Fix bug where Buffers were never freed

The issue was that, when reiniting Buffers, the intrusive linkedlist
node was clobbered and we lost reference to it. That meant most of the
Buffers would be memory leaks. Now, we save the node during
reinitializion.

docs/TODO.md

@@ -2,6 +2,7 @@
 
 These are in rough order of my priority, though no promises I do them in this order.
 
+- [ ] Fix mouse resizing
 - [ ] Add gap support
 - [ ] Support window tag/order caching between WM restarts (within a river session)
 - [ ] Add build-time options for including the wallpaper (and maybe bar)

src/Buffer.zig

@@ -76,6 +76,15 @@ pub fn init(shm: *wl.Shm, width: u31, height: u31) !Buffer {
     };
 }
 
+/// Re-initialize this buffer with new dimensions, preserving its position in
+/// any intrusive linked list. Equivalent to deinit + init but keeps node intact.
+pub fn reinit(buffer: *Buffer, shm: *wl.Shm, width: u31, height: u31) !void {
+    const saved_node = buffer.node;
+    buffer.deinit();
+    buffer.* = try Buffer.init(shm, width, height);
+    buffer.node = saved_node;
+}
+
 pub fn deinit(buffer: *Buffer) void {
     _ = buffer.pixman_image.unref();
     buffer.wl_buffer.destroy();

src/BufferPool.zig

@@ -37,7 +37,7 @@ pub fn deinit(buffer_pool: *BufferPool) void {
 /// Get a buffer with the specified dimensions. If possible, an idle buffer is
 /// reused, otherwise a new one is created.
 pub fn nextBuffer(buffer_pool: *BufferPool, wl_shm: *wl.Shm, width: u31, height: u31) !*Buffer {
-    log.debug("looking for buffer with dimensions {}x{}, total existing buffers: {}", .{ width, height, buffer_pool.len });
+    log.debug("Looking for buffer with dimensions {}x{}, total existing buffers: {}", .{ width, height, buffer_pool.len });
     defer {
         // Clear up extra buffers
         if (buffer_pool.len > max_buffer_multiplicity * buffer_pool.surface_count) {
@@ -71,8 +71,7 @@ fn findSuitableBuffer(buffer_pool: *BufferPool, wl_shm: *wl.Shm, width: u31, hei
     // No buffer has matching dimensions, however we do have an unbusy
     // buffer which we can just re-init.
     if (first_unbusy_buffer) |buffer| {
-        buffer.deinit();
+        try buffer.reinit(wl_shm, width, height);
-        buffer.* = try Buffer.init(wl_shm, width, height);
         buffer.setListener();
         return buffer;
     }
@@ -81,7 +80,7 @@ fn findSuitableBuffer(buffer_pool: *BufferPool, wl_shm: *wl.Shm, width: u31, hei
 }
 
 fn newBuffer(buffer_pool: *BufferPool, wl_shm: *wl.Shm, width: u31, height: u31) !*Buffer {
-    log.debug("creating new buffer {}x{}", .{ width, height });
+    log.debug("Creating new {}x{} buffer", .{ width, height });
     const buffer = try utils.gpa.create(Buffer);
     errdefer utils.gpa.destroy(buffer);
     buffer.* = try Buffer.init(wl_shm, width, height);
@@ -92,8 +91,8 @@ fn newBuffer(buffer_pool: *BufferPool, wl_shm: *wl.Shm, width: u31, height: u31)
 }
 
 fn cullBuffers(buffer_pool: *BufferPool) void {
-    log.debug("culling extra buffers", .{});
     var overhead = buffer_pool.len - max_buffer_multiplicity * buffer_pool.surface_count;
+    log.debug("Culling extra buffers {d}->{d}", .{ buffer_pool.len, buffer_pool.surface_count });
     var it = buffer_pool.buffers.first;
     while (it) |node| {
         if (overhead == 0) break;