Add dynamic_combobox: a combobox with a runtime-populated item list

include/avnd/concepts/dynamic_items.hpp

@@ -0,0 +1,20 @@
+#pragma once
+
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <avnd/concepts/parameter.hpp>
+
+#include <functional>
+#include <string>
+#include <vector>
+
+namespace avnd
+{
+// enum-ish parameter carrying an update_items callback for runtime item lists.
+template <typename T>
+concept dynamic_items_parameter = enum_ish_parameter<T> && requires(T t) {
+  {
+    t.update_items
+  } -> std::convertible_to<std::function<void(std::vector<std::string>)>>;
+};
+}

include/avnd/concepts/folder_items.hpp

@@ -0,0 +1,19 @@
+#pragma once
+
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <avnd/concepts/parameter.hpp>
+
+#include <string_view>
+
+namespace avnd
+{
+// A combobox whose items are the files of a sibling folder port, populated by
+// the host at edit time. The port exposes folder_port() (the sibling port's
+// name) and extensions() (accepted suffixes).
+template <typename T>
+concept folder_items_parameter = enum_ish_parameter<T> && requires {
+  { T::folder_port() } -> std::convertible_to<std::string_view>;
+  { T::extensions() } -> std::convertible_to<std::string_view>;
+};
+}

include/halp/dynamic_combobox.hpp

@@ -0,0 +1,46 @@
+#pragma once
+
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <halp/polyfill.hpp>
+#include <halp/static_string.hpp>
+
+#include <array>
+#include <functional>
+#include <string>
+#include <string_view>
+#include <vector>
+
+namespace halp
+{
+// Combobox whose items are set at runtime via update_items. Bindings without
+// support leave update_items empty and use the static range() fallback.
+template <static_string lit>
+struct dynamic_combobox
+{
+  enum widget
+  {
+    combobox
+  };
+
+  struct range
+  {
+    std::array<std::string_view, 1> values{"-"};
+    int init{0};
+  };
+
+  static clang_buggy_consteval auto name() { return std::string_view{lit.value}; }
+
+  int value{0};
+
+  std::function<void(std::vector<std::string>)> update_items;
+
+  operator int&() noexcept { return value; }
+  operator const int&() const noexcept { return value; }
+  auto& operator=(int t) noexcept
+  {
+    value = t;
+    return *this;
+  }
+};
+}

include/halp/folder_combobox.hpp

@@ -0,0 +1,52 @@
+#pragma once
+
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+
+#include <halp/polyfill.hpp>
+#include <halp/static_string.hpp>
+
+#include <array>
+#include <string>
+#include <string_view>
+
+namespace halp
+{
+// Combobox whose items are the files of a sibling folder port, listed by the
+// host at edit time (and refreshed when the folder changes) — no execution
+// needed. The VALUE is the selected file name (a string), so an object can use
+// it directly as a file name. `folder_port` names the sibling path/folder
+// port; `extensions` is a space-separated list of accepted suffixes (empty =
+// all files); `init` is the initially selected file name — it stays selected
+// even while the file does not exist yet, so chains of processes that write
+// then read conventionally-named files keep working with default values.
+template <
+    static_string lit, static_string folder = "Folder", static_string exts = "",
+    static_string init_value = "-">
+struct folder_combobox
+{
+  enum widget
+  {
+    combobox
+  };
+
+  struct range
+  {
+    std::array<std::string_view, 1> values{init_value.value};
+    std::string_view init{init_value.value};
+  };
+
+  static clang_buggy_consteval auto name() { return std::string_view{lit.value}; }
+  static clang_buggy_consteval auto folder_port() { return std::string_view{folder.value}; }
+  static clang_buggy_consteval auto extensions() { return std::string_view{exts.value}; }
+
+  std::string value{};
+
+  operator std::string&() noexcept { return value; }
+  operator const std::string&() const noexcept { return value; }
+  auto& operator=(std::string t) noexcept
+  {
+    value = std::move(t);
+    return *this;
+  }
+};
+}