font: CodepointMap supports clone

src/config/Config.zig

@@ -2965,11 +2965,7 @@ pub const RepeatableCodepointMap = struct {
 
     /// Deep copy of the struct. Required by Config.
     pub fn clone(self: *const Self, alloc: Allocator) !Self {
-        // TODO(fontmem): clone the codemap descriptors
-
-        return .{
-            .map = .{ .list = try self.map.list.clone(alloc) },
-        };
+        return .{ .map = try self.map.clone(alloc) };
     }
 
     /// Compare if two of our value are requal. Required by Config.

src/font/CodepointMap.zig

@@ -30,6 +30,18 @@ pub fn deinit(self: *CodepointMap, alloc: Allocator) void {
     self.list.deinit(alloc);
 }
 
+/// Deep copy of the struct. The given allocator is expected to
+/// be an arena allocator of some sort since the struct itself
+/// doesn't support fine-grained deallocation of fields.
+pub fn clone(self: *const CodepointMap, alloc: Allocator) !CodepointMap {
+    var list = try self.list.clone(alloc);
+    for (list.items(.descriptor)) |*d| {
+        d.* = try d.clone(alloc);
+    }
+
+    return .{ .list = list };
+}
+
 /// Add an entry to the map.
 ///
 /// For conflicting codepoints, entries added later take priority over

src/font/discovery.zig

@@ -86,6 +86,21 @@ pub const Descriptor = struct {
         return hasher.final();
     }
 
+    /// Deep copy of the struct. The given allocator is expected to
+    /// be an arena allocator of some sort since the descriptor
+    /// itself doesn't support fine-grained deallocation of fields.
+    pub fn clone(self: *const Descriptor, alloc: Allocator) !Descriptor {
+        // We can't do any errdefer cleanup in here. As documented we
+        // expect the allocator to be an arena so any errors should be
+        // cleaned up somewhere else.
+
+        var copy = self.*;
+        copy.family = if (self.family) |src| try alloc.dupeZ(u8, src) else null;
+        copy.style = if (self.style) |src| try alloc.dupeZ(u8, src) else null;
+        copy.variations = try alloc.dupe(Variation, self.variations);
+        return copy;
+    }
+
     /// Convert to Fontconfig pattern to use for lookup. The pattern does
     /// not have defaults filled/substituted (Fontconfig thing) so callers
     /// must still do this.