Improve panic! messages in hex-literal

hex-literal/src/lib.rs

@@ -86,12 +86,16 @@ struct TokenTreeIter {
 }
 
 impl TokenTreeIter {
+    /// Constructs a new `TokenTreeIter` from a given `proc_macro::Literal`.
+    ///
+    /// # Panics
+    /// This panics if the given `Literal` is not a string literal.
     fn new(input: Literal) -> Self {
         let mut buf: Vec<u8> = input.to_string().into();
 
         match buf.as_slice() {
             [b'"', .., b'"'] => (),
-            _ => panic!("expected string literals"),
+            _ => panic!("expected string literal, got `{}`", input),
         };
         buf.pop();
         let mut iter = buf.into_iter().exclude_comments();
@@ -102,6 +106,11 @@ impl TokenTreeIter {
         }
     }
 
+    /// Parses a single hex character (a-f/A-F/0-9) as a `u8` from the `TokenTreeIter`'s
+    /// internal buffer, ignoring whitespace.
+    ///
+    /// # Panics
+    /// This panics if a non-hex, non-whitespace character is encountered.
     fn next_hex_val(&mut self) -> Option<u8> {
         loop {
             let v = self.buf.next()?;
@@ -110,7 +119,7 @@ impl TokenTreeIter {
                 b'A'..=b'F' => v - 55,
                 b'a'..=b'f' => v - 87,
                 b' ' | b'\r' | b'\n' | b'\t' => continue,
-                _ => panic!("encountered invalid character"),
+                c => panic!("encountered invalid character: `{}`", c as char),
             };
             return Some(n);
         }
@@ -120,6 +129,13 @@ impl TokenTreeIter {
 impl Iterator for TokenTreeIter {
     type Item = TokenTree;
 
+    /// Produces hex values (as `u8` literals) parsed from the `TokenTreeIter`'s
+    /// internal buffer, alternating with commas to separate the elements of the
+    /// generated array of bytes.
+    ///
+    /// # Panics
+    /// This panics if the internal buffer contains an odd number of hex
+    /// characters.
     fn next(&mut self) -> Option<TokenTree> {
         let v = if self.is_punct {
             TokenTree::Punct(Punct::new(',', Spacing::Alone))
@@ -145,7 +161,7 @@ pub fn hex(input: TokenStream) -> TokenStream {
     for tt in ignore_groups(input) {
         let iter = match tt {
             TokenTree::Literal(literal) => TokenTreeIter::new(literal),
-            _ => panic!("expected string literals"),
+            unexpected => panic!("expected string literal, got `{}`", unexpected),
         };
         out_ts.extend(iter);
     }

hex-literal/tests/basic.rs

@@ -0,0 +1,83 @@
+use hex_literal::hex;
+
+#[test]
+fn single_literal() {
+    assert_eq!(hex!("ff e4"), [0xff, 0xe4]);
+}
+
+#[test]
+fn empty() {
+    let nothing: [u8; 0] = hex!();
+    let empty_literals: [u8; 0] = hex!("" "" "");
+    let expected: [u8; 0] = [];
+    assert_eq!(nothing, expected);
+    assert_eq!(empty_literals, expected);
+}
+
+#[test]
+fn upper_case() {
+    assert_eq!(hex!("AE DF 04 B2"), [0xae, 0xdf, 0x04, 0xb2]);
+    assert_eq!(hex!("FF BA 8C 00 01"), [0xff, 0xba, 0x8c, 0x00, 0x01]);
+}
+
+#[test]
+fn mixed_case() {
+    assert_eq!(hex!("bF dd E4 Cd"), [0xbf, 0xdd, 0xe4, 0xcd]);
+}
+
+#[test]
+fn multiple_literals() {
+    assert_eq!(
+        hex!(
+            "01 dd f7 7f"
+            "ee f0 d8"
+        ),
+        [0x01, 0xdd, 0xf7, 0x7f, 0xee, 0xf0, 0xd8]
+    );
+    assert_eq!(
+        hex!(
+            "ff"
+            "e8 d0"
+            ""
+            "01 1f"
+            "ab"
+        ),
+        [0xff, 0xe8, 0xd0, 0x01, 0x1f, 0xab]
+    );
+}
+
+#[test]
+fn no_spacing() {
+    assert_eq!(hex!("abf0d8bb0f14"), [0xab, 0xf0, 0xd8, 0xbb, 0x0f, 0x14]);
+    assert_eq!(
+        hex!("09FFd890cbcCd1d08F"),
+        [0x09, 0xff, 0xd8, 0x90, 0xcb, 0xcc, 0xd1, 0xd0, 0x8f]
+    );
+}
+
+#[test]
+fn allows_various_spacing() {
+    // newlines
+    assert_eq!(
+        hex!(
+            "f
+            f
+            d
+            0
+            e
+
+            8
+            "
+        ),
+        [0xff, 0xd0, 0xe8]
+    );
+    // tabs
+    assert_eq!(hex!("9f	d		1		f07	3		01	"), [0x9f, 0xd1, 0xf0, 0x73, 0x01]);
+    // spaces
+    assert_eq!(hex!(" e    e d0  9 1   f  f  "), [0xee, 0xd0, 0x91, 0xff]);
+}
+
+#[test]
+fn can_use_const() {
+    const _: [u8; 4] = hex!("ff d3 01 7f");
+}

hex-literal/tests/comments.rs

@@ -0,0 +1,41 @@
+use hex_literal::hex;
+
+#[test]
+fn single_line_comments() {
+    assert_eq!(hex!("dd 03 // comment"), [0xdd, 0x03]);
+    assert_eq!(
+        hex!(
+            "00 04 f0 // a comment here
+            54 fe // another comment"
+        ),
+        [0x00, 0x04, 0xf0, 0x54, 0xfe]
+    );
+    assert_eq!(
+        hex!(
+            "// initial comment
+            01 02"
+        ),
+        [0x01, 0x02]
+    );
+}
+
+#[test]
+fn block_comments() {
+    assert_eq!(
+        hex!("00 01 02 /* intervening comment */ 03 04"),
+        [0x00, 0x01, 0x02, 0x03, 0x04]
+    );
+    assert_eq!(hex!("/* initial comment */ ff df dd"), [0xff, 0xdf, 0xdd]);
+    assert_eq!(
+        hex!(
+            "8f ff 7d /*
+            comment
+            on
+            several
+            lines
+            */
+            d0 a3"
+        ),
+        [0x8f, 0xff, 0x7d, 0xd0, 0xa3]
+    );
+}