feat(app): signal WINCH for .resize system event

This allows the application to automatically re-draw and resize if the
application receives the signal by the terminal emulator.

src/app.zig

@@ -28,11 +28,17 @@ pub fn App(comptime E: type) type {
         thread: ?Thread = null,
         quit_event: Thread.ResetEvent,
         termios: ?posix.termios = null,
+        winch_registered: bool = false,
 
-        pub const SignalHandler = struct {
+        // global variable for the registered handler for WINCH
-            context: *anyopaque,
+        var handler_ctx: *anyopaque = undefined;
-            callback: *const fn (context: *anyopaque) void,
+        /// registered WINCH handler to report resize events
-        };
+        fn handleWinch(_: c_int) callconv(.C) void {
+            const this: *@This() = @ptrCast(@alignCast(handler_ctx));
+            // NOTE this does not have to be done if in-band resize events are supported
+            // -> the signal might not work correctly when hosting the application over ssh!
+            this.postEvent(.resize);
+        }
 
         pub const init: @This() = .{
             .queue = .{},
@@ -45,6 +51,17 @@ pub fn App(comptime E: type) type {
             // post init event (as the very first element to be in the queue - event loop)
             this.postEvent(.init);
 
+            if (!this.winch_registered) {
+                handler_ctx = this;
+                var act = posix.Sigaction{
+                    .handler = .{ .handler = handleWinch },
+                    .mask = posix.empty_sigset,
+                    .flags = 0,
+                };
+                posix.sigaction(posix.SIG.WINCH, &act, null);
+                this.winch_registered = true;
+            }
+
             this.quit_event.reset();
             this.thread = try Thread.spawn(.{}, @This().run, .{this});
 
@@ -159,7 +176,7 @@ pub fn App(comptime E: type) type {
                                                 'Q' => input.F2,
                                                 'R' => input.F3,
                                                 'S' => input.F4,
-                                                else => unreachable, // switch case prevents in this case form ever happening
+                                                else => unreachable,
                                             },
                                         };
                                         this.postEvent(.{ .key = key });
@@ -205,7 +222,7 @@ pub fn App(comptime E: type) type {
                                     'I' => this.postEvent(.{ .focus = true }),
                                     'O' => this.postEvent(.{ .focus = false }),
                                     'M', 'm' => {
-                                        std.debug.assert(sequence.len >= 4);
+                                        assert(sequence.len >= 4);
                                         if (sequence[2] != '<') break;
 
                                         const delim1 = mem.indexOfScalarPos(u8, sequence, 3, ';') orelse break;
@@ -252,7 +269,7 @@ pub fn App(comptime E: type) type {
                                         // Device Status Report
                                         // CSI Ps n
                                         // CSI ? Ps n
-                                        std.debug.assert(sequence.len >= 3);
+                                        assert(sequence.len >= 3);
                                     },
                                     't' => {
                                         // XTWINOPS
@@ -267,6 +284,7 @@ pub fn App(comptime E: type) type {
 
                                             _ = width_char;
                                             _ = height_char;
+                                            this.postEvent(.resize);
                                             // this.postEvent(.{ .size = .{
                                             //     .x = fmt.parseUnsigned(u16, width_char, 10) catch break,
                                             //     .y = fmt.parseUnsigned(u16, height_char, 10) catch break,
@@ -298,7 +316,7 @@ pub fn App(comptime E: type) type {
                             0x0a, 0x0d => .{ .cp = input.Enter },
                             0x01...0x07, 0x0b...0x0c, 0x0e...0x1a => .{ .cp = b + 0x60, .mod = .{ .ctrl = true } },
                             0x1b => escape: {
-                                std.debug.assert(read_bytes == 1);
+                                assert(read_bytes == 1);
                                 break :escape .{ .cp = input.Escape };
                             },
                             0x7f => .{ .cp = input.Backspace },
@@ -333,6 +351,7 @@ const mem = std.mem;
 const fmt = std.fmt;
 const posix = std.posix;
 const Thread = std.Thread;
+const assert = std.debug.assert;
 const code_point = @import("code_point");
 const event = @import("event.zig");
 const input = @import("input.zig");

src/event.zig

@@ -8,6 +8,8 @@ pub const SystemEvent = union(enum) {
     init,
     /// Quit event to signify the end of the event loop (rendering should stop afterwards)
     quit,
+    /// Resize event to signify that the application should re-draw to resize
+    resize,
     /// Error event to notify other containers about a recoverable error
     err: struct {
         /// actual error