Remove IterDelimited.

itertools has `with_position` which does the same thing.

Cargo.lock

@@ -3471,6 +3471,7 @@ dependencies = [
 name = "rustc_ast_pretty"
 version = "0.0.0"
 dependencies = [
+ "itertools",
  "rustc_ast",
  "rustc_span",
  "thin-vec",

compiler/rustc_ast_pretty/Cargo.toml

@@ -5,6 +5,7 @@ edition = "2021"
 
 [dependencies]
 # tidy-alphabetical-start
+itertools = "0.11"
 rustc_ast = { path = "../rustc_ast" }
 rustc_span = { path = "../rustc_span" }
 thin-vec = "0.2.12"

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1,4 +1,3 @@
-mod delimited;
 mod expr;
 mod item;
 
@@ -23,8 +22,6 @@ use rustc_span::{BytePos, FileName, Span, DUMMY_SP};
 use std::borrow::Cow;
 use thin_vec::ThinVec;
 
-pub use self::delimited::IterDelimited;
-
 pub enum MacHeader<'a> {
     Path(&'a ast::Path),
     Keyword(&'static str),

compiler/rustc_ast_pretty/src/pprust/state/delimited.rs

@@ -1,41 +0,0 @@
-use std::iter::Peekable;
-use std::mem;
-use std::ops::Deref;
-
-pub struct Delimited<I: Iterator> {
-    is_first: bool,
-    iter: Peekable<I>,
-}
-
-pub trait IterDelimited: Iterator + Sized {
-    fn delimited(self) -> Delimited<Self> {
-        Delimited { is_first: true, iter: self.peekable() }
-    }
-}
-
-impl<I: Iterator> IterDelimited for I {}
-
-pub struct IteratorItem<T> {
-    value: T,
-    pub is_first: bool,
-    pub is_last: bool,
-}
-
-impl<I: Iterator> Iterator for Delimited<I> {
-    type Item = IteratorItem<I::Item>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        let value = self.iter.next()?;
-        let is_first = mem::replace(&mut self.is_first, false);
-        let is_last = self.iter.peek().is_none();
-        Some(IteratorItem { value, is_first, is_last })
-    }
-}
-
-impl<T> Deref for IteratorItem<T> {
-    type Target = T;
-
-    fn deref(&self) -> &Self::Target {
-        &self.value
-    }
-}

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -1,6 +1,6 @@
 use crate::pp::Breaks::Inconsistent;
-use crate::pprust::state::{AnnNode, IterDelimited, PrintState, State, INDENT_UNIT};
+use crate::pprust::state::{AnnNode, PrintState, State, INDENT_UNIT};
-
+use itertools::{Itertools, Position};
 use rustc_ast::ptr::P;
 use rustc_ast::token;
 use rustc_ast::util::literal::escape_byte_str_symbol;
@@ -149,10 +149,12 @@ impl<'a> State<'a> {
             return;
         }
         self.cbox(0);
-        for field in fields.iter().delimited() {
+        for (pos, field) in fields.iter().with_position() {
+            let is_first = matches!(pos, Position::First | Position::Only);
+            let is_last = matches!(pos, Position::Last | Position::Only);
             self.maybe_print_comment(field.span.hi());
             self.print_outer_attributes(&field.attrs);
-            if field.is_first {
+            if is_first {
                 self.space_if_not_bol();
             }
             if !field.is_shorthand {
@@ -160,7 +162,7 @@ impl<'a> State<'a> {
                 self.word_nbsp(":");
             }
             self.print_expr(&field.expr);
-            if !field.is_last || has_rest {
+            if !is_last || has_rest {
                 self.word_space(",");
             } else {
                 self.trailing_comma_or_space();

compiler/rustc_ast_pretty/src/pprust/state/item.rs

@@ -1,8 +1,8 @@
 use crate::pp::Breaks::Inconsistent;
-use crate::pprust::state::delimited::IterDelimited;
 use crate::pprust::state::{AnnNode, PrintState, State, INDENT_UNIT};
 
 use ast::StaticItem;
+use itertools::{Itertools, Position};
 use rustc_ast as ast;
 use rustc_ast::GenericBound;
 use rustc_ast::ModKind;
@@ -712,9 +712,10 @@ impl<'a> State<'a> {
                     self.word("{");
                     self.zerobreak();
                     self.ibox(0);
-                    for use_tree in items.iter().delimited() {
+                    for (pos, use_tree) in items.iter().with_position() {
+                        let is_last = matches!(pos, Position::Last | Position::Only);
                         self.print_use_tree(&use_tree.0);
-                        if !use_tree.is_last {
+                        if !is_last {
                             self.word(",");
                             if let ast::UseTreeKind::Nested(_) = use_tree.0.kind {
                                 self.hardbreak();