Auto merge of rust-lang#125518 - saethlin:check-arguments-new-in-const, r=joboet

Move the checks for Arguments constructors to inline const

Thanks `@Skgland` for pointing out this opportunity: rust-lang#117804 (comment)

Author: bors

core/src/fmt/mod.rs

@@ -338,23 +338,19 @@ pub struct Arguments<'a> {
 impl<'a> Arguments<'a> {
     #[inline]
     #[rustc_const_unstable(feature = "const_fmt_arguments_new", issue = "none")]
-    pub const fn new_const(pieces: &'a [&'static str]) -> Self {
-        if pieces.len() > 1 {
-            // Since panic!() expands to panic_fmt(format_args!()), using panic! here is both a
-            // bit silly and also significantly increases the amount of MIR generated by panics.
-            crate::panicking::panic_nounwind("invalid args");
-        }
+    pub const fn new_const<const N: usize>(pieces: &'a [&'static str; N]) -> Self {
+        const { assert!(N <= 1) };
         Arguments { pieces, fmt: None, args: &[] }
     }
 
     /// When using the format_args!() macro, this function is used to generate the
     /// Arguments structure.
     #[inline]
-    pub fn new_v1(pieces: &'a [&'static str], args: &'a [rt::Argument<'a>]) -> Arguments<'a> {
-        if pieces.len() < args.len() || pieces.len() > args.len() + 1 {
-            // See Arguments::new_const for why we don't use panic!.
-            crate::panicking::panic_nounwind("invalid args");
-        }
+    pub fn new_v1<const P: usize, const A: usize>(
+        pieces: &'a [&'static str; P],
+        args: &'a [rt::Argument<'a>; A],
+    ) -> Arguments<'a> {
+        const { assert!(P >= A && P <= A + 1, "invalid args") }
         Arguments { pieces, fmt: None, args }
     }