Skip parsing functions that are not in Route.Action enum

Allow custom functions with arbitrary signatures and avoid any issues of
trying to parse functions that are not Jeztig route action functions
(i.e. index, get, post, put, patch, delete).

demo/src/app/views/root.zig

@@ -3,8 +3,13 @@ const jetzig = @import("jetzig");
 pub fn index(request: *jetzig.Request, data: *jetzig.Data) !jetzig.View {
     var root = try data.object();
     try root.put("message", data.string("Welcome to Jetzig!"));
+    try root.put("number", data.integer(customFunction(100, 200, 300)));
 
     try request.response.headers.append("x-example-header", "example header value");
 
     return request.render(.ok);
 }
+
+fn customFunction(a: i32, b: i32, c: i32) i32 {
+    return a + b + c;
+}

src/GenerateRoutes.zig

@@ -430,6 +430,11 @@ fn parseFunction(
         var args = std.ArrayList(Arg).init(self.allocator);
         defer args.deinit();
 
+        if (!isActionFunctionName(function_name)) {
+            self.allocator.free(function_name);
+            return null;
+        }
+
         while (it.next()) |arg| {
             if (arg.name_token) |arg_token| {
                 const arg_name = self.ast.tokenSlice(arg_token);
@@ -478,3 +483,11 @@ fn parseTypeExpr(self: *Self, node: std.zig.Ast.Node) ![]const u8 {
 fn asNodeIndex(index: usize) std.zig.Ast.Node.Index {
     return @as(std.zig.Ast.Node.Index, @intCast(index));
 }
+
+fn isActionFunctionName(name: []const u8) bool {
+    inline for (@typeInfo(jetzig.views.Route.Action).Enum.fields) |field| {
+        if (std.mem.eql(u8, field.name, name)) return true;
+    }
+
+    return false;
+}