print: Use inch for US and LR

Closes #143

Part-of: <https://gitlab.gnome.org/GNOME/loupe/-/merge_requests/240>

Cargo.lock

@@ -1610,6 +1610,7 @@ dependencies = [
  "env_logger",
  "futures",
  "gettext-rs",
+ "gettext-sys",
  "gio",
  "glycin",
  "gtk4",

Cargo.toml

@@ -52,3 +52,7 @@ features = ["v1_4"]
 [dependencies.gettext-rs]
 version = "0.7.0"
 features = ["gettext-system"]
+
+[dependencies.gettext-sys]
+version = "0.21.3"
+features = ["gettext-system"]

src/widgets/print.rs

@@ -380,6 +380,20 @@ mod imp {
                             .round(obj.image().image_size().0 as f64 * obj.width_unit_factor()),
                     );
 
+                    // Default to inch for USA and Liberia
+                    if let Some(unit_locale) = getlocale(gettextrs::LocaleCategory::LcMeasurement) {
+                        if let Some(locale) = unit_locale
+                            .split(|x| *x == b'_')
+                            .nth(1)
+                            .and_then(|x| x.get(0..2))
+                        {
+                            if locale == b"US" || locale == b"LR" {
+                                imp.margin_unit.set_selected(Unit::Inch as u32);
+                                imp.size_unit.set_selected(Unit::Inch as u32);
+                            }
+                        }
+                    }
+
                     imp.print_operation.cancel();
 
                     let orientation = match obj.page_setup().orientation() {
@@ -902,3 +916,15 @@ extern "C" {
         max: std::ffi::c_double,
     );
 }
+
+// TODO: Upstream to gettext if possible
+pub fn getlocale(category: gettextrs::LocaleCategory) -> Option<Vec<u8>> {
+    unsafe {
+        let ret = gettext_sys::setlocale(category as i32, std::ptr::null());
+        if ret.is_null() {
+            None
+        } else {
+            Some(std::ffi::CStr::from_ptr(ret).to_bytes().to_owned())
+        }
+    }
+}