Use .next() instead of .nth(0) on iterators.

src/librustc/mir/mod.rs

@@ -1446,7 +1446,7 @@ impl<'tcx> Debug for TerminatorKind<'tcx> {
         match successor_count {
             0 => Ok(()),
 
-            1 => write!(fmt, " -> {:?}", self.successors().nth(0).unwrap()),
+            1 => write!(fmt, " -> {:?}", self.successors().next().unwrap()),
 
             _ => {
                 write!(fmt, " -> [")?;

src/librustc/ty/util.rs

@@ -357,7 +357,7 @@ impl<'tcx> TyCtxt<'tcx> {
         let mut dtor_did = None;
         let ty = self.type_of(adt_did);
         self.for_each_relevant_impl(drop_trait, ty, |impl_did| {
-            if let Some(item) = self.associated_items(impl_did).in_definition_order().nth(0) {
+            if let Some(item) = self.associated_items(impl_did).in_definition_order().next() {
                 if validate(self, impl_did).is_ok() {
                     dtor_did = Some(item.def_id);
                 }

src/librustc_mir/transform/simplify.rs

@@ -230,7 +230,7 @@ impl<'a, 'tcx> CfgSimplifier<'a, 'tcx> {
         };
 
         let first_succ = {
-            if let Some(&first_succ) = terminator.successors().nth(0) {
+            if let Some(&first_succ) = terminator.successors().next() {
                 if terminator.successors().all(|s| *s == first_succ) {
                     let count = terminator.successors().count();
                     self.pred_count[first_succ] -= (count - 1) as u32;

src/librustc_mir/util/elaborate_drops.rs

@@ -549,7 +549,7 @@ where
         debug!("destructor_call_block({:?}, {:?})", self, succ);
         let tcx = self.tcx();
         let drop_trait = tcx.lang_items().drop_trait().unwrap();
-        let drop_fn = tcx.associated_items(drop_trait).in_definition_order().nth(0).unwrap();
+        let drop_fn = tcx.associated_items(drop_trait).in_definition_order().next().unwrap();
         let ty = self.place_ty(self.place);
         let substs = tcx.mk_substs_trait(ty, &[]);
 

src/librustc_mir_build/hair/pattern/_match.rs

@@ -1000,7 +1000,7 @@ impl<'tcx> Constructor<'tcx> {
                         PatKind::Leaf { subpatterns }
                     }
                 }
-                ty::Ref(..) => PatKind::Deref { subpattern: subpatterns.nth(0).unwrap() },
+                ty::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
                 ty::Slice(_) | ty::Array(..) => bug!("bad slice pattern {:?} {:?}", self, ty),
                 _ => PatKind::Wild,
             },

src/librustc_parse/parser/expr.rs

@@ -955,7 +955,7 @@ impl<'a> Parser<'a> {
         };
         let kind = if es.len() == 1 && !trailing_comma {
             // `(e)` is parenthesized `e`.
-            ExprKind::Paren(es.into_iter().nth(0).unwrap())
+            ExprKind::Paren(es.into_iter().next().unwrap())
         } else {
             // `(e,)` is a tuple with only one field, `e`.
             ExprKind::Tup(es)

src/librustc_parse/parser/pat.rs

@@ -479,7 +479,7 @@ impl<'a> Parser<'a> {
         // Here, `(pat,)` is a tuple pattern.
         // For backward compatibility, `(..)` is a tuple pattern as well.
         Ok(if fields.len() == 1 && !(trailing_comma || fields[0].is_rest()) {
-            PatKind::Paren(fields.into_iter().nth(0).unwrap())
+            PatKind::Paren(fields.into_iter().next().unwrap())
         } else {
             PatKind::Tuple(fields)
         })

src/librustc_parse/parser/ty.rs

@@ -198,7 +198,7 @@ impl<'a> Parser<'a> {
         })?;
 
         if ts.len() == 1 && !trailing {
-            let ty = ts.into_iter().nth(0).unwrap().into_inner();
+            let ty = ts.into_iter().next().unwrap().into_inner();
             let maybe_bounds = allow_plus == AllowPlus::Yes && self.token.is_like_plus();
             match ty.kind {
                 // `(TY_BOUND_NOPAREN) + BOUND + ...`.

src/librustc_span/source_map.rs

@@ -620,7 +620,7 @@ impl SourceMap {
     /// if no character could be found or if an error occurred while retrieving the code snippet.
     pub fn span_extend_to_prev_char(&self, sp: Span, c: char) -> Span {
         if let Ok(prev_source) = self.span_to_prev_source(sp) {
-            let prev_source = prev_source.rsplit(c).nth(0).unwrap_or("").trim_start();
+            let prev_source = prev_source.rsplit(c).next().unwrap_or("").trim_start();
             if !prev_source.is_empty() && !prev_source.contains('\n') {
                 return sp.with_lo(BytePos(sp.lo().0 - prev_source.len() as u32));
             }
@@ -640,7 +640,7 @@ impl SourceMap {
         for ws in &[" ", "\t", "\n"] {
             let pat = pat.to_owned() + ws;
             if let Ok(prev_source) = self.span_to_prev_source(sp) {
-                let prev_source = prev_source.rsplit(&pat).nth(0).unwrap_or("").trim_start();
+                let prev_source = prev_source.rsplit(&pat).next().unwrap_or("").trim_start();
                 if !prev_source.is_empty() && (!prev_source.contains('\n') || accept_newlines) {
                     return sp.with_lo(BytePos(sp.lo().0 - prev_source.len() as u32));
                 }
@@ -655,7 +655,7 @@ impl SourceMap {
     pub fn span_until_char(&self, sp: Span, c: char) -> Span {
         match self.span_to_snippet(sp) {
             Ok(snippet) => {
-                let snippet = snippet.split(c).nth(0).unwrap_or("").trim_end();
+                let snippet = snippet.split(c).next().unwrap_or("").trim_end();
                 if !snippet.is_empty() && !snippet.contains('\n') {
                     sp.with_hi(BytePos(sp.lo().0 + snippet.len() as u32))
                 } else {

src/librustc_typeck/check/closure.rs

@@ -675,7 +675,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // The `Future` trait has only one associted item, `Output`,
         // so check that this is what we see.
         let output_assoc_item =
-            self.tcx.associated_items(future_trait).in_definition_order().nth(0).unwrap().def_id;
+            self.tcx.associated_items(future_trait).in_definition_order().next().unwrap().def_id;
         if output_assoc_item != predicate.projection_ty.item_def_id {
             span_bug!(
                 cause_span,

src/librustc_typeck/check/mod.rs

@@ -5244,7 +5244,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .tcx
                     .associated_items(future_trait)
                     .in_definition_order()
-                    .nth(0)
+                    .next()
                     .unwrap()
                     .def_id;
                 let predicate =

src/tools/unicode-table-generator/src/main.rs

@@ -147,7 +147,7 @@ fn main() {
         eprintln!("Must provide path to write unicode tables to");
         eprintln!(
             "e.g. {} src/libcore/unicode/unicode_data.rs",
-            std::env::args().nth(0).unwrap_or_default()
+            std::env::args().next().unwrap_or_default()
         );
         std::process::exit(1);
     });