implementing RFC 1623. This fixes #35897.

src/librustc_typeck/collect.rs

@@ -1554,7 +1554,7 @@ fn type_of_def_id<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
             NodeItem(item) => {
                 match item.node {
                     ItemStatic(ref t, _, _) | ItemConst(ref t, _) => {
-                        ccx.icx(&()).to_ty(&ExplicitRscope, &t)
+                        ccx.icx(&()).to_ty(&ElidableRscope::new(ty::ReStatic), &t)
                     }
                     ItemFn(ref decl, unsafety, _, abi, ref generics, _) => {
                         let tofd = AstConv::ty_of_bare_fn(&ccx.icx(generics), unsafety, abi, &decl,

src/test/compile-fail/rfc1623.rs

@@ -0,0 +1,101 @@
+// 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.
+
+#![allow(dead_code)]
+
+fn non_elidable<'a, 'b>(a: &'a u8, b: &'b u8) -> &'a u8 {
+    a
+}
+
+// the boundaries of elision
+static NON_ELIDABLE_FN: &fn(&u8, &u8) -> &u8 = &(non_elidable as fn(&u8, &u8) -> &u8);
+//~^ ERROR missing lifetime specifier [E0106]
+
+struct SomeStruct<'x, 'y, 'z: 'x> {
+    foo: &'x Foo<'z>,
+    bar: &'x Bar<'z>,
+    f: &'y for<'a, 'b: 'a> Fn(&'a Foo<'b>) -> &'a Bar<'b>,
+}
+
+fn id<T>(t: T) -> T {
+    t
+}
+
+static SOME_STRUCT: &SomeStruct = SomeStruct {
+    foo: &Foo { bools: &[false, true] },
+    bar: &Bar { bools: &[true, true] },
+    f: &id,
+};
+
+// very simple test for a 'static static with default lifetime
+static STATIC_STR: &'static str = "&'static str";
+const CONST_STR: &'static str = "&'static str";
+
+// this should be the same as without default:
+static EXPLICIT_STATIC_STR: &'static str = "&'static str";
+const EXPLICIT_CONST_STR: &'static str = "&'static str";
+
+// a function that elides to an unbound lifetime for both in- and output
+fn id_u8_slice(arg: &[u8]) -> &[u8] {
+    arg
+}
+
+// one with a function, argument elided
+static STATIC_SIMPLE_FN: &'static fn(&[u8]) -> &[u8] = &(id_u8_slice as fn(&[u8]) -> &[u8]);
+const CONST_SIMPLE_FN: &'static fn(&[u8]) -> &[u8] = &(id_u8_slice as fn(&[u8]) -> &[u8]);
+
+// this should be the same as without elision
+static STATIC_NON_ELIDED_fN: &'static for<'a> fn(&'a [u8]) -> &'a [u8] =
+    &(id_u8_slice as for<'a> fn(&'a [u8]) -> &'a [u8]);
+const CONST_NON_ELIDED_fN: &'static for<'a> fn(&'a [u8]) -> &'a [u8] =
+    &(id_u8_slice as for<'a> fn(&'a [u8]) -> &'a [u8]);
+
+// another function that elides, each to a different unbound lifetime
+fn multi_args(a: &u8, b: &u8, c: &u8) {}
+
+static STATIC_MULTI_FN: &'static fn(&u8, &u8, &u8) = &(multi_args as fn(&u8, &u8, &u8));
+const CONST_MULTI_FN: &'static fn(&u8, &u8, &u8) = &(multi_args as fn(&u8, &u8, &u8));
+
+struct Foo<'a> {
+    bools: &'a [bool],
+}
+
+static STATIC_FOO: Foo<'static> = Foo { bools: &[true, false] };
+const CONST_FOO: Foo<'static> = Foo { bools: &[true, false] };
+
+type Bar<'a> = Foo<'a>;
+
+static STATIC_BAR: Bar<'static> = Bar { bools: &[true, false] };
+const CONST_BAR: Bar<'static> = Bar { bools: &[true, false] };
+
+type Baz<'a> = fn(&'a [u8]) -> Option<u8>;
+
+fn baz(e: &[u8]) -> Option<u8> {
+    e.first().map(|x| *x)
+}
+
+static STATIC_BAZ: &'static Baz<'static> = &(baz as Baz);
+const CONST_BAZ: &'static Baz<'static> = &(baz as Baz);
+
+static BYTES: &'static [u8] = &[1, 2, 3];
+
+fn main() {
+    let x = &[1u8, 2, 3];
+    let y = x;
+
+    // this works, so lifetime < `'static` is valid
+    assert_eq!(Some(1), STATIC_BAZ(y));
+    assert_eq!(Some(1), CONST_BAZ(y));
+
+    let y = &[1u8, 2, 3];
+
+    STATIC_BAZ(BYTES); // BYTES has static lifetime
+    CONST_BAZ(y); // interestingly this does not get reported
+}

src/test/compile-fail/rfc1623.rs.bk

@@ -0,0 +1,98 @@
+// 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.
+
+#![allow(dead_code)]
+
+fn non_elidable<'a, 'b>(a: &'a u8, b: &'b u8) -> &'a u8 { a }
+
+// the boundaries of elision
+static NON_ELIDABLE_FN : &fn(&u8, &u8) -> &u8 =
+//~^ ERROR: missing lifetime specifier
+        &(non_elidable as fn(&u8, &u8) -> &u8);
+
+struct SomeStruct<'x, 'y, 'z: 'x> {
+    foo: &'x Foo<'z>,
+    bar: &'x Bar<'z>,
+    f: &'y for<'a, 'b: 'a> Fn(&'a Foo<'b>) -> &'a Bar<'b>,
+}
+
+fn id<T>(t: T) -> T { t }
+
+static SOME_STRUCT : &SomeStruct = SomeStruct {
+    foo: &Foo { bools: &[false, true] },
+    bar: &Bar { bools: &[true, true] },
+    f: &id,
+};
+
+// very simple test for a 'static static with default lifetime
+static STATIC_STR : &'static str = "&'static str";
+const CONST_STR : &'static str = "&'static str";
+
+// this should be the same as without default:
+static EXPLICIT_STATIC_STR : &'static str = "&'static str";
+const EXPLICIT_CONST_STR : &'static str = "&'static str";
+
+// a function that elides to an unbound lifetime for both in- and output
+fn id_u8_slice(arg: &[u8]) -> &[u8] { arg }
+
+// one with a function, argument elided
+static STATIC_SIMPLE_FN : &'static fn(&[u8]) -> &[u8] =
+        &(id_u8_slice as fn(&[u8]) -> &[u8]);
+const CONST_SIMPLE_FN : &'static fn(&[u8]) -> &[u8] =
+        &(id_u8_slice as fn(&[u8]) -> &[u8]);
+
+// this should be the same as without elision
+static STATIC_NON_ELIDED_fN : &'static for<'a> fn(&'a [u8]) -> &'a [u8] =
+        &(id_u8_slice as for<'a> fn(&'a [u8]) -> &'a [u8]);
+const CONST_NON_ELIDED_fN : &'static for<'a> fn(&'a [u8]) -> &'a [u8] =
+        &(id_u8_slice as for<'a> fn(&'a [u8]) -> &'a [u8]);
+
+// another function that elides, each to a different unbound lifetime
+fn multi_args(a: &u8, b: &u8, c: &u8) { }
+
+static STATIC_MULTI_FN : &'static fn(&u8, &u8, &u8) =
+        &(multi_args as fn(&u8, &u8, &u8));
+const CONST_MULTI_FN : &'static fn(&u8, &u8, &u8) =
+        &(multi_args as fn(&u8, &u8, &u8));
+
+struct Foo<'a> {
+    bools: &'a [bool]
+}
+
+static STATIC_FOO : Foo<'static> = Foo { bools: &[true, false] };
+const CONST_FOO : Foo<'static> = Foo { bools: &[true, false] };
+
+type Bar<'a> = Foo<'a>;
+
+static STATIC_BAR : Bar<'static> = Bar { bools: &[true, false] };
+const CONST_BAR : Bar<'static> = Bar { bools: &[true, false] };
+
+type Baz<'a> = fn(&'a [u8]) -> Option<u8>;
+
+fn baz(e: &[u8]) -> Option<u8> { e.first().map(|x| *x) }
+
+static STATIC_BAZ : &'static Baz<'static> = &(baz as Baz);
+const CONST_BAZ : &'static Baz<'static> = &(baz as Baz);
+
+static BYTES : &'static [u8] = &[1, 2, 3];
+
+fn main() {
+    let x = &[1u8, 2, 3];
+    let y = x;
+
+    //this works, so lifetime < `'static` is valid
+    assert_eq!(Some(1), STATIC_BAZ(y));
+    assert_eq!(Some(1), CONST_BAZ(y));
+
+    let y = &[1u8, 2, 3];
+    //^~ ERROR: borrowed values does not live long enough
+    STATIC_BAZ(BYTES); // BYTES has static lifetime
+    CONST_BAZ(y); // This forces static lifetime, which y has not
+}

src/test/run-pass/rfc1623.rs

@@ -0,0 +1,81 @@
+// 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.
+
+#![allow(dead_code)]
+
+// very simple test for a 'static static with default lifetime
+static STATIC_STR: &str = "&'static str";
+const CONST_STR: &str = "&'static str";
+
+// this should be the same as without default:
+static EXPLICIT_STATIC_STR: &'static str = "&'static str";
+const EXPLICIT_CONST_STR: &'static str = "&'static str";
+
+// a function that elides to an unbound lifetime for both in- and output
+fn id_u8_slice(arg: &[u8]) -> &[u8] {
+    arg
+}
+
+// one with a function, argument elided
+static STATIC_SIMPLE_FN: &fn(&[u8]) -> &[u8] = &(id_u8_slice as fn(&[u8]) -> &[u8]);
+const CONST_SIMPLE_FN: &fn(&[u8]) -> &[u8] = &(id_u8_slice as fn(&[u8]) -> &[u8]);
+
+// this should be the same as without elision
+static STATIC_NON_ELIDED_fN: &for<'a> fn(&'a [u8]) -> &'a [u8] =
+    &(id_u8_slice as for<'a> fn(&'a [u8]) -> &'a [u8]);
+const CONST_NON_ELIDED_fN: &for<'a> fn(&'a [u8]) -> &'a [u8] =
+    &(id_u8_slice as for<'a> fn(&'a [u8]) -> &'a [u8]);
+
+// another function that elides, each to a different unbound lifetime
+fn multi_args(a: &u8, b: &u8, c: &u8) {}
+
+static STATIC_MULTI_FN: &fn(&u8, &u8, &u8) = &(multi_args as fn(&u8, &u8, &u8));
+const CONST_MULTI_FN: &fn(&u8, &u8, &u8) = &(multi_args as fn(&u8, &u8, &u8));
+
+struct Foo<'a> {
+    bools: &'a [bool],
+}
+
+static STATIC_FOO: Foo = Foo { bools: &[true, false] };
+const CONST_FOO: Foo = Foo { bools: &[true, false] };
+
+type Bar<'a> = Foo<'a>;
+
+static STATIC_BAR: Bar = Bar { bools: &[true, false] };
+const CONST_BAR: Bar = Bar { bools: &[true, false] };
+
+type Baz<'a> = fn(&'a [u8]) -> Option<u8>;
+
+fn baz(e: &[u8]) -> Option<u8> {
+    e.first().map(|x| *x)
+}
+
+static STATIC_BAZ: &Baz = &(baz as Baz);
+const CONST_BAZ: &Baz = &(baz as Baz);
+
+static BYTES: &[u8] = &[1, 2, 3];
+
+fn main() {
+    // make sure that the lifetime is actually elided (and not defaulted)
+    let x = &[1u8, 2, 3];
+    STATIC_SIMPLE_FN(x);
+    CONST_SIMPLE_FN(x);
+
+    STATIC_BAZ(BYTES); // neees static lifetime
+    CONST_BAZ(BYTES);
+
+    // make sure this works with different lifetimes
+    let a = &1;
+    {
+        let b = &2;
+        let c = &3;
+        CONST_MULTI_FN(a, b, c);
+    }
+}

src/test/run-pass/rfc1623.rs.bk

@@ -0,0 +1,81 @@
+// 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.
+
+#![allow(dead_code)]
+
+// very simple test for a 'static static with default lifetime
+static STATIC_STR : &str = "&'static str";
+const CONST_STR : &str = "&'static str";
+
+// this should be the same as without default:
+static EXPLICIT_STATIC_STR : &'static str = "&'static str";
+const EXPLICIT_CONST_STR : &'static str = "&'static str";
+
+// a function that elides to an unbound lifetime for both in- and output
+fn id_u8_slice(arg: &[u8]) -> &[u8] { arg }
+
+// one with a function, argument elided
+static STATIC_SIMPLE_FN : &fn(&[u8]) -> &[u8] =
+        &(id_u8_slice as fn(&[u8]) -> &[u8]);
+const CONST_SIMPLE_FN : &fn(&[u8]) -> &[u8] =
+        &(id_u8_slice as fn(&[u8]) -> &[u8]);
+
+// this should be the same as without elision
+static STATIC_NON_ELIDED_fN : &for<'a> fn(&'a [u8]) -> &'a [u8] =
+        &(id_u8_slice as for<'a> fn(&'a [u8]) -> &'a [u8]);
+const CONST_NON_ELIDED_fN : &for<'a> fn(&'a [u8]) -> &'a [u8] =
+        &(id_u8_slice as for<'a> fn(&'a [u8]) -> &'a [u8]);
+
+// another function that elides, each to a different unbound lifetime
+fn multi_args(a: &u8, b: &u8, c: &u8) { }
+
+static STATIC_MULTI_FN : &fn(&u8, &u8, &u8) =
+        &(multi_args as fn(&u8, &u8, &u8));
+const CONST_MULTI_FN : &fn(&u8, &u8, &u8) =
+        &(multi_args as fn(&u8, &u8, &u8));
+
+struct Foo<'a> {
+    bools: &'a [bool]
+}
+
+static STATIC_FOO : Foo = Foo { bools: &[true, false] };
+const CONST_FOO : Foo = Foo { bools: &[true, false] };
+
+type Bar<'a> = Foo<'a>;
+
+static STATIC_BAR : Bar = Bar { bools: &[true, false] };
+const CONST_BAR : Bar = Bar { bools: &[true, false] };
+
+type Baz<'a> = fn(&'a [u8]) -> Option<u8>;
+
+fn baz(e: &[u8]) -> Option<u8> { e.first().map(|x| *x) }
+
+static STATIC_BAZ : &Baz = &(baz as Baz);
+const CONST_BAZ : &Baz = &(baz as Baz);
+
+static BYTES : &[u8] = &[1, 2, 3];
+
+fn main() {
+    // make sure that the lifetime is actually elided (and not defaulted)
+    let x = &[1u8, 2, 3];
+    STATIC_SIMPLE_FN(x);
+    CONST_SIMPLE_FN(x);
+
+    STATIC_BAZ(BYTES); // neees static lifetime
+    CONST_BAZ(BYTES);
+
+    // make sure this works with different lifetimes
+    let a = &1;
+    {
+        let b = &2;
+        let c = &3;
+        CONST_MULTI_FN(a, b, c);
+    }
+}