feat: install signal crash handler to reset terminal before dumping stack traces

This currently requires cloning std.debug to grant access to the standard trace
dump handler. Hopefully in future this could be made public in the standard
library.

src/main.zig

@@ -148,8 +148,10 @@ pub fn main() anyerror!void {
         return list_languages.list(a, stdout.writer(), tty_config);
     }
 
-    if (builtin.os.tag != .windows)
+    if (std.posix.getenv("JITDEBUG")) |_|
-        if (std.posix.getenv("JITDEBUG")) |_| thespian.install_debugger();
+        thespian.install_debugger()
+    else if (@hasDecl(renderer, "install_crash_handler"))
+        renderer.install_crash_handler();
 
     if (args.debug_wait) {
         std.debug.print("press return to start", .{});

src/renderer/vaxis/renderer.zig

@@ -118,6 +118,34 @@ pub fn panic_in_progress() bool {
     return in_panic.load(.acquire);
 }
 
+pub fn install_crash_handler() void {
+    if (!std.debug.have_segfault_handling_support) {
+        @compileError("segfault handler not supported for this target");
+    }
+    const act = std.posix.Sigaction{
+        .handler = .{ .sigaction = handle_crash },
+        .mask = std.posix.empty_sigset,
+        .flags = (std.posix.SA.SIGINFO | std.posix.SA.RESTART),
+    };
+
+    std.posix.sigaction(std.posix.SIG.BUS, &act, null);
+    std.posix.sigaction(std.posix.SIG.SEGV, &act, null);
+    std.posix.sigaction(std.posix.SIG.ABRT, &act, null);
+    std.posix.sigaction(std.posix.SIG.FPE, &act, null);
+    std.posix.sigaction(std.posix.SIG.ILL, &act, null);
+}
+
+fn handle_crash(sig: i32, info: *const std.posix.siginfo_t, ctx_ptr: ?*anyopaque) callconv(.c) noreturn {
+    in_panic.store(true, .release);
+    const cleanup = panic_cleanup;
+    panic_cleanup = null;
+    if (cleanup) |self| {
+        self.vx.deinit(self.allocator, self.tty.anyWriter());
+        self.tty.deinit();
+    }
+    @import("std/debug.zig").handleSegfaultPosix(sig, info, ctx_ptr);
+}
+
 pub fn run(self: *Self) Error!void {
     self.vx.sgr = .legacy;
     self.vx.conpty_hacks = true;