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

4 files changed, 34 insertions, 22 deletions

diff --git a/src/test/ui/fmt/format-string-error.rs b/src/test/ui/fmt/format-string-error.rs
index 691c06a2402..eae4f3cb547 100644
--- a/src/test/ui/fmt/format-string-error.rs
+++ b/src/test/ui/fmt/format-string-error.rs
@@ -6,10 +6,12 @@ fn main() {
     println!("{{}}");
     println!("}");
     //~^ ERROR invalid format string: unmatched `}` found
-    let _ = format!("{_foo}", _foo = 6usize);
-    //~^ ERROR invalid format string: invalid argument name `_foo`
     let _ = format!("{_}", _ = 6usize);
     //~^ ERROR invalid format string: invalid argument name `_`
+    let _ = format!("{a:_}", a = "", _ = 0);
+    //~^ ERROR invalid format string: invalid argument name `_`
+    let _ = format!("{a:._$}", a = "", _ = 0);
+    //~^ ERROR invalid format string: invalid argument name `_`
     let _ = format!("{");
     //~^ ERROR invalid format string: expected `'}'` but string was terminated
     let _ = format!("}");
diff --git a/src/test/ui/fmt/format-string-error.stderr b/src/test/ui/fmt/format-string-error.stderr
index 32119b18774..8b018480fb0 100644
--- a/src/test/ui/fmt/format-string-error.stderr
+++ b/src/test/ui/fmt/format-string-error.stderr
@@ -16,24 +16,32 @@ LL |     println!("}");
    |
    = note: if you intended to print `}`, you can escape it using `}}`
 
-error: invalid format string: invalid argument name `_foo`
+error: invalid format string: invalid argument name `_`
   --> $DIR/format-string-error.rs:9:23
    |
-LL |     let _ = format!("{_foo}", _foo = 6usize);
-   |                       ^^^^ invalid argument name in format string
+LL |     let _ = format!("{_}", _ = 6usize);
+   |                       ^ invalid argument name in format string
    |
-   = note: argument names cannot start with an underscore
+   = note: argument name cannot be a single underscore
 
 error: invalid format string: invalid argument name `_`
-  --> $DIR/format-string-error.rs:11:23
+  --> $DIR/format-string-error.rs:11:25
    |
-LL |     let _ = format!("{_}", _ = 6usize);
-   |                       ^ invalid argument name in format string
+LL |     let _ = format!("{a:_}", a = "", _ = 0);
+   |                         ^ invalid argument name in format string
+   |
+   = note: argument name cannot be a single underscore
+
+error: invalid format string: invalid argument name `_`
+  --> $DIR/format-string-error.rs:13:26
+   |
+LL |     let _ = format!("{a:._$}", a = "", _ = 0);
+   |                          ^ invalid argument name in format string
    |
-   = note: argument names cannot start with an underscore
+   = note: argument name cannot be a single underscore
 
 error: invalid format string: expected `'}'` but string was terminated
-  --> $DIR/format-string-error.rs:13:23
+  --> $DIR/format-string-error.rs:15:23
    |
 LL |     let _ = format!("{");
    |                      -^ expected `'}'` in format string
@@ -43,7 +51,7 @@ LL |     let _ = format!("{");
    = note: if you intended to print `{`, you can escape it using `{{`
 
 error: invalid format string: unmatched `}` found
-  --> $DIR/format-string-error.rs:15:22
+  --> $DIR/format-string-error.rs:17:22
    |
 LL |     let _ = format!("}");
    |                      ^ unmatched `}` in format string
@@ -51,7 +59,7 @@ LL |     let _ = format!("}");
    = note: if you intended to print `}`, you can escape it using `}}`
 
 error: invalid format string: expected `'}'`, found `'\'`
-  --> $DIR/format-string-error.rs:17:23
+  --> $DIR/format-string-error.rs:19:23
    |
 LL |     let _ = format!("{\}");
    |                      -^ expected `}` in format string
@@ -61,7 +69,7 @@ LL |     let _ = format!("{\}");
    = note: if you intended to print `{`, you can escape it using `{{`
 
 error: invalid format string: expected `'}'` but string was terminated
-  --> $DIR/format-string-error.rs:19:35
+  --> $DIR/format-string-error.rs:21:35
    |
 LL |     let _ = format!("\n\n\n{\n\n\n");
    |                            -      ^ expected `'}'` in format string
@@ -71,7 +79,7 @@ LL |     let _ = format!("\n\n\n{\n\n\n");
    = note: if you intended to print `{`, you can escape it using `{{`
 
 error: invalid format string: expected `'}'` but string was terminated
-  --> $DIR/format-string-error.rs:25:3
+  --> $DIR/format-string-error.rs:27:3
    |
 LL |     {"###);
    |     -^ expected `'}'` in format string
@@ -81,7 +89,7 @@ LL |     {"###);
    = note: if you intended to print `{`, you can escape it using `{{`
 
 error: invalid format string: expected `'}'` but string was terminated
-  --> $DIR/format-string-error.rs:33:1
+  --> $DIR/format-string-error.rs:35:1
    |
 LL |     {
    |     - because of this opening brace
@@ -92,7 +100,7 @@ LL | "###);
    = note: if you intended to print `{`, you can escape it using `{{`
 
 error: invalid format string: unmatched `}` found
-  --> $DIR/format-string-error.rs:39:2
+  --> $DIR/format-string-error.rs:41:2
    |
 LL |     }
    |     ^ unmatched `}` in format string
@@ -100,7 +108,7 @@ LL |     }
    = note: if you intended to print `}`, you can escape it using `}}`
 
 error: invalid format string: unmatched `}` found
-  --> $DIR/format-string-error.rs:47:9
+  --> $DIR/format-string-error.rs:49:9
    |
 LL |         }
    |         ^ unmatched `}` in format string
@@ -108,10 +116,10 @@ LL |         }
    = note: if you intended to print `}`, you can escape it using `}}`
 
 error: 3 positional arguments in format string, but there are 2 arguments
-  --> $DIR/format-string-error.rs:51:15
+  --> $DIR/format-string-error.rs:53:15
    |
 LL |     println!("{} {} {}", 1, 2);
    |               ^^ ^^ ^^   -  -
 
-error: aborting due to 13 previous errors
+error: aborting due to 14 previous errors
 
diff --git a/src/test/ui/ifmt.rs b/src/test/ui/ifmt.rs
index 841be20ef86..1a070843cc4 100644
--- a/src/test/ui/ifmt.rs
+++ b/src/test/ui/ifmt.rs
@@ -90,6 +90,7 @@ pub fn main() {
     t!(format!("{foo} {bar}", foo=0, bar=1), "0 1");
     t!(format!("{foo} {1} {bar} {0}", 0, 1, foo=2, bar=3), "2 1 3 0");
     t!(format!("{} {0}", "a"), "a a");
+    t!(format!("{_foo}", _foo = 6usize), "6");
     t!(format!("{foo_bar}", foo_bar=1), "1");
     t!(format!("{}", 5 + 5), "10");
     t!(format!("{:#4}", C), "☃123");
@@ -125,6 +126,7 @@ pub fn main() {
     t!(format!("{:.*}", 4, "aaaaaaaaaaaaaaaaaa"), "aaaa");
     t!(format!("{:.1$}", "aaaaaaaaaaaaaaaaaa", 4), "aaaa");
     t!(format!("{:.a$}", "aaaaaaaaaaaaaaaaaa", a=4), "aaaa");
+    t!(format!("{:._a$}", "aaaaaaaaaaaaaaaaaa", _a=4), "aaaa");
     t!(format!("{:1$}", "a", 4), "a   ");
     t!(format!("{1:0$}", 4, "a"), "a   ");
     t!(format!("{:a$}", "a", a=4), "a   ");
diff --git a/src/test/ui/issues/issue-27033.stderr b/src/test/ui/issues/issue-27033.stderr
index 2d6d2ef41bd..d3f8407f8e2 100644
--- a/src/test/ui/issues/issue-27033.stderr
+++ b/src/test/ui/issues/issue-27033.stderr
@@ -6,8 +6,8 @@ LL |         None @ _ => {}
    | 
   ::: $SRC_DIR/libstd/prelude/v1.rs:LL:COL
    |
-LL | pub use crate::option::Option::{self, Some, None};
-   |                                             ---- the unit variant `None` is defined here
+LL | pub use crate::option::Option::{self, None, Some};
+   |                                       ---- the unit variant `None` is defined here
 
 error[E0530]: match bindings cannot shadow constants
   --> $DIR/issue-27033.rs:8:9