Add list.Head.prependList/appendList

The existing insertList never compiled.

example/list.zig

@@ -27,23 +27,31 @@ pub fn main() void {
         var one = B{ .data = 1 };
         var two = B{ .data = 2 };
         var three = B{ .data = 3 };
-        var four = B{ .data = 4 };
-        var five = B{ .data = 5 };
 
         std.debug.print("length: {} empty: {}\n", .{ a.length(), a.empty() });
 
         a.append(&one);
         a.append(&two);
         a.append(&three);
-        a.append(&four);
+
-        a.append(&five);
+        std.debug.print("length: {} empty: {}\n", .{ a.length(), a.empty() });
+
+        var b: wl.list.Head(B, .link) = undefined;
+        b.init();
+
+        var four = B{ .data = 4 };
+        var five = B{ .data = 5 };
+        b.append(&four);
+        b.append(&five);
+
+        a.appendList(&b);
 
         std.debug.print("length: {} empty: {}\n", .{ a.length(), a.empty() });
 
         {
             std.debug.print("forward\n", .{});
             var it = a.iterator(.forward);
-            while (it.next()) |b| std.debug.print("{}\n", .{b.data});
+            while (it.next()) |x| std.debug.print("{}\n", .{x.data});
         }
 
         three.link.swapWith(&four.link);
@@ -51,7 +59,7 @@ pub fn main() void {
         {
             std.debug.print("reverse swapped 3/4\n", .{});
             var it = a.iterator(.reverse);
-            while (it.next()) |b| std.debug.print("{}\n", .{b.data});
+            while (it.next()) |x| std.debug.print("{}\n", .{x.data});
         }
     }
     {

src/wayland_server_core.zig

@@ -406,6 +406,17 @@ pub const list = struct {
                 old_other_prev.insert(link);
             }
         }
+
+        /// private helper that doesn't handle empty lists and assumes that
+        /// other is the link of a Head.
+        fn insertList(link: *Link, other: *Link) void {
+            other.next.?.prev = link;
+            other.prev.?.next = link.next;
+            link.next.?.prev = other.prev;
+            link.next = other.next;
+
+            other.* = .{ .prev = null, .next = null };
+        }
     };
 
     pub const Direction = enum {
@@ -463,6 +474,16 @@ pub const list = struct {
                 head.link.prev.?.insert(link);
             }
 
+            pub fn prependList(head: *Self, other: *Self) void {
+                if (other.empty()) return;
+                head.link.insertList(&other.link);
+            }
+
+            pub fn appendList(head: *Self, other: *Self) void {
+                if (other.empty()) return;
+                head.link.prev.?.insertList(&other.link);
+            }
+
             pub fn length(head: *const Self) usize {
                 var count: usize = 0;
                 var current = head.link.next.?;
@@ -476,14 +497,6 @@ pub const list = struct {
                 return head.link.next == &head.link;
             }
 
-            pub fn insertList(head: *Self, other: *Self) void {
-                if (other.empty()) return;
-                other.link.next.?.prev = head.link;
-                other.link.prev.?.next = head.link.next;
-                head.link.next.?.prev = other.link.prev;
-                head.link.next = other.link.next;
-            }
-
             /// Removal of elements during iteration is illegal
             pub fn Iterator(comptime direction: Direction) type {
                 return struct {