Auto merge of #48516 - petrochenkov:stabsl, r=nikomatsakis

Stabilize slice patterns without `..`

And merge `feature(advanced_slice_patterns)` into `feature(slice_patterns)`.

The detailed description can be found in #48836.

Slice patterns were unstable for long time since before 1.0 due to many bugs in the implementation, now this stabilization is possible primarily due to work of @arielb1 who [wrote the new MIR-based implementation of slice patterns](#32202) and @mikhail-m1 who [fixed one remaining class of codegen issues](#47926).

Reference PR rust-lang/reference#259
cc #23121
fixes #48836

src/doc/unstable-book/src/language-features/slice-patterns.md

@@ -4,25 +4,29 @@ The tracking issue for this feature is: [#23121]
 
 [#23121]: https://github.com/rust-lang/rust/issues/23121
 
-See also
-[`advanced_slice_patterns`](language-features/advanced-slice-patterns.html).
-
 ------------------------
 
-
-If you want to match against a slice or array, you can use `&` with the
-`slice_patterns` feature:
+The `slice_patterns` feature gate lets you use `..` to indicate any number of
+elements inside a pattern matching a slice. This wildcard can only be used once
+for a given array. If there's an pattern before the `..`, the subslice will be
+matched against that pattern. For example:
 
 ```rust
 #![feature(slice_patterns)]
 
+fn is_symmetric(list: &[u32]) -> bool {
+    match list {
+        &[] | &[_] => true,
+        &[x, ref inside.., y] if x == y => is_symmetric(inside),
+        &[..] => false,
+    }
+}
+
 fn main() {
-    let v = vec!["match_this", "1"];
+    let sym = &[0, 1, 4, 2, 4, 1, 0];
+    assert!(is_symmetric(sym));
 
-    match &v[..] {
-        &["match_this", second] => println!("The second element is {}", second),
-        _ => {},
-    }
+    let not_sym = &[0, 1, 7, 2, 4, 1, 0];
+    assert!(!is_symmetric(not_sym));
 }
 ```
-

src/liballoc/lib.rs

@@ -111,7 +111,6 @@
 #![feature(ptr_internals)]
 #![feature(rustc_attrs)]
 #![feature(slice_get_slice)]
-#![feature(slice_patterns)]
 #![feature(slice_rsplit)]
 #![feature(specialization)]
 #![feature(staged_api)]

src/libcore/benches/lib.rs

@@ -11,7 +11,6 @@
 #![deny(warnings)]
 
 #![feature(flt2dec)]
-#![feature(slice_patterns)]
 #![feature(test)]
 
 extern crate core;

src/libcore/tests/lib.rs

@@ -37,6 +37,7 @@
 #![feature(raw)]
 #![feature(refcell_replace_swap)]
 #![feature(slice_patterns)]
+#![feature(slice_rotate)]
 #![feature(sort_internals)]
 #![feature(specialization)]
 #![feature(step_trait)]

src/librustc/benches/lib.rs

@@ -10,7 +10,6 @@
 
 #![deny(warnings)]
 
-#![feature(slice_patterns)]
 #![feature(test)]
 
 extern crate test;

src/librustc_apfloat/lib.rs

@@ -47,7 +47,7 @@
 #![forbid(unsafe_code)]
 
 #![feature(i128_type)]
-#![feature(slice_patterns)]
+#![cfg_attr(stage0, feature(slice_patterns))]
 #![feature(try_from)]
 
 // See librustc_cratesio_shim/Cargo.toml for a comment explaining this.

src/librustc_const_eval/lib.rs

@@ -20,7 +20,6 @@
 #![deny(warnings)]
 
 #![feature(rustc_diagnostic_macros)]
-#![feature(slice_patterns)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(macro_lifetime_matcher)]

src/librustc_lint/lib.rs

@@ -31,7 +31,6 @@
 #![feature(macro_vis_matcher)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(slice_patterns)]
 #![cfg_attr(stage0, feature(never_type))]
 
 #[macro_use]

src/librustc_trans/lib.rs

@@ -30,7 +30,7 @@
 #![feature(libc)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(slice_patterns)]
+#![cfg_attr(stage0, feature(slice_patterns))]
 #![feature(conservative_impl_trait)]
 #![feature(optin_builtin_traits)]
 #![feature(inclusive_range_fields)]

src/librustc_trans_utils/lib.rs

@@ -24,7 +24,6 @@
 #![feature(i128_type)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
-#![feature(slice_patterns)]
 #![feature(conservative_impl_trait)]
 
 extern crate ar;

src/librustc_typeck/diagnostics.rs

@@ -3559,8 +3559,6 @@ elements in the array being matched.
 Example of erroneous code:
 
 ```compile_fail,E0527
-#![feature(slice_patterns)]
-
 let r = &[1, 2, 3, 4];
 match r {
     &[a, b] => { // error: pattern requires 2 elements but array
@@ -3625,8 +3623,6 @@ An array or slice pattern was matched against some other type.
 Example of erroneous code:
 
 ```compile_fail,E0529
-#![feature(slice_patterns)]
-
 let r: f32 = 1.0;
 match r {
     [a, b] => { // error: expected an array or slice, found `f32`
@@ -3639,8 +3635,6 @@ Ensure that the pattern and the expression being matched on are of consistent
 types:
 
 ```
-#![feature(slice_patterns)]
-
 let r = [1.0, 2.0];
 match r {
     [a, b] => { // ok!

src/librustc_typeck/lib.rs

@@ -72,7 +72,7 @@ This API is completely unstable and subject to change.
 
 #![allow(non_camel_case_types)]
 
-#![feature(advanced_slice_patterns)]
+#![cfg_attr(stage0, feature(advanced_slice_patterns))]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(conservative_impl_trait)]

src/librustdoc/lib.rs

@@ -20,7 +20,7 @@
 #![feature(box_syntax)]
 #![feature(fs_read_write)]
 #![feature(set_stdio)]
-#![feature(slice_patterns)]
+#![cfg_attr(stage0, feature(slice_patterns))]
 #![feature(test)]
 #![feature(unicode)]
 #![feature(vec_remove_item)]

src/libsyntax/feature_gate.rs

@@ -145,7 +145,6 @@ declare_features! (
     // rustc internal
     (active, rustc_diagnostic_macros, "1.0.0", None, None),
     (active, rustc_const_unstable, "1.0.0", None, None),
-    (active, advanced_slice_patterns, "1.0.0", Some(23121), None),
     (active, box_syntax, "1.0.0", Some(27779), None),
     (active, placement_in_syntax, "1.0.0", Some(27779), None),
     (active, unboxed_closures, "1.0.0", Some(29625), None),
@@ -474,6 +473,8 @@ declare_features! (
     (removed, allocator, "1.0.0", None, None),
     // Allows the `#[simd]` attribute -- removed in favor of `#[repr(simd)]`
     (removed, simd, "1.0.0", Some(27731), None),
+    // Merged into `slice_patterns`
+    (removed, advanced_slice_patterns, "1.0.0", Some(23121), None),
 );
 
 declare_features! (
@@ -1655,17 +1656,10 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
         match pattern.node {
-            PatKind::Slice(_, Some(_), ref last) if !last.is_empty() => {
-                gate_feature_post!(&self, advanced_slice_patterns,
-                                  pattern.span,
-                                  "multiple-element slice matches anywhere \
-                                   but at the end of a slice (e.g. \
-                                   `[0, ..xs, 0]`) are experimental")
-            }
-            PatKind::Slice(..) => {
+            PatKind::Slice(_, Some(ref subslice), _) => {
                 gate_feature_post!(&self, slice_patterns,
-                                  pattern.span,
-                                  "slice pattern syntax is experimental");
+                                   subslice.span,
+                                   "syntax for subslices in slice patterns is not yet stabilized");
             }
             PatKind::Box(..) => {
                 gate_feature_post!(&self, box_patterns,

src/libsyntax/parse/parser.rs

@@ -3618,7 +3618,7 @@ impl<'a> Parser<'a> {
                         slice = Some(P(Pat {
                             id: ast::DUMMY_NODE_ID,
                             node: PatKind::Wild,
-                            span: self.span,
+                            span: self.prev_span,
                         }));
                         before_slice = false;
                     }

src/test/compile-fail/borrowck/borrowck-describe-lvalue.rs

@@ -13,7 +13,6 @@
 //[mir]compile-flags: -Z borrowck=mir
 
 #![feature(slice_patterns)]
-#![feature(advanced_slice_patterns)]
 
 pub struct Foo {
   x: u32

src/test/compile-fail/borrowck/borrowck-match-binding-is-assignment.rs

@@ -13,8 +13,6 @@
 
 // Test that immutable pattern bindings cannot be reassigned.
 
-#![feature(slice_patterns)]
-
 enum E {
     Foo(isize)
 }

src/test/compile-fail/borrowck/borrowck-move-out-from-array.rs

@@ -11,7 +11,8 @@
 // revisions: ast mir
 //[mir]compile-flags: -Z borrowck=mir
 
-#![feature(box_syntax, slice_patterns, advanced_slice_patterns)]
+#![feature(box_syntax)]
+#![feature(slice_patterns)]
 
 fn move_out_from_begin_and_end() {
     let a = [box 1, box 2];

src/test/compile-fail/borrowck/borrowck-vec-pattern-element-loan.rs

@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(advanced_slice_patterns)]
 #![feature(slice_patterns)]
 
 fn a<'a>() -> &'a [isize] {

src/test/compile-fail/issue-12369.rs

@@ -9,7 +9,6 @@
 // except according to those terms.
 
 #![feature(slice_patterns)]
-#![allow(unused_variables)]
 #![deny(unreachable_patterns)]
 
 fn main() {

src/test/compile-fail/issue-13482-2.rs

@@ -10,8 +10,6 @@
 
 // compile-flags:-Z verbose
 
-#![feature(slice_patterns)]
-
 fn main() {
     let x = [1,2];
     let y = match x {

src/test/compile-fail/issue-13482.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(slice_patterns)]
-
 fn main() {
   let x = [1,2];
   let y = match x {

src/test/compile-fail/issue-15381.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(slice_patterns)]
-
 fn main() {
     let values: Vec<u8> = vec![1,2,3,4,5,6,7,8];
 

src/test/compile-fail/issue-41255.rs

@@ -10,7 +10,6 @@
 
 // Matching against float literals should result in a linter error
 
-#![feature(slice_patterns)]
 #![feature(exclusive_range_pattern)]
 #![allow(unused)]
 #![forbid(illegal_floating_point_literal_pattern)]

src/test/compile-fail/issue-6804.rs

@@ -10,7 +10,6 @@
 
 // Matching against NaN should result in a warning
 
-#![feature(slice_patterns)]
 #![allow(unused)]
 #![deny(illegal_floating_point_literal_pattern)]
 

src/test/compile-fail/match-byte-array-patterns-2.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(advanced_slice_patterns, slice_patterns)]
-
 fn main() {
     let buf = &[0, 1, 2, 3];
 

src/test/compile-fail/match-byte-array-patterns.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(advanced_slice_patterns, slice_patterns)]
+#![feature(slice_patterns)]
 #![deny(unreachable_patterns)]
 
 fn main() {

src/test/compile-fail/match-ref-ice.rs

@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(slice_patterns)]
 #![deny(unreachable_patterns)]
 
 // The arity of `ref x` is always 1. If the pattern is compared to some non-structural type whose

src/test/compile-fail/match-slice-patterns.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(advanced_slice_patterns, slice_patterns)]
+#![feature(slice_patterns)]
 
 fn check(list: &[Option<()>]) {
     match list {

src/test/compile-fail/match-vec-fixed.rs

@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(slice_patterns)]
 #![deny(unreachable_patterns)]
 
 fn a() {

src/test/compile-fail/match-vec-mismatch-2.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(slice_patterns)]
-
 fn main() {
     match () {
         [()] => { }

src/test/compile-fail/match-vec-unreachable.rs

@@ -10,7 +10,6 @@
 
 #![feature(slice_patterns)]
 #![deny(unreachable_patterns)]
-#![allow(unused_variables)]
 
 fn main() {
     let x: Vec<(isize, isize)> = Vec::new();

src/test/compile-fail/move-out-of-slice-1.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(slice_patterns, box_patterns)]
+#![feature(box_patterns)]
 
 struct A;