Debug and ReleaseSafe different output

[bmacho]

Zig Version

0.10.1

Steps to Reproduce and Observed Behavior

The following code

const std = @import("std");
const print = std.debug.print;

fn foo() fn() *u32 {
	
	const T = struct {

        fn bar() *u32 {
            var x: u32 = 123;
            return &x;
        }

	};
	
	return T.bar;
}

pub fn main() void {

    print("Result: {}", .{foo()().*});

}

gives different outputs with different build flags. It prints Result: 123 for

zig build-exe example.zig & example.exe

and Result: 00 for

zig build-exe example.zig -O ReleaseSafe & example.exe

It works for me locally also on godbolt:

• debug https://zig.godbolt.org/z/hbz39cP6M
• -O ReleaseSafe https://zig.godbolt.org/z/6beca1vh3

Expected Behavior

I expected to have the same output, or the program to panic at runtime, or to not to compile at all.

[bmacho]

I have no idea about the expected behaviour, but this smells bad.

The code is from the ziggit.dev thread https://ziggit.dev/t/how-to-declare-local-functions-in-functions/1234/

[ifreund]

Dereferencing a pointer to the stack variable x after bar() has returned is illegal behavior.

See #2646 and #2301