Make with_x11_visual take ID instead of a pointer

At the moment, the with_x11_visual function takes a pointer and
immediately dereferences it to get the visual info inside. As it is safe
to pass a null pointer to this function, it is unsound. This commit
replaces the pointer parameter with a visual ID, and then uses that ID
to look up the actual visual under
the X11 setup. As this is what was already practically happening before,
this change shouldn't cause any performance downgrades.

This is a breaking change, but it's done in the name of soundness so it
should be okay. It should be trivial for end users to accommodate it,
as it's just a matter of getting the visual ID from the pointer to the
visual before passing it in.

Signed-off-by: John Nunley <dev@notgull.net>

CHANGELOG.md

@@ -58,6 +58,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - **Breaking** `RedrawEventsCleared` removed ([#2900](https://github.com/rust-windowing/winit/issues/2900))
 - **Breaking** `MainEventsCleared` removed ([#2900](https://github.com/rust-windowing/winit/issues/2900))
 - Added `AboutToWait` event which is emitted when the event loop is about to block and wait for new events ([#2900](https://github.com/rust-windowing/winit/issues/2900))
+- **Breaking:** `with_x11_visual` now takes the visual ID instead of the bare pointer.
 
 # 0.29.0-beta.0
 

src/platform/x11.rs

@@ -1,5 +1,3 @@
-use std::ptr;
-
 use crate::{
     event_loop::{EventLoopBuilder, EventLoopWindowTarget},
     monitor::MonitorHandle,
@@ -7,7 +5,7 @@ use crate::{
 };
 
 use crate::dpi::Size;
-use crate::platform_impl::{x11::ffi::XVisualInfo, ApplicationName, Backend, XLIB_ERROR_HOOKS};
+use crate::platform_impl::{ApplicationName, Backend, XLIB_ERROR_HOOKS};
 
 pub use crate::platform_impl::{x11::util::WindowType as XWindowType, XNotSupported};
 
@@ -19,6 +17,9 @@ pub use crate::platform_impl::{x11::util::WindowType as XWindowType, XNotSupport
 pub type XlibErrorHook =
     Box<dyn Fn(*mut std::ffi::c_void, *mut std::ffi::c_void) -> bool + Send + Sync>;
 
+/// A unique identifer for an X11 visual.
+pub type XVisualID = u32;
+
 /// Hook to winit's xlib error handling callback.
 ///
 /// This method is provided as a safe way to handle the errors comming from X11
@@ -84,7 +85,8 @@ impl WindowExtX11 for Window {}
 
 /// Additional methods on [`WindowBuilder`] that are specific to X11.
 pub trait WindowBuilderExtX11 {
-    fn with_x11_visual<T>(self, visual_infos: *const T) -> Self;
+    /// Create this window with a specific X11 visual.
+    fn with_x11_visual(self, visual_id: XVisualID) -> Self;
 
     fn with_x11_screen(self, screen_id: i32) -> Self;
 
@@ -120,11 +122,8 @@ pub trait WindowBuilderExtX11 {
 
 impl WindowBuilderExtX11 for WindowBuilder {
     #[inline]
-    fn with_x11_visual<T>(mut self, visual_infos: *const T) -> Self {
+    fn with_x11_visual(mut self, visual_id: XVisualID) -> Self {
-        {
+        self.platform_specific.visual_id = Some(visual_id);
-            self.platform_specific.visual_infos =
-                Some(unsafe { ptr::read(visual_infos as *const XVisualInfo) });
-        }
         self
     }
 

src/platform_impl/linux/mod.rs

@@ -24,7 +24,7 @@ use std::time::Duration;
 #[cfg(x11_platform)]
 pub use self::x11::XNotSupported;
 #[cfg(x11_platform)]
-use self::x11::{ffi::XVisualInfo, util::WindowType as XWindowType, X11Error, XConnection, XError};
+use self::x11::{util::WindowType as XWindowType, X11Error, XConnection, XError};
 #[cfg(x11_platform)]
 use crate::platform::x11::XlibErrorHook;
 use crate::{
@@ -96,7 +96,7 @@ pub struct PlatformSpecificWindowBuilderAttributes {
     pub name: Option<ApplicationName>,
     pub activation_token: Option<ActivationToken>,
     #[cfg(x11_platform)]
-    pub visual_infos: Option<XVisualInfo>,
+    pub visual_id: Option<x11rb::protocol::xproto::Visualid>,
     #[cfg(x11_platform)]
     pub screen_id: Option<i32>,
     #[cfg(x11_platform)]
@@ -113,7 +113,7 @@ impl Default for PlatformSpecificWindowBuilderAttributes {
             name: None,
             activation_token: None,
             #[cfg(x11_platform)]
-            visual_infos: None,
+            visual_id: None,
             #[cfg(x11_platform)]
             screen_id: None,
             #[cfg(x11_platform)]

src/platform_impl/linux/x11/mod.rs

@@ -886,6 +886,9 @@ pub enum X11Error {
 
     /// Got an invalid activation token.
     InvalidActivationToken(Vec<u8>),
+
+    /// Could not find a matching X11 visual for this visualid
+    NoSuchVisual(xproto::Visualid),
 }
 
 impl fmt::Display for X11Error {
@@ -902,6 +905,13 @@ impl fmt::Display for X11Error {
                 "Invalid activation token: {}",
                 std::str::from_utf8(s).unwrap_or("<invalid utf8>")
             ),
+            X11Error::NoSuchVisual(visualid) => {
+                write!(
+                    f,
+                    "Could not find a matching X11 visual for ID `{:x}`",
+                    visualid
+                )
+            }
         }
     }
 }

src/platform_impl/linux/x11/window.rs

@@ -214,30 +214,45 @@ impl UnownedWindow {
             None => xconn.default_screen_index() as c_int,
         };
 
+        // An iterator over all of the visuals combined with their depths.
+        let mut all_visuals = xconn
+            .xcb_connection()
+            .setup()
+            .roots
+            .iter()
+            .flat_map(|root| &root.allowed_depths)
+            .flat_map(|depth| {
+                depth
+                    .visuals
+                    .iter()
+                    .map(move |visual| (visual, depth.depth))
+            });
+
         // creating
-        let (visual, depth, require_colormap) = match pl_attribs.visual_infos {
+        let (visualtype, depth, require_colormap) = match pl_attribs.visual_id {
-            Some(vi) => (vi.visualid as _, vi.depth as _, false),
+            Some(vi) => {
+                // Find this specific visual.
+                let (visualtype, depth) = all_visuals
+                    .find(|(visual, _)| visual.visual_id == vi)
+                    .ok_or_else(|| os_error!(OsError::XError(X11Error::NoSuchVisual(vi).into())))?;
+
+                (Some(visualtype), depth, true)
+            }
             None if window_attrs.transparent => {
                 // Find a suitable visual, true color with 32 bits of depth.
-                xconn.xcb_connection().setup().roots
+                all_visuals
-                    .iter()
+                    .find_map(|(visual, depth)| {
-                    .flat_map(|root| &root.allowed_depths)
+                        (visual.class == xproto::VisualClass::TRUE_COLOR)
-                    .filter(|depth| depth.depth == 32)
+                            .then_some((Some(visual), depth, true))
-                    .flat_map(|depth| depth.visuals.iter().map(move |visual| (visual, depth.depth)))
-                    .find(|(visual, _)| {
-                        visual.class == xproto::VisualClass::TRUE_COLOR
                     })
-                    .map_or_else(|| {
+                    .unwrap_or_else(|| {
                         debug!("Could not set transparency, because XMatchVisualInfo returned zero for the required parameters");
-                        (x11rb::COPY_FROM_PARENT as _, x11rb::COPY_FROM_PARENT as _, false)
+                        (None as _, x11rb::COPY_FROM_PARENT as _, false)
-                    }, |(visual, depth)| (visual.visual_id, depth, true))
+                    })
             }
-            _ => (
+            _ => (None, x11rb::COPY_FROM_PARENT as _, false),
-                x11rb::COPY_FROM_PARENT as _,
-                x11rb::COPY_FROM_PARENT as _,
-                false,
-            ),
         };
+        let visual = visualtype.map_or(x11rb::COPY_FROM_PARENT, |v| v.visual_id);
 
         let window_attributes = {
             use xproto::EventMask;
@@ -260,8 +275,8 @@ impl UnownedWindow {
             }
 
             // Add a colormap if needed.
-            let colormap_visual = match pl_attribs.visual_infos {
+            let colormap_visual = match pl_attribs.visual_id {
-                Some(vi) => Some(vi.visualid as u32),
+                Some(vi) => Some(vi),
                 None if require_colormap => Some(visual),
                 _ => None,
             };