Suggestion: make returning pointer to stack memory created in the same scope a compiler error

[Jarred-Sumner]

One spot where Zig lags behind C compilers in memory safety: returning a pointer to a temporary created in the same scope (specifically when the value is not comptime known)

For people new to manual memory management, this is a footgun

In C:

static char *myFunction() {
  char buf[200];
  buf[0] = 'h';
  buf[1] = 'e';
  buf[2] = 'y';
  buf[3] = '!';

  return buf;
}

int main(void) { myFunction(); }

Compile:

$ clang hey.c

hey.c:11:10: warning: address of stack memory associated with local variable 'buf' returned [-Wreturn-stack-address]
  return buf;
         ^~~
1 warning generated.

In Zig:

fn myFunction() []u8 {
    var buf: [100]u8 = undefined;
    buf[0.."hello".len].* = "hello".*;
    return buf[0..];
}

pub fn main() anyerror!void {
  std.mem.doNotOptimizeAway(myFunction());
}

Compile:

$ zig build-exe hey.zig
# no error

[andrewrk]

duplicate of #2646