treat for<'a> T: 'a as T: 'static

closes #26217

src/librustc/middle/traits/fulfill.rs

@@ -413,17 +413,33 @@ fn process_predicate<'a,'tcx>(selcx: &mut SelectionContext<'a,'tcx>,
         }
 
         ty::Predicate::TypeOutlives(ref binder) => {
-            // For now, we just check that there are no higher-ranked
-            // regions.  If there are, we will call this obligation an
-            // error. Eventually we should be able to support some
-            // cases here, I imagine (e.g., `for<'a> int : 'a`).
+            // Check if there are higher-ranked regions.
             match selcx.tcx().no_late_bound_regions(binder) {
+                // If there are, inspect the underlying type further.
                 None => {
-                    errors.push(
-                        FulfillmentError::new(
-                            obligation.clone(),
-                            CodeSelectionError(Unimplemented)))
+                    // Convert from `Binder<OutlivesPredicate<Ty, Region>>` to `Binder<Ty>`.
+                    let binder = binder.map_bound_ref(|pred| pred.0);
+
+                    // Check if the type has any bound regions.
+                    match selcx.tcx().no_late_bound_regions(&binder) {
+                        // If so, this obligation is an error (for now). Eventually we should be
+                        // able to support additional cases here, like `for<'a> &'a str: 'a`.
+                        None => {
+                            errors.push(
+                                FulfillmentError::new(
+                                    obligation.clone(),
+                                    CodeSelectionError(Unimplemented)))
+                        }
+                        // Otherwise, we have something of the form `for<'a> T: 'a`, which
+                        // we can treat as `T: 'static`.
+                        Some(t_a) => {
+                            register_region_obligation(t_a, ty::ReStatic,
+                                                       obligation.cause.clone(),
+                                                       region_obligations);
+                        }
+                    }
                 }
+                // If there aren't, register the obligation.
                 Some(ty::OutlivesPredicate(t_a, r_b)) => {
                     register_region_obligation(t_a, r_b,
                                                obligation.cause.clone(),

src/test/compile-fail/issue-26217.rs

@@ -0,0 +1,16 @@
+// 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.
+
+fn foo<T>() where for<'a> T: 'a {}
+
+fn main<'a>() {
+    foo::<&'a i32>();
+    //~^ ERROR the type `&'a i32` does not fulfill the required lifetime
+}

src/test/compile-fail/hrtb-type-outlives.rs → src/test/run-pass/hrtb-type-outlives.rs

@@ -34,10 +34,7 @@ impl<'a,X> Foo<&'a isize> for SomeStruct<X>
 }
 
 fn one() {
-    // In fact there is no good reason for this to be an error, but
-    // whatever, I'm mostly concerned it doesn't ICE right now:
     want_foo::<SomeStruct<usize>>();
-    //~^ ERROR requirement `for<'a> usize : 'a` is not satisfied
 }
 
 ///////////////////////////////////////////////////////////////////////////
@@ -53,7 +50,6 @@ impl<'a,X:'a> Foo<&'a isize> for AnotherStruct<X>
 
 fn two() {
     want_foo::<AnotherStruct<usize>>();
-    //~^ ERROR requirement `for<'a> usize : 'a` is not satisfied
 }
 
 fn main() { }