termio: free resources for discarded messages

Messages can own allocated data or a derived config. Some paths (writer
thread draining, mailbox shutdown with unread messages, and queue push
failures) discarded messages without releasing those resources.

This change adds Message.deinit and uses it whenever a message is
discarded.

src/Surface.zig

@@ -872,10 +872,9 @@ fn queueIo(
         switch (msg) {
             .write_small,
             .write_stable,
-            => return,
-
-            .write_alloc => |v| {
-                v.alloc.free(v.data);
+            .write_alloc,
+            => {
+                msg.deinit();
                 return;
             },
 

src/termio/Thread.zig

@@ -298,7 +298,7 @@ fn drainMailbox(
 
     // If we're draining, we just drain the mailbox and return.
     if (self.flags.drain) {
-        while (mailbox.pop(global.io())) |_| {}
+        while (mailbox.pop(global.io())) |msg| msg.deinit();
         return;
     }
 

src/termio/mailbox.zig

@@ -47,6 +47,7 @@ pub const Mailbox = union(enum) {
     pub fn deinit(self: *Mailbox, alloc: Allocator) void {
         switch (self.*) {
             .spsc => |*v| {
+                while (v.queue.pop(global.io())) |msg| msg.deinit();
                 v.queue.destroy(alloc);
                 v.wakeup.deinit();
             },
@@ -76,6 +77,7 @@ pub const Mailbox = union(enum) {
                 // lock so we need to unlock.
                 mb.wakeup.notify() catch |err| {
                     log.warn("failed to wake up writer, data will be dropped err={}", .{err});
+                    msg.deinit();
                     return;
                 };
 
@@ -90,7 +92,7 @@ pub const Mailbox = union(enum) {
                 // here.
                 if (mutex) |m| m.unlock(global.io());
                 defer if (mutex) |m| m.lockUncancelable(global.io());
-                _ = mb.queue.push(global.io(), msg, .{ .forever = {} });
+                if (mb.queue.push(global.io(), msg, .{ .forever = {} }) == 0) msg.deinit();
             },
         }
     }

src/termio/message.zig

@@ -102,6 +102,19 @@ pub const Message = union(enum) {
         };
     }
 
+    /// Free resources owned by a message that will not be processed.
+    /// The message is invalid after this call.
+    pub fn deinit(self: *const Message) void {
+        switch (self.*) {
+            .change_config => |v| {
+                v.ptr.deinit();
+                v.alloc.destroy(v.ptr);
+            },
+            .write_alloc => |v| v.alloc.free(v.data),
+            else => {},
+        }
+    }
+
     /// The types of size reports that we support.
     pub const SizeReport = terminal.size_report.Style;
 };