Appease X11 users with niri/wayland specific postfixup wrapper (#212)

* Appease X11 users with niri/wayland specific postfixup wrapper

* Linux: stay on native Wayland under niri in the app, not the Nix wrapper

Move the niri check from the flake's wrapper into apps/solvecraft/src/main.rs
next to the XWayland default, so it applies to every niri user, not only
Nix builds (flake.nix is back to main's, which also clears the conflict
with #210). SOLVECRAFT_WAYLAND=1 still keeps native Wayland, and =0 now
forces XWayland. docs/nix.md notes the trade-off: no file drag-and-drop
on native Wayland.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT

---------

Co-authored-by: bherbruck <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>

apps/solvecraft/src/main.rs

@@ -175,10 +175,12 @@ fn main() -> eframe::Result {
     #[cfg(all(unix, not(target_os = "macos")))]
     let mut options = options;
     #[cfg(all(unix, not(target_os = "macos")))]
-    // winit has no file drag-and-drop on Wayland (only on X11), so dropping files from the file
-    // manager showed a "no" cursor. Run through XWayland when it's there; SOLVECRAFT_WAYLAND=1
-    // keeps the native Wayland backend.
-    if std::env::var_os("DISPLAY").is_some() && std::env::var_os("SOLVECRAFT_WAYLAND").is_none() {
+    if prefer_x11(
+        std::env::var_os("DISPLAY").is_some(),
+        std::env::var_os("WAYLAND_DISPLAY").is_some(),
+        std::env::var("XDG_CURRENT_DESKTOP").ok().as_deref(),
+        std::env::var("SOLVECRAFT_WAYLAND").ok().as_deref(),
+    ) {
         options.event_loop_builder = Some(Box::new(|b| {
             use winit::platform::x11::EventLoopBuilderExtX11;
             b.with_x11();
@@ -236,6 +238,45 @@ fn main() -> eframe::Result {
     )
 }
 
+/// Whether to run through XWayland rather than native Wayland. winit has no file drag-and-drop
+/// on Wayland (only on X11), so dropping files from the file manager showed a "no" cursor: use
+/// XWayland when it's there. Except on niri, whose XWayland (xwayland-satellite) breaks window
+/// management (maximize/restore), so it stays on native Wayland and gives up file drops.
+/// `SOLVECRAFT_WAYLAND=1` keeps native Wayland, `SOLVECRAFT_WAYLAND=0` forces XWayland.
+#[cfg(all(unix, not(target_os = "macos")))]
+fn prefer_x11(display: bool, wayland_display: bool, desktop: Option<&str>, wayland_override: Option<&str>) -> bool {
+    match wayland_override.map(str::trim) {
+        Some("0") => return display,
+        Some(_) => return false,
+        None => {}
+    }
+    let niri = desktop.is_some_and(|d| d.split(':').any(|name| name.trim().eq_ignore_ascii_case("niri")));
+    display && !(niri && wayland_display)
+}
+
+#[cfg(all(test, unix, not(target_os = "macos")))]
+mod backend_tests {
+    use super::prefer_x11;
+
+    #[test]
+    fn xwayland_by_default_native_wayland_on_niri_and_the_override_wins() {
+        // XWayland whenever there's an X display, for file drag-and-drop.
+        assert!(prefer_x11(true, true, Some("GNOME"), None));
+        assert!(prefer_x11(true, false, None, None));
+        assert!(!prefer_x11(false, true, Some("KDE"), None));
+        // niri (alone or in a desktop list) under Wayland stays native.
+        assert!(!prefer_x11(true, true, Some("niri"), None));
+        assert!(!prefer_x11(true, true, Some("niri:GNOME"), None));
+        // niri without a Wayland socket (nested X session) still uses X11.
+        assert!(prefer_x11(true, false, Some("niri"), None));
+        // SOLVECRAFT_WAYLAND: anything but 0 keeps Wayland, 0 forces XWayland (when present).
+        assert!(!prefer_x11(true, true, Some("GNOME"), Some("1")));
+        assert!(!prefer_x11(true, true, Some("GNOME"), Some("")));
+        assert!(prefer_x11(true, true, Some("niri"), Some("0")));
+        assert!(!prefer_x11(false, true, Some("niri"), Some("0")));
+    }
+}
+
 #[cfg(test)]
 mod icon_tests {
     #[test]

docs/nix.md

@@ -87,6 +87,19 @@ For older builds, including 0.3.0, set Anti-aliasing to 1x and restart when usin
 If that window cannot show the settings dialog, edit only the `msaa` field to `1` in
 `~/.local/share/solvecraft/graphics.json`; preserve any other settings.
 
+## Wayland, XWayland and niri
+
+On Linux the app runs through XWayland whenever an X display is available, because
+winit only supports dragging files from a file manager into the window on X11. On
+niri (detected from `XDG_CURRENT_DESKTOP` with a Wayland socket present) it stays on
+native Wayland instead, since window management such as maximize/restore misbehaves
+under niri's XWayland. The trade-off: **on native Wayland, dropping files onto the
+window does not work**; use File > Open or pass the file on the command line.
+This applies to every build, not only the Nix package.
+
+Override the choice with `SOLVECRAFT_WAYLAND=1` (always native Wayland) or
+`SOLVECRAFT_WAYLAND=0` (XWayland whenever an X display is available).
+
 ## Development shells
 
 `nix develop` supplies runtime libraries and uses the Rust/C toolchain already on