Debug print char 0 as '\0' rather than '\u{0}'

Author: dtolnay

alloc/tests/fmt.rs

@@ -69,7 +69,7 @@ fn test_format_macro_interface() {
     t!(format!("{:?}", "true"), "\"true\"");
     t!(format!("{:?}", "foo\nbar"), "\"foo\\nbar\"");
     t!(format!("{:?}", "foo\n\"bar\"\r\n\'baz\'\t\\qux\\"), r#""foo\n\"bar\"\r\n'baz'\t\\qux\\""#);
-    t!(format!("{:?}", "foo\0bar\x01baz\u{7f}q\u{75}x"), r#""foo\u{0}bar\u{1}baz\u{7f}qux""#);
+    t!(format!("{:?}", "foo\0bar\x01baz\u{7f}q\u{75}x"), r#""foo\0bar\u{1}baz\u{7f}qux""#);
     t!(format!("{:o}", 10_usize), "12");
     t!(format!("{:x}", 10_usize), "a");
     t!(format!("{:X}", 10_usize), "A");

alloc/tests/str.rs

@@ -1116,7 +1116,7 @@ fn test_escape_debug() {
     assert_eq!("abc".escape_debug().to_string(), "abc");
     assert_eq!("a c".escape_debug().to_string(), "a c");
     assert_eq!("éèê".escape_debug().to_string(), "éèê");
-    assert_eq!("\r\n\t".escape_debug().to_string(), "\\r\\n\\t");
+    assert_eq!("\0\r\n\t".escape_debug().to_string(), "\\0\\r\\n\\t");
     assert_eq!("'\"\\".escape_debug().to_string(), "\\'\\\"\\\\");
     assert_eq!("\u{7f}\u{ff}".escape_debug().to_string(), "\\u{7f}\u{ff}");
     assert_eq!("\u{100}\u{ffff}".escape_debug().to_string(), "\u{100}\\u{ffff}");

core/src/char/methods.rs

@@ -421,6 +421,7 @@ impl char {
     #[inline]
     pub(crate) fn escape_debug_ext(self, args: EscapeDebugExtArgs) -> EscapeDebug {
         let init_state = match self {
+            '\0' => EscapeDefaultState::Backslash('0'),
             '\t' => EscapeDefaultState::Backslash('t'),
             '\r' => EscapeDefaultState::Backslash('r'),
             '\n' => EscapeDefaultState::Backslash('n'),

core/tests/char.rs

@@ -197,7 +197,7 @@ fn test_escape_debug() {
     assert_eq!(string('~'), "~");
     assert_eq!(string('é'), "é");
     assert_eq!(string('文'), "文");
-    assert_eq!(string('\x00'), "\\u{0}");
+    assert_eq!(string('\x00'), "\\0");
     assert_eq!(string('\x1f'), "\\u{1f}");
     assert_eq!(string('\x7f'), "\\u{7f}");
     assert_eq!(string('\u{80}'), "\\u{80}");