Update to Rust programming language.

src-tauri/src/lib.rs

@@ -0,0 +1,71 @@
+// Taken from https://github.com/Vurich/const-concat/issues/13
+
+#![no_std]
+
+use core::mem::ManuallyDrop;
+
+const unsafe fn transmute_prefix<From, To>(from: From) -> To {
+    union Transmute<From, To> {
+        from: ManuallyDrop<From>,
+        to: ManuallyDrop<To>,
+    }
+
+    ManuallyDrop::into_inner(
+        Transmute {
+            from: ManuallyDrop::new(from),
+        }
+        .to,
+    )
+}
+
+/// # Safety
+///
+/// `Len1 + Len2 >= Len3`
+#[doc(hidden)]
+#[allow(non_upper_case_globals)]
+pub const unsafe fn concat<const Len1: usize, const Len2: usize, const Len3: usize>(
+    arr1: [u8; Len1],
+    arr2: [u8; Len2],
+) -> [u8; Len3] {
+    #[repr(C)]
+    struct Concat<A, B>(A, B);
+    transmute_prefix(Concat(arr1, arr2))
+}
+
+#[macro_export]
+macro_rules! const_concat {
+    () => ("");
+    ($a:expr) => ($a);
+
+    ($a:expr, $b:expr $(,)?) => {{
+        const A: &str = $a;
+        const B: &str = $b;
+        const BYTES: [u8; { A.len() + B.len() }] = unsafe {
+            $crate::concat::<
+                { A.len() },
+                { B.len() },
+                { A.len() + B.len() }
+            >(
+                *A.as_ptr().cast(),
+                *B.as_ptr().cast(),
+            )
+        };
+        unsafe { ::core::str::from_utf8_unchecked(&BYTES) }
+    }};
+
+    ($a:expr, $b:expr, $($rest:expr),+ $(,)?) => {{
+        const TAIL: &str = $crate::const_concat!($b, $($rest),+);
+        $crate::const_concat!($a, TAIL)
+    }}
+}
+
+#[test]
+fn tests() {
+    const SALUTATION: &str = "Hello";
+    const TARGET: &str = "world";
+    const GREETING: &str = const_concat!(SALUTATION, ", ", TARGET, "!");
+    const GREETING_TRAILING_COMMA: &str = const_concat!(SALUTATION, ", ", TARGET, "!",);
+
+    assert_eq!(GREETING, "Hello, world!");
+    assert_eq!(GREETING_TRAILING_COMMA, "Hello, world!");
+}