librustc: Have the kind checker check sub-bounds in trait casts.

This can break code that looked like:

    struct S<T> {
        val: T,
    }
    trait Gettable<T> {
        ...
    }
    impl<T: Copy> Gettable<T> for S<T> {
        ...
    }
    let t: Box<S<String>> = box S {
        val: "one".to_string(),
    };
    let a = t as Box<Gettable<String>>;
    //                        ^ note no `Copy` bound

Change this code to:

    impl<T> Gettable<T> for S<T> {
    //   ^ remove `Copy` bound
        ...
    }

Closes #14061.

[breaking-change]

Author: pcwalton

src/librustc/middle/kind.rs

@@ -13,6 +13,7 @@ use middle::freevars::freevar_entry;
 use middle::freevars;
 use middle::subst;
 use middle::ty;
+use middle::typeck::{MethodCall, NoAdjustment};
 use middle::typeck;
 use util::ppaux::{Repr, ty_to_str};
 use util::ppaux::UserString;
@@ -261,7 +262,15 @@ pub fn check_expr(cx: &mut Context, e: &Expr) {
         ExprCast(ref source, _) => {
             let source_ty = ty::expr_ty(cx.tcx, &**source);
             let target_ty = ty::expr_ty(cx.tcx, e);
-            check_trait_cast(cx, source_ty, target_ty, source.span);
+            let method_call = MethodCall {
+                expr_id: e.id,
+                adjustment: NoAdjustment,
+            };
+            check_trait_cast(cx,
+                             source_ty,
+                             target_ty,
+                             source.span,
+                             method_call);
         }
         ExprRepeat(ref element, ref count_expr) => {
             let count = ty::eval_repeat_count(cx.tcx, &**count_expr);
@@ -281,7 +290,15 @@ pub fn check_expr(cx: &mut Context, e: &Expr) {
                 ty::AutoObject(..) => {
                     let source_ty = ty::expr_ty(cx.tcx, e);
                     let target_ty = ty::expr_ty_adjusted(cx.tcx, e);
-                    check_trait_cast(cx, source_ty, target_ty, e.span);
+                    let method_call = MethodCall {
+                        expr_id: e.id,
+                        adjustment: typeck::AutoObject,
+                    };
+                    check_trait_cast(cx,
+                                     source_ty,
+                                     target_ty,
+                                     e.span,
+                                     method_call);
                 }
                 ty::AutoAddEnv(..) |
                 ty::AutoDerefRef(..) => {}
@@ -364,15 +381,62 @@ fn check_bounds_on_type_parameters(cx: &mut Context, e: &Expr) {
     }
 }
 
-fn check_trait_cast(cx: &mut Context, source_ty: ty::t, target_ty: ty::t, span: Span) {
+fn check_type_parameter_bounds_in_vtable_result(
+        cx: &mut Context,
+        span: Span,
+        vtable_res: &typeck::vtable_res) {
+    for origins in vtable_res.iter() {
+        for origin in origins.iter() {
+            let (type_param_defs, substs) = match *origin {
+                typeck::vtable_static(def_id, ref tys, _) => {
+                    let type_param_defs =
+                        ty::lookup_item_type(cx.tcx, def_id).generics
+                                                            .types
+                                                            .clone();
+                    (type_param_defs, (*tys).clone())
+                }
+                _ => {
+                    // Nothing to do here.
+                    continue
+                }
+            };
+            for type_param_def in type_param_defs.iter() {
+                let typ = substs.types.get(type_param_def.space,
+                                           type_param_def.index);
+                check_typaram_bounds(cx, span, *typ, type_param_def)
+            }
+        }
+    }
+}
+
+fn check_trait_cast(cx: &mut Context,
+                    source_ty: ty::t,
+                    target_ty: ty::t,
+                    span: Span,
+                    method_call: MethodCall) {
     check_cast_for_escaping_regions(cx, source_ty, target_ty, span);
     match ty::get(target_ty).sty {
-        ty::ty_uniq(ty) | ty::ty_rptr(_, ty::mt{ ty, .. }) => match ty::get(ty).sty {
-            ty::ty_trait(box ty::TyTrait { bounds, .. }) => {
-                check_trait_cast_bounds(cx, span, source_ty, bounds);
+        ty::ty_uniq(ty) | ty::ty_rptr(_, ty::mt{ ty, .. }) => {
+            match ty::get(ty).sty {
+                ty::ty_trait(box ty::TyTrait { bounds, .. }) => {
+                     match cx.tcx.vtable_map.borrow().find(&method_call) {
+                        None => {
+                            cx.tcx.sess.span_bug(span,
+                                                 "trait cast not in vtable \
+                                                  map?!")
+                        }
+                        Some(vtable_res) => {
+                            check_type_parameter_bounds_in_vtable_result(
+                                cx,
+                                span,
+                                vtable_res)
+                        }
+                    };
+                    check_trait_cast_bounds(cx, span, source_ty, bounds);
+                }
+                _ => {}
             }
-            _ => {}
-        },
+        }
         _ => {}
     }
 }

src/librustc/middle/typeck/check/vtable.rs

@@ -398,6 +398,9 @@ fn search_for_vtable(vcx: &VtableContext,
         // Resolve any sub bounds. Note that there still may be free
         // type variables in substs. This might still be OK: the
         // process of looking up bounds might constrain some of them.
+        //
+        // This does not check built-in traits because those are handled
+        // later in the kind checking pass.
         let im_generics =
             ty::lookup_item_type(tcx, impl_did).generics;
         let subres = lookup_vtables(vcx,

src/librustc/middle/typeck/mod.rs

@@ -216,9 +216,9 @@ pub type vtable_res = VecPerParamSpace<vtable_param_res>;
 #[deriving(Clone)]
 pub enum vtable_origin {
     /*
-      Statically known vtable. def_id gives the class or impl item
+      Statically known vtable. def_id gives the impl item
       from whence comes the vtable, and tys are the type substs.
-      vtable_res is the vtable itself
+      vtable_res is the vtable itself.
      */
     vtable_static(ast::DefId, subst::Substs, vtable_res),
 

src/test/compile-fail/kindck-impl-type-params.rs

@@ -0,0 +1,39 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Issue #14061: tests the interaction between generic implementation
+// parameter bounds and trait objects.
+
+struct S<T>;
+
+trait Gettable<T> {}
+
+impl<T: Send + Copy> Gettable<T> for S<T> {}
+
+fn f<T>(val: T) {
+    let t: S<T> = S;
+    let a = &t as &Gettable<T>;
+    //~^ ERROR instantiating a type parameter with an incompatible type `T`
+    let a: &Gettable<T> = &t;
+    //~^ ERROR instantiating a type parameter with an incompatible type `T`
+}
+
+fn main() {
+    let t: S<&int> = S;
+    let a = &t as &Gettable<&int>;
+    //~^ ERROR instantiating a type parameter with an incompatible type `&int`
+    let t: Box<S<String>> = box S;
+    let a = t as Box<Gettable<String>>;
+    //~^ ERROR instantiating a type parameter with an incompatible type
+    let t: Box<S<String>> = box S;
+    let a: Box<Gettable<String>> = t;
+    //~^ ERROR instantiating a type parameter with an incompatible type
+}
+