Use <stdin> when emitting stdin as filename (#4298)

# Conflicts:
#	src/config/file_lines.rs
#	src/rustfmt/main.rs
#	src/test/mod.rs

src/config/file_lines.rs

@@ -39,7 +39,7 @@ impl fmt::Display for FileName {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             FileName::Real(p) => write!(f, "{}", p.to_str().unwrap()),
-            FileName::Stdin => write!(f, "stdin"),
+            FileName::Stdin => write!(f, "<stdin>"),
         }
     }
 }

src/test/mod.rs

@@ -466,9 +466,9 @@ fn stdin_formatting_smoke_test() {
     }
 
     #[cfg(not(windows))]
-    assert_eq!(buf, "stdin:\n\nfn main() {}\n".as_bytes());
+    assert_eq!(buf, "<stdin>:\n\nfn main() {}\n".as_bytes());
     #[cfg(windows)]
-    assert_eq!(buf, "stdin:\n\nfn main() {}\r\n".as_bytes());
+    assert_eq!(buf, "<stdin>:\n\nfn main() {}\r\n".as_bytes());
 }
 
 #[test]
@@ -1013,5 +1013,5 @@ fn verify_check_l_works_with_stdin() {
         .wait_with_output()
         .expect("Failed to wait on rustfmt child");
     assert!(output.status.success());
-    assert_eq!(std::str::from_utf8(&output.stdout).unwrap(), "stdin\n");
+    assert_eq!(std::str::from_utf8(&output.stdout).unwrap(), "<stdin>\n");
 }

tests/writemode/target/stdin.json

@@ -1 +1 @@
-[{"name":"stdin","mismatches":[{"original_begin_line":1,"original_end_line":6,"expected_begin_line":1,"expected_end_line":2,"original":"\nfn\n some( )\n{\n}\nfn main () {}\n","expected":"fn some() {}\nfn main() {}\n"}]}]
+[{"name":"<stdin>","mismatches":[{"original_begin_line":1,"original_end_line":6,"expected_begin_line":1,"expected_end_line":2,"original":"\nfn\n some( )\n{\n}\nfn main () {}\n","expected":"fn some() {}\nfn main() {}\n"}]}]

tests/writemode/target/stdin.xml

@@ -1,2 +1,2 @@
-<?xml version="1.0" encoding="utf-8"?>
-<checkstyle version="4.3"><file name="stdin"><error line="1" severity="warning" message="Should be `fn some() {}`" /><error line="2" severity="warning" message="Should be `fn main() {}`" /></file></checkstyle>
+<?xml version="1.0" encoding="utf-8"?>
+<checkstyle version="4.3"><file name="<stdin>"><error line="1" severity="warning" message="Should be `fn some() {}`" /><error line="2" severity="warning" message="Should be `fn main() {}`" /></file></checkstyle>