Add safety comments to public unsafe functions (#484)

- [x] Changelog updated / no changelog update needed

agb/examples/object_text_render.rs

@@ -24,76 +24,74 @@ fn entry(gba: agb::Gba) -> ! {
 fn main(mut gba: agb::Gba) -> ! {
     let (mut unmanaged, _sprites) = gba.display.object.get_unmanaged();
 
-    loop {
-        let mut palette = [0x0; 16];
-        palette[1] = 0xFF_FF;
-        palette[2] = 0x00_FF;
-        let palette = Palette16::new(palette);
-        let palette = PaletteVram::new(&palette).unwrap();
+    let mut palette = [0x0; 16];
+    palette[1] = 0xFF_FF;
+    palette[2] = 0x00_FF;
+    let palette = Palette16::new(palette);
+    let palette = PaletteVram::new(&palette).unwrap();
 
-        let timer = gba.timers.timers();
-        let mut timer: agb::timer::Timer = timer.timer2;
+    let timer = gba.timers.timers();
+    let mut timer: agb::timer::Timer = timer.timer2;
 
-        timer.set_enabled(true);
-        timer.set_divider(agb::timer::Divider::Divider256);
+    timer.set_enabled(true);
+    timer.set_divider(agb::timer::Divider::Divider256);
 
-        let mut wr = ObjectTextRender::new(&FONT, Size::S16x16, palette);
-        let start = timer.value();
+    let mut wr = ObjectTextRender::new(&FONT, Size::S16x16, palette);
+    let start = timer.value();
 
-        let player_name = "You";
-        let _ = writeln!(
+    let player_name = "You";
+    let _ = writeln!(
             wr,
             "Woah!{change2} {player_name}! {change1}Hey there! I have a bunch of text I want to show you. However, you will find that the amount of text I can display is limited. Who'd have thought! Good thing that my text system supports scrolling! It only took around 20 jank versions to get here!",
             change2 = ChangeColour::new(2),
             change1 = ChangeColour::new(1),
         );
-        let end = timer.value();
+    let end = timer.value();
 
-        agb::println!(
-            "Write took {} cycles",
-            256 * (end.wrapping_sub(start) as u32)
-        );
+    agb::println!(
+        "Write took {} cycles",
+        256 * (end.wrapping_sub(start) as u32)
+    );
 
-        let vblank = agb::interrupt::VBlank::get();
-        let mut input = agb::input::ButtonController::new();
+    let vblank = agb::interrupt::VBlank::get();
+    let mut input = agb::input::ButtonController::new();
+
+    let start = timer.value();
+
+    wr.layout((WIDTH, 40).into(), TextAlignment::Justify, 2);
+    let end = timer.value();
+
+    agb::println!(
+        "Layout took {} cycles",
+        256 * (end.wrapping_sub(start) as u32)
+    );
+
+    let mut line_done = false;
+    let mut frame = 0;
+
+    loop {
+        vblank.wait_for_vblank();
+        input.update();
+        let oam = &mut unmanaged.iter();
+        wr.commit(oam);
 
         let start = timer.value();
-
-        wr.layout((WIDTH, 40).into(), TextAlignment::Justify, 2);
+        if frame % 4 == 0 {
+            line_done = !wr.next_letter_group();
+        }
+        if line_done && input.is_just_pressed(Button::A) {
+            line_done = false;
+            wr.pop_line();
+        }
+        wr.update((0, HEIGHT - 40).into());
         let end = timer.value();
 
+        frame += 1;
+
         agb::println!(
-            "Layout took {} cycles",
-            256 * (end.wrapping_sub(start) as u32)
+            "Took {} cycles, line done {}",
+            256 * (end.wrapping_sub(start) as u32),
+            line_done
         );
-
-        let mut line_done = false;
-        let mut frame = 0;
-
-        loop {
-            vblank.wait_for_vblank();
-            input.update();
-            let oam = &mut unmanaged.iter();
-            wr.commit(oam);
-
-            let start = timer.value();
-            if frame % 4 == 0 {
-                line_done = !wr.next_letter_group();
-            }
-            if line_done && input.is_just_pressed(Button::A) {
-                line_done = false;
-                wr.pop_line();
-            }
-            wr.update((0, HEIGHT - 40).into());
-            let end = timer.value();
-
-            frame += 1;
-
-            agb::println!(
-                "Took {} cycles, line done {}",
-                256 * (end.wrapping_sub(start) as u32),
-                line_done
-            );
-        }
     }
 }

agb/src/lib.rs

@@ -231,6 +231,10 @@ pub struct Gba {
 impl Gba {
     #[doc(hidden)]
     #[must_use]
+    /// # Safety
+    ///
+    /// May only be called a single time. It is not needed to call this due to
+    /// it being called internally by the [`entry`] macro.
     pub unsafe fn new_in_entry() -> Self {
         Self::single_new()
     }

agb/src/sync/mod.rs

@@ -33,6 +33,8 @@ pub fn memory_write_hint<T>(val: *mut T) {
 /// This seems to be a problem caused by Rust issue #62256:
 /// <https://github.com/rust-lang/rust/issues/62256>
 ///
+/// # Safety
+///
 /// **WARNING FOR ANYONE WHO FINDS THIS**: This implementation will *only* be
 /// correct on the GBA, and should not be used on any other platform. The GBA
 /// is very old, and has no atomics to begin with - only a main thread and