auto merge of #5112 : luqmana/rust/3469, r=graydon

So this is a partial fix for #3469. Partial because it only works for simple constant expressions like `32/2` and `2+2` and not for any actual constants.

For example:
```
const FOO: uint = 2+2;
let v: [int * FOO];
```

results in:
```
error: expected constant expr for vector length: Non-constant path in constant expr
```

This seems to be because at the point of error (`typeck::astconv`) the def_map doesn't contain the constant and thus it can't lookup the actual expression (`2+2` in this case).

So, feedback on what I have so far and suggestions for how to address the constant issue?

5 files changed, 12 insertions, 23 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index e5fb2ad153c..65eeff5bbab 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -386,7 +386,6 @@ pub enum vstore {
 #[auto_decode]
 #[deriving_eq]
 pub enum expr_vstore {
-    // FIXME (#3469): Change uint to @expr (actually only constant exprs)
     expr_vstore_fixed(Option<uint>),   // [1,2,3,4]
     expr_vstore_uniq,                  // ~[1,2,3,4]
     expr_vstore_box,                   // @[1,2,3,4]
@@ -916,7 +915,7 @@ pub enum ty_ {
     ty_box(mt),
     ty_uniq(mt),
     ty_vec(mt),
-    ty_fixed_length_vec(mt, uint),
+    ty_fixed_length_vec(mt, @expr),
     ty_ptr(mt),
     ty_rptr(Option<@Lifetime>, mt),
     ty_closure(@TyClosure),
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index a8952f313a5..159b23f4f99 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -622,10 +622,10 @@ pub fn noop_fold_ty(t: &ty_, fld: @ast_fold) -> ty_ {
         }
         ty_tup(ref tys) => ty_tup(tys.map(|ty| fld.fold_ty(*ty))),
         ty_path(path, id) => ty_path(fld.fold_path(path), fld.new_id(id)),
-        ty_fixed_length_vec(ref mt, vs) => {
+        ty_fixed_length_vec(ref mt, e) => {
             ty_fixed_length_vec(
                 fold_mt(mt, fld),
-                vs
+                fld.fold_expr(e)
             )
         }
         ty_mac(ref mac) => ty_mac(fold_mac(*mac))
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 8a883b73a64..c7e93635d4c 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -642,7 +642,8 @@ pub impl Parser {
                 self.obsolete(*self.last_span, ObsoleteMutVector);
             }
 
-            // Parse the `* 3` in `[ int * 3 ]`
+            // Parse the `* e` in `[ int * e ]`
+            // where `e` is a const expression
             let t = match self.maybe_parse_fixed_vstore_with_star() {
                 None => ty_vec(mt),
                 Some(suffix) => ty_fixed_length_vec(mt, suffix)
@@ -814,23 +815,9 @@ pub impl Parser {
         })
     }
 
-    fn maybe_parse_fixed_vstore_with_star(&self) -> Option<uint> {
+    fn maybe_parse_fixed_vstore_with_star(&self) -> Option<@ast::expr> {
         if self.eat(&token::BINOP(token::STAR)) {
-            match *self.token {
-                token::LIT_INT_UNSUFFIXED(i) if i >= 0i64 => {
-                    self.bump();
-                    Some(i as uint)
-                }
-                _ => {
-                    self.fatal(
-                        fmt!(
-                            "expected integral vector length \
-                            but found `%s`",
-                            token_to_str(self.reader, &copy *self.token)
-                        )
-                    );
-                }
-            }
+            Some(self.parse_expr())
         } else {
             None
         }
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 71f3de17414..93583a1487a 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -425,7 +425,7 @@ pub fn print_type_ex(s: @ps, &&ty: @ast::Ty, print_colons: bool) {
         }
         print_type(s, mt.ty);
         word(s.s, ~" * ");
-        word(s.s, fmt!("%u", v));
+        print_expr(s, v);
         word(s.s, ~"]");
       }
       ast::ty_mac(_) => {
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 6a0f1a2ec46..a159c98d21b 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -246,7 +246,10 @@ pub fn visit_ty<E>(t: @Ty, e: E, v: vt<E>) {
             (v.visit_ty)(f.decl.output, e, v);
         },
         ty_path(p, _) => visit_path(p, e, v),
-        ty_fixed_length_vec(ref mt, _) => (v.visit_ty)(mt.ty, e, v),
+        ty_fixed_length_vec(ref mt, ex) => {
+            (v.visit_ty)(mt.ty, e, v);
+            (v.visit_expr)(ex, e, v);
+        },
         ty_nil | ty_bot | ty_mac(_) | ty_infer => ()
     }
 }