missing compile error for address-of constant data

[andrewrk]

test "sample" {
    var x: []u8 = &[_]u8{'h', 'i'};
    x[0] = 0;
}

Segfaults at runtime. Expected behavior is compile error. Address of constant data should be a const pointer.

Thanks to @allochi for discovering this bug.

[andrewrk]

Confirmed still a bug in master branch.

[helinwang]

Thanks for looking at the issue!
Could I know why this is closed, I still hit a similar issue:

    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer {
        const leaked = gpa.deinit();
        if (leaked) expect(false) catch @panic("TEST FAIL");
    }
    var allocator = gpa.allocator;

    var files = try std.ArrayList([]const u8).initCapacity(&allocator, 100);
    defer files.deinit();

The code segfault with:

Segmentation fault at address 0x0
/snap/zig/4341/lib/std/mem/Allocator.zig:289:40: 0x23be1b in std.mem.Allocator.allocAdvancedWithRetAddr (main)
    const byte_slice = try self.allocFn(self, byte_count, a, len_align, return_address);

[Vexu]

You are copying the interface out of the implementation, see #591.

[helinwang]

Thanks! I checked the issue, as mentioned in the issue, the problem is due to

Any struct that uses @fieldParentPtr on an "interface" field relies on the API user not making a copy of the interface field.

I created a snippet to somewhat illustrate the issue, in case anyone else find it helpful.

const Point = struct {
    x: f32,
    y: f32,
};

fn setYBasedOnX(x: *f32, y: f32) void {
    const point = @fieldParentPtr(Point, "x", x);
    point.y = y;
}

test "field parent pointer" {
    var point = Point{
        .x = 0.1234,
        .y = 0.5678,
    };
    var x = @as(f32, 3.0);
    setYBasedOnX(&x, 0.9);
    std.debug.print("{}", .{point}); // point.x being accidentally set to 0.9!
}