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Rollup merge of rust-lang#33539 - nikomatsakis:static-error, r=pnkfelix
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fix DFS for region error reporting

This was causing terrible error reports, because the algorithm was incorrectly identifying the constraints.

r? @eddyb
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steveklabnik committed May 11, 2016
2 parents 130e76b + de0906f commit 4b8e7cb
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Showing 2 changed files with 36 additions and 3 deletions.
3 changes: 0 additions & 3 deletions src/librustc/infer/region_inference/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1240,9 +1240,6 @@ impl<'a, 'gcx, 'tcx> RegionVarBindings<'a, 'gcx, 'tcx> {
orig_node_idx,
node_idx);

// figure out the direction from which this node takes its
// values, and search for concrete regions etc in that direction
let dir = graph::INCOMING;
process_edges(self, &mut state, graph, node_idx, dir);
}

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36 changes: 36 additions & 0 deletions src/test/compile-fail/region-invariant-static-error-reporting.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,36 @@
// 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.

// This test checks that the error messages you get for this example
// at least mention `'a` and `'static`. The precise messages can drift
// over time, but this test used to exhibit some pretty bogus messages
// that were not remotely helpful.

// error-pattern:cannot infer
// error-pattern:cannot outlive the lifetime 'a
// error-pattern:must be valid for the static lifetime
// error-pattern:cannot infer
// error-pattern:cannot outlive the lifetime 'a
// error-pattern:must be valid for the static lifetime

struct Invariant<'a>(Option<&'a mut &'a mut ()>);

fn mk_static() -> Invariant<'static> { Invariant(None) }

fn unify<'a>(x: Option<Invariant<'a>>, f: fn(Invariant<'a>)) {
let bad = if x.is_some() {
x.unwrap()
} else {
mk_static()
};
f(bad);
}

fn main() {}

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