Auto merge of #66887 - dtolnay:rollup-uxowp8d, r=Centril

Rollup of 4 pull requests

Successful merges:

 - #66818 (Format libstd/os with rustfmt)
 - #66819 (Format libstd/sys with rustfmt)
 - #66820 (Format libstd with rustfmt)
 - #66847 (Allow any identifier as format arg name)

Failed merges:

r? @ghost

Author: bors

src/libfmt_macros/lib.rs

@@ -442,20 +442,9 @@ impl<'a> Parser<'a> {
             Some(ArgumentIs(i))
         } else {
             match self.cur.peek() {
-                Some(&(_, c)) if c.is_alphabetic() => {
+                Some(&(_, c)) if rustc_lexer::is_id_start(c) => {
                     Some(ArgumentNamed(Symbol::intern(self.word())))
                 }
-                Some(&(pos, c)) if c == '_' => {
-                    let invalid_name = self.string(pos);
-                    self.err_with_note(format!("invalid argument name `{}`", invalid_name),
-                                       "invalid argument name",
-                                       "argument names cannot start with an underscore",
-                                        self.to_span_index(pos).to(
-                                            self.to_span_index(pos + invalid_name.len())
-                                        ),
-                                        );
-                    Some(ArgumentNamed(Symbol::intern(invalid_name)))
-                },
 
                 // This is an `ArgumentNext`.
                 // Record the fact and do the resolution after parsing the
@@ -611,22 +600,34 @@ impl<'a> Parser<'a> {
     /// Rust identifier, except that it can't start with `_` character.
     fn word(&mut self) -> &'a str {
         let start = match self.cur.peek() {
-            Some(&(pos, c)) if c != '_' && rustc_lexer::is_id_start(c) => {
+            Some(&(pos, c)) if rustc_lexer::is_id_start(c) => {
                 self.cur.next();
                 pos
             }
             _ => {
-                return &self.input[..0];
+                return "";
             }
         };
+        let mut end = None;
         while let Some(&(pos, c)) = self.cur.peek() {
             if rustc_lexer::is_id_continue(c) {
                 self.cur.next();
             } else {
-                return &self.input[start..pos];
+                end = Some(pos);
+                break;
             }
         }
-        &self.input[start..self.input.len()]
+        let end = end.unwrap_or(self.input.len());
+        let word = &self.input[start..end];
+        if word == "_" {
+            self.err_with_note(
+                "invalid argument name `_`",
+                "invalid argument name",
+                "argument name cannot be a single underscore",
+                self.to_span_index(start).to(self.to_span_index(end)),
+            );
+        }
+        word
     }
 
     /// Optionally parses an integer at the current position. This doesn't deal

src/libstd/ascii.rs

@@ -17,7 +17,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use core::ascii::{EscapeDefault, escape_default};
+pub use core::ascii::{escape_default, EscapeDefault};
 
 /// Extension methods for ASCII-subset only operations.
 ///

src/libstd/backtrace.rs

@@ -95,10 +95,10 @@ use crate::env;
 use crate::fmt;
 use crate::sync::atomic::{AtomicUsize, Ordering::SeqCst};
 use crate::sync::Mutex;
-use crate::sys_common::backtrace::{output_filename, lock};
+use crate::sys_common::backtrace::{lock, output_filename};
 use crate::vec::Vec;
-use backtrace_rs as backtrace;
 use backtrace::BytesOrWideString;
+use backtrace_rs as backtrace;
 
 /// A captured OS thread stack backtrace.
 ///

src/libstd/benches/hash/map.rs

@@ -1,7 +1,7 @@
 #![cfg(test)]
 
-use test::Bencher;
 use std::collections::HashMap;
+use test::Bencher;
 
 #[bench]
 fn new_drop(b: &mut Bencher) {

src/libstd/collections/mod.rs

@@ -413,20 +413,20 @@
 #[doc(hidden)]
 pub use crate::ops::Bound;
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use alloc_crate::collections::{BinaryHeap, BTreeMap, BTreeSet};
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use alloc_crate::collections::{LinkedList, VecDeque};
-#[stable(feature = "rust1", since = "1.0.0")]
 pub use alloc_crate::collections::{binary_heap, btree_map, btree_set};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use alloc_crate::collections::{linked_list, vec_deque};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use alloc_crate::collections::{BTreeMap, BTreeSet, BinaryHeap};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use alloc_crate::collections::{LinkedList, VecDeque};
 
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::hash_map::HashMap;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::hash_set::HashSet;
 
-#[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
+#[unstable(feature = "try_reserve", reason = "new API", issue = "48043")]
 pub use alloc_crate::collections::TryReserveError;
 
 mod hash;