better debug for Peek (#86)

Author: samuelcolvin

crates/jiter/src/parse.rs

@@ -1,8 +1,10 @@
+use std::fmt;
+
 use crate::errors::{json_err, JsonResult, LinePosition};
 use crate::number_decoder::AbstractNumberDecoder;
 use crate::string_decoder::{AbstractStringDecoder, Tape};
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[derive(Copy, Clone, PartialEq, Eq)]
 pub struct Peek(u8);
 
 #[allow(non_upper_case_globals)] // while testing
@@ -18,6 +20,23 @@ impl Peek {
     pub const Object: Self = Self(b'{');
 }
 
+impl fmt::Debug for Peek {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.0 {
+            b'n' => write!(f, "Null"),
+            b't' => write!(f, "True"),
+            b'f' => write!(f, "False"),
+            b'-' => write!(f, "Minus"),
+            b'I' => write!(f, "Infinity"),
+            b'N' => write!(f, "NaN"),
+            b'"' => write!(f, "String"),
+            b'[' => write!(f, "Array"),
+            b'{' => write!(f, "Object"),
+            _ => write!(f, "Peek({:?})", self.0 as char),
+        }
+    }
+}
+
 impl Peek {
     pub const fn new(next: u8) -> Self {
         Self(next)

crates/jiter/tests/main.rs

@@ -1173,6 +1173,13 @@ fn jiter_wrong_types() {
     expect_wrong_type!(next_float, JsonType::Float);
 }
 
+#[test]
+fn peek_debug() {
+    assert_eq!(format!("{:?}", Peek::True), "True");
+    assert_eq!(format!("{:?}", Peek::False), "False");
+    assert_eq!(format!("{:?}", Peek::new(b'4')), "Peek('4')");
+}
+
 #[test]
 fn jiter_invalid_numbers() {
     let mut jiter = Jiter::new(b" -a", false);