Extend object safety so that methods with Sized:Self are exempt.

Author: nikomatsakis

src/librustc/middle/traits/object_safety.rs

@@ -157,19 +157,25 @@ fn supertraits_reference_self<'tcx>(tcx: &ty::ctxt<'tcx>,
 fn trait_has_sized_self<'tcx>(tcx: &ty::ctxt<'tcx>,
                               trait_def_id: ast::DefId)
                               -> bool
+{
+    let trait_def = ty::lookup_trait_def(tcx, trait_def_id);
+    let trait_predicates = ty::lookup_predicates(tcx, trait_def_id);
+    generics_require_sized_self(tcx, &trait_def.generics, &trait_predicates)
+}
+
+fn generics_require_sized_self<'tcx>(tcx: &ty::ctxt<'tcx>,
+                                     generics: &ty::Generics<'tcx>,
+                                     predicates: &ty::GenericPredicates<'tcx>)
+                                     -> bool
 {
     let sized_def_id = match tcx.lang_items.sized_trait() {
         Some(def_id) => def_id,
         None => { return false; /* No Sized trait, can't require it! */ }
     };
 
     // Search for a predicate like `Self : Sized` amongst the trait bounds.
-    let trait_def = ty::lookup_trait_def(tcx, trait_def_id);
-    let free_substs = ty::construct_free_substs(tcx, &trait_def.generics, ast::DUMMY_NODE_ID);
-
-    let trait_predicates = ty::lookup_predicates(tcx, trait_def_id);
-    let predicates = trait_predicates.instantiate(tcx, &free_substs).predicates.into_vec();
-
+    let free_substs = ty::construct_free_substs(tcx, generics, ast::DUMMY_NODE_ID);
+    let predicates = predicates.instantiate(tcx, &free_substs).predicates.into_vec();
     elaborate_predicates(tcx, predicates)
         .any(|predicate| {
             match predicate {
@@ -192,6 +198,12 @@ fn object_safety_violations_for_method<'tcx>(tcx: &ty::ctxt<'tcx>,
                                              method: &ty::Method<'tcx>)
                                              -> Option<MethodViolationCode>
 {
+    // Any method that has a `Self : Sized` requisite is otherwise
+    // exempt from the regulations.
+    if generics_require_sized_self(tcx, &method.generics, &method.predicates) {
+        return None;
+    }
+
     // The method's first parameter must be something that derefs to
     // `&self`. For now, we only accept `&self` and `Box<Self>`.
     match method.explicit_self {

src/librustc_trans/trans/meth.rs

@@ -815,9 +815,6 @@ fn emit_vtable_methods<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                         param_substs,
                         substs.clone()).val;
 
-                    // currently, at least, by-value self is not object safe
-                    assert!(m.explicit_self != ty::ByValueExplicitSelfCategory);
-
                     Some(fn_ref).into_iter()
                 }
             }

src/test/compile-fail/object-safety-by-value-self.rs

@@ -9,7 +9,8 @@
 // except according to those terms.
 
 // Check that we correctly prevent users from making trait objects
-// from traits with a `fn(self)` method.
+// from traits with a `fn(self)` method, unless `where Self : Sized`
+// is present on the method.
 
 trait Bar {
     fn bar(self);
@@ -19,6 +20,11 @@ trait Baz {
     fn baz(self: Self);
 }
 
+trait Quux {
+    // Legal because of the where clause:
+    fn baz(self: Self) where Self : Sized;
+}
+
 fn make_bar<T:Bar>(t: &T) -> &Bar {
     t
         //~^ ERROR `Bar` is not object-safe
@@ -43,5 +49,13 @@ fn make_baz_explicit<T:Baz>(t: &T) -> &Baz {
         //~| NOTE method `baz` has a receiver type of `Self`
 }
 
+fn make_quux<T:Quux>(t: &T) -> &Quux {
+    t
+}
+
+fn make_quux_explicit<T:Quux>(t: &T) -> &Quux {
+    t as &Quux
+}
+
 fn main() {
 }

src/test/compile-fail/object-safety-generics.rs

@@ -9,12 +9,18 @@
 // except according to those terms.
 
 // Check that we correctly prevent users from making trait objects
-// from traits with generic methods.
+// from traits with generic methods, unless `where Self : Sized` is
+// present.
 
 trait Bar {
     fn bar<T>(&self, t: T);
 }
 
+trait Quux {
+    fn bar<T>(&self, t: T)
+        where Self : Sized;
+}
+
 fn make_bar<T:Bar>(t: &T) -> &Bar {
     t
         //~^ ERROR `Bar` is not object-safe
@@ -27,5 +33,13 @@ fn make_bar_explicit<T:Bar>(t: &T) -> &Bar {
         //~| NOTE method `bar` has generic type parameters
 }
 
+fn make_quux<T:Quux>(t: &T) -> &Quux {
+    t
+}
+
+fn make_quux_explicit<T:Quux>(t: &T) -> &Quux {
+    t as &Quux
+}
+
 fn main() {
 }

src/test/compile-fail/object-safety-mentions-Self.rs

@@ -9,7 +9,8 @@
 // except according to those terms.
 
 // Check that we correctly prevent users from making trait objects
-// form traits that make use of `Self` in an argument or return position.
+// form traits that make use of `Self` in an argument or return
+// position, unless `where Self : Sized` is present..
 
 trait Bar {
     fn bar(&self, x: &Self);
@@ -19,6 +20,10 @@ trait Baz {
     fn bar(&self) -> Self;
 }
 
+trait Quux {
+    fn get(&self, s: &Self) -> Self where Self : Sized;
+}
+
 fn make_bar<T:Bar>(t: &T) -> &Bar {
     t
         //~^ ERROR `Bar` is not object-safe
@@ -43,5 +48,13 @@ fn make_baz_explicit<T:Baz>(t: &T) -> &Baz {
         //~| NOTE method `bar` references the `Self` type in its arguments or return type
 }
 
+fn make_quux<T:Quux>(t: &T) -> &Quux {
+    t
+}
+
+fn make_quux_explicit<T:Quux>(t: &T) -> &Quux {
+    t as &Quux
+}
+
 fn main() {
 }

src/test/run-pass/object-safety-sized-self-by-value-self.rs

@@ -0,0 +1,46 @@
+// Copyright 2014 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.
+
+// Check that a trait is still object-safe (and usable) if it has
+// methods with by-value self so long as they require `Self : Sized`.
+
+trait Counter {
+    fn tick(&mut self) -> u32;
+    fn get(self) -> u32 where Self : Sized;
+}
+
+struct CCounter {
+    c: u32
+}
+
+impl Counter for CCounter {
+    fn tick(&mut self) -> u32 { self.c += 1; self.c }
+    fn get(self) -> u32 where Self : Sized { self.c }
+}
+
+fn tick1<C:Counter>(mut c: C) -> u32 {
+    tick2(&mut c);
+    c.get()
+}
+
+fn tick2(c: &mut Counter) {
+    tick3(c);
+}
+
+fn tick3<C:?Sized+Counter>(c: &mut C) {
+    c.tick();
+    c.tick();
+}
+
+fn main() {
+    let mut c = CCounter { c: 0 };
+    let value = tick1(c);
+    assert_eq!(value, 2);
+}

src/test/run-pass/object-safety-sized-self-generic-method.rs

@@ -0,0 +1,46 @@
+// Copyright 2014 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.
+
+// Check that a trait is still object-safe (and usable) if it has
+// generic methods so long as they require `Self : Sized`.
+
+trait Counter {
+    fn tick(&mut self) -> u32;
+    fn with<F:FnOnce(u32)>(&self, f: F) where Self : Sized;
+}
+
+struct CCounter {
+    c: u32
+}
+
+impl Counter for CCounter {
+    fn tick(&mut self) -> u32 { self.c += 1; self.c }
+    fn with<F:FnOnce(u32)>(&self, f: F) { f(self.c); }
+}
+
+fn tick1<C:Counter>(c: &mut C) {
+    tick2(c);
+    c.with(|i| ());
+}
+
+fn tick2(c: &mut Counter) {
+    tick3(c);
+}
+
+fn tick3<C:?Sized+Counter>(c: &mut C) {
+    c.tick();
+    c.tick();
+}
+
+fn main() {
+    let mut c = CCounter { c: 0 };
+    tick1(&mut c);
+    assert_eq!(c.tick(), 3);
+}

src/test/run-pass/object-safety-sized-self-return-Self.rs

@@ -0,0 +1,47 @@
+// Copyright 2014 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.
+
+// Check that a trait is still object-safe (and usable) if it has
+// methods that return `Self` so long as they require `Self : Sized`.
+
+trait Counter {
+    fn new() -> Self where Self : Sized;
+    fn tick(&mut self) -> u32;
+}
+
+struct CCounter {
+    c: u32
+}
+
+impl Counter for CCounter {
+    fn new() -> CCounter { CCounter { c: 0 } }
+    fn tick(&mut self) -> u32 { self.c += 1; self.c }
+}
+
+fn preticked<C:Counter>() -> C {
+    let mut c: C = Counter::new();
+    tick(&mut c);
+    c
+}
+
+fn tick(c: &mut Counter) {
+    tick_generic(c);
+}
+
+fn tick_generic<C:?Sized+Counter>(c: &mut C) {
+    c.tick();
+    c.tick();
+}
+
+fn main() {
+    let mut c = preticked::<CCounter>();
+    tick(&mut c);
+    assert_eq!(c.tick(), 5);
+}