rustc: Allow constants to be used in patterns. r=nmatsakis

src/librustc/middle/borrowck/gather_loans.rs

@@ -447,8 +447,7 @@ impl gather_loan_ctxt {
                   alt_id: ast::node_id) {
         do self.bccx.cat_pattern(discr_cmt, root_pat) |cmt, pat| {
             match pat.node {
-              ast::pat_ident(bm, _, _)
-                    if !self.pat_is_variant_or_struct(pat) => {
+              ast::pat_ident(bm, _, _) if self.pat_is_binding(pat) => {
                 match bm {
                   ast::bind_by_value | ast::bind_by_move => {
                     // copying does not borrow anything, so no check
@@ -502,5 +501,9 @@ impl gather_loan_ctxt {
     fn pat_is_variant_or_struct(&self, pat: @ast::pat) -> bool {
         pat_util::pat_is_variant_or_struct(self.bccx.tcx.def_map, pat)
     }
+
+    fn pat_is_binding(&self, pat: @ast::pat) -> bool {
+        pat_util::pat_is_binding(self.bccx.tcx.def_map, pat)
+    }
 }
 

src/librustc/middle/check_alt.rs

@@ -1,7 +1,7 @@
 use syntax::ast::*;
 use syntax::ast_util::{variant_def_ids, dummy_sp, unguarded_pat};
 use const_eval::{eval_const_expr, const_val, const_int, const_bool,
-                    compare_const_vals};
+                 compare_const_vals, lookup_const_by_id};
 use syntax::codemap::span;
 use syntax::print::pprust::pat_to_str;
 use util::ppaux::ty_to_str;
@@ -229,6 +229,10 @@ fn pat_ctor_id(tcx: ty::ctxt, p: @pat) -> Option<ctor> {
       pat_ident(_, _, _) | pat_enum(_, _) => {
         match tcx.def_map.find(pat.id) {
           Some(def_variant(_, id)) => Some(variant(id)),
+          Some(def_const(did)) => {
+            let const_expr = lookup_const_by_id(tcx, did).get();
+            Some(val(eval_const_expr(tcx, const_expr)))
+          }
           _ => None
         }
       }
@@ -255,7 +259,7 @@ fn is_wild(tcx: ty::ctxt, p: @pat) -> bool {
       pat_wild => { true }
       pat_ident(_, _, _) => {
         match tcx.def_map.find(pat.id) {
-          Some(def_variant(_, _)) => { false }
+          Some(def_variant(_, _)) | Some(def_const(*)) => { false }
           _ => { true }
         }
       }
@@ -344,6 +348,20 @@ fn specialize(tcx: ty::ctxt, r: ~[@pat], ctor_id: ctor, arity: uint,
             if variant(id) == ctor_id { Some(vec::tail(r)) }
             else { None }
           }
+          Some(def_const(did)) => {
+            let const_expr = lookup_const_by_id(tcx, did).get();
+            let e_v = eval_const_expr(tcx, const_expr);
+            let match_ = match ctor_id {
+                val(v) => compare_const_vals(e_v, v) == 0,
+                range(c_lo, c_hi) => {
+                    compare_const_vals(c_lo, e_v) >= 0 &&
+                        compare_const_vals(c_hi, e_v) <= 0
+                }
+                single => true,
+                _ => fail ~"type error"
+            };
+            if match_ { Some(vec::tail(r)) } else { None }
+          }
           _ => Some(vec::append(vec::from_elem(arity, wild()), vec::tail(r)))
         }
       }
@@ -491,6 +509,7 @@ fn is_refutable(tcx: ty::ctxt, pat: &pat) -> bool {
             return true;
         }
       }
+      Some(def_const(*)) => return true,
       _ => ()
     }
 

src/librustc/middle/const_eval.rs

@@ -149,21 +149,23 @@ fn classify(e: @expr,
 
 fn lookup_const(tcx: ty::ctxt, e: @expr) -> Option<@expr> {
     match tcx.def_map.find(e.id) {
-        Some(ast::def_const(def_id)) => {
-            if ast_util::is_local(def_id) {
-                match tcx.items.find(def_id.node) {
-                    None => None,
-                    Some(ast_map::node_item(it, _)) => match it.node {
-                        item_const(_, const_expr) => Some(const_expr),
-                        _ => None
-                    },
-                    Some(_) => None
-                }
-            }
-            else { None }
+        Some(ast::def_const(def_id)) => lookup_const_by_id(tcx, def_id),
+        _ => None
+    }
+}
+
+fn lookup_const_by_id(tcx: ty::ctxt, def_id: ast::def_id) -> Option<@expr> {
+    if ast_util::is_local(def_id) {
+        match tcx.items.find(def_id.node) {
+            None => None,
+            Some(ast_map::node_item(it, _)) => match it.node {
+                item_const(_, const_expr) => Some(const_expr),
+                _ => None
+            },
+            Some(_) => None
         }
-        Some(_) => None,
-        None => None
+    } else {
+        None
     }
 }
 

src/librustc/middle/pat_util.rs

@@ -7,7 +7,8 @@ use syntax::codemap::span;
 use std::map::HashMap;
 
 export pat_binding_ids, pat_bindings, pat_id_map, PatIdMap;
-export pat_is_variant_or_struct, pat_is_binding_or_wild;
+export pat_is_variant_or_struct, pat_is_binding, pat_is_binding_or_wild;
+export pat_is_const;
 
 type PatIdMap = std::map::HashMap<ident, node_id>;
 
@@ -33,9 +34,31 @@ fn pat_is_variant_or_struct(dm: resolve::DefMap, pat: @pat) -> bool {
     }
 }
 
+fn pat_is_const(dm: resolve::DefMap, pat: &pat) -> bool {
+    match pat.node {
+        pat_ident(_, _, None) => {
+            match dm.find(pat.id) {
+                Some(def_const(*)) => true,
+                _ => false
+            }
+        }
+        _ => false
+    }
+}
+
+fn pat_is_binding(dm: resolve::DefMap, pat: @pat) -> bool {
+    match pat.node {
+        pat_ident(*) => {
+            !pat_is_variant_or_struct(dm, pat) &&
+            !pat_is_const(dm, pat)
+        }
+        _ => false
+    }
+}
+
 fn pat_is_binding_or_wild(dm: resolve::DefMap, pat: @pat) -> bool {
     match pat.node {
-        pat_ident(*) => !pat_is_variant_or_struct(dm, pat),
+        pat_ident(*) => pat_is_binding(dm, pat),
         pat_wild => true,
         _ => false
     }
@@ -45,8 +68,7 @@ fn pat_bindings(dm: resolve::DefMap, pat: @pat,
                 it: fn(binding_mode, node_id, span, @path)) {
     do walk_pat(pat) |p| {
         match p.node {
-          pat_ident(binding_mode, pth, _)
-                if !pat_is_variant_or_struct(dm, p) => {
+          pat_ident(binding_mode, pth, _) if pat_is_binding(dm, p) => {
             it(binding_mode, p.id, p.span, pth);
           }
           _ => {}

src/librustc/middle/resolve.rs

@@ -310,7 +310,7 @@ impl AllowCapturingSelfFlag : cmp::Eq {
 
 enum BareIdentifierPatternResolution {
     FoundStructOrEnumVariant(def),
-    FoundConst,
+    FoundConst(def),
     BareIdentifierPatternUnresolved
 }
 
@@ -4308,11 +4308,17 @@ impl Resolver {
                                                         self.session
                                                         .str_of(ident)));
                         }
-                        FoundConst => {
+                        FoundConst(def) if mode == RefutableMode => {
+                            debug!("(resolving pattern) resolving `%s` to \
+                                    constant",
+                                    self.session.str_of(ident));
+
+                            self.record_def(pattern.id, def);
+                        }
+                        FoundConst(_) => {
                             self.session.span_err(pattern.span,
-                                                  ~"pattern variable \
-                                                   conflicts with a constant \
-                                                   in scope");
+                                                  ~"only refutable patterns \
+                                                    allowed here");
                         }
                         BareIdentifierPatternUnresolved => {
                             debug!("(resolving pattern) binding `%s`",
@@ -4465,8 +4471,8 @@ impl Resolver {
                             def @ def_variant(*) | def @ def_class(*) => {
                                 return FoundStructOrEnumVariant(def);
                             }
-                            def_const(*) => {
-                                return FoundConst;
+                            def @ def_const(*) => {
+                                return FoundConst(def);
                             }
                             _ => {
                                 return BareIdentifierPatternUnresolved;

src/librustc/middle/trans/alt.rs

@@ -158,7 +158,8 @@ fn macros() { include!("macros.rs"); } // FIXME(#3114): Macro import/export.
 // expression.
 enum Lit {
     UnitLikeStructLit(ast::node_id),    // the node ID of the pattern
-    ExprLit(@ast::expr)
+    ExprLit(@ast::expr),
+    ConstLit(ast::def_id),              // the def ID of the constant
 }
 
 // An option identifying a branch (either a literal, a enum variant or a
@@ -168,11 +169,43 @@ enum Opt {
     var(/* disr val */int, /* variant dids */{enm: def_id, var: def_id}),
     range(@ast::expr, @ast::expr)
 }
+
 fn opt_eq(tcx: ty::ctxt, a: &Opt, b: &Opt) -> bool {
     match (*a, *b) {
-      (lit(ExprLit(a)), lit(ExprLit(b))) =>
-            const_eval::compare_lit_exprs(tcx, a, b) == 0,
-      (lit(UnitLikeStructLit(a)), lit(UnitLikeStructLit(b))) => a == b,
+      (lit(a), lit(b)) => {
+        match (a, b) {
+            (UnitLikeStructLit(a), UnitLikeStructLit(b)) => a == b,
+            _ => {
+                let a_expr;
+                match a {
+                    ExprLit(existing_a_expr) => a_expr = existing_a_expr,
+                    ConstLit(a_const) => {
+                        let e = const_eval::lookup_const_by_id(tcx, a_const);
+                        a_expr = e.get();
+                    }
+                    UnitLikeStructLit(_) => {
+                        fail ~"UnitLikeStructLit should have been handled \
+                               above"
+                    }
+                }
+
+                let b_expr;
+                match b {
+                    ExprLit(existing_b_expr) => b_expr = existing_b_expr,
+                    ConstLit(b_const) => {
+                        let e = const_eval::lookup_const_by_id(tcx, b_const);
+                        b_expr = e.get();
+                    }
+                    UnitLikeStructLit(_) => {
+                        fail ~"UnitLikeStructLit should have been handled \
+                               above"
+                    }
+                }
+
+                const_eval::compare_lit_exprs(tcx, a_expr, b_expr) == 0
+            }
+        }
+      }
       (range(a1, a2), range(b1, b2)) => {
         const_eval::compare_lit_exprs(tcx, a1, b1) == 0 &&
         const_eval::compare_lit_exprs(tcx, a2, b2) == 0
@@ -200,6 +233,10 @@ fn trans_opt(bcx: block, o: &Opt) -> opt_result {
             let datumblock = datum::scratch_datum(bcx, struct_ty, true);
             return single_result(datumblock.to_result(bcx));
         }
+        lit(ConstLit(lit_id)) => {
+            let llval = consts::get_const_val(bcx.ccx(), lit_id);
+            return single_result(rslt(bcx, llval));
+        }
         var(disr_val, _) => {
             return single_result(rslt(bcx, C_int(ccx, disr_val)));
         }
@@ -353,7 +390,7 @@ fn enter_match(bcx: block, dm: DefMap, m: &[@Match/&r],
                 let self = br.pats[col];
                 match self.node {
                     ast::pat_ident(_, path, None) => {
-                        if !pat_is_variant_or_struct(dm, self) {
+                        if pat_is_binding(dm, self) {
                             let binding_info =
                                 br.data.bindings_map.get(path_to_ident(path));
                             Store(bcx, val, binding_info.llmatch);
@@ -388,8 +425,7 @@ fn enter_default(bcx: block, dm: DefMap, m: &[@Match/&r],
         match p.node {
           ast::pat_wild | ast::pat_rec(_, _) | ast::pat_tup(_) |
           ast::pat_struct(*) => Some(~[]),
-          ast::pat_ident(_, _, None)
-                if !pat_is_variant_or_struct(dm, p) => Some(~[]),
+          ast::pat_ident(_, _, None) if pat_is_binding(dm, p) => Some(~[]),
           _ => None
         }
     }
@@ -451,6 +487,15 @@ fn enter_opt(bcx: block, m: &[@Match/&r], opt: &Opt, col: uint,
                     None
                 }
             }
+            ast::pat_ident(_, _, None) if pat_is_const(tcx.def_map, p) => {
+                let const_def = tcx.def_map.get(p.id);
+                let const_def_id = ast_util::def_id_of_def(const_def);
+                if opt_eq(tcx, &lit(ConstLit(const_def_id)), opt) {
+                    Some(~[])
+                } else {
+                    None
+                }
+            }
             ast::pat_lit(l) => {
                 if opt_eq(tcx, &lit(ExprLit(l)), opt) {Some(~[])} else {None}
             }
@@ -675,6 +720,10 @@ fn get_options(ccx: @crate_ctxt, m: &[@Match], col: uint) -> ~[Opt] {
                         add_to_set(ccx.tcx, &found,
                                    lit(UnitLikeStructLit(cur.id)));
                     }
+                    Some(ast::def_const(const_did)) => {
+                        add_to_set(ccx.tcx, &found,
+                                   lit(ConstLit(const_did)));
+                    }
                     _ => {}
                 }
             }

src/librustc/middle/trans/consts.rs

@@ -95,6 +95,22 @@ fn const_autoderef(cx: @crate_ctxt, ty: ty::t, v: ValueRef)
     }
 }
 
+fn get_const_val(cx: @crate_ctxt, def_id: ast::def_id) -> ValueRef {
+    if !ast_util::is_local(def_id) {
+        cx.tcx.sess.bug(~"cross-crate constants");
+    }
+    if !cx.const_values.contains_key(def_id.node) {
+        match cx.tcx.items.get(def_id.node) {
+            ast_map::node_item(@{
+                node: ast::item_const(_, subexpr), _
+            }, _) => {
+                trans_const(cx, subexpr, def_id.node);
+            }
+            _ => cx.tcx.sess.bug(~"expected a const to be an item")
+        }
+    }
+    cx.const_values.get(def_id.node)
+}
 
 fn const_expr(cx: @crate_ctxt, e: @ast::expr) -> ValueRef {
     let _icx = cx.insn_ctxt("const_expr");
@@ -359,18 +375,7 @@ fn const_expr(cx: @crate_ctxt, e: @ast::expr) -> ValueRef {
               C_struct(~[f, C_null(T_opaque_box_ptr(cx))])
           }
           Some(ast::def_const(def_id)) => {
-            assert ast_util::is_local(def_id);
-            if ! cx.const_values.contains_key(def_id.node) {
-                match cx.tcx.items.get(def_id.node) {
-                    ast_map::node_item(@{
-                        node: ast::item_const(_, subexpr), _
-                    }, _) => {
-                        trans_const(cx, subexpr, def_id.node);
-                    }
-                    _ => cx.sess.span_bug(e.span, ~"expected item")
-                }
-            }
-            cx.const_values.get(def_id.node)
+            get_const_val(cx, def_id)
           }
           _ => cx.sess.span_bug(e.span, ~"expected a const or fn def")
         }

src/librustc/middle/typeck/check.rs

@@ -389,8 +389,7 @@ fn check_fn(ccx: @crate_ctxt,
         let visit_pat = fn@(p: @ast::pat, &&e: (), v: visit::vt<()>) {
             match p.node {
               ast::pat_ident(_, path, _)
-                  if !pat_util::pat_is_variant_or_struct(fcx.ccx.tcx.def_map,
-                                                         p) => {
+                  if pat_util::pat_is_binding(fcx.ccx.tcx.def_map, p) => {
                 assign(p.span, p.id, None);
                 debug!("Pattern binding %s is assigned to %s",
                        tcx.sess.str_of(path.idents[0]),

src/librustc/middle/typeck/check/alt.rs

@@ -1,6 +1,6 @@
 use syntax::print::pprust;
 use syntax::ast_util::{walk_pat};
-use pat_util::{pat_is_variant_or_struct};
+use pat_util::{pat_is_binding, pat_is_const, pat_is_variant_or_struct};
 
 fn check_alt(fcx: @fn_ctxt,
              expr: @ast::expr,
@@ -74,7 +74,7 @@ fn check_legality_of_move_bindings(fcx: @fn_ctxt,
     if !any_by_move { return; } // pointless micro-optimization
     for pats.each |pat| {
         do walk_pat(*pat) |p| {
-            if !pat_is_variant_or_struct(def_map, p) {
+            if pat_is_binding(def_map, p) {
                 match p.node {
                     ast::pat_ident(ast::bind_by_move, _, sub) => {
                         // check legality of moving out of the enum
@@ -391,8 +391,12 @@ fn check_pat(pcx: pat_ctxt, pat: @ast::pat, expected: ty::t) {
         }
         fcx.write_ty(pat.id, b_ty);
       }
-      ast::pat_ident(bm, name, sub)
-            if !pat_is_variant_or_struct(tcx.def_map, pat) => {
+      ast::pat_ident(*) if pat_is_const(tcx.def_map, pat) => {
+        let const_did = ast_util::def_id_of_def(tcx.def_map.get(pat.id));
+        let const_tpt = ty::lookup_item_type(tcx, const_did);
+        fcx.write_ty(pat.id, const_tpt.ty);
+      }
+      ast::pat_ident(bm, name, sub) if pat_is_binding(tcx.def_map, pat) => {
         let vid = lookup_local(fcx, pat.span, pat.id);
         let mut typ = ty::mk_var(tcx, vid);
 

src/test/run-pass/consts-in-patterns.rs

@@ -0,0 +1,13 @@
+const FOO: int = 10;
+const BAR: int = 3;
+
+fn main() {
+    let x: int = 3;
+    let y = match x {
+        FOO => 1,
+        BAR => 2,
+        _ => 3
+    };
+    assert y == 2;
+}
+