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31 changes: 24 additions & 7 deletions src/librustc_typeck/outlives/utils.rs
Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,7 @@ pub fn insert_outlives_predicate<'tcx>(
) {
// If the `'a` region is bound within the field type itself, we
// don't want to propagate this constraint to the header.
if !is_free_region(outlived_region) {
if !is_free_region(tcx, outlived_region) {
return;
}

Expand Down Expand Up @@ -120,27 +120,44 @@ pub fn insert_outlives_predicate<'tcx>(
}

UnpackedKind::Lifetime(r) => {
if !is_free_region(r) {
if !is_free_region(tcx, r) {
return;
}
required_predicates.insert(ty::OutlivesPredicate(kind, outlived_region));
}
}
}

fn is_free_region(region: Region<'_>) -> bool {
fn is_free_region<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>, region: Region<'_>) -> bool {
// First, screen for regions that might appear in a type header.
match region {
// *These* correspond to `T: 'a` relationships where `'a` is
// either declared on the type or `'static`:
// These correspond to `T: 'a` relationships:
//
// struct Foo<'a, T> {
// field: &'a T, // this would generate a ReEarlyBound referencing `'a`
// field2: &'static T, // this would generate a ReStatic
// }
//
// We care about these, so fall through.
RegionKind::ReStatic | RegionKind::ReEarlyBound(_) => true,
RegionKind::ReEarlyBound(_) => true,

// These correspond to `T: 'static` relationships which can be
// rather surprising. We are therefore putting this behind a
// feature flag:
//
// struct Foo<'a, T> {
// field: &'static T, // this would generate a ReStatic
// }
RegionKind::ReStatic => {
if tcx
.sess
.features_untracked()
.infer_static_outlives_requirements
{
true
} else {
false
}
}

// Late-bound regions can appear in `fn` types:
//
Expand Down
9 changes: 9 additions & 0 deletions src/libsyntax/feature_gate.rs
Original file line number Diff line number Diff line change
Expand Up @@ -396,6 +396,9 @@ declare_features! (
// Infer outlives requirements; RFC 2093
(active, infer_outlives_requirements, "1.26.0", Some(44493), None),

// Infer outlives requirements; RFC 2093
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This should use a different comment than the previous entry, to distinguish it. Infer 'static outlives requirements, perhaps?

(active, infer_static_outlives_requirements, "1.26.0", Some(44493), None),

// Multiple patterns with `|` in `if let` and `while let`
(active, if_while_or_patterns, "1.26.0", Some(48215), None),

Expand Down Expand Up @@ -1057,6 +1060,12 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
"infer outlives requirements is an experimental feature",
cfg_fn!(infer_outlives_requirements))),

// RFC #2093
("infer_static_outlives_requirements", Normal, Gated(Stability::Unstable,
"infer_static_outlives_requirements",
"infer 'static lifetime requirements",
cfg_fn!(infer_static_outlives_requirements))),

// RFC 2070
("panic_implementation", Normal, Gated(Stability::Unstable,
"panic_implementation",
Expand Down
23 changes: 23 additions & 0 deletions src/test/ui/rfc-2093-infer-outlives/dont-infer-static.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
// 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.

// ignore-tidy-linelength

#![feature(infer_outlives_requirements)]

struct Foo<U> {
bar: Bar<U> //~ ERROR 16:5: 16:16: the parameter type `U` may not live long enough [E0310]
}
struct Bar<T: 'static> {
x: T,
}

fn main() {}

17 changes: 17 additions & 0 deletions src/test/ui/rfc-2093-infer-outlives/dont-infer-static.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,17 @@
error[E0310]: the parameter type `U` may not live long enough
--> $DIR/dont-infer-static.rs:16:5
|
LL | struct Foo<U> {
| - help: consider adding an explicit lifetime bound `U: 'static`...
LL | bar: Bar<U> //~ ERROR 16:5: 16:16: the parameter type `U` may not live long enough [E0310]
| ^^^^^^^^^^^
|
note: ...so that the type `U` will meet its required lifetime bounds
--> $DIR/dont-infer-static.rs:16:5
|
LL | bar: Bar<U> //~ ERROR 16:5: 16:16: the parameter type `U` may not live long enough [E0310]
| ^^^^^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0310`.
25 changes: 25 additions & 0 deletions src/test/ui/rfc-2093-infer-outlives/infer-static.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,25 @@
// 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.

#![feature(rustc_attrs)]
#![feature(infer_outlives_requirements)]
#![feature(infer_static_outlives_requirements)]

#[rustc_outlives]
struct Foo<U> { //~ ERROR 16:1: 18:2: rustc_outlives
bar: Bar<U>
}
struct Bar<T: 'static> {
x: T,
}

fn main() {}


12 changes: 12 additions & 0 deletions src/test/ui/rfc-2093-infer-outlives/infer-static.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
error: rustc_outlives
--> $DIR/infer-static.rs:16:1
|
LL | / struct Foo<U> { //~ ERROR 16:1: 18:2: rustc_outlives
LL | | bar: Bar<U>
LL | | }
| |_^
|
= note: U : 'static

error: aborting due to previous error