Auto merge of #117928 - nnethercote:rustc_ast_pretty, r=fee1-dead

`rustc_ast_pretty` cleanups

Some improvements I found while looking at this code.

r? `@fee1-dead`

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();
@@ -279,7 +281,7 @@ impl<'a> State<'a> {
         self.print_expr_maybe_paren(expr, parser::PREC_PREFIX)
     }
 
-    pub fn print_expr(&mut self, expr: &ast::Expr) {
+    pub(super) fn print_expr(&mut self, expr: &ast::Expr) {
         self.print_expr_outer_attr_style(expr, true)
     }
 
@@ -679,7 +681,7 @@ impl<'a> State<'a> {
     }
 }
 
-pub fn reconstruct_format_args_template_string(pieces: &[FormatArgsPiece]) -> String {
+fn reconstruct_format_args_template_string(pieces: &[FormatArgsPiece]) -> String {
     let mut template = "\"".to_string();
     for piece in pieces {
         match piece {

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;
@@ -20,7 +20,7 @@ impl<'a> State<'a> {
         }
     }
 
-    pub(crate) fn print_foreign_item(&mut self, item: &ast::ForeignItem) {
+    fn print_foreign_item(&mut self, item: &ast::ForeignItem) {
         let ast::Item { id, span, ident, ref attrs, ref kind, ref vis, tokens: _ } = *item;
         self.ann.pre(self, AnnNode::SubItem(id));
         self.hardbreak_if_not_bol();
@@ -518,7 +518,7 @@ impl<'a> State<'a> {
         }
     }
 
-    pub(crate) fn print_assoc_item(&mut self, item: &ast::AssocItem) {
+    fn print_assoc_item(&mut self, item: &ast::AssocItem) {
         let ast::Item { id, span, ident, ref attrs, ref kind, ref vis, tokens: _ } = *item;
         self.ann.pre(self, AnnNode::SubItem(id));
         self.hardbreak_if_not_bol();
@@ -621,7 +621,7 @@ impl<'a> State<'a> {
         self.print_where_clause_parts(where_clause.has_where_token, &where_clause.predicates);
     }
 
-    pub(crate) fn print_where_clause_parts(
+    fn print_where_clause_parts(
         &mut self,
         has_where_token: bool,
         predicates: &[ast::WherePredicate],
@@ -668,7 +668,7 @@ impl<'a> State<'a> {
         }
     }
 
-    pub fn print_where_bound_predicate(
+    pub(crate) fn print_where_bound_predicate(
         &mut self,
         where_bound_predicate: &ast::WhereBoundPredicate,
     ) {
@@ -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();