[BUG] pango::shape_full does not work when passing paragraph_text

[LeoSchae]

Bug description

The wrapper pango::shape_full around pango::ffi::pango_shape_full seems to incorrectly pass the text and paragraph_text. The function pango::shape_with_flags seems to have the same problem.

When use_safe is set to true in the below code example, the image will not contain any text and the log contains:
(process:215897): Pango-CRITICAL **: 17:28:02.640: pango_shape_internal: assertion 'paragraph_text + paragraph_length >= item_text + item_length' failed
Calling pango::ffi::pango_shape_full directly (i.e. setting use_safe to false) and passing the texts and lengths as pointers fixes the problem.

Code Example (using pango, cairo and pangocairo):

fn test() {
    let s = cairo::ImageSurface::create(Format::ARgb32, 100, 100).unwrap();
    let c = cairo::Context::new(&s).unwrap();
    let pc = create_context(&c);
    let mut fd = pango::FontDescription::new();
    fd.set_size(13 * pango::SCALE);
    pc.set_font_description(Some(&fd));
    
    let text = "Hallo!";
    let glyphs = pango::itemize(&pc, text, 0, text.len() as i32, &AttrList::new(), None);
    let glyphs = glyphs.into_iter().map(|i| {
        let mut glyphs = pango::GlyphString::new();
        let item_text = &text[i.offset() as usize..(i.offset() + i.length()) as usize];
        
        let use_safe = true;
        if use_safe {
            // This branch does not produce the correct image
            pango::shape_full(item_text, Some(text), &i.analysis(), &mut glyphs);
        } else {
            // This works as expected
            unsafe {
                pango::ffi::pango_shape_full(
                    std::mem::transmute(item_text.as_ptr()),
                    item_text.len() as i32,
                    std::mem::transmute(text.as_ptr()),
                    text.len() as i32,
                    i.analysis().as_ptr(),
                    glyphs.as_ptr()
                );
            }
        }
        
        (i, glyphs)
    });
    
    for (i, mut glyphs) in glyphs {
        let font = i.analysis().font();
        c.move_to(10.0, 75.0);
        pangocairo::functions::show_glyph_string(&c, &font, &mut glyphs);
    }

    // save to png
    let mut file = File::create("test.png").unwrap();
    s.write_to_png(&mut file).unwrap();
}

Remarks

The wrapper passes item_text.to_glib_none().0 as the pointer. Running

let item_text = "test";
let p0: usize = std::mem::transmute(item_text.as_ptr());
let c: *const c_char = item_text.to_glib_none().0;
let p1: usize = std::mem::transmute(c);
assert_eq!(p0, p1);

panics with message:

assertion `left == right` failed                                                                                                                                                           
  left: 93825029359978                                                                                                                                                                     
 right: 93825038488816

It seems to me, that item_text.to_glib_none().0 does not point to the original memory location of the text.

[bilelmoussaoui]

This was fixed in #1681