Auto merge of #35712 - oli-obk:exclusive_range_patterns, r=nikomatsakis

exclusive range patterns

adds `..` patterns to the language under a feature gate (`exclusive_range_pattern`).

This allows turning

``` rust
match i {
    0...9 => {},
    10...19 => {},
    20...29 => {},
    _ => {}
}
```

into

``` rust
match i {
    0..10 => {},
    10..20 => {},
    20..30 => {},
    _ => {}
}
```

Author: bors

src/librustc/hir/intravisit.rs

@@ -661,7 +661,7 @@ pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat) {
             walk_list!(visitor, visit_pat, optional_subpattern);
         }
         PatKind::Lit(ref expression) => visitor.visit_expr(expression),
-        PatKind::Range(ref lower_bound, ref upper_bound) => {
+        PatKind::Range(ref lower_bound, ref upper_bound, _) => {
             visitor.visit_expr(lower_bound);
             visitor.visit_expr(upper_bound)
         }

src/librustc/hir/lowering.rs

@@ -1250,8 +1250,10 @@ impl<'a> LoweringContext<'a> {
                 PatKind::Ref(ref inner, mutbl) => {
                     hir::PatKind::Ref(self.lower_pat(inner), self.lower_mutability(mutbl))
                 }
-                PatKind::Range(ref e1, ref e2) => {
-                    hir::PatKind::Range(P(self.lower_expr(e1)), P(self.lower_expr(e2)))
+                PatKind::Range(ref e1, ref e2, ref end) => {
+                    hir::PatKind::Range(P(self.lower_expr(e1)),
+                                        P(self.lower_expr(e2)),
+                                        self.lower_range_end(end))
                 }
                 PatKind::Slice(ref before, ref slice, ref after) => {
                     hir::PatKind::Slice(before.iter().map(|x| self.lower_pat(x)).collect(),
@@ -1264,6 +1266,13 @@ impl<'a> LoweringContext<'a> {
         })
     }
 
+    fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
+        match *e {
+            RangeEnd::Included => hir::RangeEnd::Included,
+            RangeEnd::Excluded => hir::RangeEnd::Excluded,
+        }
+    }
+
     fn lower_expr(&mut self, e: &Expr) -> hir::Expr {
         hir::Expr {
             id: e.id,

src/librustc/hir/mod.rs

@@ -572,6 +572,12 @@ pub enum BindingMode {
     BindByValue(Mutability),
 }
 
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub enum RangeEnd {
+    Included,
+    Excluded,
+}
+
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum PatKind {
     /// Represents a wildcard pattern (`_`)
@@ -603,8 +609,8 @@ pub enum PatKind {
     Ref(P<Pat>, Mutability),
     /// A literal
     Lit(P<Expr>),
-    /// A range pattern, e.g. `1...2`
-    Range(P<Expr>, P<Expr>),
+    /// A range pattern, e.g. `1...2` or `1..2`
+    Range(P<Expr>, P<Expr>, RangeEnd),
     /// `[a, b, ..i, y, z]` is represented as:
     ///     `PatKind::Slice(box [a, b], Some(i), box [y, z])`
     Slice(HirVec<P<Pat>>, Option<P<Pat>>, HirVec<P<Pat>>),

src/librustc/hir/print.rs

@@ -24,7 +24,7 @@ use syntax::symbol::keywords;
 use syntax_pos::{self, BytePos};
 
 use hir;
-use hir::{PatKind, RegionTyParamBound, TraitTyParamBound, TraitBoundModifier};
+use hir::{PatKind, RegionTyParamBound, TraitTyParamBound, TraitBoundModifier, RangeEnd};
 
 use std::io::{self, Write, Read};
 
@@ -1732,10 +1732,13 @@ impl<'a> State<'a> {
                 self.print_pat(&inner)?;
             }
             PatKind::Lit(ref e) => self.print_expr(&e)?,
-            PatKind::Range(ref begin, ref end) => {
+            PatKind::Range(ref begin, ref end, ref end_kind) => {
                 self.print_expr(&begin)?;
                 space(&mut self.s)?;
-                word(&mut self.s, "...")?;
+                match *end_kind {
+                    RangeEnd::Included => word(&mut self.s, "...")?,
+                    RangeEnd::Excluded => word(&mut self.s, "..")?,
+                }
                 self.print_expr(&end)?;
             }
             PatKind::Slice(ref before, ref slice, ref after) => {

src/librustc_const_eval/_match.rs

@@ -24,6 +24,7 @@ use pattern::{FieldPattern, Pattern, PatternKind};
 use pattern::{PatternFoldable, PatternFolder};
 
 use rustc::hir::def_id::DefId;
+use rustc::hir::RangeEnd;
 use rustc::ty::{self, AdtKind, Ty, TyCtxt, TypeFoldable};
 
 use rustc::mir::Field;
@@ -206,8 +207,8 @@ pub enum Constructor {
     Variant(DefId),
     /// Literal values.
     ConstantValue(ConstVal),
-    /// Ranges of literal values (2..5).
-    ConstantRange(ConstVal, ConstVal),
+    /// Ranges of literal values (`2...5` and `2..5`).
+    ConstantRange(ConstVal, ConstVal, RangeEnd),
     /// Array patterns of length n.
     Slice(usize),
 }
@@ -686,8 +687,8 @@ fn pat_constructors(_cx: &mut MatchCheckCtxt,
             Some(vec![Variant(adt_def.variants[variant_index].did)]),
         PatternKind::Constant { ref value } =>
             Some(vec![ConstantValue(value.clone())]),
-        PatternKind::Range { ref lo, ref hi } =>
-            Some(vec![ConstantRange(lo.clone(), hi.clone())]),
+        PatternKind::Range { ref lo, ref hi, ref end } =>
+            Some(vec![ConstantRange(lo.clone(), hi.clone(), end.clone())]),
         PatternKind::Array { .. } => match pcx.ty.sty {
             ty::TyArray(_, length) => Some(vec![Slice(length)]),
             _ => span_bug!(pat.span, "bad ty {:?} for array pattern", pcx.ty)
@@ -791,17 +792,33 @@ fn slice_pat_covered_by_constructor(_tcx: TyCtxt, _span: Span,
 
 fn range_covered_by_constructor(tcx: TyCtxt, span: Span,
                                 ctor: &Constructor,
-                                from: &ConstVal, to: &ConstVal)
+                                from: &ConstVal, to: &ConstVal,
+                                end: RangeEnd)
                                 -> Result<bool, ErrorReported> {
-    let (c_from, c_to) = match *ctor {
-        ConstantValue(ref value)        => (value, value),
-        ConstantRange(ref from, ref to) => (from, to),
-        Single                          => return Ok(true),
-        _                               => bug!()
-    };
-    let cmp_from = compare_const_vals(tcx, span, c_from, from)?;
-    let cmp_to = compare_const_vals(tcx, span, c_to, to)?;
-    Ok(cmp_from != Ordering::Less && cmp_to != Ordering::Greater)
+    let cmp_from = |c_from| Ok(compare_const_vals(tcx, span, c_from, from)? != Ordering::Less);
+    let cmp_to = |c_to| compare_const_vals(tcx, span, c_to, to);
+    match *ctor {
+        ConstantValue(ref value) => {
+            let to = cmp_to(value)?;
+            let end = (to != Ordering::Greater) ||
+                      (end == RangeEnd::Excluded && to == Ordering::Equal);
+            Ok(cmp_from(value)? && end)
+        },
+        ConstantRange(ref from, ref to, RangeEnd::Included) => {
+            let to = cmp_to(to)?;
+            let end = (to != Ordering::Greater) ||
+                      (end == RangeEnd::Excluded && to == Ordering::Equal);
+            Ok(cmp_from(from)? && end)
+        },
+        ConstantRange(ref from, ref to, RangeEnd::Excluded) => {
+            let to = cmp_to(to)?;
+            let end = (to == Ordering::Less) ||
+                      (end == RangeEnd::Excluded && to == Ordering::Equal);
+            Ok(cmp_from(from)? && end)
+        }
+        Single => Ok(true),
+        _ => bug!(),
+    }
 }
 
 fn patterns_for_variant<'p, 'a: 'p, 'tcx: 'a>(
@@ -872,7 +889,7 @@ fn specialize<'p, 'a: 'p, 'tcx: 'a>(
                 },
                 _ => {
                     match range_covered_by_constructor(
-                        cx.tcx, pat.span, constructor, value, value
+                        cx.tcx, pat.span, constructor, value, value, RangeEnd::Included
                             ) {
                         Ok(true) => Some(vec![]),
                         Ok(false) => None,
@@ -882,9 +899,9 @@ fn specialize<'p, 'a: 'p, 'tcx: 'a>(
             }
         }
 
-        PatternKind::Range { ref lo, ref hi } => {
+        PatternKind::Range { ref lo, ref hi, ref end } => {
             match range_covered_by_constructor(
-                cx.tcx, pat.span, constructor, lo, hi
+                cx.tcx, pat.span, constructor, lo, hi, end.clone()
             ) {
                 Ok(true) => Some(vec![]),
                 Ok(false) => None,

src/librustc_const_eval/pattern.rs

@@ -15,7 +15,7 @@ use rustc::middle::const_val::ConstVal;
 use rustc::mir::{Field, BorrowKind, Mutability};
 use rustc::ty::{self, TyCtxt, AdtDef, Ty, TypeVariants, Region};
 use rustc::ty::subst::{Substs, Kind};
-use rustc::hir::{self, PatKind};
+use rustc::hir::{self, PatKind, RangeEnd};
 use rustc::hir::def::{Def, CtorKind};
 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
 
@@ -90,6 +90,7 @@ pub enum PatternKind<'tcx> {
     Range {
         lo: ConstVal,
         hi: ConstVal,
+        end: RangeEnd,
     },
 
     /// matches against a slice, checking the length and extracting elements
@@ -228,9 +229,12 @@ impl<'tcx> fmt::Display for Pattern<'tcx> {
             PatternKind::Constant { ref value } => {
                 print_const_val(value, f)
             }
-            PatternKind::Range { ref lo, ref hi } => {
+            PatternKind::Range { ref lo, ref hi, ref end } => {
                 print_const_val(lo, f)?;
-                write!(f, "...")?;
+                match *end {
+                    RangeEnd::Included => write!(f, "...")?,
+                    RangeEnd::Excluded => write!(f, "..")?,
+                }
                 print_const_val(hi, f)
             }
             PatternKind::Slice { ref prefix, ref slice, ref suffix } |
@@ -291,11 +295,11 @@ impl<'a, 'gcx, 'tcx> PatternContext<'a, 'gcx, 'tcx> {
 
             PatKind::Lit(ref value) => self.lower_lit(value),
 
-            PatKind::Range(ref lo, ref hi) => {
+            PatKind::Range(ref lo, ref hi, ref end) => {
                 match (self.lower_lit(lo), self.lower_lit(hi)) {
                     (PatternKind::Constant { value: lo },
                      PatternKind::Constant { value: hi }) => {
-                        PatternKind::Range { lo: lo, hi: hi }
+                        PatternKind::Range { lo: lo, hi: hi, end: end.clone() }
                     }
                     _ => PatternKind::Wild
                 }
@@ -871,10 +875,12 @@ impl<'tcx> PatternFoldable<'tcx> for PatternKind<'tcx> {
             },
             PatternKind::Range {
                 ref lo,
-                ref hi
+                ref hi,
+                ref end,
             } => PatternKind::Range {
                 lo: lo.fold_with(folder),
-                hi: hi.fold_with(folder)
+                hi: hi.fold_with(folder),
+                end: end.clone(),
             },
             PatternKind::Slice {
                 ref prefix,

src/librustc_mir/build/matches/mod.rs

@@ -19,6 +19,7 @@ use rustc_data_structures::bitvec::BitVector;
 use rustc::middle::const_val::ConstVal;
 use rustc::ty::{AdtDef, Ty};
 use rustc::mir::*;
+use rustc::hir;
 use hair::*;
 use syntax::ast::{Name, NodeId};
 use syntax_pos::Span;
@@ -318,11 +319,12 @@ enum TestKind<'tcx> {
         ty: Ty<'tcx>,
     },
 
-    // test whether the value falls within an inclusive range
+    // test whether the value falls within an inclusive or exclusive range
     Range {
         lo: Literal<'tcx>,
         hi: Literal<'tcx>,
         ty: Ty<'tcx>,
+        end: hir::RangeEnd,
     },
 
     // test length of the slice is equal to len

src/librustc_mir/build/matches/test.rs

@@ -23,6 +23,7 @@ use rustc_data_structures::bitvec::BitVector;
 use rustc::middle::const_val::ConstVal;
 use rustc::ty::{self, Ty};
 use rustc::mir::*;
+use rustc::hir::RangeEnd;
 use syntax_pos::Span;
 use std::cmp::Ordering;
 
@@ -69,13 +70,14 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 }
             }
 
-            PatternKind::Range { ref lo, ref hi } => {
+            PatternKind::Range { ref lo, ref hi, ref end } => {
                 Test {
                     span: match_pair.pattern.span,
                     kind: TestKind::Range {
                         lo: Literal::Value { value: lo.clone() },
                         hi: Literal::Value { value: hi.clone() },
                         ty: match_pair.pattern.ty.clone(),
+                        end: end.clone(),
                     },
                 }
             }
@@ -324,15 +326,18 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 }
             }
 
-            TestKind::Range { ref lo, ref hi, ty } => {
+            TestKind::Range { ref lo, ref hi, ty, ref end } => {
                 // Test `val` by computing `lo <= val && val <= hi`, using primitive comparisons.
                 let lo = self.literal_operand(test.span, ty.clone(), lo.clone());
                 let hi = self.literal_operand(test.span, ty.clone(), hi.clone());
                 let val = Operand::Consume(lvalue.clone());
 
                 let fail = self.cfg.start_new_block();
                 let block = self.compare(block, fail, test.span, BinOp::Le, lo, val.clone());
-                let block = self.compare(block, fail, test.span, BinOp::Le, val, hi);
+                let block = match *end {
+                    RangeEnd::Included => self.compare(block, fail, test.span, BinOp::Le, val, hi),
+                    RangeEnd::Excluded => self.compare(block, fail, test.span, BinOp::Lt, val, hi),
+                };
 
                 vec![block, fail]
             }

src/librustc_passes/consts.rs

@@ -45,7 +45,7 @@ use rustc::util::common::ErrorReported;
 use rustc::util::nodemap::NodeSet;
 use rustc::lint::builtin::CONST_ERR;
 
-use rustc::hir::{self, PatKind};
+use rustc::hir::{self, PatKind, RangeEnd};
 use syntax::ast;
 use syntax_pos::Span;
 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
@@ -157,7 +157,21 @@ impl<'a, 'tcx> Visitor<'tcx> for CheckCrateVisitor<'a, 'tcx> {
             PatKind::Lit(ref lit) => {
                 self.check_const_eval(lit);
             }
-            PatKind::Range(ref start, ref end) => {
+            PatKind::Range(ref start, ref end, RangeEnd::Excluded) => {
+                let const_cx = ConstContext::with_tables(self.tcx, self.tables);
+                match const_cx.compare_lit_exprs(p.span, start, end) {
+                    Ok(Ordering::Less) => {}
+                    Ok(Ordering::Equal) |
+                    Ok(Ordering::Greater) => {
+                        span_err!(self.tcx.sess,
+                                  start.span,
+                                  E0579,
+                                  "lower range bound must be less than upper");
+                    }
+                    Err(ErrorReported) => {}
+                }
+            }
+            PatKind::Range(ref start, ref end, RangeEnd::Included) => {
                 let const_cx = ConstContext::with_tables(self.tcx, self.tables);
                 match const_cx.compare_lit_exprs(p.span, start, end) {
                     Ok(Ordering::Less) |

src/librustc_passes/diagnostics.rs

@@ -223,6 +223,24 @@ pub impl Foo for Bar {
 ```
 "##,
 
+
+E0579: r##"
+When matching against an exclusive range, the compiler verifies that the range
+is non-empty. Exclusive range patterns include the start point but not the end
+point, so this is equivalent to requiring the start of the range to be less
+than the end of the range.
+
+For example:
+
+```compile_fail
+match 5u32 {
+    // This range is ok, albeit pointless.
+    1 .. 2 => {}
+    // This range is empty, and the compiler can tell.
+    5 .. 5 => {}
+}
+```
+"##,
 }
 
 register_diagnostics! {

src/librustc_typeck/check/_match.rs

@@ -76,7 +76,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 self.demand_suptype(pat.span, expected, pat_ty);
                 pat_ty
             }
-            PatKind::Range(ref begin, ref end) => {
+            PatKind::Range(ref begin, ref end, _) => {
                 let lhs_ty = self.check_expr(begin);
                 let rhs_ty = self.check_expr(end);
 

src/libsyntax/ast.rs

@@ -547,6 +547,12 @@ pub enum BindingMode {
     ByValue(Mutability),
 }
 
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub enum RangeEnd {
+    Included,
+    Excluded,
+}
+
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub enum PatKind {
     /// Represents a wildcard pattern (`_`)
@@ -583,8 +589,8 @@ pub enum PatKind {
     Ref(P<Pat>, Mutability),
     /// A literal
     Lit(P<Expr>),
-    /// A range pattern, e.g. `1...2`
-    Range(P<Expr>, P<Expr>),
+    /// A range pattern, e.g. `1...2` or `1..2`
+    Range(P<Expr>, P<Expr>, RangeEnd),
     /// `[a, b, ..i, y, z]` is represented as:
     ///     `PatKind::Slice(box [a, b], Some(i), box [y, z])`
     Slice(Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>),