Some refactoring and WIP on issue #2263.

src/rustc/middle/ty.rs

@@ -81,7 +81,7 @@ export ty_opaque_box, mk_opaque_box;
 export ty_constr_arg;
 export ty_float, mk_float, mk_mach_float, type_is_fp;
 export ty_fn, fn_ty, mk_fn;
-export ty_fn_proto, ty_fn_ret, ty_fn_ret_style;
+export ty_fn_proto, ty_fn_ret, ty_fn_ret_style, tys_in_fn_ty;
 export ty_int, mk_int, mk_mach_int, mk_char;
 export ty_str, mk_str, type_is_str;
 export ty_vec, mk_vec, type_is_vec;
@@ -2090,6 +2090,11 @@ fn is_fn_ty(fty: t) -> bool {
     }
 }
 
+// Returns a vec of all the input and output types of fty.
+fn tys_in_fn_ty(fty: fn_ty) -> [t] {
+    fty.inputs.map({|a| a.ty}) + [fty.output]
+}
+
 // Just checks whether it's a fn that returns bool,
 // not its purity.
 fn is_pred_ty(fty: t) -> bool {

src/rustc/middle/typeck/check.rs

@@ -69,7 +69,8 @@ type parameter).
 import astconv::{ast_conv, ast_ty_to_ty};
 import collect::{methods}; // ccx.to_ty()
 import method::{methods};  // methods for method::lookup
-import regionmanip::{universally_quantify_regions_before_call,
+import middle::ty::tys_in_fn_ty;
+import regionmanip::{universally_quantify_from_sty,
                      region_of, replace_bound_regions,
                      collect_bound_regions_in_tys};
 import rscope::*;
@@ -718,7 +719,31 @@ fn check_expr_with_unifier(fcx: @fn_ctxt,
 
         let mut bot = false;
 
-        let fty = universally_quantify_regions_before_call(fcx, sp, fty);
+        // Replace all region parameters in the arguments and return
+        // type with fresh region variables.
+
+        #debug["check_call_or_bind: before universal quant., fty=%s",
+               fcx.ty_to_str(fty)];
+
+        // This is subtle: we expect `fty` to be a function type, which
+        // normally introduce a level of binding.  In this case, we want to
+        // process the types bound by the function but not by any nested
+        // functions.  Therefore, we match one level of structure.
+        let fty =
+            alt structure_of(fcx, sp, fty) {
+              sty @ ty::ty_fn(inner_fty) {
+                let all_tys = tys_in_fn_ty(inner_fty);
+                universally_quantify_from_sty(fcx, sp, all_tys, sty)
+              }
+              sty {
+                #debug["not a fn ty: %?", sty];
+
+                // if not a function type, we're gonna' report an error at
+                // some point, since the user is trying to call this thing
+                fty
+              }
+            };
+
         #debug["check_call_or_bind: after universal quant., fty=%s",
                fcx.ty_to_str(fty)];
 

src/rustc/middle/typeck/check/method.rs

@@ -1,7 +1,7 @@
 /* Code to handle method lookups (which can be quite complex) */
 
 import syntax::ast_map;
-import regionmanip::universally_quantify_regions;
+import regionmanip::universally_quantify_from_sty;
 import middle::typeck::infer::{ty_and_region_var_methods};
 
 enum lookup = {
@@ -188,13 +188,12 @@ impl methods for lookup {
 
                     // Here "self" refers to the callee side...
                     let self_ty =
-                        universally_quantify_regions(
-                            self.fcx, self.expr.span, self_ty);
+                        universally_quantify_from_sty(
+                            self.fcx, self.expr.span, [self_ty],
+                            ty::get(self_ty).struct);
 
                     // ... and "ty" refers to the caller side.
-                    let ty =
-                        universally_quantify_regions(
-                            self.fcx, self.expr.span, self.self_ty);
+                    let ty = self.self_ty;
 
                     // if we can assign the caller to the callee, that's a
                     // potential match.  Collect those in the vector.

src/rustc/middle/typeck/check/regionmanip.rs

@@ -1,11 +1,11 @@
-import middle::typeck::infer::{ty_and_region_var_methods};
 import syntax::print::pprust::{expr_to_str};
 
 // Helper functions related to manipulating region types.
 
-// Helper for the other universally_quantify_*() routines.  Extracts the bound
-// regions from bound_tys and then replaces those same regions with fresh
-// variables in `sty`, returning the resulting type.
+// Extracts the bound regions from bound_tys and then replaces those same
+// regions in `sty` with fresh region variables, returning the resulting type.
+// Does not descend into fn types.  This is used when deciding whether an impl
+// applies at a given call site.  See also universally_quantify_before_call().
 fn universally_quantify_from_sty(fcx: @fn_ctxt,
                                  span: span,
                                  bound_tys: [ty::t],
@@ -30,44 +30,6 @@ fn universally_quantify_from_sty(fcx: @fn_ctxt,
     }
 }
 
-// Replaces all region parameters in the given type with region variables.
-// Does not descend into fn types.  This is used when deciding whether an impl
-// applies at a given call site.  See also universally_quantify_before_call().
-fn universally_quantify_regions(fcx: @fn_ctxt,
-                                span: span,
-                                ty: ty::t) -> ty::t {
-    universally_quantify_from_sty(fcx, span, [ty], ty::get(ty).struct)
-}
-
-// Expects a function type.  Replaces all region parameters in the arguments
-// and return type with fresh region variables. This is used when typechecking
-// function calls, bind expressions, and method calls.
-fn universally_quantify_regions_before_call(fcx: @fn_ctxt,
-                                            span: span,
-                                            ty: ty::t) -> ty::t {
-
-    #debug["universally_quantify_before_call(ty=%s)",
-           fcx.ty_to_str(ty)];
-
-    // This is subtle: we expect `ty` to be a function type, which normally
-    // introduce a level of binding.  In this case, we want to process the
-    // types bound by the function but not by any nested functions.
-    // Therefore, we match one level of structure.
-    alt structure_of(fcx, span, ty) {
-      sty @ ty::ty_fn(fty) {
-        let all_tys = fty.inputs.map({|a| a.ty}) + [fty.output];
-        universally_quantify_from_sty(fcx, span, all_tys, sty)
-      }
-      sty {
-        #debug["not a fn ty: %?", sty];
-
-        // if not a function type, we're gonna' report an error
-        // at some point, since the user is trying to call this thing
-        ty
-      }
-    }
-}
-
 fn replace_bound_regions(
     tcx: ty::ctxt,
     span: span,

src/rustc/middle/typeck/infer.rs

@@ -147,12 +147,14 @@ import std::smallintmap::smallintmap;
 import std::smallintmap::map;
 import std::map::hashmap;
 import middle::ty;
-import middle::ty::{ty_vid, region_vid, vid};
-import syntax::ast;
+import middle::ty::{ty_vid, tys_in_fn_ty, region_vid, vid};
+import syntax::{ast, ast_util};
 import syntax::ast::{ret_style};
 import util::ppaux::{ty_to_str, mt_to_str};
 import result::{result, extensions, ok, err, map, map2, iter2};
-import ty::type_is_bot;
+import ty::{mk_fn, type_is_bot};
+import check::regionmanip::{collect_bound_regions_in_tys,
+                            replace_bound_regions};
 import driver::session::session;
 import util::common::{indent, indenter};
 
@@ -453,6 +455,18 @@ impl ty_and_region_var_methods for infer_ctxt {
     fn next_region_var() -> ty::region {
         ret ty::re_var(self.next_region_var_id());
     }
+
+    fn ty_to_str(t: ty::t) -> str {
+        ty_to_str(self.tcx,
+                  self.resolve_type_vars_if_possible(t))
+    }
+
+    fn resolve_type_vars_if_possible(typ: ty::t) -> ty::t {
+        alt infer::resolve_deep(self, typ, false) {
+          result::ok(new_type) { ret new_type; }
+          result::err(_) { ret typ; }
+        }
+    }
 }
 
 impl unify_methods for infer_ctxt {
@@ -1579,6 +1593,67 @@ impl of combine for sub {
         }
     }
 
+    fn fns(a: ty::fn_ty, b: ty::fn_ty) -> cres<ty::fn_ty> {
+        // Rather than checking the subtype relationship between `a` and `b`
+        // as-is, we need to do some extra work here in order to make sure
+        // that function subtyping works correctly with respect to regions
+        // (issue #2263).
+
+        // First, we instantiate each bound region in the subtype with a fresh
+        // region variable.
+        let a_isr =
+            collect_bound_regions_in_tys(self.tcx,
+                                         @nil,
+                                         tys_in_fn_ty(a)) {
+            |br|
+            let rvar = self.infcx().next_region_var();
+            #debug["Bound region %s maps to %s",
+                   bound_region_to_str(self.tcx, br),
+                   region_to_str(self.tcx, rvar)];
+            rvar
+        };
+
+        let a_ty = replace_bound_regions(self.tcx,
+                                         ast_util::dummy_sp(),
+                                         a_isr,
+                                         mk_fn(self.tcx, a));
+        #debug["a_ty: %s", self.infcx().ty_to_str(a_ty)];
+
+        // Second, we instantiate each bound region in the supertype with a
+        // fresh concrete region.
+        let b_isr =
+            collect_bound_regions_in_tys(self.tcx,
+                                         @nil,
+                                         tys_in_fn_ty(b)) {
+            |br| ty::re_bound(br) };
+            // FIXME: or maybe re_skolemized? What would that look like?
+            // (issue #2263)
+
+        let b_ty = replace_bound_regions(self.tcx,
+                                         ast_util::dummy_sp(),
+                                         b_isr,
+                                         mk_fn(self.tcx, b));
+        #debug["b_ty: %s", self.infcx().ty_to_str(b_ty)];
+
+        // Turn back into ty::fn_ty.
+        alt (ty::get(a_ty).struct, ty::get(b_ty).struct) {
+          (ty::ty_fn(a_fn_ty), ty::ty_fn(b_fn_ty)) {
+            // Try to compare the supertype and subtype now that they've been
+            // instantiated.
+            super_fns(self, a_fn_ty, b_fn_ty)
+
+          }
+          _ {
+            // Shouldn't happen.
+            self.infcx().tcx.sess.bug(
+                #fmt["%s: at least one of %s and %s isn't a fn_ty",
+                     self.tag(),
+                     self.infcx().ty_to_str(a_ty),
+                     self.infcx().ty_to_str(b_ty)]);
+          }
+        }
+    }
+
     // Traits please:
 
     fn flds(a: ty::field, b: ty::field) -> cres<ty::field> {
@@ -1598,10 +1673,6 @@ impl of combine for sub {
         super_args(self, a, b)
     }
 
-    fn fns(a: ty::fn_ty, b: ty::fn_ty) -> cres<ty::fn_ty> {
-        super_fns(self, a, b)
-    }
-
     fn substs(as: ty::substs, bs: ty::substs) -> cres<ty::substs> {
         super_substs(self, as, bs)
     }