diff --git a/src/librustc/infer/mod.rs b/src/librustc/infer/mod.rs index 59431f3f02dce..39fc50666a8ce 100644 --- a/src/librustc/infer/mod.rs +++ b/src/librustc/infer/mod.rs @@ -830,6 +830,33 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> { result.map(move |t| InferOk { value: t, obligations: fields.obligations }) } + // Clear the "obligations in snapshot" flag, invoke the closure, + // then restore the flag to its original value. This flag is a + // debugging measure designed to detect cases where we start a + // snapshot, create type variables, register obligations involving + // those type variables in the fulfillment cx, and then have to + // unroll the snapshot, leaving "dangling type variables" behind. + // In such cases, the flag will be set by the fulfillment cx, and + // an assertion will fail when rolling the snapshot back. Very + // useful, much better than grovelling through megabytes of + // RUST_LOG output. + // + // HOWEVER, in some cases the flag is wrong. In particular, we + // sometimes create a "mini-fulfilment-cx" in which we enroll + // obligations. As long as this fulfillment cx is fully drained + // before we return, this is not a problem, as there won't be any + // escaping obligations in the main cx. In those cases, you can + // use this function. + pub fn save_and_restore_obligations_in_snapshot_flag(&self, func: F) -> R + where F: FnOnce(&Self) -> R + { + let flag = self.obligations_in_snapshot.get(); + self.obligations_in_snapshot.set(false); + let result = func(self); + self.obligations_in_snapshot.set(flag); + result + } + fn start_snapshot(&self) -> CombinedSnapshot { debug!("start_snapshot()"); diff --git a/src/librustc/traits/specialize/mod.rs b/src/librustc/traits/specialize/mod.rs index f3ba4d16eb0b2..2f63526bf6c27 100644 --- a/src/librustc/traits/specialize/mod.rs +++ b/src/librustc/traits/specialize/mod.rs @@ -203,32 +203,34 @@ fn fulfill_implication<'a, 'gcx, 'tcx>(infcx: &InferCtxt<'a, 'gcx, 'tcx>, // attempt to prove all of the predicates for impl2 given those for impl1 // (which are packed up in penv) - let mut fulfill_cx = FulfillmentContext::new(); - for oblig in obligations.into_iter() { - fulfill_cx.register_predicate_obligation(&infcx, oblig); - } - match fulfill_cx.select_all_or_error(infcx) { - Err(errors) => { - // no dice! - debug!("fulfill_implication: for impls on {:?} and {:?}, could not fulfill: {:?} given \ - {:?}", - source_trait_ref, - target_trait_ref, - errors, - infcx.parameter_environment.caller_bounds); - Err(()) + infcx.save_and_restore_obligations_in_snapshot_flag(|infcx| { + let mut fulfill_cx = FulfillmentContext::new(); + for oblig in obligations.into_iter() { + fulfill_cx.register_predicate_obligation(&infcx, oblig); } + match fulfill_cx.select_all_or_error(infcx) { + Err(errors) => { + // no dice! + debug!("fulfill_implication: for impls on {:?} and {:?}, \ + could not fulfill: {:?} given {:?}", + source_trait_ref, + target_trait_ref, + errors, + infcx.parameter_environment.caller_bounds); + Err(()) + } - Ok(()) => { - debug!("fulfill_implication: an impl for {:?} specializes {:?}", - source_trait_ref, - target_trait_ref); + Ok(()) => { + debug!("fulfill_implication: an impl for {:?} specializes {:?}", + source_trait_ref, + target_trait_ref); - // Now resolve the *substitution* we built for the target earlier, replacing - // the inference variables inside with whatever we got from fulfillment. - Ok(infcx.resolve_type_vars_if_possible(&target_substs)) + // Now resolve the *substitution* we built for the target earlier, replacing + // the inference variables inside with whatever we got from fulfillment. + Ok(infcx.resolve_type_vars_if_possible(&target_substs)) + } } - } + }) } pub struct SpecializesCache { diff --git a/src/test/compile-fail/issue-36053-2.rs b/src/test/compile-fail/issue-36053-2.rs new file mode 100644 index 0000000000000..7da529487aa86 --- /dev/null +++ b/src/test/compile-fail/issue-36053-2.rs @@ -0,0 +1,21 @@ +// Copyright 2016 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 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// Regression test for #36053. ICE was caused due to obligations +// being added to a special, dedicated fulfillment cx during +// a probe. + +use std::iter::once; +fn main() { + once::<&str>("str").fuse().filter(|a: &str| true).count(); + //~^ ERROR no method named `count` + //~| ERROR E0281 + //~| ERROR E0281 +} diff --git a/src/test/run-pass/issue-36053.rs b/src/test/run-pass/issue-36053.rs new file mode 100644 index 0000000000000..2411996cf054b --- /dev/null +++ b/src/test/run-pass/issue-36053.rs @@ -0,0 +1,32 @@ +// Copyright 2016 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 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// Regression test for #36053. ICE was caused due to obligations being +// added to a special, dedicated fulfillment cx during a +// probe. Problem seems to be related to the particular definition of +// `FusedIterator` in std but I was not able to isolate that into an +// external crate. + +#![feature(fused)] +use std::iter::FusedIterator; + +struct Thing<'a>(&'a str); +impl<'a> Iterator for Thing<'a> { + type Item = &'a str; + fn next(&mut self) -> Option<&'a str> { + None + } +} + +impl<'a> FusedIterator for Thing<'a> {} + +fn main() { + Thing("test").fuse().filter(|_| true).count(); +}