Stabilize "RangeFrom" patterns in 1.55

compiler/rustc_ast/src/ast.rs

@@ -675,7 +675,9 @@ pub enum BindingMode {
 
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum RangeEnd {
+    /// `..=` or `...`
     Included(RangeSyntax),
+    /// `..`
     Excluded,
 }
 
@@ -687,6 +689,7 @@ pub enum RangeSyntax {
     DotDotEq,
 }
 
+/// All the different flavors of pattern that Rust recognizes.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub enum PatKind {
     /// Represents a wildcard pattern (`_`).
@@ -727,7 +730,7 @@ pub enum PatKind {
     /// A literal.
     Lit(P<Expr>),
 
-    /// A range pattern (e.g., `1...2`, `1..=2` or `1..2`).
+    /// A range pattern (e.g., `1...2`, `1..2`, `1..`, `..2`, `1..=2`, `..=2`).
     Range(Option<P<Expr>>, Option<P<Expr>>, Spanned<RangeEnd>),
 
     /// A slice pattern `[a, b, c]`.

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -540,6 +540,22 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
 
     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
         match &pattern.kind {
+            PatKind::Slice(pats) => {
+                for pat in pats {
+                    let inner_pat = match &pat.kind {
+                        PatKind::Ident(.., Some(pat)) => pat,
+                        _ => pat,
+                    };
+                    if let PatKind::Range(Some(_), None, Spanned { .. }) = inner_pat.kind {
+                        gate_feature_post!(
+                            &self,
+                            half_open_range_patterns,
+                            pat.span,
+                            "`X..` patterns in slices are experimental"
+                        );
+                    }
+                }
+            }
             PatKind::Box(..) => {
                 gate_feature_post!(
                     &self,
@@ -548,7 +564,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                     "box pattern syntax is experimental"
                 );
             }
-            PatKind::Range(_, _, Spanned { node: RangeEnd::Excluded, .. }) => {
+            PatKind::Range(_, Some(_), Spanned { node: RangeEnd::Excluded, .. }) => {
                 gate_feature_post!(
                     &self,
                     exclusive_range_pattern,

compiler/rustc_parse/src/parser/pat.rs

@@ -715,7 +715,6 @@ impl<'a> Parser<'a> {
         } else if self.eat(&token::DotDotEq) {
             RangeEnd::Included(RangeSyntax::DotDotEq)
         } else if self.eat(&token::DotDot) {
-            self.sess.gated_spans.gate(sym::exclusive_range_pattern, self.prev_token.span);
             RangeEnd::Excluded
         } else {
             return None;
@@ -735,7 +734,6 @@ impl<'a> Parser<'a> {
             Some(self.parse_pat_range_end()?)
         } else {
             // Parsing e.g. `X..`.
-            self.sess.gated_spans.gate(sym::half_open_range_patterns, begin.span.to(re.span));
             if let RangeEnd::Included(_) = re.node {
                 // FIXME(Centril): Consider semantic errors instead in `ast_validation`.
                 // Possibly also do this for `X..=` in *expression* contexts.

src/doc/unstable-book/src/language-features/exclusive-range-pattern.md

@@ -0,0 +1,26 @@
+# `exclusive_range_pattern`
+
+The tracking issue for this feature is: [#37854].
+
+
+[#67264]: https://github.com/rust-lang/rust/issues/67264
+[#37854]: https://github.com/rust-lang/rust/issues/37854
+-----
+
+The `exclusive_range_pattern` feature allows non-inclusive range
+patterns (`0..10`) to be used in appropriate pattern matching
+contexts. It also can be combined with `#![feature(half_open_range_patterns]`
+to be able to use RangeTo patterns (`..10`).
+
+It also enabled RangeFrom patterns but that has since been
+stabilized.
+
+```rust
+#![feature(exclusive_range_pattern)]
+    let x = 5;
+    match x {
+        0..10 => println!("single digit"),
+        10 => println!("ten isn't part of the above range"),
+        _ => println!("nor is everything else.")
+    }
+```

src/doc/unstable-book/src/language-features/half-open-range-patterns.md

@@ -0,0 +1,27 @@
+# `half_open_range_patterns`
+
+The tracking issue for this feature is: [#67264]
+It is part of the `#![exclusive_range_pattern]` feature,
+tracked at [#37854].
+
+[#67264]: https://github.com/rust-lang/rust/issues/67264
+[#37854]: https://github.com/rust-lang/rust/issues/37854
+-----
+
+The `half_open_range_patterns` feature allows RangeTo patterns
+(`..10`) to be used in appropriate pattern matching contexts.
+This requires also enabling the `exclusive_range_pattern` feature.
+
+It also enabled RangeFrom patterns but that has since been
+stabilized.
+
+```rust
+#![feature(half_open_range_patterns)]
+#![feature(exclusive_range_pattern)]
+    let x = 5;
+    match x {
+        ..0 => println!("negative!"), // "RangeTo" pattern. Unstable.
+        0 => println!("zero!"),
+        1.. => println!("positive!"), // "RangeFrom" pattern. Stable.
+    }
+```

src/test/ui/half-open-range-patterns/feature-gate-half-open-range-patterns.rs

@@ -11,12 +11,8 @@ fn foo() {
     //~| ERROR range-to patterns with `...` are not allowed
     if let ..5 = 0 {}
     //~^ ERROR half-open range patterns are unstable
-    if let 5.. = 0 {}
-    //~^ ERROR half-open range patterns are unstable
     if let 5..= = 0 {}
-    //~^ ERROR half-open range patterns are unstable
-    //~| ERROR inclusive range with no end
+    //~^ ERROR inclusive range with no end
     if let 5... = 0 {}
-    //~^ ERROR half-open range patterns are unstable
-    //~| ERROR inclusive range with no end
+    //~^ ERROR inclusive range with no end
 }

src/test/ui/half-open-range-patterns/feature-gate-half-open-range-patterns.stderr

@@ -5,15 +5,15 @@ LL |     if let ...5 = 0 {}
    |            ^^^ help: use `..=` instead
 
 error[E0586]: inclusive range with no end
-  --> $DIR/feature-gate-half-open-range-patterns.rs:16:13
+  --> $DIR/feature-gate-half-open-range-patterns.rs:14:13
    |
 LL |     if let 5..= = 0 {}
    |             ^^^ help: use `..` instead
    |
    = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
 
 error[E0586]: inclusive range with no end
-  --> $DIR/feature-gate-half-open-range-patterns.rs:19:13
+  --> $DIR/feature-gate-half-open-range-patterns.rs:16:13
    |
 LL |     if let 5... = 0 {}
    |             ^^^ help: use `..` instead
@@ -47,34 +47,7 @@ LL |     if let ..5 = 0 {}
    = note: see issue #67264 <https://github.com/rust-lang/rust/issues/67264> for more information
    = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
 
-error[E0658]: half-open range patterns are unstable
-  --> $DIR/feature-gate-half-open-range-patterns.rs:14:12
-   |
-LL |     if let 5.. = 0 {}
-   |            ^^^
-   |
-   = note: see issue #67264 <https://github.com/rust-lang/rust/issues/67264> for more information
-   = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
-
-error[E0658]: half-open range patterns are unstable
-  --> $DIR/feature-gate-half-open-range-patterns.rs:16:12
-   |
-LL |     if let 5..= = 0 {}
-   |            ^^^^
-   |
-   = note: see issue #67264 <https://github.com/rust-lang/rust/issues/67264> for more information
-   = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
-
-error[E0658]: half-open range patterns are unstable
-  --> $DIR/feature-gate-half-open-range-patterns.rs:19:12
-   |
-LL |     if let 5... = 0 {}
-   |            ^^^^
-   |
-   = note: see issue #67264 <https://github.com/rust-lang/rust/issues/67264> for more information
-   = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
-
-error: aborting due to 9 previous errors
+error: aborting due to 6 previous errors
 
 Some errors have detailed explanations: E0586, E0658.
 For more information about an error, try `rustc --explain E0586`.

src/test/ui/half-open-range-patterns/range_pat_interactions0.rs

@@ -0,0 +1,32 @@
+// run-pass
+#![allow(incomplete_features)]
+#![feature(exclusive_range_pattern)]
+#![feature(half_open_range_patterns)]
+#![feature(inline_const)]
+
+fn main() {
+    let mut if_lettable = vec![];
+    let mut first_or = vec![];
+    let mut or_two = vec![];
+    let mut range_from = vec![];
+    let mut bottom = vec![];
+
+    for x in -9 + 1..=(9 - 2) {
+        if let -1..=0 | 2..3 | 4 = x {
+            if_lettable.push(x)
+        }
+        match x {
+            1 | -3..0 => first_or.push(x),
+            y @ (0..5 | 6) => or_two.push(y),
+            y @ 0..const { 5 + 1 } => assert_eq!(y, 5),
+            y @ -5.. => range_from.push(y),
+            y @ ..-7 => assert_eq!(y, -8),
+            y => bottom.push(y),
+        }
+    }
+    assert_eq!(if_lettable, [-1, 0, 2, 4]);
+    assert_eq!(first_or, [-3, -2, -1, 1]);
+    assert_eq!(or_two, [0, 2, 3, 4, 6]);
+    assert_eq!(range_from, [-5, -4, 7]);
+    assert_eq!(bottom, [-7, -6]);
+}

src/test/ui/half-open-range-patterns/range_pat_interactions1.rs

@@ -0,0 +1,29 @@
+fn main() {
+    let mut if_lettable = Vec::<i32>::new();
+    let mut first_or = Vec::<i32>::new();
+    let mut or_two = Vec::<i32>::new();
+    let mut range_from = Vec::<i32>::new();
+    let mut bottom = Vec::<i32>::new();
+    let mut errors_only = Vec::<i32>::new();
+
+    for x in -9 + 1..=(9 - 2) {
+        if let n @ 2..3|4 = x {
+            //~^ error: variable `n` is not bound in all patterns
+            //~| exclusive range pattern syntax is experimental
+            errors_only.push(x);
+        } else if let 2..3 | 4 = x {
+            //~^ exclusive range pattern syntax is experimental
+            if_lettable.push(x);
+        }
+        match x as i32 {
+            0..5+1 => errors_only.push(x),
+            //~^ error: expected one of `=>`, `if`, or `|`, found `+`
+            1 | -3..0 => first_or.push(x),
+            y @ (0..5 | 6) => or_two.push(y),
+            y @ 0..const { 5 + 1 } => assert_eq!(y, 5),
+            y @ -5.. => range_from.push(y),
+            y @ ..-7 => assert_eq!(y, -8),
+            y => bottom.push(y),
+        }
+    }
+}

src/test/ui/half-open-range-patterns/range_pat_interactions1.stderr

@@ -0,0 +1,36 @@
+error: expected one of `=>`, `if`, or `|`, found `+`
+  --> $DIR/range_pat_interactions1.rs:19:17
+   |
+LL |             0..5+1 => errors_only.push(x),
+   |                 ^ expected one of `=>`, `if`, or `|`
+
+error[E0408]: variable `n` is not bound in all patterns
+  --> $DIR/range_pat_interactions1.rs:10:25
+   |
+LL |         if let n @ 2..3|4 = x {
+   |                -        ^ pattern doesn't bind `n`
+   |                |
+   |                variable not in all patterns
+
+error[E0658]: exclusive range pattern syntax is experimental
+  --> $DIR/range_pat_interactions1.rs:10:20
+   |
+LL |         if let n @ 2..3|4 = x {
+   |                    ^^^^
+   |
+   = note: see issue #37854 <https://github.com/rust-lang/rust/issues/37854> for more information
+   = help: add `#![feature(exclusive_range_pattern)]` to the crate attributes to enable
+
+error[E0658]: exclusive range pattern syntax is experimental
+  --> $DIR/range_pat_interactions1.rs:14:23
+   |
+LL |         } else if let 2..3 | 4 = x {
+   |                       ^^^^
+   |
+   = note: see issue #37854 <https://github.com/rust-lang/rust/issues/37854> for more information
+   = help: add `#![feature(exclusive_range_pattern)]` to the crate attributes to enable
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0408, E0658.
+For more information about an error, try `rustc --explain E0408`.

src/test/ui/half-open-range-patterns/range_pat_interactions2.rs

@@ -0,0 +1,21 @@
+fn main() {
+    let mut first_or = Vec::<i32>::new();
+    let mut or_two = Vec::<i32>::new();
+    let mut range_from = Vec::<i32>::new();
+    let mut bottom = Vec::<i32>::new();
+    let mut errors_only = Vec::<i32>::new();
+
+    for x in -9 + 1..=(9 - 2) {
+        match x as i32 {
+            0..=(5+1) => errors_only.push(x),
+            //~^ error: inclusive range with no end
+            //~| error: expected one of `=>`, `if`, or `|`, found `(`
+            1 | -3..0 => first_or.push(x),
+            y @ (0..5 | 6) => or_two.push(y),
+            y @ 0..const { 5 + 1 } => assert_eq!(y, 5),
+            y @ -5.. => range_from.push(y),
+            y @ ..-7 => assert_eq!(y, -8),
+            y => bottom.push(y),
+        }
+    }
+}

src/test/ui/half-open-range-patterns/range_pat_interactions2.stderr

@@ -0,0 +1,17 @@
+error[E0586]: inclusive range with no end
+  --> $DIR/range_pat_interactions2.rs:10:14
+   |
+LL |             0..=(5+1) => errors_only.push(x),
+   |              ^^^ help: use `..` instead
+   |
+   = note: inclusive ranges must be bounded at the end (`..=b` or `a..=b`)
+
+error: expected one of `=>`, `if`, or `|`, found `(`
+  --> $DIR/range_pat_interactions2.rs:10:17
+   |
+LL |             0..=(5+1) => errors_only.push(x),
+   |                 ^ expected one of `=>`, `if`, or `|`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0586`.

src/test/ui/half-open-range-patterns/range_pat_interactions3.rs

@@ -0,0 +1,24 @@
+fn main() {
+    let mut first_or = Vec::<i32>::new();
+    let mut or_two = Vec::<i32>::new();
+    let mut range_from = Vec::<i32>::new();
+    let mut bottom = Vec::<i32>::new();
+
+    for x in -9 + 1..=(9 - 2) {
+        match x as i32 {
+            8.. => bottom.push(x),
+            1 | -3..0 => first_or.push(x),
+            //~^ exclusive range pattern syntax is experimental
+            y @ (0..5 | 6) => or_two.push(y),
+            //~^ exclusive range pattern syntax is experimental
+            y @ 0..const { 5 + 1 } => assert_eq!(y, 5),
+            //~^ inline-const is experimental
+            //~| exclusive range pattern syntax is experimental
+            y @ -5.. => range_from.push(y),
+            y @ ..-7 => assert_eq!(y, -8),
+            //~^ half-open range patterns are unstable
+            //~| exclusive range pattern syntax is experimental
+            y => bottom.push(y),
+        }
+    }
+}

src/test/ui/half-open-range-patterns/range_pat_interactions3.stderr

@@ -0,0 +1,57 @@
+error[E0658]: half-open range patterns are unstable
+  --> $DIR/range_pat_interactions3.rs:18:17
+   |
+LL |             y @ ..-7 => assert_eq!(y, -8),
+   |                 ^^^^
+   |
+   = note: see issue #67264 <https://github.com/rust-lang/rust/issues/67264> for more information
+   = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
+
+error[E0658]: inline-const is experimental
+  --> $DIR/range_pat_interactions3.rs:14:20
+   |
+LL |             y @ 0..const { 5 + 1 } => assert_eq!(y, 5),
+   |                    ^^^^^
+   |
+   = note: see issue #76001 <https://github.com/rust-lang/rust/issues/76001> for more information
+   = help: add `#![feature(inline_const)]` to the crate attributes to enable
+
+error[E0658]: exclusive range pattern syntax is experimental
+  --> $DIR/range_pat_interactions3.rs:10:17
+   |
+LL |             1 | -3..0 => first_or.push(x),
+   |                 ^^^^^
+   |
+   = note: see issue #37854 <https://github.com/rust-lang/rust/issues/37854> for more information
+   = help: add `#![feature(exclusive_range_pattern)]` to the crate attributes to enable
+
+error[E0658]: exclusive range pattern syntax is experimental
+  --> $DIR/range_pat_interactions3.rs:12:18
+   |
+LL |             y @ (0..5 | 6) => or_two.push(y),
+   |                  ^^^^
+   |
+   = note: see issue #37854 <https://github.com/rust-lang/rust/issues/37854> for more information
+   = help: add `#![feature(exclusive_range_pattern)]` to the crate attributes to enable
+
+error[E0658]: exclusive range pattern syntax is experimental
+  --> $DIR/range_pat_interactions3.rs:14:17
+   |
+LL |             y @ 0..const { 5 + 1 } => assert_eq!(y, 5),
+   |                 ^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #37854 <https://github.com/rust-lang/rust/issues/37854> for more information
+   = help: add `#![feature(exclusive_range_pattern)]` to the crate attributes to enable
+
+error[E0658]: exclusive range pattern syntax is experimental
+  --> $DIR/range_pat_interactions3.rs:18:17
+   |
+LL |             y @ ..-7 => assert_eq!(y, -8),
+   |                 ^^^^
+   |
+   = note: see issue #37854 <https://github.com/rust-lang/rust/issues/37854> for more information
+   = help: add `#![feature(exclusive_range_pattern)]` to the crate attributes to enable
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/half-open-range-patterns/slice_pattern_syntax_problem0.rs

@@ -0,0 +1,16 @@
+#![feature(half_open_range_patterns)]
+#![feature(exclusive_range_pattern)]
+
+fn main() {
+    let xs = [13, 1, 5, 2, 3, 1, 21, 8];
+    let [a, b, c, rest @ ..] = xs;
+    // Consider the following example:
+    assert!(a == 13 && b == 1 && c == 5 && rest.len() == 5);
+
+    // What if we wanted to pull this apart without individually binding a, b, and c?
+    let [first_three @ ..3, rest @ 2..] = xs;
+    //~^ pattern requires 2 elements but array has 8
+    // This is somewhat unintuitive and makes slice patterns exceedingly verbose.
+    // We want to stabilize half-open RangeFrom (`X..`) patterns
+    // but without banning us from using them for a more efficient slice pattern syntax.
+}

src/test/ui/half-open-range-patterns/slice_pattern_syntax_problem0.stderr

@@ -0,0 +1,9 @@
+error[E0527]: pattern requires 2 elements but array has 8
+  --> $DIR/slice_pattern_syntax_problem0.rs:11:9
+   |
+LL |     let [first_three @ ..3, rest @ 2..] = xs;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected 8 elements
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0527`.

src/test/ui/half-open-range-patterns/slice_pattern_syntax_problem1.rs

@@ -0,0 +1,9 @@
+// Instead of allowing the previous case, maintain the feature gate for slice patterns for now.
+fn main() {
+    let xs = [13, 1, 5, 2, 3, 1, 21, 8];
+    let [a @ 3.., b @ ..3, c @ 4..6, ..] = xs;
+    //~^ `X..` patterns in slices are experimental
+    //~| half-open range patterns are unstable
+    //~| exclusive range pattern syntax is experimental
+    //~| exclusive range pattern syntax is experimental
+}

src/test/ui/half-open-range-patterns/slice_pattern_syntax_problem1.stderr

@@ -0,0 +1,39 @@
+error[E0658]: half-open range patterns are unstable
+  --> $DIR/slice_pattern_syntax_problem1.rs:4:23
+   |
+LL |     let [a @ 3.., b @ ..3, c @ 4..6, ..] = xs;
+   |                       ^^^
+   |
+   = note: see issue #67264 <https://github.com/rust-lang/rust/issues/67264> for more information
+   = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
+
+error[E0658]: `X..` patterns in slices are experimental
+  --> $DIR/slice_pattern_syntax_problem1.rs:4:10
+   |
+LL |     let [a @ 3.., b @ ..3, c @ 4..6, ..] = xs;
+   |          ^^^^^^^
+   |
+   = note: see issue #67264 <https://github.com/rust-lang/rust/issues/67264> for more information
+   = help: add `#![feature(half_open_range_patterns)]` to the crate attributes to enable
+
+error[E0658]: exclusive range pattern syntax is experimental
+  --> $DIR/slice_pattern_syntax_problem1.rs:4:23
+   |
+LL |     let [a @ 3.., b @ ..3, c @ 4..6, ..] = xs;
+   |                       ^^^
+   |
+   = note: see issue #37854 <https://github.com/rust-lang/rust/issues/37854> for more information
+   = help: add `#![feature(exclusive_range_pattern)]` to the crate attributes to enable
+
+error[E0658]: exclusive range pattern syntax is experimental
+  --> $DIR/slice_pattern_syntax_problem1.rs:4:32
+   |
+LL |     let [a @ 3.., b @ ..3, c @ 4..6, ..] = xs;
+   |                                ^^^^
+   |
+   = note: see issue #37854 <https://github.com/rust-lang/rust/issues/37854> for more information
+   = help: add `#![feature(exclusive_range_pattern)]` to the crate attributes to enable
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/half-open-range-patterns/slice_pattern_syntax_problem2.rs

@@ -0,0 +1,10 @@
+// run-pass
+
+fn main() {
+    let xs = [13, 1, 5, 2, 3, 1, 21, 8];
+    if let [3..=14, ..] = xs {
+        /* this variant must pass for now, unfortunately.
+         * This test is included here to help inform a future plan for these.
+         */
+    };
+}