Change:
Compiling with works fine, definitely does not, though: And, if the bound in is removed, the code compiles fine with or without . So... somehow the test runner is causing a tuple of arity 3 specifically to be inferred to something completely ridiculous.
cc I guess?
points out that specifically having causes the problem.
cc me
FYI: discovered this problem while working on
Slightly more minimized:
contains: This causes the problem.
I'll take a look at it.
Oh, I see you tracked it down -- I thought it might be something like that. This is in fact something I was talking to about as a possible danger of the way we're treating builtin bounds right now, though in a different context.
In fact, I think that the for a tuple ought to be a coherence violation to begin with, actually.
(I think there was language about specifically this in the OIBIT RFC)
I agree with comments here and after a quick chat on IRC with him, we agreed that implementations of built-in traits (and likely default trait impls in the future) should be allowed just on and .

Discussion:
<ins> // Copyright 2015 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. //! Implementations checker: builtin traits and default impls are allowed just //! for structs and enums. use middle::def; use middle::ty; use syntax::ast::{Item, ItemImpl}; use syntax::ast; use syntax::ast_util; use syntax::visit; use util::ppaux::UserString; pub fn check(tcx: &ty::ctxt) { let mut impls = ImplsChecker { tcx: tcx }; visit::walk_crate(&mut impls, tcx.map.krate()); } struct ImplsChecker<'cx, 'tcx:'cx> { tcx: &'cx ty::ctxt<'tcx> } impl<'cx, 'tcx,'v> visit::Visitor<'v> for ImplsChecker<'cx, 'tcx> { fn visit_item(&mut self, item: &'v ast::Item) { match item.node { ast::ItemImpl(_, _, _, Some(ref opt_trait), _, _) => { let trait_ref = ty::node_id_to_trait_ref(self.tcx, opt_trait.ref_id); if let Some(_) = self.tcx.lang_items.to_builtin_kind(trait_ref.def_id) { match trait_ref.self_ty().sty { ty::ty_struct(..) | ty::ty_enum(..) => {} _ => { self.tcx.sess.span_err( item.span, &format!("builtin traits can only be  implemented on structs or enums")[]); } } } } _ => {} } } } </ins>

use util::nodemap::{DefIdMap, FnvHashMap}; use util::ppaux::Repr; <ins> mod impls; </ins> mod orphan; mod overlap; mod unsafety;

inference_context: new_infer_ctxt(crate_context.tcx), inherent_impls: RefCell::new(FnvHashMap::new()), }.check(crate_context.tcx.map.krate()); <ins> impls::check(crate_context.tcx); </ins> unsafety::check(crate_context.tcx); orphan::check(crate_context.tcx); overlap::check(crate_context.tcx);

pub should_fail: ShouldFail, } <ins> unsafe impl Send for TestDesc {} </ins> #[derive(Show)] pub struct TestDescAndFn { pub desc: TestDesc,

TrBench(BenchSamples), } <ins> unsafe impl Send for TestResult {} </ins> enum OutputLocation<T> { Pretty(Box<term::Terminal<term::WriterWrapper> + Send>), Raw(T),

pub type MonitorMsg = (TestDesc, TestResult, Vec<u8> ); <del> unsafe impl Send for MonitorMsg {} </del> fn run_tests<F>(opts: &TestOpts, tests: Vec<TestDescAndFn> ,

<ins> // Copyright 2015 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. use std::marker::Send; enum TestE { A } struct MyType; unsafe impl Send for TestE {} unsafe impl Send for MyType {} unsafe impl Send for (MyType, MyType) {} //~^ ERROR builtin traits can only be implemented on structs or enums unsafe impl Send for &'static MyType {} //~^ ERROR builtin traits can only be implemented on structs or enums unsafe impl Send for [MyType] {} //~^ ERROR builtin traits can only be implemented on structs or enums unsafe impl Send for &'static [MyType] {} //~^ ERROR builtin traits can only be implemented on structs or enums fn is_send<T: Send>() {} fn main() { is_send::<(MyType, TestE)>(); } </ins>