rustc: Remove the dummy hack from check_match

Turns out you can create &'static T quite easily in a constant, I just forgot
about this!

Author: alexcrichton

src/librustc/middle/check_match.rs

@@ -32,7 +32,7 @@ use syntax::ptr::P;
 use syntax::visit::{mod, Visitor, FnKind};
 use util::ppaux::ty_to_string;
 
-pub const DUMMY_WILD_PAT: Pat = Pat {
+pub const DUMMY_WILD_PAT: &'static Pat = &Pat {
     id: DUMMY_NODE_ID,
     node: PatWild(PatWildSingle),
     span: DUMMY_SP
@@ -297,12 +297,11 @@ fn raw_pat<'a>(p: &'a Pat) -> &'a Pat {
 }
 
 fn check_exhaustive(cx: &MatchCheckCtxt, sp: Span, matrix: &Matrix) {
-    match is_useful(cx, matrix, &[&DUMMY_WILD_PAT], ConstructWitness) {
+    match is_useful(cx, matrix, &[DUMMY_WILD_PAT], ConstructWitness) {
         UsefulWithWitness(pats) => {
-            let dummy = DUMMY_WILD_PAT.clone();
             let witness = match pats.as_slice() {
                 [ref witness] => &**witness,
-                [] => &dummy,
+                [] => DUMMY_WILD_PAT,
                 _ => unreachable!()
             };
             span_err!(cx.tcx.sess, sp, E0004,
@@ -556,9 +555,8 @@ fn is_useful(cx: &MatchCheckCtxt,
                             let arity = constructor_arity(cx, &c, left_ty);
                             let mut result = {
                                 let pat_slice = pats.as_slice();
-                                let dummy = DUMMY_WILD_PAT.clone();
                                 let subpats = Vec::from_fn(arity, |i| {
-                                    pat_slice.get(i).map_or(&dummy, |p| &**p)
+                                    pat_slice.get(i).map_or(DUMMY_WILD_PAT, |p| &**p)
                                 });
                                 vec![construct_witness(cx, &c, subpats, left_ty)]
                             };
@@ -580,9 +578,8 @@ fn is_useful(cx: &MatchCheckCtxt,
                 }).collect();
                 match is_useful(cx, &matrix, v.tail(), witness) {
                     UsefulWithWitness(pats) => {
-                        let dummy = DUMMY_WILD_PAT.clone();
                         let arity = constructor_arity(cx, &constructor, left_ty);
-                        let wild_pats = Vec::from_elem(arity, &dummy);
+                        let wild_pats = Vec::from_elem(arity, DUMMY_WILD_PAT);
                         let enum_pat = construct_witness(cx, &constructor, wild_pats, left_ty);
                         let mut new_pats = vec![enum_pat];
                         new_pats.extend(pats.into_iter());
@@ -603,11 +600,10 @@ fn is_useful_specialized(cx: &MatchCheckCtxt, &Matrix(ref m): &Matrix,
                          v: &[&Pat], ctor: Constructor, lty: ty::t,
                          witness: WitnessPreference) -> Usefulness {
     let arity = constructor_arity(cx, &ctor, lty);
-    let dummy = DUMMY_WILD_PAT.clone();
     let matrix = Matrix(m.iter().filter_map(|r| {
-        specialize(cx, r.as_slice(), &dummy, &ctor, 0u, arity)
+        specialize(cx, r.as_slice(), &ctor, 0u, arity)
     }).collect());
-    match specialize(cx, v, &dummy, &ctor, 0u, arity) {
+    match specialize(cx, v, &ctor, 0u, arity) {
         Some(v) => is_useful(cx, &matrix, v.as_slice(), witness),
         None => NotUseful
     }
@@ -729,15 +725,15 @@ fn range_covered_by_constructor(ctor: &Constructor,
 /// different patterns.
 /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
 /// fields filled with wild patterns.
-pub fn specialize<'a>(cx: &MatchCheckCtxt, r: &[&'a Pat], dummy: &'a Pat,
+pub fn specialize<'a>(cx: &MatchCheckCtxt, r: &[&'a Pat],
                       constructor: &Constructor, col: uint, arity: uint) -> Option<Vec<&'a Pat>> {
     let &Pat {
         id: pat_id, node: ref node, span: pat_span
     } = raw_pat(r[col]);
     let head: Option<Vec<&Pat>> = match node {
 
         &PatWild(_) =>
-            Some(Vec::from_elem(arity, dummy)),
+            Some(Vec::from_elem(arity, DUMMY_WILD_PAT)),
 
         &PatIdent(_, _, _) => {
             let opt_def = cx.tcx.def_map.borrow().find_copy(&pat_id);
@@ -750,7 +746,7 @@ pub fn specialize<'a>(cx: &MatchCheckCtxt, r: &[&'a Pat], dummy: &'a Pat,
                 } else {
                     None
                 },
-                _ => Some(Vec::from_elem(arity, dummy))
+                _ => Some(Vec::from_elem(arity, DUMMY_WILD_PAT))
             }
         }
 
@@ -764,7 +760,7 @@ pub fn specialize<'a>(cx: &MatchCheckCtxt, r: &[&'a Pat], dummy: &'a Pat,
                 DefVariant(..) | DefStruct(..) => {
                     Some(match args {
                         &Some(ref args) => args.iter().map(|p| &**p).collect(),
-                        &None => Vec::from_elem(arity, dummy)
+                        &None => Vec::from_elem(arity, DUMMY_WILD_PAT)
                     })
                 }
                 _ => None
@@ -800,7 +796,7 @@ pub fn specialize<'a>(cx: &MatchCheckCtxt, r: &[&'a Pat], dummy: &'a Pat,
                 let args = struct_fields.iter().map(|sf| {
                     match pattern_fields.iter().find(|f| f.ident.name == sf.name) {
                         Some(ref f) => &*f.pat,
-                        _ => dummy
+                        _ => DUMMY_WILD_PAT
                     }
                 }).collect();
                 args
@@ -843,13 +839,13 @@ pub fn specialize<'a>(cx: &MatchCheckCtxt, r: &[&'a Pat], dummy: &'a Pat,
                 // Fixed-length vectors.
                 Single => {
                     let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect();
-                    pats.grow_fn(arity - before.len() - after.len(), |_| dummy);
+                    pats.grow_fn(arity - before.len() - after.len(), |_| DUMMY_WILD_PAT);
                     pats.extend(after.iter().map(|p| &**p));
                     Some(pats)
                 },
                 Slice(length) if before.len() + after.len() <= length && slice.is_some() => {
                     let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect();
-                    pats.grow_fn(arity - before.len() - after.len(), |_| dummy);
+                    pats.grow_fn(arity - before.len() - after.len(), |_| DUMMY_WILD_PAT);
                     pats.extend(after.iter().map(|p| &**p));
                     Some(pats)
                 },
@@ -919,7 +915,7 @@ fn check_fn(cx: &mut MatchCheckCtxt,
 
 fn is_refutable<A>(cx: &MatchCheckCtxt, pat: &Pat, refutable: |&Pat| -> A) -> Option<A> {
     let pats = Matrix(vec!(vec!(pat)));
-    match is_useful(cx, &pats, [&DUMMY_WILD_PAT], ConstructWitness) {
+    match is_useful(cx, &pats, [DUMMY_WILD_PAT], ConstructWitness) {
         UsefulWithWitness(pats) => {
             assert_eq!(pats.len(), 1);
             Some(refutable(&*pats[0]))

src/librustc/middle/trans/_match.rs

@@ -351,19 +351,6 @@ struct Match<'a, 'p: 'a, 'blk: 'a, 'tcx: 'blk> {
     pats: Vec<&'p ast::Pat>,
     data: &'a ArmData<'p, 'blk, 'tcx>,
     bound_ptrs: Vec<(Ident, ValueRef)>,
-
-    // This is a pointer to an instance of check_match::DUMMY_WILD_PAT. The
-    // check_match code requires that we pass this in (with the same lifetime as
-    // the patterns passed in). Unfortunately this is required to be propagated
-    // into this structure in order to get the lifetimes to work.
-    //
-    // Lots of the `check_match` code will deal with &DUMMY_WILD_PAT when
-    // returning references, which used to have the `'static` lifetime before
-    // const was added to the language. The DUMMY_WILD_PAT does not implement
-    // Sync, however, so it must be a const, which longer has a static lifetime,
-    // hence we're passing it in here. This certainly isn't crucial, and if it
-    // can be removed, please do!
-    dummy: &'p ast::Pat,
 }
 
 impl<'a, 'p, 'blk, 'tcx> Repr for Match<'a, 'p, 'blk, 'tcx> {
@@ -416,7 +403,6 @@ fn expand_nested_bindings<'a, 'p, 'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
         *pats.get_mut(col) = pat;
         Match {
             pats: pats,
-            dummy: br.dummy,
             data: &*br.data,
             bound_ptrs: bound_ptrs
         }
@@ -464,7 +450,6 @@ fn enter_match<'a, 'b, 'p, 'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
             }
             Match {
                 pats: pats,
-                dummy: br.dummy,
                 data: br.data,
                 bound_ptrs: bound_ptrs
             }
@@ -559,8 +544,7 @@ fn enter_opt<'a, 'p, 'blk, 'tcx>(
 
     let mcx = check_match::MatchCheckCtxt { tcx: bcx.tcx() };
     enter_match(bcx, dm, m, col, val, |pats|
-        check_match::specialize(&mcx, pats.as_slice(), m[0].dummy, &ctor, col,
-                                variant_size)
+        check_match::specialize(&mcx, pats.as_slice(), &ctor, col, variant_size)
     )
 }
 
@@ -1041,7 +1025,7 @@ fn compile_submatch_continue<'a, 'p, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
     match adt_vals {
         Some(field_vals) => {
             let pats = enter_match(bcx, dm, m, col, val, |pats|
-                check_match::specialize(&mcx, pats, m[0].dummy,
+                check_match::specialize(&mcx, pats,
                                         &check_match::Single, col,
                                         field_vals.len())
             );
@@ -1365,7 +1349,6 @@ fn trans_match_inner<'blk, 'tcx>(scope_cx: Block<'blk, 'tcx>,
         bindings_map: create_bindings_map(bcx, &**arm.pats.get(0), discr_expr, &*arm.body)
     }).collect();
 
-    let dummy = check_match::DUMMY_WILD_PAT.clone();
     let mut static_inliner = StaticInliner::new(scope_cx.tcx());
     let arm_pats: Vec<Vec<P<ast::Pat>>> = arm_datas.iter().map(|arm_data| {
         arm_data.arm.pats.iter().map(|p| static_inliner.fold_pat((*p).clone())).collect()
@@ -1374,7 +1357,6 @@ fn trans_match_inner<'blk, 'tcx>(scope_cx: Block<'blk, 'tcx>,
     for (arm_data, pats) in arm_datas.iter().zip(arm_pats.iter()) {
         matches.extend(pats.iter().map(|p| Match {
             pats: vec![&**p],
-            dummy: &dummy,
             data: arm_data,
             bound_ptrs: Vec::new(),
         }));

src/test/compile-fail/issue-17718-const-naming.rs

@@ -12,5 +12,6 @@
 
 const foo: int = 3;
 //~^ ERROR: should have an uppercase name such as
+//~^^ ERROR: constant item is never used
 
 fn main() {}

src/test/compile-fail/lint-dead-code-1.rs

@@ -39,8 +39,8 @@ pub const pub_const: int = 0;
 const priv_const: int = 0; //~ ERROR: constant item is never used
 const used_const: int = 0;
 pub const used_const2: int = used_const;
-const USED_CONST: int = 0;
-const CONST_USED_IN_ENUM_DISCRIMINANT: int = 10;
+const USED_CONST: int = 1;
+const CONST_USED_IN_ENUM_DISCRIMINANT: int = 11;
 
 pub type typ = *const UsedStruct4;
 pub struct PubStruct;
@@ -68,7 +68,10 @@ pub struct PubStruct2 {
 
 pub enum pub_enum { foo1, bar1 }
 pub enum pub_enum2 { a(*const StructUsedInEnum) }
-pub enum pub_enum3 { Foo = STATIC_USED_IN_ENUM_DISCRIMINANT }
+pub enum pub_enum3 {
+    Foo = STATIC_USED_IN_ENUM_DISCRIMINANT,
+    Bar = CONST_USED_IN_ENUM_DISCRIMINANT,
+}
 
 enum priv_enum { foo2, bar2 } //~ ERROR: enum is never used
 enum used_enum {
@@ -89,6 +92,7 @@ pub fn pub_fn() {
     let i = 1i;
     match i {
         USED_STATIC => (),
+        USED_CONST => (),
         _ => ()
     }
     f::<StructUsedInGeneric>();