diff --git a/src/expr.rs b/src/expr.rs
index c849d58efae..4f58c19c8fd 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -216,7 +216,7 @@ impl Rewrite for ast::Block {
                 // Extract comment between unsafe and block start.
                 let trimmed = &snippet[6..open_pos].trim();
 
-                if trimmed.len() > 0 {
+                if !trimmed.is_empty() {
                     // 9 = "unsafe  {".len(), 7 = "unsafe ".len()
                     format!("unsafe {} ", rewrite_comment(trimmed, true, width - 9, offset + 7))
                 } else {
@@ -733,7 +733,7 @@ fn rewrite_call(context: &RewriteContext,
     let callee_str = try_opt!(callee.rewrite(context, max_callee_width, offset));
     debug!("rewrite_call, callee_str: `{}`", callee_str);
 
-    if args.len() == 0 {
+    if args.is_empty() {
         return Some(format!("{}()", callee_str));
     }
 
@@ -799,7 +799,7 @@ fn rewrite_struct_lit<'a>(context: &RewriteContext,
                           offset: usize)
                           -> Option<String> {
     debug!("rewrite_struct_lit: width {}, offset {}", width, offset);
-    assert!(fields.len() > 0 || base.is_some());
+    assert!(!fields.is_empty() || base.is_some());
 
     enum StructLitField<'a> {
         Regular(&'a ast::Field),
@@ -1008,7 +1008,7 @@ fn rewrite_unary_op(context: &RewriteContext,
         ast::UnOp::UnNeg => "-",
     };
 
-    let subexpr = try_opt!(expr.rewrite(context, width - operator_str.len(), offset));
+    let subexpr = try_opt!(expr.rewrite(context, try_opt!(width.checked_sub(operator_str.len())), offset));
 
     Some(format!("{}{}", operator_str, subexpr))
 }
diff --git a/src/imports.rs b/src/imports.rs
index a0ba88de6f2..cf9e174f9b0 100644
--- a/src/imports.rs
+++ b/src/imports.rs
@@ -51,13 +51,13 @@ impl Rewrite for ast::ViewPath {
 
 fn rewrite_single_use_list(path_str: String, vpi: ast::PathListItem) -> String {
     if let ast::PathListItem_::PathListIdent{ name, .. } = vpi.node {
-        if path_str.len() == 0 {
+        if path_str.is_empty() {
             name.to_string()
         } else {
             format!("{}::{}", path_str, name)
         }
     } else {
-        if path_str.len() != 0 {
+        if !path_str.is_empty() {
             path_str
         } else {
             // This catches the import: use {self}, which is a compiler error, so we just
@@ -86,7 +86,7 @@ pub fn rewrite_use_list(width: usize,
     }
 
     // 2 = ::
-    let path_separation_w = if path_str.len() > 0 {
+    let path_separation_w = if !path_str.is_empty() {
         2
     } else {
         0
@@ -151,7 +151,7 @@ pub fn rewrite_use_list(width: usize,
 
     let list = write_list(&items[first_index..], &fmt);
 
-    Some(if path_str.len() == 0 {
+    Some(if path_str.is_empty() {
             format!("{{{}}}", list)
         } else {
             format!("{}::{{{}}}", path_str, list)
diff --git a/src/items.rs b/src/items.rs
index e853dc90c30..e39638ba427 100644
--- a/src/items.rs
+++ b/src/items.rs
@@ -178,7 +178,7 @@ impl<'a> FmtVisitor<'a> {
         result.push(')');
 
         // Return type.
-        if ret_str.len() > 0 {
+        if !ret_str.is_empty() {
             // If we've already gone multi-line, or the return type would push
             // over the max width, then put the return type on a new line.
             if result.contains("\n") ||
@@ -200,11 +200,11 @@ impl<'a> FmtVisitor<'a> {
 
             // Comment between return type and the end of the decl.
             let snippet_lo = fd.output.span().hi;
-            if where_clause.predicates.len() == 0 {
+            if where_clause.predicates.is_empty() {
                 let snippet_hi = span.hi;
                 let snippet = self.snippet(codemap::mk_sp(snippet_lo, snippet_hi));
                 let snippet = snippet.trim();
-                if snippet.len() > 0 {
+                if !snippet.is_empty() {
                     result.push(' ');
                     result.push_str(snippet);
                 }
@@ -342,7 +342,7 @@ impl<'a> FmtVisitor<'a> {
     fn newline_for_brace(&self, where_clause: &ast::WhereClause) -> bool {
         match self.config.fn_brace_style {
             BraceStyle::AlwaysNextLine => true,
-            BraceStyle::SameLineWhere if where_clause.predicates.len() > 0 => true,
+            BraceStyle::SameLineWhere if !where_clause.predicates.is_empty() => true,
             _ => false,
         }
     }
@@ -399,7 +399,7 @@ impl<'a> FmtVisitor<'a> {
 
                 let mut result = String::new();
 
-                if types.len() > 0 {
+                if !types.is_empty() {
                     let items = itemize_list(self.codemap,
                                              types.iter(),
                                              ")",
@@ -482,7 +482,7 @@ impl<'a> FmtVisitor<'a> {
         let header_str = self.format_header(item_name, ident, vis);
         result.push_str(&header_str);
 
-        if struct_def.fields.len() == 0 {
+        if struct_def.fields.is_empty() {
             result.push(';');
             return result;
         }
@@ -513,7 +513,7 @@ impl<'a> FmtVisitor<'a> {
                                  terminator,
                                  |field| {
                                      // Include attributes and doc comments, if present
-                                     if field.node.attrs.len() > 0 {
+                                     if !field.node.attrs.is_empty() {
                                          field.node.attrs[0].span.lo
                                      } else {
                                          field.span.lo
@@ -602,7 +602,7 @@ impl<'a> FmtVisitor<'a> {
                        -> String {
         let mut result = self.rewrite_generics(generics, offset, span);
 
-        if generics.where_clause.predicates.len() > 0 || result.contains('\n') {
+        if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
             result.push_str(&self.rewrite_where_clause(&generics.where_clause,
                                                        self.config,
                                                        self.block_indent,
@@ -635,7 +635,7 @@ impl<'a> FmtVisitor<'a> {
 
         let indent = self.block_indent + self.config.tab_spaces;
         let mut attr_str = self.rewrite_attrs(&field.node.attrs, indent);
-        if attr_str.len() > 0 {
+        if !attr_str.is_empty() {
             attr_str.push('\n');
             attr_str.push_str(&make_indent(indent));
         }
@@ -651,7 +651,7 @@ impl<'a> FmtVisitor<'a> {
         // there is a where clause at all.
         let lifetimes: &[_] = &generics.lifetimes;
         let tys: &[_] = &generics.ty_params;
-        if lifetimes.len() + tys.len() == 0 {
+        if lifetimes.is_empty() && tys.is_empty() {
             return String::new();
         }
 
@@ -671,7 +671,7 @@ impl<'a> FmtVisitor<'a> {
 
         // Extract comments between generics.
         let lt_spans = lifetimes.iter().map(|l| {
-            let hi = if l.bounds.len() == 0 {
+            let hi = if l.bounds.is_empty() {
                 l.lifetime.span.hi
             } else {
                 l.bounds[l.bounds.len() - 1].span.hi
@@ -705,7 +705,7 @@ impl<'a> FmtVisitor<'a> {
                             indent: usize,
                             span_end: BytePos)
                             -> String {
-        if where_clause.predicates.len() == 0 {
+        if where_clause.predicates.is_empty() {
             return String::new();
         }
 
@@ -833,7 +833,7 @@ fn span_for_ty_param(ty: &ast::TyParam) -> Span {
     if let Some(ref def) = ty.default {
         return codemap::mk_sp(lo, def.span.hi);
     }
-    if ty.bounds.len() == 0 {
+    if ty.bounds.is_empty() {
         return ty.span;
     }
     let hi = match ty.bounds[ty.bounds.len() - 1] {
diff --git a/src/lists.rs b/src/lists.rs
index dd1a489b847..12c8d14574a 100644
--- a/src/lists.rs
+++ b/src/lists.rs
@@ -92,7 +92,7 @@ impl ListItem {
 // FIXME: this has grown into a monstrosity
 // TODO: add unit tests
 pub fn write_list<'b>(items: &[ListItem], formatting: &ListFormatting<'b>) -> String {
-    if items.len() == 0 {
+    if items.is_empty() {
         return String::new();
     }
 
@@ -270,7 +270,7 @@ impl<'a, T, I, F1, F2, F3> Iterator for ListItems<'a, I, F1, F2, F3>
                                                                           (self.get_lo)(&item)))
                                           .unwrap();
             let pre_snippet = pre_snippet.trim();
-            let pre_comment = if pre_snippet.len() > 0 {
+            let pre_comment = if !pre_snippet.is_empty() {
                 Some(pre_snippet.to_owned())
             } else {
                 None
@@ -328,7 +328,7 @@ impl<'a, T, I, F1, F2, F3> Iterator for ListItems<'a, I, F1, F2, F3>
                 post_snippet = post_snippet[..(post_snippet.len() - 1)].trim_matches(white_space);
             }
 
-            let post_comment = if post_snippet.len() > 0 {
+            let post_comment = if !post_snippet.is_empty() {
                 Some(post_snippet.to_owned())
             } else {
                 None
diff --git a/src/types.rs b/src/types.rs
index 8792580d872..5969c1e1018 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -190,9 +190,9 @@ fn rewrite_segment(segment: &ast::PathSegment,
     let offset = offset + ident_len;
 
     let params = match segment.parameters {
-        ast::PathParameters::AngleBracketedParameters(ref data) if data.lifetimes.len() > 0 ||
-                                                                   data.types.len() > 0 ||
-                                                                   data.bindings.len() > 0 => {
+        ast::PathParameters::AngleBracketedParameters(ref data) if !data.lifetimes.is_empty() ||
+                                                                   !data.types.is_empty() ||
+                                                                   !data.bindings.is_empty() => {
             let param_list = data.lifetimes.iter()
                                            .map(SegmentParam::LifeTime)
                                            .chain(data.types.iter()
@@ -267,7 +267,7 @@ impl Rewrite for ast::WherePredicate {
                                                                           ref bounded_ty,
                                                                           ref bounds,
                                                                           ..}) => {
-                    if bound_lifetimes.len() > 0 {
+                    if !bound_lifetimes.is_empty() {
                         let lifetime_str = bound_lifetimes.iter().map(|lt| {
                                            lt.rewrite(context, width, offset).unwrap()
                                        }).collect::<Vec<_>>().join(", ");
@@ -319,7 +319,7 @@ impl Rewrite for ast::WherePredicate {
 
 impl Rewrite for ast::LifetimeDef {
     fn rewrite(&self, _: &RewriteContext, _: usize, _: usize) -> Option<String> {
-        if self.bounds.len() == 0 {
+        if self.bounds.is_empty() {
             Some(pprust::lifetime_to_string(&self.lifetime))
         } else {
             Some(format!("{}: {}",
@@ -351,7 +351,7 @@ impl Rewrite for ast::TyParam {
     fn rewrite(&self, context: &RewriteContext, width: usize, offset: usize) -> Option<String> {
         let mut result = String::with_capacity(128);
         result.push_str(&self.ident.to_string());
-        if self.bounds.len() > 0 {
+        if !self.bounds.is_empty() {
             result.push_str(": ");
 
             let bounds = self.bounds.iter().map(|ty_bound| {
@@ -372,7 +372,7 @@ impl Rewrite for ast::TyParam {
 // FIXME: this assumes everything will fit on one line
 impl Rewrite for ast::PolyTraitRef {
     fn rewrite(&self, context: &RewriteContext, width: usize, offset: usize) -> Option<String> {
-        if self.bound_lifetimes.len() > 0 {
+        if !self.bound_lifetimes.is_empty() {
             let lifetime_str = self.bound_lifetimes.iter().map(|lt| {
                 lt.rewrite(context, width, offset).unwrap()
             }).collect::<Vec<_>>().join(", ");
diff --git a/src/visitor.rs b/src/visitor.rs
index 2489a8c1a9d..fccd619d403 100644
--- a/src/visitor.rs
+++ b/src/visitor.rs
@@ -267,7 +267,7 @@ impl<'a> FmtVisitor<'a> {
 
     // Returns true if we should skip the following item.
     pub fn visit_attrs(&mut self, attrs: &[ast::Attribute]) -> bool {
-        if attrs.len() == 0 {
+        if attrs.is_empty() {
             return false;
         }
 
@@ -299,7 +299,7 @@ impl<'a> FmtVisitor<'a> {
                 // with the usual doc comment token.
                 let multi_line = a_str.starts_with("//") && comment.matches('\n').count() > 1;
                 let comment = comment.trim();
-                if comment.len() > 0 {
+                if !comment.is_empty() {
                     result.push_str(&indent);
                     result.push_str(comment);
                     result.push('\n');
@@ -355,7 +355,7 @@ impl<'a> FmtVisitor<'a> {
         };
         // 1 = ";"
         match vp.rewrite(&context, self.config.max_width - offset - 1, offset) {
-            Some(ref s) if s.len() == 0 => {
+            Some(ref s) if s.is_empty() => {
                 // Format up to last newline
                 let prev_span = codemap::mk_sp(self.last_pos, span.lo);
                 let span_end = match self.snippet(prev_span).rfind('\n') {