Add checkup in tail function and return Option type

src/compiletest/compiletest.rs

@@ -90,7 +90,7 @@ pub fn parse_config(args: Vec<String> ) -> Config {
 
     assert!(!args.is_empty());
     let argv0 = args[0].clone();
-    let args_ = args.tail();
+    let args_ = args.tail().unwrap();
     if args[1] == "-h" || args[1] == "--help" {
         let message = format!("Usage: {} [OPTIONS] [TESTNAME...]", argv0);
         println!("{}", getopts::usage(&message, &groups));

src/libcollections/slice.rs

@@ -462,7 +462,7 @@ impl<T> [T] {
     /// Returns all but the first element of a slice.
     #[unstable(feature = "collections", reason = "likely to be renamed")]
     #[inline]
-    pub fn tail(&self) -> &[T] {
+    pub fn tail(&self) -> Option<&[T]> {
         core_slice::SliceExt::tail(self)
     }
 

src/libcore/slice.rs

@@ -78,7 +78,7 @@ pub trait SliceExt {
     fn chunks<'a>(&'a self, size: usize) -> Chunks<'a, Self::Item>;
     fn get<'a>(&'a self, index: usize) -> Option<&'a Self::Item>;
     fn first<'a>(&'a self) -> Option<&'a Self::Item>;
-    fn tail<'a>(&'a self) -> &'a [Self::Item];
+    fn tail<'a>(&'a self) -> Option<&'a [Self::Item]>;
     fn init<'a>(&'a self) -> &'a [Self::Item];
     fn last<'a>(&'a self) -> Option<&'a Self::Item>;
     unsafe fn get_unchecked<'a>(&'a self, index: usize) -> &'a Self::Item;
@@ -207,7 +207,9 @@ impl<T> SliceExt for [T] {
     }
 
     #[inline]
-    fn tail(&self) -> &[T] { &self[1..] }
+    fn tail(&self) -> Option<&[T]> {
+        if self.len() == 0 { None } else { Some(&self[1..]) }
+    }
 
     #[inline]
     fn init(&self) -> &[T] {

src/librustc/middle/check_match.rs

@@ -693,12 +693,12 @@ fn is_useful(cx: &MatchCheckCtxt,
             Some(constructor) => {
                 let matrix = rows.iter().filter_map(|r| {
                     if pat_is_binding_or_wild(&cx.tcx.def_map, raw_pat(r[0])) {
-                        Some(r.tail().to_vec())
+                        Some(r.tail().unwrap().to_vec())
                     } else {
                         None
                     }
                 }).collect();
-                match is_useful(cx, &matrix, v.tail(), witness) {
+                match is_useful(cx, &matrix, v.tail().unwrap(), witness) {
                     UsefulWithWitness(pats) => {
                         let arity = constructor_arity(cx, &constructor, left_ty);
                         let wild_pats: Vec<_> = repeat(DUMMY_WILD_PAT).take(arity).collect();

src/librustdoc/lib.rs

@@ -192,7 +192,7 @@ pub fn usage(argv0: &str) {
 }
 
 pub fn main_args(args: &[String]) -> isize {
-    let matches = match getopts::getopts(args.tail(), &opts()) {
+    let matches = match getopts::getopts(args.tail().unwrap(), &opts()) {
         Ok(m) => m,
         Err(err) => {
             println!("{}", err);

src/librustdoc/passes.rs

@@ -352,7 +352,7 @@ pub fn unindent(s: &str) -> String {
 
     if lines.len() >= 1 {
         let mut unindented = vec![ lines[0].trim().to_string() ];
-        unindented.push_all(&lines.tail().iter().map(|&line| {
+        unindented.push_all(&lines.tail().unwrap().iter().map(|&line| {
             if line.chars().all(|c| c.is_whitespace()) {
                 line.to_string()
             } else {

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

@@ -1081,7 +1081,7 @@ impl<'a> MethodDef<'a> {
                     subpats.push(p);
                     idents
                 };
-                for self_arg_name in self_arg_names.tail() {
+                for self_arg_name in self_arg_names.tail().unwrap() {
                     let (p, idents) = mk_self_pat(cx, &self_arg_name[..]);
                     subpats.push(p);
                     self_pats_idents.push(idents);

src/libtest/lib.rs

@@ -364,7 +364,7 @@ Test Attributes:
 
 // Parses command line arguments into test options
 pub fn parse_opts(args: &[String]) -> Option<OptRes> {
-    let args_ = args.tail();
+    let args_ = args.tail().unwrap();
     let matches =
         match getopts::getopts(args_, &optgroups()) {
           Ok(m) => m,