Add some more common escaping scheme identity checks

sailfish/src/escape.rs

@@ -4,8 +4,22 @@ use array_vec::ArrayStr;
 
 use super::Buffer;
 
-pub(crate) struct CommonIdents<E: Escape>(PhantomData<E>);
+/// Holds computed constants for common escaping scheme identity checks.
+pub struct CommonIdents<E: Escape>(PhantomData<E>);
 
+/// Converts an array of ASCII bytes to an array of characters.
+pub const fn ascii_chars<const N: usize>(s: &[u8; N]) -> [char; N] {
+    assert!(s.is_ascii());
+    let mut chars = ['\0'; N];
+    let mut i = 0;
+    while i < s.len() {
+        chars[i] = s[i] as char;
+        i += 1;
+    }
+    chars
+}
+
+/// Returns `true` if, for the given escaping scheme `E`, every character in `set` requires no escaping.
 pub const fn are_all_chars_identity<E: Escape + ~const EscapeMeta>(set: &[char]) -> bool {
     let mut i = 0;
     while i < set.len() {
@@ -17,19 +31,31 @@ pub const fn are_all_chars_identity<E: Escape + ~const EscapeMeta>(set: &[char])
     true
 }
 
+const ALPHA_LOWERCASE_CHARS: &[char] = &ascii_chars(b"abcdefghijklmnopqrstuvwxyz");
+const ALPHA_UPPERCASE_CHARS: &[char] = &ascii_chars(b"ABCDEFGHIJKLMNOPQRSTUVWXYZ");
+const DIGIT_CHARS: &[char] = &ascii_chars(b"0123456789");
+const BOOL_CHARS: &[char] = &ascii_chars(b"truefals");
+
 impl<E: Escape> CommonIdents<E> {
+    /// True if lowercase ASCII alphabetic characters will never need escaping.
+    pub const ALPHA_LOWERCASE: bool = are_all_chars_identity::<E>(ALPHA_LOWERCASE_CHARS);
+    /// True if uppercase ASCII alphabetic characters will never need escaping.
+    pub const ALPHA_UPPERCASE: bool = are_all_chars_identity::<E>(ALPHA_UPPERCASE_CHARS);
+    /// True if base10 digit characters will never need escaping.
+    pub const DIGITS: bool = are_all_chars_identity::<E>(DIGIT_CHARS);
+
     /// True if `true` and `false` will never need escaping.
-    pub const BOOLS: bool =
-        are_all_chars_identity::<E>(&['t', 'r', 'u', 'e', 'f', 'a', 'l', 's']);
+    pub const BOOLS: bool = are_all_chars_identity::<E>(BOOL_CHARS);
     /// True if unsigned integers will never need escaping.
-    pub const UINTS: bool =
-        are_all_chars_identity::<E>(&['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']);
+    pub const UINTS: bool = Self::DIGITS;
     /// True if signed integers will never need escaping.
-    pub const INTS: bool = Self::UINTS && are_all_chars_identity::<E>(&['-']);
+    pub const INTS: bool = Self::DIGITS && are_all_chars_identity::<E>(&['-']);
     /// True if floats (using [`ryu`]'s formatting) will never need escaping.
-    pub const FLOATS: bool = Self::INTS && are_all_chars_identity::<E>(&['.', 'e']);
+    pub const FLOATS: bool =
+        Self::DIGITS && are_all_chars_identity::<E>(&['-', '.', 'e']);
 }
 
+/// Constant metadata about an impl of [`Escape`].
 #[const_trait]
 pub trait EscapeMeta {
     /// Returns `true` if the escaping scheme will never map the given character, regardless of its