syntax: make OptVec immutable.

This is the first step to replacing OptVec with a new representation:
remove all mutability. Any mutations have to go via `Vec` and then make
to `OptVec`.

Many of the uses of OptVec are unnecessary now that Vec has no-alloc
emptiness (and have been converted to Vec): the only ones that really
need it are the AST and sty's (and so on) where there are a *lot* of
instances of them, and they're (mostly) immutable.

15 files changed, 79 insertions, 126 deletions

diff --git a/src/librustc/metadata/tydecode.rs b/src/librustc/metadata/tydecode.rs
index 1e9b98073fa..eb452c1fd71 100644
--- a/src/librustc/metadata/tydecode.rs
+++ b/src/librustc/metadata/tydecode.rs
@@ -192,13 +192,13 @@ fn parse_region_substs(st: &mut PState, conv: conv_did) -> ty::RegionSubsts {
     match next(st) {
         'e' => ty::ErasedRegions,
         'n' => {
-            let mut regions = opt_vec::Empty;
+            let mut regions = vec!();
             while peek(st) != '.' {
                 let r = parse_region(st, |x,y| conv(x,y));
                 regions.push(r);
             }
             assert_eq!(next(st), '.');
-            ty::NonerasedRegions(regions)
+            ty::NonerasedRegions(opt_vec::from(regions))
         }
         _ => fail!("parse_bound_region: bad input")
     }
diff --git a/src/librustc/middle/borrowck/move_data.rs b/src/librustc/middle/borrowck/move_data.rs
index de4059142e4..93a1ba309c2 100644
--- a/src/librustc/middle/borrowck/move_data.rs
+++ b/src/librustc/middle/borrowck/move_data.rs
@@ -26,8 +26,6 @@ use middle::typeck;
 use syntax::ast;
 use syntax::ast_util;
 use syntax::codemap::Span;
-use syntax::opt_vec::OptVec;
-use syntax::opt_vec;
 use util::ppaux::Repr;
 
 pub struct MoveData {
@@ -316,15 +314,15 @@ impl MoveData {
 
     fn existing_base_paths(&self,
                            lp: @LoanPath)
-                           -> OptVec<MovePathIndex> {
-        let mut result = opt_vec::Empty;
+                           -> Vec<MovePathIndex> {
+        let mut result = vec!();
         self.add_existing_base_paths(lp, &mut result);
         result
     }
 
     fn add_existing_base_paths(&self,
                                lp: @LoanPath,
-                               result: &mut OptVec<MovePathIndex>) {
+                               result: &mut Vec<MovePathIndex>) {
         /*!
          * Adds any existing move path indices for `lp` and any base
          * paths of `lp` to `result`, but does not add new move paths
diff --git a/src/librustc/middle/cfg/construct.rs b/src/librustc/middle/cfg/construct.rs
index a742ff336b2..b84e923f77d 100644
--- a/src/librustc/middle/cfg/construct.rs
+++ b/src/librustc/middle/cfg/construct.rs
@@ -14,7 +14,6 @@ use middle::typeck;
 use middle::ty;
 use syntax::ast;
 use syntax::ast_util;
-use syntax::opt_vec;
 use util::nodemap::NodeMap;
 
 struct CFGBuilder<'a> {
@@ -470,7 +469,7 @@ impl<'a> CFGBuilder<'a> {
     fn add_contained_edge(&mut self,
                           source: CFGIndex,
                           target: CFGIndex) {
-        let data = CFGEdgeData {exiting_scopes: opt_vec::Empty};
+        let data = CFGEdgeData {exiting_scopes: vec!() };
         self.graph.add_edge(source, target, data);
     }
 
@@ -479,9 +478,10 @@ impl<'a> CFGBuilder<'a> {
                         from_index: CFGIndex,
                         to_loop: LoopScope,
                         to_index: CFGIndex) {
-        let mut data = CFGEdgeData {exiting_scopes: opt_vec::Empty};
+        let mut data = CFGEdgeData {exiting_scopes: vec!() };
         let mut scope_id = from_expr.id;
         while scope_id != to_loop.loop_id {
+
             data.exiting_scopes.push(scope_id);
             scope_id = self.tcx.region_maps.encl_scope(scope_id);
         }
diff --git a/src/librustc/middle/cfg/mod.rs b/src/librustc/middle/cfg/mod.rs
index 5b4a5f89ea9..9c2dcd74351 100644
--- a/src/librustc/middle/cfg/mod.rs
+++ b/src/librustc/middle/cfg/mod.rs
@@ -19,7 +19,6 @@ use middle::graph;
 use middle::ty;
 use middle::typeck;
 use syntax::ast;
-use syntax::opt_vec::OptVec;
 use util::nodemap::NodeMap;
 
 mod construct;
@@ -36,7 +35,7 @@ pub struct CFGNodeData {
 }
 
 pub struct CFGEdgeData {
-    exiting_scopes: OptVec<ast::NodeId>
+    exiting_scopes: Vec<ast::NodeId>
 }
 
 pub type CFGIndex = graph::NodeIndex;
diff --git a/src/librustc/middle/resolve_lifetime.rs b/src/librustc/middle/resolve_lifetime.rs
index 49d8c5acb17..2919d67136f 100644
--- a/src/librustc/middle/resolve_lifetime.rs
+++ b/src/librustc/middle/resolve_lifetime.rs
@@ -21,7 +21,6 @@ use driver::session::Session;
 use util::nodemap::NodeMap;
 use syntax::ast;
 use syntax::codemap::Span;
-use syntax::opt_vec;
 use syntax::opt_vec::OptVec;
 use syntax::parse::token::special_idents;
 use syntax::parse::token;
@@ -413,7 +412,7 @@ pub fn early_bound_lifetimes<'a>(generics: &'a ast::Generics) -> Vec<ast::Lifeti
         .collect()
 }
 
-pub fn free_lifetimes(ty_params: &OptVec<ast::TyParam>) -> OptVec<ast::Name> {
+pub fn free_lifetimes(ty_params: &OptVec<ast::TyParam>) -> Vec<ast::Name> {
     /*!
      * Gathers up and returns the names of any lifetimes that appear
      * free in `ty_params`. Of course, right now, all lifetimes appear
@@ -421,14 +420,14 @@ pub fn free_lifetimes(ty_params: &OptVec<ast::TyParam>) -> OptVec<ast::Name> {
      * declarations; just being forwards compatible with future extensions.
      */
 
-    let mut collector = FreeLifetimeCollector { names: opt_vec::Empty };
+    let mut collector = FreeLifetimeCollector { names: vec!() };
     for ty_param in ty_params.iter() {
         visit::walk_ty_param_bounds(&mut collector, &ty_param.bounds, ());
     }
     return collector.names;
 
     struct FreeLifetimeCollector {
-        names: OptVec<ast::Name>,
+        names: Vec<ast::Name>,
     }
 
     impl Visitor<()> for FreeLifetimeCollector {
diff --git a/src/librustc/middle/trans/cleanup.rs b/src/librustc/middle/trans/cleanup.rs
index 1acc746b197..75f236d5028 100644
--- a/src/librustc/middle/trans/cleanup.rs
+++ b/src/librustc/middle/trans/cleanup.rs
@@ -24,8 +24,6 @@ use middle::trans::glue;
 use middle::trans::type_::Type;
 use middle::ty;
 use syntax::ast;
-use syntax::opt_vec;
-use syntax::opt_vec::OptVec;
 use util::ppaux::Repr;
 
 pub struct CleanupScope<'a> {
@@ -37,9 +35,9 @@ pub struct CleanupScope<'a> {
     kind: CleanupScopeKind<'a>,
 
     // Cleanups to run upon scope exit.
-    cleanups: OptVec<~Cleanup>,
+    cleanups: Vec<~Cleanup>,
 
-    cached_early_exits: OptVec<CachedEarlyExit>,
+    cached_early_exits: Vec<CachedEarlyExit>,
     cached_landing_pad: Option<BasicBlockRef>,
 }
 
@@ -379,7 +377,7 @@ impl<'a> CleanupMethods<'a> for FunctionContext<'a> {
         assert!(orig_scopes_len > 0);
 
         // Remove any scopes that do not have cleanups on failure:
-        let mut popped_scopes = opt_vec::Empty;
+        let mut popped_scopes = vec!();
         while !self.top_scope(|s| s.needs_invoke()) {
             debug!("top scope does not need invoke");
             popped_scopes.push(self.pop_scope());
@@ -510,7 +508,7 @@ impl<'a> CleanupHelperMethods<'a> for FunctionContext<'a> {
 
         let orig_scopes_len = self.scopes_len();
         let mut prev_llbb;
-        let mut popped_scopes = opt_vec::Empty;
+        let mut popped_scopes = vec!();
 
         // First we pop off all the cleanup stacks that are
         // traversed until the exit is reached, pushing them
@@ -708,14 +706,14 @@ impl<'a> CleanupScope<'a> {
     fn new(kind: CleanupScopeKind<'a>) -> CleanupScope<'a> {
         CleanupScope {
             kind: kind,
-            cleanups: opt_vec::Empty,
-            cached_early_exits: opt_vec::Empty,
+            cleanups: vec!(),
+            cached_early_exits: vec!(),
             cached_landing_pad: None,
         }
     }
 
     fn clear_cached_exits(&mut self) {
-        self.cached_early_exits = opt_vec::Empty;
+        self.cached_early_exits = vec!();
         self.cached_landing_pad = None;
     }
 
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index 86cb4e9b010..a08a20e97d2 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -5072,11 +5072,10 @@ pub fn construct_parameter_environment(
 
     // map bound 'a => free 'a
     let region_params = {
-        fn push_region_params(accum: OptVec<ty::Region>,
+        fn push_region_params(mut accum: Vec<ty::Region>,
                               free_id: ast::NodeId,
                               region_params: &[RegionParameterDef])
-                              -> OptVec<ty::Region> {
-            let mut accum = accum;
+                              -> Vec<ty::Region> {
             for r in region_params.iter() {
                 accum.push(
                     ty::ReFree(ty::FreeRegion {
@@ -5086,14 +5085,14 @@ pub fn construct_parameter_environment(
             accum
         }
 
-        let t = push_region_params(opt_vec::Empty, free_id, item_region_params);
+        let t = push_region_params(vec!(), free_id, item_region_params);
         push_region_params(t, free_id, method_region_params)
     };
 
     let free_substs = substs {
         self_ty: self_ty,
         tps: type_params,
-        regions: ty::NonerasedRegions(region_params)
+        regions: ty::NonerasedRegions(opt_vec::from(region_params))
     };
 
     //
diff --git a/src/librustc/middle/typeck/check/method.rs b/src/librustc/middle/typeck/check/method.rs
index 055a996e8ec..023f0836140 100644
--- a/src/librustc/middle/typeck/check/method.rs
+++ b/src/librustc/middle/typeck/check/method.rs
@@ -104,6 +104,7 @@ use syntax::ast::{MutMutable, MutImmutable};
 use syntax::ast;
 use syntax::codemap::Span;
 use syntax::parse::token;
+use syntax::opt_vec;
 
 #[deriving(Eq)]
 pub enum CheckTraitsFlag {
@@ -1102,8 +1103,8 @@ impl<'a> LookupContext<'a> {
 
         // Determine values for the early-bound lifetime parameters.
         // FIXME -- permit users to manually specify lifetimes
-        let mut all_regions = match candidate.rcvr_substs.regions {
-            NonerasedRegions(ref v) => v.clone(),
+        let mut all_regions: Vec<Region> = match candidate.rcvr_substs.regions {
+            NonerasedRegions(ref v) => v.iter().map(|r| r.clone()).collect(),
             ErasedRegions => tcx.sess.span_bug(self.span, "ErasedRegions")
         };
         let m_regions =
@@ -1119,7 +1120,7 @@ impl<'a> LookupContext<'a> {
         let all_substs = substs {
             tps: vec::append(candidate.rcvr_substs.tps.clone(),
                                 m_substs.as_slice()),
-            regions: NonerasedRegions(all_regions),
+            regions: NonerasedRegions(opt_vec::from(all_regions)),
             self_ty: candidate.rcvr_substs.self_ty,
         };
 
diff --git a/src/librustc/middle/typeck/infer/combine.rs b/src/librustc/middle/typeck/infer/combine.rs
index 2af6ed0266a..794631f9721 100644
--- a/src/librustc/middle/typeck/infer/combine.rs
+++ b/src/librustc/middle/typeck/infer/combine.rs
@@ -160,7 +160,7 @@ pub trait Combine {
 
                     assert_eq!(num_region_params, a_rs.len());
                     assert_eq!(num_region_params, b_rs.len());
-                    let mut rs = opt_vec::Empty;
+                    let mut rs = vec!();
                     for i in range(0, num_region_params) {
                         let a_r = *a_rs.get(i);
                         let b_r = *b_rs.get(i);
@@ -176,7 +176,7 @@ pub trait Combine {
                         };
                         rs.push(if_ok!(r));
                     }
-                    Ok(ty::NonerasedRegions(rs))
+                    Ok(ty::NonerasedRegions(opt_vec::from(rs)))
                 }
             }
         }
diff --git a/src/librustc/middle/typeck/infer/error_reporting.rs b/src/librustc/middle/typeck/infer/error_reporting.rs
index 53c39068fb9..4cd9d46ff7a 100644
--- a/src/librustc/middle/typeck/infer/error_reporting.rs
+++ b/src/librustc/middle/typeck/infer/error_reporting.rs
@@ -80,8 +80,6 @@ use syntax::ast;
 use syntax::ast_map;
 use syntax::ast_util;
 use syntax::ast_util::name_to_dummy_lifetime;
-use syntax::opt_vec;
-use syntax::opt_vec::OptVec;
 use syntax::parse::token;
 use syntax::print::pprust;
 use util::ppaux::UserString;
@@ -90,10 +88,10 @@ use util::ppaux::note_and_explain_region;
 
 pub trait ErrorReporting {
     fn report_region_errors(&self,
-                            errors: &OptVec<RegionResolutionError>);
+                            errors: &Vec<RegionResolutionError>);
 
-    fn process_errors(&self, errors: &OptVec<RegionResolutionError>)
-                      -> OptVec<RegionResolutionError>;
+    fn process_errors(&self, errors: &Vec<RegionResolutionError>)
+                      -> Vec<RegionResolutionError>;
 
     fn report_type_error(&self, trace: TypeTrace, terr: &ty::type_err);
 
@@ -151,7 +149,7 @@ trait ErrorReportingHelpers {
 
 impl<'a> ErrorReporting for InferCtxt<'a> {
     fn report_region_errors(&self,
-                            errors: &OptVec<RegionResolutionError>) {
+                            errors: &Vec<RegionResolutionError>) {
         let p_errors = self.process_errors(errors);
         let errors = if p_errors.is_empty() { errors } else { &p_errors };
         for error in errors.iter() {
@@ -195,12 +193,12 @@ impl<'a> ErrorReporting for InferCtxt<'a> {
     // complete view of what lifetimes should be the same.
     // If the return value is an empty vector, it means that processing
     // failed (so the return value of this method should not be used)
-    fn process_errors(&self, errors: &OptVec<RegionResolutionError>)
-                      -> OptVec<RegionResolutionError> {
+    fn process_errors(&self, errors: &Vec<RegionResolutionError>)
+                      -> Vec<RegionResolutionError> {
         let mut var_origins = Vec::new();
         let mut trace_origins = Vec::new();
         let mut same_regions = Vec::new();
-        let mut processed_errors = opt_vec::Empty;
+        let mut processed_errors = Vec::new();
         for error in errors.iter() {
             match *error {
                 ConcreteFailure(origin, sub, sup) => {
@@ -239,7 +237,7 @@ impl<'a> ErrorReporting for InferCtxt<'a> {
                 // declaration, we want to make sure that they are, in fact,
                 // from the same scope
                 if sr.scope_id != common_scope_id {
-                    return opt_vec::Empty;
+                    return vec!();
                 }
             }
             let pe = ProcessedErrors(var_origins, trace_origins, same_regions);
diff --git a/src/librustc/middle/typeck/infer/region_inference/mod.rs b/src/librustc/middle/typeck/infer/region_inference/mod.rs
index 7d2159b5b68..7c13c15ffec 100644
--- a/src/librustc/middle/typeck/infer/region_inference/mod.rs
+++ b/src/librustc/middle/typeck/infer/region_inference/mod.rs
@@ -29,8 +29,6 @@ use std::uint;
 use std::slice;
 use collections::{HashMap, HashSet};
 use syntax::ast;
-use syntax::opt_vec;
-use syntax::opt_vec::OptVec;
 
 mod doc;
 
@@ -561,9 +559,9 @@ impl<'a> RegionVarBindings<'a> {
     constraints, assuming such values can be found; if they cannot,
     errors are reported.
     */
-    pub fn resolve_regions(&self) -> OptVec<RegionResolutionError> {
+    pub fn resolve_regions(&self) -> Vec<RegionResolutionError> {
         debug!("RegionVarBindings: resolve_regions()");
-        let mut errors = opt_vec::Empty;
+        let mut errors = vec!();
         let v = self.infer_variable_values(&mut errors);
         let mut values = self.values.borrow_mut();
         *values.get() = Some(v);
@@ -815,7 +813,7 @@ type RegionGraph = graph::Graph<(), Constraint>;
 
 impl<'a> RegionVarBindings<'a> {
     fn infer_variable_values(&self,
-                             errors: &mut OptVec<RegionResolutionError>)
+                             errors: &mut Vec<RegionResolutionError>)
                              -> Vec<VarValue> {
         let mut var_data = self.construct_var_data();
         self.expansion(var_data.as_mut_slice());
@@ -1004,7 +1002,7 @@ impl<'a> RegionVarBindings<'a> {
 
     fn collect_concrete_region_errors(
         &self,
-        errors: &mut OptVec<RegionResolutionError>)
+        errors: &mut Vec<RegionResolutionError>)
     {
         let constraints = self.constraints.borrow();
         for (constraint, _) in constraints.get().iter() {
@@ -1033,7 +1031,7 @@ impl<'a> RegionVarBindings<'a> {
     fn extract_values_and_collect_conflicts(
         &self,
         var_data: &[VarData],
-        errors: &mut OptVec<RegionResolutionError>)
+        errors: &mut Vec<RegionResolutionError>)
         -> Vec<VarValue> {
         debug!("extract_values_and_collect_conflicts()");
 
@@ -1157,7 +1155,7 @@ impl<'a> RegionVarBindings<'a> {
         var_data: &[VarData],
         dup_vec: &mut [uint],
         node_idx: RegionVid,
-        errors: &mut OptVec<RegionResolutionError>)
+        errors: &mut Vec<RegionResolutionError>)
     {
         // Errors in expanding nodes result from a lower-bound that is
         // not contained by an upper-bound.
@@ -1206,7 +1204,7 @@ impl<'a> RegionVarBindings<'a> {
         var_data: &[VarData],
         dup_vec: &mut [uint],
         node_idx: RegionVid,
-        errors: &mut OptVec<RegionResolutionError>)
+        errors: &mut Vec<RegionResolutionError>)
     {
         // Errors in contracting nodes result from two upper-bounds
         // that have no intersection.
diff --git a/src/librustc/middle/typeck/variance.rs b/src/librustc/middle/typeck/variance.rs
index db74ad99d81..cee87565e3e 100644
--- a/src/librustc/middle/typeck/variance.rs
+++ b/src/librustc/middle/typeck/variance.rs
@@ -904,32 +904,33 @@ impl<'a> SolveContext<'a> {
         let num_inferred = self.terms_cx.num_inferred();
         while index < num_inferred {
             let item_id = inferred_infos.get(index).item_id;
-            let mut item_variances = ty::ItemVariances {
-                self_param: None,
-                type_params: opt_vec::Empty,
-                region_params: opt_vec::Empty
-            };
+            let mut self_param = None;
+            let mut type_params = vec!();
+            let mut region_params = vec!();
+
             while index < num_inferred &&
                   inferred_infos.get(index).item_id == item_id {
                 let info = inferred_infos.get(index);
                 match info.kind {
                     SelfParam => {
-                        assert!(item_variances.self_param.is_none());
-                        item_variances.self_param =
-                            Some(*solutions.get(index));
+                        assert!(self_param.is_none());
+                        self_param = Some(*solutions.get(index));
                     }
                     TypeParam => {
-                        item_variances.type_params
-                                      .push(*solutions.get(index));
+                        type_params.push(*solutions.get(index));
                     }
                     RegionParam => {
-                        item_variances.region_params
-                                      .push(*solutions.get(index));
+                        region_params.push(*solutions.get(index));
                     }
                 }
                 index += 1;
             }
 
+            let item_variances = ty::ItemVariances {
+                self_param: self_param,
+                type_params: opt_vec::from(type_params),
+                region_params: opt_vec::from(region_params)
+            };
             debug!("item_id={} item_variances={}",
                     item_id,
                     item_variances.repr(tcx));
diff --git a/src/libsyntax/ext/deriving/generic.rs b/src/libsyntax/ext/deriving/generic.rs
index 546c3eac41c..7aa98a60781 100644
--- a/src/libsyntax/ext/deriving/generic.rs
+++ b/src/libsyntax/ext/deriving/generic.rs
@@ -360,27 +360,32 @@ impl<'a> TraitDef<'a> {
                            methods: Vec<@ast::Method> ) -> @ast::Item {
         let trait_path = self.path.to_path(cx, self.span, type_ident, generics);
 
-        let mut trait_generics = self.generics.to_generics(cx, self.span,
-                                                           type_ident, generics);
+        let Generics { mut lifetimes, ty_params } =
+            self.generics.to_generics(cx, self.span, type_ident, generics);
+        let mut ty_params = opt_vec::take_vec(ty_params);
+
         // Copy the lifetimes
-        for l in generics.lifetimes.iter() {
-            trait_generics.lifetimes.push(*l)
-        };
+        lifetimes.extend(&mut generics.lifetimes.iter().map(|l| *l));
+
         // Create the type parameters.
-        for ty_param in generics.ty_params.iter() {
+        ty_params.extend(&mut generics.ty_params.iter().map(|ty_param| {
             // I don't think this can be moved out of the loop, since
             // a TyParamBound requires an ast id
-            let mut bounds = opt_vec::from(
+            let mut bounds =
                 // extra restrictions on the generics parameters to the type being derived upon
                 self.additional_bounds.map(|p| {
                     cx.typarambound(p.to_path(cx, self.span,
                                                   type_ident, generics))
-                }));
+                });
             // require the current trait
             bounds.push(cx.typarambound(trait_path.clone()));
 
-            trait_generics.ty_params.push(cx.typaram(ty_param.ident, bounds, None));
-        }
+            cx.typaram(ty_param.ident, opt_vec::from(bounds), None)
+        }));
+        let trait_generics = Generics {
+            lifetimes: lifetimes,
+            ty_params: opt_vec::from(ty_params)
+        };
 
         // Create the reference to the trait.
         let trait_ref = cx.trait_ref(trait_path);
diff --git a/src/libsyntax/opt_vec.rs b/src/libsyntax/opt_vec.rs
index aeb521468d2..425a5a9a5fa 100644
--- a/src/libsyntax/opt_vec.rs
+++ b/src/libsyntax/opt_vec.rs
@@ -37,25 +37,6 @@ pub fn from<T>(t: Vec<T> ) -> OptVec<T> {
 }
 
 impl<T> OptVec<T> {
-    pub fn push(&mut self, t: T) {
-        match *self {
-            Vec(ref mut v) => {
-                v.push(t);
-                return;
-            }
-            Empty => {
-                *self = Vec(vec!(t));
-            }
-        }
-    }
-
-    pub fn pop(&mut self) -> Option<T> {
-        match *self {
-            Vec(ref mut v) => v.pop(),
-            Empty => None
-        }
-    }
-
     pub fn last<'a>(&'a self) -> Option<&'a T> {
         match *self {
             Vec(ref v) => v.last(),
@@ -102,16 +83,6 @@ impl<T> OptVec<T> {
         }
     }
 
-    pub fn swap_remove(&mut self, index: uint) {
-        match *self {
-            Empty => { fail!("index out of bounds"); }
-            Vec(ref mut v) => {
-                assert!(index < v.len());
-                v.swap_remove(index);
-            }
-        }
-    }
-
     #[inline]
     pub fn iter<'r>(&'r self) -> Items<'r, T> {
         match *self {
@@ -142,17 +113,6 @@ pub fn take_vec<T>(v: OptVec<T>) -> Vec<T> {
     }
 }
 
-impl<T:Clone> OptVec<T> {
-    pub fn prepend(&self, t: T) -> OptVec<T> {
-        let mut v0 = vec!(t);
-        match *self {
-            Empty => {}
-            Vec(ref v1) => { v0.push_all(v1.as_slice()); }
-        }
-        return Vec(v0);
-    }
-}
-
 impl<A:Eq> Eq for OptVec<A> {
     fn eq(&self, other: &OptVec<A>) -> bool {
         // Note: cannot use #[deriving(Eq)] here because
@@ -208,10 +168,7 @@ impl<'a, T> DoubleEndedIterator<&'a T> for Items<'a, T> {
 
 impl<A> FromIterator<A> for OptVec<A> {
     fn from_iterator<T: Iterator<A>>(iterator: &mut T) -> OptVec<A> {
-        let mut r = Empty;
-        for x in *iterator {
-            r.push(x);
-        }
-        r
+        let v: Vec<A> = iterator.collect();
+        from(v)
     }
 }
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 5398844d52a..3e2b88c1cf1 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -632,7 +632,7 @@ impl<'a> Parser<'a> {
                                   f: |&mut Parser| -> T)
                                   -> OptVec<T> {
         let mut first = true;
-        let mut v = opt_vec::Empty;
+        let mut v = Vec::new();
         while self.token != token::GT
             && self.token != token::BINOP(token::SHR) {
             match sep {
@@ -644,7 +644,7 @@ impl<'a> Parser<'a> {
             }
             v.push(f(self));
         }
-        return v;
+        return opt_vec::from(v);
     }
 
     pub fn parse_seq_to_gt<T>(
@@ -681,7 +681,7 @@ impl<'a> Parser<'a> {
                                    f: |&mut Parser| -> T)
                                    -> Vec<T> {
         let mut first: bool = true;
-        let mut v: Vec<T> = Vec::new();
+        let mut v = vec!();
         while self.token != *ket {
             match sep.sep {
               Some(ref t) => {
@@ -3437,7 +3437,7 @@ impl<'a> Parser<'a> {
             return None;
         }
 
-        let mut result = opt_vec::Empty;
+        let mut result = vec!();
         loop {
             match self.token {
                 token::LIFETIME(lifetime) => {
@@ -3462,7 +3462,7 @@ impl<'a> Parser<'a> {
             }
         }
 
-        return Some(result);
+        return Some(opt_vec::from(result));
     }
 
     // matches typaram = IDENT optbounds ( EQ ty )?