafe {
+                            self.require_unsafe(expr.span, "call to unsafe function")
+                        }
+                    }
+                    _ => {}
                 }
             }
             hir::ExprUnary(hir::UnDeref, ref base) => {

src/librustc/middle/intrinsicck.rs

@@ -66,11 +66,8 @@ fn unpack_option_like<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
 impl<'a, 'tcx> ExprVisitor<'a, 'tcx> {
     fn def_id_is_transmute(&self, def_id: DefId) -> bool {
-        let intrinsic = match self.tcx.type_of(def_id).sty {
-            ty::TyFnDef(.., bfty) => bfty.abi() == RustIntrinsic,
-            _ => return false
-        };
-        intrinsic && self.tcx.item_name(def_id) == "transmute"
+        self.tcx.fn_sig(def_id).abi() == RustIntrinsic &&
+        self.tcx.item_name(def_id) == "transmute"
     }
 
     fn check_transmute(&self, span: Span, from: Ty<'tcx>, to: Ty<'tcx>) {
@@ -153,22 +150,14 @@ impl<'a, 'tcx> Visitor<'tcx> for ExprVisitor<'a, 'tcx> {
         } else {
             Def::Err
         };
-        match def {
-            Def::Fn(did) if self.def_id_is_transmute(did) => {
+        if let Def::Fn(did) = def {
+            if self.def_id_is_transmute(did) {
                 let typ = self.tables.node_id_to_type(expr.id);
-                let typ = self.tcx.lift_to_global(&typ).unwrap();
-                match typ.sty {
-                    ty::TyFnDef(.., sig) if sig.abi() == RustIntrinsic => {
-                        let from = sig.inputs().skip_binder()[0];
-                        let to = *sig.output().skip_binder();
-                        self.check_transmute(expr.span, from, to);
-                    }
-                    _ => {
-                        span_bug!(expr.span, "transmute wasn't a bare fn?!");
-                    }
-                }
+                let sig = typ.fn_sig(self.tcx);
+                let from = sig.inputs().skip_binder()[0];
+                let to = *sig.output().skip_binder();
+                self.check_transmute(expr.span, from, to);
             }
-            _ => {}
         }
 
         intravisit::walk_expr(self, expr);

src/librustc/traits/object_safety.rs

@@ -260,7 +260,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
         // The `Self` type is erased, so it should not appear in list of
         // arguments or return type apart from the receiver.
-        let ref sig = self.type_of(method.def_id).fn_sig();
+        let ref sig = self.fn_sig(method.def_id);
         for input_ty in &sig.skip_binder().inputs()[1..] {
             if self.contains_illegal_self_type_reference(trait_def_id, input_ty) {
                 return Some(MethodViolationCode::ReferencesSelf);

src/librustc/traits/project.rs

@@ -1137,9 +1137,19 @@ fn confirm_fn_pointer_candidate<'cx, 'gcx, 'tcx>(
     -> Progress<'tcx>
 {
     let fn_type = selcx.infcx().shallow_resolve(fn_pointer_vtable.fn_ty);
-    let sig = fn_type.fn_sig();
+    let sig = fn_type.fn_sig(selcx.tcx());
+    let Normalized {
+        value: sig,
+        obligations
+    } = normalize_with_depth(selcx,
+                             obligation.param_env,
+                             obligation.cause.clone(),
+                             obligation.recursion_depth+1,
+                             &sig);
+
     confirm_callable_candidate(selcx, obligation, sig, util::TupleArgumentsFlag::Yes)
         .with_addl_obligations(fn_pointer_vtable.nested)
+        .with_addl_obligations(obligations)
 }
 
 fn confirm_closure_candidate<'cx, 'gcx, 'tcx>(
@@ -1149,7 +1159,7 @@ fn confirm_closure_candidate<'cx, 'gcx, 'tcx>(
     -> Progress<'tcx>
 {
     let closure_typer = selcx.closure_typer();
-    let closure_type = closure_typer.closure_type(vtable.closure_def_id)
+    let closure_type = closure_typer.fn_sig(vtable.closure_def_id)
         .subst(selcx.tcx(), vtable.substs.substs);
     let Normalized {
         value: closure_type,

src/librustc/traits/select.rs

@@ -1404,19 +1404,15 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             }
 
             // provide an impl, but only for suitable `fn` pointers
-            ty::TyFnDef(.., ty::Binder(ty::FnSig {
-                unsafety: hir::Unsafety::Normal,
-                abi: Abi::Rust,
-                variadic: false,
-                ..
-            })) |
-            ty::TyFnPtr(ty::Binder(ty::FnSig {
-                unsafety: hir::Unsafety::Normal,
-                abi: Abi::Rust,
-                variadic: false,
-                ..
-            })) => {
-                candidates.vec.push(FnPointerCandidate);
+            ty::TyFnDef(..) | ty::TyFnPtr(_) => {
+                if let ty::Binder(ty::FnSig {
+                    unsafety: hir::Unsafety::Normal,
+                    abi: Abi::Rust,
+                    variadic: false,
+                    ..
+                }) = self_ty.fn_sig(self.tcx()) {
+                    candidates.vec.push(FnPointerCandidate);
+                }
             }
 
             _ => { }
@@ -2348,19 +2344,26 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
 
         // ok to skip binder; it is reintroduced below
         let self_ty = self.infcx.shallow_resolve(*obligation.self_ty().skip_binder());
-        let sig = self_ty.fn_sig();
+        let sig = self_ty.fn_sig(self.tcx());
         let trait_ref =
             self.tcx().closure_trait_ref_and_return_type(obligation.predicate.def_id(),
                                                          self_ty,
                                                          sig,
                                                          util::TupleArgumentsFlag::Yes)
             .map_bound(|(trait_ref, _)| trait_ref);
 
+        let Normalized { value: trait_ref, obligations } =
+            project::normalize_with_depth(self,
+                                          obligation.param_env,
+                                          obligation.cause.clone(),
+                                          obligation.recursion_depth + 1,
+                                          &trait_ref);
+
         self.confirm_poly_trait_refs(obligation.cause.clone(),
                                      obligation.param_env,
                                      obligation.predicate.to_poly_trait_ref(),
                                      trait_ref)?;
-        Ok(VtableFnPointerData { fn_ty: self_ty, nested: vec![] })
+        Ok(VtableFnPointerData { fn_ty: self_ty, nested: obligations })
     }
 
     fn confirm_closure_candidate(&mut self,
@@ -2799,7 +2802,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                                       substs: ty::ClosureSubsts<'tcx>)
                                       -> ty::PolyTraitRef<'tcx>
     {
-        let closure_type = self.infcx.closure_type(closure_def_id)
+        let closure_type = self.infcx.fn_sig(closure_def_id)
             .subst(self.tcx(), substs.substs);
         let ty::Binder((trait_ref, _)) =
             self.tcx().closure_trait_ref_and_return_type(obligation.predicate.def_id(),

src/librustc/ty/context.rs

@@ -1378,9 +1378,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     }
 
     pub fn mk_fn_def(self, def_id: DefId,
-                     substs: &'tcx Substs<'tcx>,
-                     fty: PolyFnSig<'tcx>) -> Ty<'tcx> {
-        self.mk_ty(TyFnDef(def_id, substs, fty))
+                     substs: &'tcx Substs<'tcx>) -> Ty<'tcx> {
+        self.mk_ty(TyFnDef(def_id, substs))
     }
 
     pub fn mk_fn_ptr(self, fty: PolyFnSig<'tcx>) -> Ty<'tcx> {

src/librustc/ty/fast_reject.rs

@@ -68,14 +68,15 @@ pub fn simplify_type<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
             // view of possibly unifying
             simplify_type(tcx, mt.ty, can_simplify_params)
         }
+        ty::TyFnDef(def_id, _) |
         ty::TyClosure(def_id, _) => {
             Some(ClosureSimplifiedType(def_id))
         }
         ty::TyNever => Some(NeverSimplifiedType),
         ty::TyTuple(ref tys, _) => {
             Some(TupleSimplifiedType(tys.len()))
         }
-        ty::TyFnDef(.., ref f) | ty::TyFnPtr(ref f) => {
+        ty::TyFnPtr(ref f) => {
             Some(FunctionSimplifiedType(f.skip_binder().inputs().len()))
         }
         ty::TyProjection(_) | ty::TyParam(_) => {

src/librustc/ty/flags.rs

@@ -155,9 +155,8 @@ impl FlagComputation {
                 self.add_tys(&ts[..]);
             }
 
-            &ty::TyFnDef(_, substs, f) => {
+            &ty::TyFnDef(_, substs) => {
                 self.add_substs(substs);
-                self.add_fn_sig(f);
             }
 
             &ty::TyFnPtr(f) => {

src/librustc/ty/item_path.rs

@@ -348,7 +348,7 @@ pub fn characteristic_def_id_of_type(ty: Ty) -> Option<DefId> {
                                       .filter_map(|ty| characteristic_def_id_of_type(ty))
                                       .next(),
 
-        ty::TyFnDef(def_id, ..) |
+        ty::TyFnDef(def_id, _) |
         ty::TyClosure(def_id, _) => Some(def_id),
 
         ty::TyBool |

src/librustc/ty/maps.rs

@@ -875,13 +875,12 @@ define_maps! { <'tcx>
     /// for trans. This is also the only query that can fetch non-local MIR, at present.
     [] optimized_mir: Mir(DefId) -> &'tcx mir::Mir<'tcx>,
 
-    /// Records the type of each closure. The def ID is the ID of the
+    /// Type of each closure. The def ID is the ID of the
     /// expression defining the closure.
     [] closure_kind: ItemSignature(DefId) -> ty::ClosureKind,
 
-    /// Records the type of each closure. The def ID is the ID of the
-    /// expression defining the closure.
-    [] closure_type: ItemSignature(DefId) -> ty::PolyFnSig<'tcx>,
+    /// The signature of functions and closures.
+    [] fn_sig: ItemSignature(DefId) -> ty::PolyFnSig<'tcx>,
 
     /// Caches CoerceUnsized kinds for impls on custom types.
     [] coerce_unsized_info: ItemSignature(DefId)

src/librustc/ty/mod.rs

@@ -206,7 +206,7 @@ impl AssociatedItem {
                 // late-bound regions, and we don't want method signatures to show up
                 // `as for<'r> fn(&'r MyType)`.  Pretty-printing handles late-bound
                 // regions just fine, showing `fn(&MyType)`.
-                format!("{}", tcx.type_of(self.def_id).fn_sig().skip_binder())
+                format!("{}", tcx.fn_sig(self.def_id).skip_binder())
             }
             ty::AssociatedKind::Type => format!("type {};", self.name.to_string()),
             ty::AssociatedKind::Const => {

src/librustc/ty/relate.rs

@@ -291,7 +291,7 @@ impl<'tcx> Relate<'tcx> for ty::TraitRef<'tcx> {
         if a.def_id != b.def_id {
             Err(TypeError::Traits(expected_found(relation, &a.def_id, &b.def_id)))
         } else {
-            let substs = relation.relate_item_substs(a.def_id, a.substs, b.substs)?;
+            let substs = relate_substs(relation, None, a.substs, b.substs)?;
             Ok(ty::TraitRef { def_id: a.def_id, substs: substs })
         }
     }
@@ -308,7 +308,7 @@ impl<'tcx> Relate<'tcx> for ty::ExistentialTraitRef<'tcx> {
         if a.def_id != b.def_id {
             Err(TypeError::Traits(expected_found(relation, &a.def_id, &b.def_id)))
         } else {
-            let substs = relation.relate_item_substs(a.def_id, a.substs, b.substs)?;
+            let substs = relate_substs(relation, None, a.substs, b.substs)?;
             Ok(ty::ExistentialTraitRef { def_id: a.def_id, substs: substs })
         }
     }
@@ -440,13 +440,11 @@ pub fn super_relate_tys<'a, 'gcx, 'tcx, R>(relation: &mut R,
             }
         }
 
-        (&ty::TyFnDef(a_def_id, a_substs, a_fty),
-         &ty::TyFnDef(b_def_id, b_substs, b_fty))
+        (&ty::TyFnDef(a_def_id, a_substs), &ty::TyFnDef(b_def_id, b_substs))
             if a_def_id == b_def_id =>
         {
-            let substs = relate_substs(relation, None, a_substs, b_substs)?;
-            let fty = relation.relate(&a_fty, &b_fty)?;
-            Ok(tcx.mk_fn_def(a_def_id, substs, fty))
+            let substs = relation.relate_item_substs(a_def_id, a_substs, b_substs)?;
+            Ok(tcx.mk_fn_def(a_def_id, substs))
         }
 
         (&ty::TyFnPtr(a_fty), &ty::TyFnPtr(b_fty)) =>

src/librustc/ty/structural_impls.rs

@@ -531,10 +531,8 @@ impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
             ty::TyDynamic(ref trait_ty, ref region) =>
                 ty::TyDynamic(trait_ty.fold_with(folder), region.fold_with(folder)),
             ty::TyTuple(ts, defaulted) => ty::TyTuple(ts.fold_with(folder), defaulted),
-            ty::TyFnDef(def_id, substs, f) => {
-                ty::TyFnDef(def_id,
-                            substs.fold_with(folder),
-                            f.fold_with(folder))
+            ty::TyFnDef(def_id, substs) => {
+                ty::TyFnDef(def_id, substs.fold_with(folder))
             }
             ty::TyFnPtr(f) => ty::TyFnPtr(f.fold_with(folder)),
             ty::TyRef(ref r, tm) => {
@@ -568,9 +566,7 @@ impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
             ty::TyDynamic(ref trait_ty, ref reg) =>
                 trait_ty.visit_with(visitor) || reg.visit_with(visitor),
             ty::TyTuple(ts, _) => ts.visit_with(visitor),
-            ty::TyFnDef(_, substs, ref f) => {
-                substs.visit_with(visitor) || f.visit_with(visitor)
-            }
+            ty::TyFnDef(_, substs) => substs.visit_with(visitor),
             ty::TyFnPtr(ref f) => f.visit_with(visitor),
             ty::TyRef(r, ref tm) => r.visit_with(visitor) || tm.visit_with(visitor),
             ty::TyClosure(_did, ref substs) => substs.visit_with(visitor),