Negative case of `len()` -> `is_empty()`

`s/([^\(\s]+\.)len\(\) [(?:!=)>] 0/!$1is_empty()/g`

src/compiletest/compiletest.rs

@@ -368,7 +368,7 @@ pub fn make_metrics_test_closure(config: &Config, testfile: &Path) -> test::Test
 fn extract_gdb_version(full_version_line: Option<String>) -> Option<String> {
     match full_version_line {
         Some(ref full_version_line)
-          if full_version_line.trim().len() > 0 => {
+          if !full_version_line.trim().is_empty() => {
             let full_version_line = full_version_line.trim();
 
             // used to be a regex "(^|[^0-9])([0-9]\.[0-9])([^0-9]|$)"
@@ -408,7 +408,7 @@ fn extract_lldb_version(full_version_line: Option<String>) -> Option<String> {
 
     match full_version_line {
         Some(ref full_version_line)
-          if full_version_line.trim().len() > 0 => {
+          if !full_version_line.trim().is_empty() => {
             let full_version_line = full_version_line.trim();
 
             for (pos, l) in full_version_line.char_indices() {
@@ -426,7 +426,7 @@ fn extract_lldb_version(full_version_line: Option<String>) -> Option<String> {
                 let vers = full_version_line[pos + 5..].chars().take_while(|c| {
                     c.is_digit(10)
                 }).collect::<String>();
-                if vers.len() > 0 { return Some(vers) }
+                if !vers.is_empty() { return Some(vers) }
             }
             println!("Could not extract LLDB version from line '{}'",
                      full_version_line);

src/libcollections/btree/node.rs

@@ -1225,7 +1225,7 @@ impl<K, V> Node<K, V> {
     /// because we have one too many, and our parent now has one too few
     fn split(&mut self) -> (K, V, Node<K, V>) {
         // Necessary for correctness, but in a private function
-        debug_assert!(self.len() > 0);
+        debug_assert!(!self.is_empty());
 
         let mut right = if self.is_leaf() {
             Node::new_leaf(self.capacity())

src/libcore/char.rs

@@ -227,7 +227,7 @@ impl CharExt for char {
 #[inline]
 pub fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> Option<usize> {
     // Marked #[inline] to allow llvm optimizing it away
-    if code < MAX_ONE_B && dst.len() >= 1 {
+    if code < MAX_ONE_B && !dst.is_empty() {
         dst[0] = code as u8;
         Some(1)
     } else if code < MAX_TWO_B && dst.len() >= 2 {
@@ -258,7 +258,7 @@ pub fn encode_utf8_raw(code: u32, dst: &mut [u8]) -> Option<usize> {
 #[inline]
 pub fn encode_utf16_raw(mut ch: u32, dst: &mut [u16]) -> Option<usize> {
     // Marked #[inline] to allow llvm optimizing it away
-    if (ch & 0xFFFF) == ch  && dst.len() >= 1 {
+    if (ch & 0xFFFF) == ch && !dst.is_empty() {
         // The BMP falls through (assuming non-surrogate, as it should)
         dst[0] = ch as u16;
         Some(1)

src/libfmt_macros/lib.rs

@@ -371,7 +371,7 @@ impl<'a> Parser<'a> {
             None => {
                 let tmp = self.cur.clone();
                 match self.word() {
-                    word if word.len() > 0 => {
+                    word if !word.is_empty() => {
                         if self.consume('$') {
                             CountIsName(word)
                         } else {
@@ -463,7 +463,7 @@ mod tests {
     fn musterr(s: &str) {
         let mut p = Parser::new(s);
         p.next();
-        assert!(p.errors.len() != 0);
+        assert!(!p.errors.is_empty());
     }
 
     #[test]

src/libgetopts/lib.rs

@@ -804,7 +804,7 @@ fn format_option(opt: &OptGroup) -> String {
     }
 
     // Use short_name is possible, but fallback to long_name.
-    if opt.short_name.len() > 0 {
+    if !opt.short_name.is_empty() {
         line.push('-');
         line.push_str(&opt.short_name[..]);
     } else {

src/librustc/metadata/encoder.rs

@@ -469,7 +469,7 @@ fn each_auxiliary_node_id<F>(item: &ast::Item, callback: F) -> bool where
         ast::ItemStruct(ref struct_def, _) => {
             // If this is a newtype struct, return the constructor.
             match struct_def.ctor_id {
-                Some(ctor_id) if struct_def.fields.len() > 0 &&
+                Some(ctor_id) if !struct_def.fields.is_empty() &&
                         struct_def.fields[0].node.kind.is_unnamed() => {
                     continue_ = callback(ctor_id);
                 }

src/librustc/metadata/loader.rs

@@ -307,13 +307,13 @@ impl<'a> Context<'a> {
     }
 
     pub fn report_load_errs(&mut self) {
-        let message = if self.rejected_via_hash.len() > 0 {
+        let message = if !self.rejected_via_hash.is_empty() {
             format!("found possibly newer version of crate `{}`",
                     self.ident)
-        } else if self.rejected_via_triple.len() > 0 {
+        } else if !self.rejected_via_triple.is_empty() {
             format!("couldn't find crate `{}` with expected target triple {}",
                     self.ident, self.triple)
-        } else if self.rejected_via_kind.len() > 0 {
+        } else if !self.rejected_via_kind.is_empty() {
             format!("found staticlib `{}` instead of rlib or dylib", self.ident)
         } else {
             format!("can't find crate for `{}`", self.ident)
@@ -325,7 +325,7 @@ impl<'a> Context<'a> {
         };
         self.sess.span_err(self.span, &message[..]);
 
-        if self.rejected_via_triple.len() > 0 {
+        if !self.rejected_via_triple.is_empty() {
             let mismatches = self.rejected_via_triple.iter();
             for (i, &CrateMismatch{ ref path, ref got }) in mismatches.enumerate() {
                 self.sess.fileline_note(self.span,
@@ -333,7 +333,7 @@ impl<'a> Context<'a> {
                             self.ident, i+1, got, path.display()));
             }
         }
-        if self.rejected_via_hash.len() > 0 {
+        if !self.rejected_via_hash.is_empty() {
             self.sess.span_note(self.span, "perhaps this crate needs \
                                             to be recompiled?");
             let mismatches = self.rejected_via_hash.iter();
@@ -353,7 +353,7 @@ impl<'a> Context<'a> {
                 }
             }
         }
-        if self.rejected_via_kind.len() > 0 {
+        if !self.rejected_via_kind.is_empty() {
             self.sess.fileline_help(self.span, "please recompile this crate using \
                                             --crate-type lib");
             let mismatches = self.rejected_via_kind.iter();

src/librustc/middle/dead.rs

@@ -182,7 +182,7 @@ impl<'a, 'tcx> MarkSymbolVisitor<'a, 'tcx> {
 
     fn mark_live_symbols(&mut self) {
         let mut scanned = HashSet::new();
-        while self.worklist.len() > 0 {
+        while !self.worklist.is_empty() {
             let id = self.worklist.pop().unwrap();
             if scanned.contains(&id) {
                 continue

src/librustc/middle/infer/error_reporting.rs

@@ -966,7 +966,7 @@ impl<'a, 'tcx> Rebuilder<'a, 'tcx> {
     fn pick_lifetime(&self,
                      region_names: &HashSet<ast::Name>)
                      -> (ast::Lifetime, FreshOrKept) {
-        if region_names.len() > 0 {
+        if !region_names.is_empty() {
             // It's not necessary to convert the set of region names to a
             // vector of string and then sort them. However, it makes the
             // choice of lifetime name deterministic and thus easier to test.

src/librustc/middle/infer/region_inference/mod.rs

@@ -246,7 +246,7 @@ impl<'a, 'tcx> RegionVarBindings<'a, 'tcx> {
     }
 
     fn in_snapshot(&self) -> bool {
-        self.undo_log.borrow().len() > 0
+        !self.undo_log.borrow().is_empty()
     }
 
     pub fn start_snapshot(&self) -> RegionSnapshot {

src/librustc/middle/liveness.rs

@@ -1527,7 +1527,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                     // for nil return types, it is ok to not return a value expl.
                 } else {
                     let ends_with_stmt = match body.expr {
-                        None if body.stmts.len() > 0 =>
+                        None if !body.stmts.is_empty() =>
                             match body.stmts.first().unwrap().node {
                                 ast::StmtSemi(ref e, _) => {
                                     ty::expr_ty(self.ir.tcx, &**e) == t_ret

src/librustc/middle/resolve_lifetime.rs

@@ -227,7 +227,7 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
                                                                                ref bounds,
                                                                                ref bound_lifetimes,
                                                                                .. }) => {
-                    if bound_lifetimes.len() > 0 {
+                    if !bound_lifetimes.is_empty() {
                         self.trait_ref_hack = true;
                         let result = self.with(LateScope(bound_lifetimes, self.scope),
                                                |old_scope, this| {
@@ -267,7 +267,7 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
                             _modifier: &ast::TraitBoundModifier) {
         debug!("visit_poly_trait_ref trait_ref={:?}", trait_ref);
 
-        if !self.trait_ref_hack || trait_ref.bound_lifetimes.len() > 0 {
+        if !self.trait_ref_hack || !trait_ref.bound_lifetimes.is_empty() {
             if self.trait_ref_hack {
                 println!("{:?}", trait_ref.span);
                 span_err!(self.sess, trait_ref.span, E0316,

src/librustc/middle/ty.rs

@@ -3665,7 +3665,7 @@ pub fn type_contents<'tcx>(cx: &ctxt<'tcx>, ty: Ty<'tcx>) -> TypeContents {
                     res = res | TC::OwnsDtor;
                 }
 
-                if variants.len() != 0 {
+                if !variants.is_empty() {
                     let repr_hints = lookup_repr_hints(cx, did);
                     if repr_hints.len() > 1 {
                         // this is an error later on, but this type isn't safe
@@ -4654,7 +4654,7 @@ pub fn expr_kind(tcx: &ctxt, expr: &ast::Expr) -> ExprKind {
             match resolve_expr(tcx, expr) {
                 def::DefVariant(tid, vid, _) => {
                     let variant_info = enum_variant_with_id(tcx, tid, vid);
-                    if variant_info.args.len() > 0 {
+                    if !variant_info.args.is_empty() {
                         // N-ary variant.
                         RvalueDatumExpr
                     } else {
@@ -5259,7 +5259,7 @@ impl<'tcx> VariantInfo<'tcx> {
 
         match ast_variant.node.kind {
             ast::TupleVariantKind(ref args) => {
-                let arg_tys = if args.len() > 0 {
+                let arg_tys = if !args.is_empty() {
                     // the regions in the argument types come from the
                     // enum def'n, and hence will all be early bound
                     ty::no_late_bound_regions(cx, &ty_fn_args(ctor_ty)).unwrap()
@@ -5280,7 +5280,7 @@ impl<'tcx> VariantInfo<'tcx> {
             ast::StructVariantKind(ref struct_def) => {
                 let fields: &[StructField] = &struct_def.fields;
 
-                assert!(fields.len() > 0);
+                assert!(!fields.is_empty());
 
                 let arg_tys = struct_def.fields.iter()
                     .map(|field| node_id_to_type(cx, field.node.id)).collect();

src/librustc/middle/ty_relate/mod.rs

@@ -544,7 +544,7 @@ pub fn super_relate_tys<'a,'tcx:'a,R>(relation: &mut R,
                                  .map(|(a, b)| relation.relate(a, b))
                                  .collect::<Result<_, _>>());
                 Ok(ty::mk_tup(tcx, ts))
-            } else if as_.len() != 0 && bs.len() != 0 {
+            } else if !(as_.is_empty() || bs.is_empty()) {
                 Err(ty::terr_tuple_size(
                     expected_found(relation, &as_.len(), &bs.len())))
             } else {

src/librustc/util/ppaux.rs

@@ -558,7 +558,7 @@ pub fn parameterized<'tcx,GG>(cx: &ctxt<'tcx>,
                     &strs[0][..]
                 },
                 tail)
-    } else if strs.len() > 0 {
+    } else if !strs.is_empty() {
         format!("{}<{}>", base, strs.connect(", "))
     } else {
         format!("{}", base)

src/librustc_back/tempdir.rs

@@ -50,7 +50,7 @@ impl TempDir {
         let mut rng = thread_rng();
         for _ in 0..NUM_RETRIES {
             let suffix: String = rng.gen_ascii_chars().take(NUM_RAND_CHARS).collect();
-            let leaf = if prefix.len() > 0 {
+            let leaf = if !prefix.is_empty() {
                 format!("{}.{}", prefix, suffix)
             } else {
                 // If we're given an empty string for a prefix, then creating a

src/librustc_lint/builtin.rs

@@ -778,7 +778,7 @@ impl NonCamelCaseTypes {
 
             // start with a non-lowercase letter rather than non-uppercase
             // ones (some scripts don't have a concept of upper/lowercase)
-            ident.len() > 0 && !ident.char_at(0).is_lowercase() && !ident.contains('_')
+            !ident.is_empty() && !ident.char_at(0).is_lowercase() && !ident.contains('_')
         }
 
         fn to_camel_case(s: &str) -> String {
@@ -1900,7 +1900,7 @@ impl LintPass for UnconditionalRecursion {
         // doesn't return (e.g. calls a `-> !` function or `loop { /*
         // no break */ }`) shouldn't be linted unless it actually
         // recurs.
-        if !reached_exit_without_self_call && self_call_spans.len() > 0 {
+        if !reached_exit_without_self_call && !self_call_spans.is_empty() {
             cx.span_lint(UNCONDITIONAL_RECURSION, sp,
                          "function cannot return without recurring");
 

src/librustc_privacy/lib.rs

@@ -1055,7 +1055,7 @@ impl<'a, 'tcx> SanePrivacyVisitor<'a, 'tcx> {
         let check_inherited = |sp: Span, vis: ast::Visibility, note: &str| {
             if vis != ast::Inherited {
                 tcx.sess.span_err(sp, "unnecessary visibility qualifier");
-                if note.len() > 0 {
+                if !note.is_empty() {
                     tcx.sess.span_note(sp, note);
                 }
             }

src/librustc_resolve/lib.rs

@@ -3072,7 +3072,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             }
         }
 
-        if values.len() > 0 &&
+        if !values.is_empty() &&
             values[smallest] != usize::MAX &&
             values[smallest] < name.len() + 2 &&
             values[smallest] <= max_distance &&
@@ -3228,7 +3228,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                                         format!("to call `{}::{}`", path_str, path_name)
                                 };
 
-                                if msg.len() > 0 {
+                                if !msg.is_empty() {
                                     msg = format!(". Did you mean {}?", msg)
                                 }
 

src/librustc_trans/back/link.rs

@@ -269,7 +269,7 @@ pub fn sanitize(s: &str) -> String {
     }
 
     // Underscore-qualify anything that didn't start as an ident.
-    if result.len() > 0 &&
+    if !result.is_empty() &&
         result.as_bytes()[0] != '_' as u8 &&
         ! (result.as_bytes()[0] as char).is_xid_start() {
         return format!("_{}", &result[..]);

src/librustc_trans/save/mod.rs

@@ -1119,7 +1119,7 @@ impl<'l, 'tcx, 'v> Visitor<'v> for DxrVisitor<'l, 'tcx> {
                         let glob_map = glob_map.as_ref().unwrap();
                         if glob_map.contains_key(&item.id) {
                             for n in glob_map.get(&item.id).unwrap() {
-                                if name_string.len() > 0 {
+                                if !name_string.is_empty() {
                                     name_string.push_str(", ");
                                 }
                                 name_string.push_str(n.as_str());

src/librustc_trans/trans/_match.rs

@@ -1112,7 +1112,7 @@ fn compile_submatch_continue<'a, 'p, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
     let mut kind = NoBranch;
     let mut test_val = val;
     debug!("test_val={}", bcx.val_to_string(test_val));
-    if opts.len() > 0 {
+    if !opts.is_empty() {
         match opts[0] {
             ConstantValue(..) | ConstantRange(..) => {
                 test_val = load_if_immediate(bcx, val, left_ty);

src/librustc_trans/trans/base.rs

@@ -2392,7 +2392,7 @@ pub fn get_item_val(ccx: &CrateContext, id: ast::NodeId) -> ValueRef {
                     ccx.sess().bug("struct variant kind unexpected in get_item_val")
                 }
             };
-            assert!(args.len() != 0);
+            assert!(!args.is_empty());
             let ty = ty::node_id_to_type(ccx.tcx(), id);
             let parent = ccx.tcx().map.get_parent(id);
             let enm = ccx.tcx().map.expect_item(parent);

src/librustc_trans/trans/callee.rs

@@ -184,7 +184,7 @@ fn trans<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, expr: &ast::Expr)
                                                     bcx.fcx.param_substs);
 
                 // Nullary variants are not callable
-                assert!(vinfo.args.len() > 0);
+                assert!(!vinfo.args.is_empty());
 
                 Callee {
                     bcx: bcx,
@@ -495,7 +495,7 @@ pub fn trans_fn_ref_with_substs<'a, 'tcx>(
 
         match map_node {
             ast_map::NodeVariant(v) => match v.node.kind {
-                ast::TupleVariantKind(ref args) => args.len() > 0,
+                ast::TupleVariantKind(ref args) => !args.is_empty(),
                 _ => false
             },
             ast_map::NodeStructCtor(_) => true,

src/librustc_trans/trans/consts.rs

@@ -781,7 +781,7 @@ fn const_expr_unadjusted<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                     let vinfo = ty::enum_variant_with_id(cx.tcx(),
                                                          enum_did,
                                                          variant_did);
-                    if vinfo.args.len() > 0 {
+                    if !vinfo.args.is_empty() {
                         // N-ary variant.
                         expr::trans_def_fn_unadjusted(cx, e, def, param_substs).val
                     } else {

src/librustc_trans/trans/debuginfo.rs

@@ -532,7 +532,7 @@ impl<'tcx> TypeMap<'tcx> {
             // Maybe check that there is no self type here.
 
             let tps = substs.types.get_slice(subst::TypeSpace);
-            if tps.len() > 0 {
+            if !tps.is_empty() {
                 output.push('<');
 
                 for &type_parameter in tps {
@@ -1102,7 +1102,7 @@ pub fn get_cleanup_debug_loc_for_ast_node<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
         if let Ok(code_snippet) = code_snippet {
             let bytes = code_snippet.as_bytes();
 
-            if bytes.len() > 0 && &bytes[bytes.len()-1..] == b"}" {
+            if !bytes.is_empty() && &bytes[bytes.len()-1..] == b"}" {
                 cleanup_span = Span {
                     lo: node_span.hi - codemap::BytePos(1),
                     hi: node_span.hi,
@@ -3834,7 +3834,7 @@ fn push_debuginfo_type_name<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
             output.push_str("fn(");
 
             let sig = ty::erase_late_bound_regions(cx.tcx(), sig);
-            if sig.inputs.len() > 0 {
+            if !sig.inputs.is_empty() {
                 for &parameter_type in &sig.inputs {
                     push_debuginfo_type_name(cx, parameter_type, true, output);
                     output.push_str(", ");
@@ -3844,7 +3844,7 @@ fn push_debuginfo_type_name<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
             }
 
             if sig.variadic {
-                if sig.inputs.len() > 0 {
+                if !sig.inputs.is_empty() {
                     output.push_str(", ...");
                 } else {
                     output.push_str("...");

src/librustc_trans/trans/expr.rs

@@ -1135,7 +1135,7 @@ fn trans_def_dps_unadjusted<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
     match def {
         def::DefVariant(tid, vid, _) => {
             let variant_info = ty::enum_variant_with_id(bcx.tcx(), tid, vid);
-            if variant_info.args.len() > 0 {
+            if !variant_info.args.is_empty() {
                 // N-ary variant.
                 let llfn = callee::trans_fn_ref(bcx.ccx(), vid,
                                                 ExprId(ref_expr.id),

src/librustc_typeck/astconv.rs

@@ -2025,7 +2025,7 @@ fn compute_object_lifetime_bound<'tcx>(
             "only a single explicit lifetime bound is permitted");
     }
 
-    if explicit_region_bounds.len() != 0 {
+    if !explicit_region_bounds.is_empty() {
         // Explicitly specified region bound. Use that.
         let r = explicit_region_bounds[0];
         return ast_region_to_region(tcx, r);
@@ -2130,11 +2130,11 @@ pub fn partition_bounds<'a>(tcx: &ty::ctxt,
                                                      &mut builtin_bounds) {
                             let segments = &b.trait_ref.path.segments;
                             let parameters = &segments[segments.len() - 1].parameters;
-                            if parameters.types().len() > 0 {
+                            if !parameters.types().is_empty() {
                                 check_type_argument_count(tcx, b.trait_ref.path.span,
                                                           parameters.types().len(), 0, 0);
                             }
-                            if parameters.lifetimes().len() > 0 {
+                            if !parameters.lifetimes().is_empty() {
                                 report_lifetime_number_error(tcx, b.trait_ref.path.span,
                                                              parameters.lifetimes().len(), 0);
                             }

src/librustc_typeck/check/method/suggest.rs

@@ -67,7 +67,7 @@ pub fn report_error<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                 }
             }
 
-            if static_sources.len() > 0 {
+            if !static_sources.is_empty() {
                 fcx.tcx().sess.fileline_note(
                     span,
                     "found defined static methods, maybe a `self` is missing?");
@@ -200,7 +200,7 @@ fn suggest_traits_to_import<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
         })
         .collect::<Vec<_>>();
 
-    if candidates.len() > 0 {
+    if !candidates.is_empty() {
         // sort from most relevant to least relevant
         candidates.sort_by(|a, b| a.cmp(b).reverse());
         candidates.dedup();

src/librustc_typeck/check/mod.rs

@@ -4258,7 +4258,7 @@ pub fn instantiate_path<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     //
     // The first step then is to categorize the segments appropriately.
 
-    assert!(segments.len() >= 1);
+    assert!(!segments.is_empty());
 
     let mut ufcs_method = None;
     let mut segment_spaces: Vec<_>;
@@ -4480,7 +4480,7 @@ pub fn instantiate_path<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
             }
         }
 
-        if data.bindings.len() > 0 {
+        if !data.bindings.is_empty() {
             span_err!(fcx.tcx().sess, data.bindings[0].span, E0182,
                       "unexpected binding of associated item in expression path \
                        (only allowed in type paths)");

src/librustc_typeck/check/wf.rs

@@ -174,7 +174,7 @@ impl<'ccx, 'tcx> CheckTypeWellFormedVisitor<'ccx, 'tcx> {
                 }
 
                 // For DST, all intermediate types must be sized.
-                if variant.fields.len() > 0 {
+                if !variant.fields.is_empty() {
                     for field in variant.fields.init() {
                         fcx.register_builtin_bound(
                             field.ty,
@@ -658,7 +658,7 @@ fn enum_variants<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     enum_def.variants.iter()
         .map(|variant| {
             match variant.node.kind {
-                ast::TupleVariantKind(ref args) if args.len() > 0 => {
+                ast::TupleVariantKind(ref args) if !args.is_empty() => {
                     let ctor_ty = ty::node_id_to_type(fcx.tcx(), variant.node.id);
 
                     // the regions in the argument types come from the

src/librustc_typeck/collect.rs

@@ -576,7 +576,7 @@ fn get_enum_variant_types<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
         // Nullary enum constructors get turned into constants; n-ary enum
         // constructors get turned into functions.
         let result_ty = match variant.node.kind {
-            ast::TupleVariantKind(ref args) if args.len() > 0 => {
+            ast::TupleVariantKind(ref args) if !args.is_empty() => {
                 let rs = ExplicitRscope;
                 let input_tys: Vec<_> = args.iter().map(|va| icx.to_ty(&rs, &*va.ty)).collect();
                 ty::mk_ctor_fn(tcx, variant_def_id, &input_tys, enum_scheme.ty)

src/librustdoc/clean/mod.rs

@@ -712,7 +712,7 @@ impl<'tcx> Clean<Option<Vec<TyParamBound>>> for subst::Substs<'tcx> {
             trait_: t.clean(cx),
             lifetimes: vec![]
         }, ast::TraitBoundModifier::None)));
-        if v.len() > 0 {Some(v)} else {None}
+        if !v.is_empty() {Some(v)} else {None}
     }
 }
 

src/librustdoc/html/format.rs

@@ -104,8 +104,8 @@ impl fmt::Display for clean::Generics {
             try!(write!(f, "{}", *life));
         }
 
-        if self.type_params.len() > 0 {
+        if !self.type_params.is_empty() {
-            if self.lifetimes.len() > 0 {
+            if !self.lifetimes.is_empty() {
                 try!(f.write_str(", "));
             }
             for (i, tp) in self.type_params.iter().enumerate() {
@@ -114,7 +114,7 @@ impl fmt::Display for clean::Generics {
                 }
                 try!(f.write_str(&tp.name));
 
-                if tp.bounds.len() > 0 {
+                if !tp.bounds.is_empty() {
                     try!(write!(f, ": {}", TyParamBounds(&tp.bounds)));
                 }
 
@@ -175,7 +175,7 @@ impl fmt::Display for clean::Lifetime {
 
 impl fmt::Display for clean::PolyTrait {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        if self.lifetimes.len() > 0 {
+        if !self.lifetimes.is_empty() {
             try!(f.write_str("for<"));
             for (i, lt) in self.lifetimes.iter().enumerate() {
                 if i > 0 {
@@ -212,7 +212,7 @@ impl fmt::Display for clean::PathParameters {
             clean::PathParameters::AngleBracketed {
                 ref lifetimes, ref types, ref bindings
             } => {
-                if lifetimes.len() > 0 || types.len() > 0 || bindings.len() > 0 {
+                if !lifetimes.is_empty() || !types.is_empty() || !bindings.is_empty() {
                     try!(f.write_str("<"));
                     let mut comma = false;
                     for lifetime in lifetimes {
@@ -541,7 +541,7 @@ impl fmt::Display for clean::Arguments {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         for (i, input) in self.values.iter().enumerate() {
             if i > 0 { try!(write!(f, ", ")); }
-            if input.name.len() > 0 {
+            if !input.name.is_empty() {
                 try!(write!(f, "{}: ", input.name));
             }
             try!(write!(f, "{}", input.type_));
@@ -585,8 +585,8 @@ impl<'a> fmt::Display for Method<'a> {
             }
         }
         for (i, input) in d.inputs.values.iter().enumerate() {
-            if i > 0 || args.len() > 0 { args.push_str(", "); }
+            if i > 0 || !args.is_empty() { args.push_str(", "); }
-            if input.name.len() > 0 {
+            if !input.name.is_empty() {
                 args.push_str(&format!("{}: ", input.name));
             }
             args.push_str(&format!("{}", input.type_));
@@ -734,7 +734,7 @@ impl<'a> fmt::Display for ConciseStability<'a> {
                 };
                 write!(f, "<a class='stability {lvl}' title='{lvl}{colon}{reason}'></a>",
                        lvl = Escape(&*lvl),
-                       colon = if stability.reason.len() > 0 { ": " } else { "" },
+                       colon = if !stability.reason.is_empty() { ": " } else { "" },
                        reason = Escape(&*stability.reason))
             }
             None => {

src/librustdoc/html/render.rs

@@ -973,7 +973,7 @@ impl DocFolder for Cache {
         // Keep track of the fully qualified path for this item.
         let pushed = if item.name.is_some() {
             let n = item.name.as_ref().unwrap();
-            if n.len() > 0 {
+            if !n.is_empty() {
                 self.stack.push(n.to_string());
                 true
             } else { false }
@@ -1208,7 +1208,7 @@ impl Context {
 
             let mut title = cx.current.connect("::");
             if pushname {
-                if title.len() > 0 {
+                if !title.is_empty() {
                     title.push_str("::");
                 }
                 title.push_str(it.name.as_ref().unwrap());
@@ -1736,8 +1736,8 @@ fn item_function(w: &mut fmt::Formatter, it: &clean::Item,
 fn item_trait(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
               t: &clean::Trait) -> fmt::Result {
     let mut bounds = String::new();
-    if t.bounds.len() > 0 {
+    if !t.bounds.is_empty() {
-        if bounds.len() > 0 {
+        if !bounds.is_empty() {
             bounds.push(' ');
         }
         bounds.push_str(": ");
@@ -1775,7 +1775,7 @@ fn item_trait(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
             try!(render_method(w, t, MethodLink::Anchor));
             try!(write!(w, ";\n"));
         }
-        if types.len() > 0 && required.len() > 0 {
+        if !types.is_empty() && !required.is_empty() {
             try!(w.write_str("\n"));
         }
         for m in &required {
@@ -1783,7 +1783,7 @@ fn item_trait(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
             try!(render_method(w, m, MethodLink::Anchor));
             try!(write!(w, ";\n"));
         }
-        if required.len() > 0 && provided.len() > 0 {
+        if !required.is_empty() && !provided.is_empty() {
             try!(w.write_str("\n"));
         }
         for m in &provided {
@@ -1810,7 +1810,7 @@ fn item_trait(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
         Ok(())
     }
 
-    if types.len() > 0 {
+    if !types.is_empty() {
         try!(write!(w, "
             <h2 id='associated-types'>Associated Types</h2>
             <div class='methods'>
@@ -1822,7 +1822,7 @@ fn item_trait(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
     }
 
     // Output the documentation for each function individually
-    if required.len() > 0 {
+    if !required.is_empty() {
         try!(write!(w, "
             <h2 id='required-methods'>Required Methods</h2>
             <div class='methods'>
@@ -1832,7 +1832,7 @@ fn item_trait(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
         }
         try!(write!(w, "</div>"));
     }
-    if provided.len() > 0 {
+    if !provided.is_empty() {
         try!(write!(w, "
             <h2 id='provided-methods'>Provided Methods</h2>
             <div class='methods'>
@@ -1882,7 +1882,7 @@ fn assoc_type(w: &mut fmt::Formatter, it: &clean::Item,
               default: &Option<clean::Type>)
               -> fmt::Result {
     try!(write!(w, "type {}", it.name.as_ref().unwrap()));
-    if bounds.len() > 0 {
+    if !bounds.is_empty() {
         try!(write!(w, ": {}", TyParamBounds(bounds)))
     }
     if let Some(ref default) = *default {
@@ -2031,7 +2031,7 @@ fn item_enum(w: &mut fmt::Formatter, it: &clean::Item,
     try!(write!(w, "</pre>"));
 
     try!(document(w, it));
-    if e.variants.len() > 0 {
+    if !e.variants.is_empty() {
         try!(write!(w, "<h2 class='variants'>Variants</h2>\n<table>"));
         for variant in &e.variants {
             try!(write!(w, "<tr><td id='variant.{name}'>{stab}<code>{name}</code></td><td>",
@@ -2170,13 +2170,13 @@ fn render_methods(w: &mut fmt::Formatter, it: &clean::Item) -> fmt::Result {
     };
     let (non_trait, traits): (Vec<_>, _) = v.into_iter()
         .partition(|i| i.impl_.trait_.is_none());
-    if non_trait.len() > 0 {
+    if !non_trait.is_empty() {
         try!(write!(w, "<h2 id='methods'>Methods</h2>"));
         for i in &non_trait {
             try!(render_impl(w, i, MethodLink::Anchor));
         }
     }
-    if traits.len() > 0 {
+    if !traits.is_empty() {
         try!(write!(w, "<h2 id='implementations'>Trait \
                           Implementations</h2>"));
         let (derived, manual): (Vec<_>, _) = traits.into_iter()
@@ -2185,7 +2185,7 @@ fn render_methods(w: &mut fmt::Formatter, it: &clean::Item) -> fmt::Result {
             let did = i.trait_did().unwrap();
             try!(render_impl(w, i, MethodLink::GotoSource(did)));
         }
-        if derived.len() > 0 {
+        if !derived.is_empty() {
             try!(write!(w, "<h3 id='derived_implementations'>\
                 Derived Implementations \
             </h3>"));

src/librustdoc/passes.rs

@@ -294,7 +294,7 @@ pub fn collapse_docs(krate: clean::Crate) -> plugins::PluginResult {
                 &clean::NameValue(ref x, _) if "doc" == *x => false,
                 _ => true
             }).cloned().collect();
-            if docstr.len() > 0 {
+            if !docstr.is_empty() {
                 a.push(clean::NameValue("doc".to_string(), docstr));
             }
             i.attrs = a;
@@ -350,7 +350,7 @@ pub fn unindent(s: &str) -> String {
         }
     });
 
-    if lines.len() >= 1 {
+    if !lines.is_empty() {
         let mut unindented = vec![ lines[0].trim().to_string() ];
         unindented.push_all(&lines.tail().iter().map(|&line| {
             if line.chars().all(|c| c.is_whitespace()) {

src/libstd/io/mod.rs

@@ -349,7 +349,7 @@ pub trait Write {
     /// This function will return the first error that `write` returns.
     #[stable(feature = "rust1", since = "1.0.0")]
     fn write_all(&mut self, mut buf: &[u8]) -> Result<()> {
-        while buf.len() > 0 {
+        while !buf.is_empty() {
             match self.write(buf) {
                 Ok(0) => return Err(Error::new(ErrorKind::WriteZero,
                                                "failed to write whole buffer")),

src/libstd/path.rs

@@ -218,7 +218,7 @@ mod platform {
                     return Some(DeviceNS(u8_slice_as_os_str(slice)));
                 }
                 match parse_two_comps(path, is_sep_byte) {
-                    Some((server, share)) if server.len() > 0 && share.len() > 0 => {
+                    Some((server, share)) if !server.is_empty() && !share.is_empty() => {
                         // \\server\share
                         return Some(UNC(u8_slice_as_os_str(server),
                                         u8_slice_as_os_str(share)));
@@ -401,7 +401,7 @@ unsafe fn u8_slice_as_os_str(s: &[u8]) -> &OsStr {
 /// Says whether the first byte after the prefix is a separator.
 fn has_physical_root(s: &[u8], prefix: Option<Prefix>) -> bool {
     let path = if let Some(p) = prefix { &s[p.len()..] } else { s };
-    path.len() > 0 && is_sep_byte(path[0])
+    !path.is_empty() && is_sep_byte(path[0])
 }
 
 // basic workhorse for splitting stem and extension
@@ -810,7 +810,7 @@ impl<'a> Iterator for Components<'a> {
                 State::StartDir => {
                     self.front = State::Body;
                     if self.has_physical_root {
-                        debug_assert!(self.path.len() > 0);
+                        debug_assert!(!self.path.is_empty());
                         self.path = &self.path[1..];
                         return Some(Component::RootDir)
                     } else if let Some(p) = self.prefix {
@@ -818,7 +818,7 @@ impl<'a> Iterator for Components<'a> {
                             return Some(Component::RootDir)
                         }
                     } else if self.include_cur_dir() {
-                        debug_assert!(self.path.len() > 0);
+                        debug_assert!(!self.path.is_empty());
                         self.path = &self.path[1..];
                         return Some(Component::CurDir)
                     }
@@ -1055,7 +1055,7 @@ impl PathBuf {
         };
 
         let extension = extension.as_ref();
-        if os_str_as_u8_slice(extension).len() > 0 {
+        if !os_str_as_u8_slice(extension).is_empty() {
             stem.push(".");
             stem.push(extension);
         }

src/libstd/rand/reader.rs

@@ -51,7 +51,7 @@ impl<R: Read> Rng for ReaderRng<R> {
         unsafe { *(bytes.as_ptr() as *const u64) }
     }
     fn fill_bytes(&mut self, mut v: &mut [u8]) {
-        while v.len() > 0 {
+        while !v.is_empty() {
             let t = v;
             match self.reader.read(t) {
                 Ok(0) => panic!("ReaderRng.fill_bytes: EOF reached"),

src/libstd/sys/common/backtrace.rs

@@ -76,7 +76,7 @@ pub fn demangle(writer: &mut Write, s: &str) -> io::Result<()> {
         try!(writer.write_all(s.as_bytes()));
     } else {
         let mut first = true;
-        while inner.len() > 0 {
+        while !inner.is_empty() {
             if !first {
                 try!(writer.write_all(b"::"));
             } else {
@@ -89,7 +89,7 @@ pub fn demangle(writer: &mut Write, s: &str) -> io::Result<()> {
             let i: usize = inner[.. (inner.len() - rest.len())].parse().unwrap();
             inner = &rest[i..];
             rest = &rest[..i];
-            while rest.len() > 0 {
+            while !rest.is_empty() {
                 if rest.starts_with("$") {
                     macro_rules! demangle {
                         ($($pat:expr, => $demangled:expr),*) => ({

src/libsyntax/ast.rs

@@ -429,14 +429,14 @@ pub struct Generics {
 }
 
 impl Generics {
-    pub fn is_parameterized(&self) -> bool {
-        self.lifetimes.len() + self.ty_params.len() > 0
-    }
     pub fn is_lt_parameterized(&self) -> bool {
-        self.lifetimes.len() > 0
+        !self.lifetimes.is_empty()
     }
     pub fn is_type_parameterized(&self) -> bool {
-        self.ty_params.len() > 0
+        !self.ty_params.is_empty()
+    }
+    pub fn is_parameterized(&self) -> bool {
+        self.is_lt_parameterized() || self.is_type_parameterized()
     }
 }
 

src/libsyntax/codemap.rs

@@ -360,7 +360,7 @@ impl Encodable for FileMap {
                     // store the length
                     try! { s.emit_u32(lines.len() as u32) };
 
-                    if lines.len() > 0 {
+                    if !lines.is_empty() {
                         // In order to preserve some space, we exploit the fact that
                         // the lines list is sorted and individual lines are
                         // probably not that long. Because of that we can store lines
@@ -569,7 +569,7 @@ impl CodeMap {
         // accidentally overflowing into the next filemap in case the last byte
         // of span is also the last byte of filemap, which leads to incorrect
         // results from CodeMap.span_to_*.
-        if src.len() > 0 && !src.ends_with("\n") {
+        if !src.is_empty() && !src.ends_with("\n") {
             src.push('\n');
         }
 
@@ -808,7 +808,7 @@ impl CodeMap {
         loop {
             let lines = files[a].lines.borrow();
             let lines = lines;
-            if lines.len() > 0 {
+            if !lines.is_empty() {
                 break;
             }
             if a == 0 {

src/libsyntax/ext/asm.rs

@@ -90,7 +90,7 @@ pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                       p.token != token::Colon &&
                       p.token != token::ModSep {
 
-                    if outputs.len() != 0 {
+                    if !outputs.is_empty() {
                         panictry!(p.eat(&token::Comma));
                     }
 
@@ -130,7 +130,7 @@ pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                       p.token != token::Colon &&
                       p.token != token::ModSep {
 
-                    if inputs.len() != 0 {
+                    if !inputs.is_empty() {
                         panictry!(p.eat(&token::Comma));
                     }
 
@@ -154,7 +154,7 @@ pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                       p.token != token::Colon &&
                       p.token != token::ModSep {
 
-                    if clobs.len() != 0 {
+                    if !clobs.is_empty() {
                         panictry!(p.eat(&token::Comma));
                     }
 

src/libsyntax/ext/base.rs

@@ -774,7 +774,7 @@ pub fn check_zero_tts(cx: &ExtCtxt,
                       sp: Span,
                       tts: &[ast::TokenTree],
                       name: &str) {
-    if tts.len() != 0 {
+    if !tts.is_empty() {
         cx.span_err(sp, &format!("{} takes no arguments", name));
     }
 }

src/libsyntax/ext/deriving/clone.rs

@@ -89,7 +89,7 @@ fn cs_clone(
         }
     }
 
-    if all_fields.len() >= 1 && all_fields[0].name.is_none() {
+    if !all_fields.is_empty() && all_fields[0].name.is_none() {
         // enum-like
         let subcalls = all_fields.iter().map(subcall).collect();
         let path = cx.expr_path(ctor_path);

src/libsyntax/ext/deriving/encodable.rs

@@ -240,7 +240,7 @@ fn encodable_substructure(cx: &mut ExtCtxt, trait_span: Span,
             let encoder = cx.expr_ident(trait_span, blkarg);
             let emit_variant_arg = cx.ident_of("emit_enum_variant_arg");
             let mut stmts = Vec::new();
-            if fields.len() > 0 {
+            if !fields.is_empty() {
                 let last = fields.len() - 1;
                 for (i, &FieldInfo { ref self_, span, .. }) in fields.iter().enumerate() {
                     let enc = cx.expr_method_call(span, self_.clone(),

src/libsyntax/ext/deriving/generic/mod.rs

@@ -912,7 +912,7 @@ impl<'a> MethodDef<'a> {
         }
 
         // transpose raw_fields
-        let fields = if raw_fields.len() > 0 {
+        let fields = if !raw_fields.is_empty() {
             let mut raw_fields = raw_fields.into_iter().map(|v| v.into_iter());
             let first_field = raw_fields.next().unwrap();
             let mut other_fields: Vec<vec::IntoIter<(Span, Option<Ident>, P<Expr>)>>

src/libsyntax/ext/format.rs

@@ -688,7 +688,7 @@ pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt, sp: Span,
     loop {
         match parser.next() {
             Some(piece) => {
-                if parser.errors.len() > 0 { break }
+                if !parser.errors.is_empty() { break }
                 cx.verify_piece(&piece);
                 match cx.trans_piece(&piece) {
                     Some(piece) => {

src/libsyntax/ext/mtwt.rs

@@ -266,7 +266,7 @@ pub fn outer_mark(ctxt: SyntaxContext) -> Mrk {
 /// Push a name... unless it matches the one on top, in which
 /// case pop and discard (so two of the same marks cancel)
 fn xor_push(marks: &mut Vec<Mrk>, mark: Mrk) {
-    if (marks.len() > 0) && (*marks.last().unwrap() == mark) {
+    if (!marks.is_empty()) && (*marks.last().unwrap() == mark) {
         marks.pop().unwrap();
     } else {
         marks.push(mark);

src/libsyntax/ext/tt/macro_parser.rs

@@ -457,7 +457,7 @@ pub fn parse(sess: &ParseSess,
                 return Failure(sp, "unexpected end of macro invocation".to_string());
             }
         } else {
-            if (bb_eis.len() > 0 && next_eis.len() > 0)
+            if (!bb_eis.is_empty() && !next_eis.is_empty())
                 || bb_eis.len() > 1 {
                 let nts = bb_eis.iter().map(|ei| {
                     match ei.top_elts.get_tt(ei.idx) {
@@ -475,9 +475,9 @@ pub fn parse(sess: &ParseSess,
             } else if bb_eis.is_empty() && next_eis.is_empty() {
                 return Failure(sp, format!("no rules expected the token `{}`",
                             pprust::token_to_string(&tok)).to_string());
-            } else if next_eis.len() > 0 {
+            } else if !next_eis.is_empty() {
                 /* Now process the next token */
-                while next_eis.len() > 0 {
+                while !next_eis.is_empty() {
                     cur_eis.push(next_eis.pop().unwrap());
                 }
                 rdr.next_token();
@@ -504,7 +504,7 @@ pub fn parse(sess: &ParseSess,
             }
         }
 
-        assert!(cur_eis.len() > 0);
+        assert!(!cur_eis.is_empty());
     }
 }
 

src/libsyntax/parse/lexer/comments.rs

@@ -63,7 +63,7 @@ pub fn strip_doc_comment_decoration(comment: &str) -> String {
         let mut i = 0;
         let mut j = lines.len();
         // first line of all-stars should be omitted
-        if lines.len() > 0 &&
+        if !lines.is_empty() &&
                 lines[0].chars().all(|c| c == '*') {
             i += 1;
         }
@@ -294,7 +294,7 @@ fn read_block_comment(rdr: &mut StringReader,
                 }
             }
         }
-        if curr_line.len() != 0 {
+        if !curr_line.is_empty() {
             trim_whitespace_prefix_and_push_line(&mut lines,
                                                  curr_line,
                                                  col);

src/libsyntax/parse/parser.rs

@@ -2254,7 +2254,7 @@ impl<'a> Parser<'a> {
                         (Vec::new(), Vec::new(), Vec::new())
                     };
 
-                    if bindings.len() > 0 {
+                    if !bindings.is_empty() {
                         let last_span = self.last_span;
                         self.span_err(last_span, "type bindings are only permitted on trait paths");
                     }
@@ -3024,7 +3024,7 @@ impl<'a> Parser<'a> {
                 try!(self.expect(&token::Comma));
 
                 if self.token == token::CloseDelim(token::Bracket)
-                        && (before_slice || after.len() != 0) {
+                        && (before_slice || !after.is_empty()) {
                     break
                 }
             }

src/libsyntax/print/pp.rs

@@ -565,7 +565,7 @@ impl<'a> Printer<'a> {
           Token::End => {
             debug!("print End -> pop End");
             let print_stack = &mut self.print_stack;
-            assert!((print_stack.len() != 0));
+            assert!((!print_stack.is_empty()));
             print_stack.pop().unwrap();
             Ok(())
           }

src/libsyntax/print/pprust.rs

@@ -1656,7 +1656,7 @@ impl<'a> State<'a> {
         try!(self.print_expr(&*args[0]));
         try!(word(&mut self.s, "."));
         try!(self.print_ident(ident.node));
-        if tys.len() > 0 {
+        if !tys.is_empty() {
             try!(word(&mut self.s, "::<"));
             try!(self.commasep(Inconsistent, tys,
                                |s, ty| s.print_type(&**ty)));
@@ -1956,7 +1956,7 @@ impl<'a> State<'a> {
                     options.push("intel");
                 }
 
-                if options.len() > 0 {
+                if !options.is_empty() {
                     try!(space(&mut self.s));
                     try!(self.word_space(":"));
                     try!(self.commasep(Inconsistent, &*options,
@@ -2214,7 +2214,7 @@ impl<'a> State<'a> {
                     },
                     |f| f.node.pat.span));
                 if etc {
-                    if fields.len() != 0 { try!(self.word_space(",")); }
+                    if !fields.is_empty() { try!(self.word_space(",")); }
                     try!(word(&mut self.s, ".."));
                 }
                 try!(space(&mut self.s));
@@ -2727,7 +2727,7 @@ impl<'a> State<'a> {
                        opt_explicit_self: Option<&ast::ExplicitSelf_>)
                        -> io::Result<()> {
         try!(self.ibox(indent_unit));
-        if generics.lifetimes.len() > 0 || generics.ty_params.len() > 0 {
+        if !generics.lifetimes.is_empty() || !generics.ty_params.is_empty() {
             try!(word(&mut self.s, "for"));
             try!(self.print_generics(generics));
         }

src/libterm/terminfo/parm.rs

@@ -123,7 +123,7 @@ pub fn expand(cap: &[u8], params: &[Param], vars: &mut Variables)
             Percent => {
                 match cur {
                     '%' => { output.push(c); state = Nothing },
-                    'c' => if stack.len() > 0 {
+                    'c' => if !stack.is_empty() {
                         match stack.pop().unwrap() {
                             // if c is 0, use 0200 (128) for ncurses compatibility
                             Number(c) => {
@@ -141,7 +141,7 @@ pub fn expand(cap: &[u8], params: &[Param], vars: &mut Variables)
                     'g' => state = GetVar,
                     '\'' => state = CharConstant,
                     '{' => state = IntConstant(0),
-                    'l' => if stack.len() > 0 {
+                    'l' => if !stack.is_empty() {
                         match stack.pop().unwrap() {
                             Words(s) => stack.push(Number(s.len() as isize)),
                             _        => return Err("a non-str was used with %l".to_string())
@@ -231,14 +231,14 @@ pub fn expand(cap: &[u8], params: &[Param], vars: &mut Variables)
                             _ => return Err("non-numbers on stack with logical or".to_string())
                         }
                     } else { return Err("stack is empty".to_string()) },
-                    '!' => if stack.len() > 0 {
+                    '!' => if !stack.is_empty() {
                         match stack.pop().unwrap() {
                             Number(0) => stack.push(Number(1)),
                             Number(_) => stack.push(Number(0)),
                             _ => return Err("non-number on stack with logical not".to_string())
                         }
                     } else { return Err("stack is empty".to_string()) },
-                    '~' => if stack.len() > 0 {
+                    '~' => if !stack.is_empty() {
                         match stack.pop().unwrap() {
                             Number(x) => stack.push(Number(!x)),
                             _         => return Err("non-number on stack with %~".to_string())
@@ -253,7 +253,7 @@ pub fn expand(cap: &[u8], params: &[Param], vars: &mut Variables)
                     },
 
                     // printf-style support for %doxXs
-                    'd'|'o'|'x'|'X'|'s' => if stack.len() > 0 {
+                    'd'|'o'|'x'|'X'|'s' => if !stack.is_empty() {
                         let flags = Flags::new();
                         let res = format(stack.pop().unwrap(), FormatOp::from_char(cur), flags);
                         if res.is_err() { return res }
@@ -278,7 +278,7 @@ pub fn expand(cap: &[u8], params: &[Param], vars: &mut Variables)
 
                     // conditionals
                     '?' => (),
-                    't' => if stack.len() > 0 {
+                    't' => if !stack.is_empty() {
                         match stack.pop().unwrap() {
                             Number(0) => state = SeekIfElse(0),
                             Number(_) => (),
@@ -303,12 +303,12 @@ pub fn expand(cap: &[u8], params: &[Param], vars: &mut Variables)
             },
             SetVar => {
                 if cur >= 'A' && cur <= 'Z' {
-                    if stack.len() > 0 {
+                    if !stack.is_empty() {
                         let idx = (cur as u8) - b'A';
                         vars.sta[idx as usize] = stack.pop().unwrap();
                     } else { return Err("stack is empty".to_string()) }
                 } else if cur >= 'a' && cur <= 'z' {
-                    if stack.len() > 0 {
+                    if !stack.is_empty() {
                         let idx = (cur as u8) - b'a';
                         vars.dyn[idx as usize] = stack.pop().unwrap();
                     } else { return Err("stack is empty".to_string()) }
@@ -352,7 +352,7 @@ pub fn expand(cap: &[u8], params: &[Param], vars: &mut Variables)
             FormatPattern(ref mut flags, ref mut fstate) => {
                 old_state = Nothing;
                 match (*fstate, cur) {
-                    (_,'d')|(_,'o')|(_,'x')|(_,'X')|(_,'s') => if stack.len() > 0 {
+                    (_,'d')|(_,'o')|(_,'x')|(_,'X')|(_,'s') => if !stack.is_empty() {
                         let res = format(stack.pop().unwrap(), FormatOp::from_char(cur), *flags);
                         if res.is_err() { return res }
                         output.push_all(&res.unwrap());

src/libtest/lib.rs

@@ -373,7 +373,7 @@ pub fn parse_opts(args: &[String]) -> Option<OptRes> {
 
     if matches.opt_present("h") { usage(&args[0]); return None; }
 
-    let filter = if matches.free.len() > 0 {
+    let filter = if !matches.free.is_empty() {
         Some(matches.free[0].clone())
     } else {
         None
@@ -588,14 +588,14 @@ impl<T: Write> ConsoleTestState<T> {
         let mut fail_out = String::new();
         for &(ref f, ref stdout) in &self.failures {
             failures.push(f.name.to_string());
-            if stdout.len() > 0 {
+            if !stdout.is_empty() {
                 fail_out.push_str(&format!("---- {} stdout ----\n\t", f.name));
                 let output = String::from_utf8_lossy(stdout);
                 fail_out.push_str(&output);
                 fail_out.push_str("\n");
             }
         }
-        if fail_out.len() > 0 {
+        if !fail_out.is_empty() {
             try!(self.write_plain("\n"));
             try!(self.write_plain(&fail_out));
         }

src/libtest/stats.rs

@@ -196,17 +196,17 @@ impl<T: Float + FromPrimitive> Stats<T> for [T] {
     }
 
     fn min(&self) -> T {
-        assert!(self.len() != 0);
+        assert!(!self.is_empty());
         self.iter().fold(self[0], |p, q| p.min(*q))
     }
 
     fn max(&self) -> T {
-        assert!(self.len() != 0);
+        assert!(!self.is_empty());
         self.iter().fold(self[0], |p, q| p.max(*q))
     }
 
     fn mean(&self) -> T {
-        assert!(self.len() != 0);
+        assert!(!self.is_empty());
         self.sum() / FromPrimitive::from_usize(self.len()).unwrap()
     }
 
@@ -284,7 +284,7 @@ impl<T: Float + FromPrimitive> Stats<T> for [T] {
 // linear interpolation. If samples are not sorted, return nonsensical value.
 fn percentile_of_sorted<T: Float + FromPrimitive>(sorted_samples: &[T],
                                                              pct: T) -> T {
-    assert!(sorted_samples.len() != 0);
+    assert!(!sorted_samples.is_empty());
     if sorted_samples.len() == 1 {
         return sorted_samples[0];
     }

src/test/bench/core-std.rs

@@ -43,7 +43,7 @@ fn maybe_run_test<F>(argv: &[String], name: String, test: F) where F: FnOnce() {
 
     if env::var_os("RUST_BENCH").is_some() {
         run_test = true
-    } else if argv.len() > 0 {
+    } else if !argv.is_empty() {
         run_test = argv.iter().any(|x| x == &"all".to_string()) || argv.iter().any(|x| x == &name)
     }
 
@@ -60,7 +60,7 @@ fn shift_push() {
     let mut v1 = repeat(1).take(30000).collect::<Vec<_>>();
     let mut v2 = Vec::new();
 
-    while v1.len() > 0 {
+    while !v1.is_empty() {
         v2.push(v1.remove(0));
     }
 }

src/test/bench/shootout-k-nucleotide.rs

@@ -252,7 +252,7 @@ fn generate_frequencies(mut input: &[u8], frame: usize) -> Table {
     }
     frequencies.lookup(code, BumpCallback);
 
-    while input.len() != 0 && input[0] != ('>' as u8) {
+    while !input.is_empty() && input[0] != ('>' as u8) {
         code = code.rotate(input[0], frame);
         frequencies.lookup(code, BumpCallback);
         input = &input[1..];

src/test/run-pass/issue-12860.rs

@@ -30,7 +30,7 @@ fn main() {
     let middle = XYZ{x: 0, y: 0, z: 0};
     border.insert(middle);
 
-    while border.len() > 0 && connected.len() < 10000 {
+    while !border.is_empty() && connected.len() < 10000 {
         let choice = *(border.iter().next().unwrap());
         border.remove(&choice);
         connected.insert(choice);

src/test/run-pass/issue-3556.rs

@@ -44,5 +44,5 @@ pub fn main()
                     "foo".to_string(), "foo".to_string(), "foo".to_string(),
                     "foo".to_string());
     let v = format!("{:?}", u);    // this is the line that causes the seg fault
-    assert!(v.len() > 0);
+    assert!(!v.is_empty());
 }