Give a more meaningful panic message in AsciiChar::new()

Including the offending character in the panic message is
not yet possible as of 1.61, so instead use #{track_caller]
to make the panic text point to where a panic happened.

Author: tormol

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [1.56.1, stable, beta, nightly]
+        rust: [1.57.0, stable, beta, nightly]
     steps:
       - uses: actions/checkout@v2
       - uses: hecrj/setup-rust-action@v1

README.md

@@ -35,7 +35,7 @@ ascii = { version = "1.0", default-features = false, features = ["alloc"] }
 
 ## Minimum supported Rust version
 
-The minimum Rust version for 1.1.\* releases is 1.56.0.
+The minimum Rust version for 1.1.\* releases is 1.57.0.
 Later 1.y.0 releases might require newer Rust versions, but the three most
 recent stable releases at the time of publishing will always be supported.  
 For example this means that if the current stable Rust version is 1.70 when

src/ascii_char.rs

@@ -326,38 +326,18 @@ impl AsciiChar {
     ///
     /// This function will panic if passed a non-ASCII character.
     ///
-    /// The panic message might not be the most descriptive due to the
-    /// current limitations of `const fn`.
+    /// The panic message might not be the most descriptive due to
+    /// current limitations of what is available in `const fn`.
+    #[inline]
     #[must_use]
+    #[track_caller]
     pub const fn new(ch: char) -> AsciiChar {
-        // It's restricted to this function, and without it
-        // we'd need to specify `AsciiChar::` or `Self::` 128 times.
-        #[allow(clippy::enum_glob_use)]
-        use AsciiChar::*;
-
-        #[rustfmt::skip]
-        const ALL: [AsciiChar; 128] = [
-            Null, SOH, SOX, ETX, EOT, ENQ, ACK, Bell,
-            BackSpace, Tab, LineFeed, VT, FF, CarriageReturn, SI, SO,
-            DLE, DC1, DC2, DC3, DC4, NAK, SYN, ETB,
-            CAN, EM, SUB, ESC, FS, GS, RS, US,
-            Space, Exclamation, Quotation, Hash, Dollar, Percent, Ampersand, Apostrophe,
-            ParenOpen, ParenClose, Asterisk, Plus, Comma, Minus, Dot, Slash,
-            _0, _1, _2, _3, _4, _5, _6, _7,
-            _8, _9, Colon, Semicolon, LessThan, Equal, GreaterThan, Question,
-            At, A, B, C, D, E, F, G,
-            H, I, J, K, L, M, N, O,
-            P, Q, R, S, T, U, V, W,
-            X, Y, Z, BracketOpen, BackSlash, BracketClose, Caret, UnderScore,
-            Grave, a, b, c, d, e, f, g,
-            h, i, j, k, l, m, n, o,
-            p, q, r, s, t, u, v, w,
-            x, y, z, CurlyBraceOpen, VerticalBar, CurlyBraceClose, Tilde, DEL,
-		];
-
-        // We want to slice here and detect `const_err` from rustc if the slice is invalid
-        #[allow(clippy::indexing_slicing)]
-        ALL[ch as usize]
+        unsafe {
+            match ch as u32 {
+                0..=127 => mem::transmute(ch as u8),
+                _ => panic!("not an ASCII character"),
+            }
+        }
     }
 
     /// Create an `AsciiChar` from a `char`, in a `const fn` way.

src/lib.rs

@@ -15,7 +15,7 @@
 //!
 //! # Minimum supported Rust version
 //!
-//! The minimum Rust version for 1.1.\* releases is 1.56.0.
+//! The minimum Rust version for 1.1.\* releases is 1.57.0.
 //! Later 1.y.0 releases might require newer Rust versions, but the three most
 //! recent stable releases at the time of publishing will always be supported.  
 //! For example this means that if the current stable Rust version is 1.70 when