better `@intCast` safety check panic message

[nektro]

Zig Version

aas0.12.0-dev.2814+7775e46e8

Steps to Reproduce and Observed Output

const std = @import("std");

pub fn main() !void {
 var x: u32 = 300;
 _ = &x;
 var y: u8 = @intCast(x);
 _ = &y;
}

thread 174582 panic: integer cast truncated bits
/run/media/meghan/dev/test2.zig:6:17: 0x1033306 in main (test2)
 var y: u8 = @intCast(x);
 ^
/home/meghan/src/zig/lib/std/start.zig:511:37: 0x1033290 in posixCallMainAndExit (test2)
 const result = root.main() catch |err| {
 ^
/home/meghan/src/zig/lib/std/start.zig:253:5: 0x1032e01 in _start (test2)
 asm volatile (switch (native_arch) {
 ^
???:?:?: 0x0 in ??? (???)
Aborted (core dumped)

Expected Output

panic: casting integer '300' into type 'u8' truncates bits

[frmdstryr]

Doesn't it require an allocator or buffer to do this? Where would the memory required to format this message come from?

[nektro]

you can write directly to a std.io.Writer without needing to allocate. the infra needed to make a panic that uses formatted printing like this is already setup, in use with indexing slices out of bounds for example.