apprt/gtk: add version helpers

This adds version helpers similar to the adwaita version helpers so that
build time and runtime version checks can be done.

src/apprt/gtk/App.zig

@@ -85,6 +85,16 @@ quit_timer: union(enum) {
 pub fn init(core_app: *CoreApp, opts: Options) !App {
     _ = opts;
 
+    // Log our GTK version
+    log.info("GTK version build={d}.{d}.{d} runtime={d}.{d}.{d}", .{
+        c.GTK_MAJOR_VERSION,
+        c.GTK_MINOR_VERSION,
+        c.GTK_MICRO_VERSION,
+        c.gtk_get_major_version(),
+        c.gtk_get_minor_version(),
+        c.gtk_get_micro_version(),
+    });
+
     // We need to export GDK_DEBUG to run on Wayland after GTK 4.14.
     // Older versions of GTK do not support these values so it is safe
     // to always set this. Forwards versions are uncertain so we'll have to

src/apprt/gtk/version.zig

@@ -0,0 +1,40 @@
+const c = @import("c.zig").c;
+
+/// Verifies that the GTK version is at least the given version.
+///
+/// This can be run in both a comptime and runtime context. If it
+/// is run in a comptime context, it will only check the version
+/// in the headers. If it is run in a runtime context, it will
+/// check the actual version of the library we are linked against.
+///
+/// This is inlined so that the comptime checks will disable the
+/// runtime checks if the comptime checks fail.
+pub inline fn atLeast(
+    comptime major: u16,
+    comptime minor: u16,
+    comptime micro: u16,
+) bool {
+    // If our header has lower versions than the given version,
+    // we can return false immediately. This prevents us from
+    // compiling against unknown symbols and makes runtime checks
+    // very slightly faster.
+    if (comptime c.GTK_MAJOR_VERSION < major or
+        c.GTK_MINOR_VERSION < minor or
+        c.GTK_MICRO_VERSION < micro) return false;
+
+    // If we're in comptime then we can't check the runtime version.
+    if (@inComptime()) return true;
+
+    // We use the functions instead of the constants such as
+    // c.GTK_MINOR_VERSION because the function gets the actual
+    // runtime version.
+    if (c.gtk_get_major_version() >= major) {
+        if (c.gtk_get_major_version() > major) return true;
+        if (c.gtk_get_minor_version() >= minor) {
+            if (c.gtk_get_minor_version() > minor) return true;
+            return c.gtk_get_micro_version() >= micro;
+        }
+    }
+
+    return false;
+}