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auto merge of : pcwalton/rust/trait-impl-bound-mismatch, r=pnkfelix

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with the corresponding trait parameter bounds.

This is a version of the patch in PR  by Florian Hahn, modified to
address Niko's feedback.

It does not address the issue of duplicate type parameter bounds, nor
does it address the issue of implementation-defined methods that contain
*fewer* bounds than the trait, because Niko's review indicates that this
should not be necessary (and indeed I believe it is not). A test has
been added to ensure that this works.

This will break code like:

    trait Foo {
        fn bar<T:Baz>();
    }

    impl Foo for Boo {
        fn bar<T:Baz + Quux>() { ... }
        //             ^~~~ ERROR
    }

This will be rejected because the implementation requires *more* bounds
than the trait. It can be fixed by either adding the missing bound to
the trait:

    trait Foo {
        fn bar<T:Baz + Quux>();
        //             ^~~~
    }

    impl Foo for Boo {
        fn bar<T:Baz + Quux>() { ... }  // OK
    }

Or by removing the bound from the impl:

    trait Foo {
        fn bar<T:Baz>();
    }

    impl Foo for Boo {
        fn bar<T:Baz>() { ... }  // OK
        //       ^ remove Quux
    }

This patch imports the relevant tests from , as well as the test
case in , which is fixed as well by this patch.

Closes .
Closes .

[breaking-change]

r? @pnkfelix
This commit is contained in:
bors 2014-07-03 01:06:38 +00:00
commit 67776ba3da
4 changed files with 200 additions and 43 deletions

107
src/librustc/middle/typeck/check/mod.rs

@ -920,49 +920,6 @@ fn compare_impl_method(tcx: &ty::ctxt,
let it = trait_m.generics.types.get_vec(subst::FnSpace).iter()
.zip(impl_m.generics.types.get_vec(subst::FnSpace).iter());
for (i, (trait_param_def, impl_param_def)) in it.enumerate() {
// Check that the impl does not require any builtin-bounds
// that the trait does not guarantee:
let extra_bounds =
impl_param_def.bounds.builtin_bounds -
trait_param_def.bounds.builtin_bounds;
if !extra_bounds.is_empty() {
tcx.sess.span_err(
impl_m_span,
format!("in method `{}`, \
type parameter {} requires `{}`, \
which is not required by \
the corresponding type parameter \
in the trait declaration",
token::get_ident(trait_m.ident),
i,
extra_bounds.user_string(tcx)).as_slice());
return;
}
// FIXME(#2687)---we should be checking that the bounds of the
// trait imply the bounds of the subtype, but it appears we
// are...not checking this.
if impl_param_def.bounds.trait_bounds.len() !=
trait_param_def.bounds.trait_bounds.len()
{
let found = impl_param_def.bounds.trait_bounds.len();
let expected = trait_param_def.bounds.trait_bounds.len();
tcx.sess.span_err(
impl_m_span,
format!("in method `{}`, type parameter {} has {} trait \
bound{}, but the corresponding type parameter in \
the trait declaration has {} trait bound{}",
token::get_ident(trait_m.ident),
i,
found,
if found == 1 {""} else {"s"},
expected,
if expected == 1 {""} else {"s"}).as_slice());
return;
}
}
// This code is best explained by example. Consider a trait:
//
// trait Trait<T> {
@ -1037,6 +994,70 @@ fn compare_impl_method(tcx: &ty::ctxt,
let trait_fty = ty::mk_bare_fn(tcx, trait_m.fty.clone());
let trait_fty = trait_fty.subst(tcx, &trait_to_skol_substs);
// Check bounds.
for (i, (trait_param_def, impl_param_def)) in it.enumerate() {
// Check that the impl does not require any builtin-bounds
// that the trait does not guarantee:
let extra_bounds =
impl_param_def.bounds.builtin_bounds -
trait_param_def.bounds.builtin_bounds;
if !extra_bounds.is_empty() {
tcx.sess.span_err(
impl_m_span,
format!("in method `{}`, \
type parameter {} requires `{}`, \
which is not required by \
the corresponding type parameter \
in the trait declaration",
token::get_ident(trait_m.ident),
i,
extra_bounds.user_string(tcx)).as_slice());
return;
}
// Check that the trait bounds of the trait imply the bounds of its
// implementation.
//
// FIXME(pcwalton): We could be laxer here regarding sub- and super-
// traits, but I doubt that'll be wanted often, so meh.
for impl_trait_bound in impl_param_def.bounds.trait_bounds.iter() {
let impl_trait_bound =
impl_trait_bound.subst(tcx, &impl_to_skol_substs);
let mut ok = false;
for trait_bound in trait_param_def.bounds.trait_bounds.iter() {
let trait_bound =
trait_bound.subst(tcx, &trait_to_skol_substs);
let infcx = infer::new_infer_ctxt(tcx);
match infer::mk_sub_trait_refs(&infcx,
true,
infer::Misc(impl_m_span),
trait_bound,
impl_trait_bound.clone()) {
Ok(_) => {
ok = true;
break
}
Err(_) => continue,
}
}
if !ok {
tcx.sess.span_err(impl_m_span,
format!("in method `{}`, type parameter {} \
requires bound `{}`, which is not \
required by the corresponding \
type parameter in the trait \
declaration",
token::get_ident(trait_m.ident),
i,
ppaux::trait_ref_to_str(
tcx,
&*impl_trait_bound)).as_slice())
}
}
}
// Check the impl method type IM is a subtype of the trait method
// type TM. To see why this makes sense, think of a vtable. The
// expected type of the function pointers in the vtable is the

78
src/test/compile-fail/trait-bounds-impl-comparison-1.rs Normal file

@ -0,0 +1,78 @@
// 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.
//
// Make sure rustc checks the type parameter bounds in implementations of traits,
// see #2687
trait A {}
trait B: A {}
trait C: A {}
trait Foo {
fn test_error1_fn<T: Eq>(&self);
fn test_error2_fn<T: Eq + Ord>(&self);
fn test_error3_fn<T: Eq + Ord>(&self);
fn test3_fn<T: Eq + Ord>(&self);
fn test4_fn<T: Eq + Ord>(&self);
fn test_error5_fn<T: A>(&self);
fn test6_fn<T: A + Eq>(&self);
fn test_error7_fn<T: A>(&self);
fn test_error8_fn<T: B>(&self);
}
impl Foo for int {
// invalid bound for T, was defined as Eq in trait
fn test_error1_fn<T: Ord>(&self) {}
//~^ ERROR in method `test_error1_fn`, type parameter 0 requires bound `core::cmp::Ord`
// invalid bound for T, was defined as Eq + Ord in trait
fn test_error2_fn<T: Eq + B>(&self) {}
//~^ ERROR in method `test_error2_fn`, type parameter 0 requires bound `B`
// invalid bound for T, was defined as Eq + Ord in trait
fn test_error3_fn<T: B + Eq>(&self) {}
//~^ ERROR in method `test_error3_fn`, type parameter 0 requires bound `B`
// multiple bounds, same order as in trait
fn test3_fn<T: Ord + Eq>(&self) {}
// multiple bounds, different order as in trait
fn test4_fn<T: Eq + Ord>(&self) {}
// parameters in impls must be equal or more general than in the defining trait
fn test_error5_fn<T: B>(&self) {}
//~^ ERROR in method `test_error5_fn`, type parameter 0 requires bound `B`
// bound `std::cmp::Eq` not enforced by this implementation, but this is OK
fn test6_fn<T: A>(&self) {}
fn test_error7_fn<T: A + Eq>(&self) {}
//~^ ERROR in method `test_error7_fn`, type parameter 0 requires bound `core::cmp::Eq`
fn test_error8_fn<T: C>(&self) {}
//~^ ERROR in method `test_error8_fn`, type parameter 0 requires bound `C`
}
trait Getter<T> { }
trait Trait {
fn method<G:Getter<int>>();
}
impl Trait for uint {
fn method<G: Getter<uint>>() {}
//~^ ERROR in method `method`, type parameter 0 requires bound `Getter<uint>`
}
fn main() {}

33
src/test/compile-fail/trait-bounds-impl-comparison-2.rs Normal file

@ -0,0 +1,33 @@
// 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.
// Issue #5886: a complex instance of issue #2687.
trait Iterator<A> {
fn next(&mut self) -> Option<A>;
}
trait IteratorUtil<A> {
fn zip<B, U: Iterator<U>>(self, other: U) -> ZipIterator<Self, U>;
}
impl<A, T: Iterator<A>> IteratorUtil<A> for T {
fn zip<B, U: Iterator<B>>(self, other: U) -> ZipIterator<T, U> {
//~^ ERROR in method `zip`, type parameter 1 requires bound `Iterator<B>`
ZipIterator{a: self, b: other}
}
}
struct ZipIterator<T, U> {
a: T, b: U
}
fn main() {}

25
src/test/run-pass/trait-bounds-impl-comparison-duplicates.rs Normal file

@ -0,0 +1,25 @@
// 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.
// Tests that type parameter bounds on an implementation need not match the
// trait exactly, as long as the implementation doesn't demand *more* bounds
// than the trait.
trait A {
fn foo<T: Eq + Ord>(&self);
}
impl A for int {
fn foo<T: Ord + Ord>(&self) {}
}
fn main() {}