Implement Application::get_locale() for Windows backend (#1874)

* Implement Application::get_locale() for Windows backend

* Cleanup Application::get_locale() in Windows backend

* Minimize extent of unsafe block
* Be less defensive about locales of zero length
* Warn on failure to retrieve locale

* Formatting in Application::get_locale() for Windows backend

Author: dfrg

druid-shell/Cargo.toml

@@ -65,7 +65,7 @@ version = "0.3.9"
 features = ["d2d1_1", "dwrite", "winbase", "libloaderapi", "errhandlingapi", "winuser",
             "shellscalingapi", "shobjidl", "combaseapi", "synchapi", "dxgi1_3", "dcomp",
             "d3d11", "dwmapi", "wincon", "fileapi", "processenv", "winbase", "handleapi",
-            "shellapi"]
+            "shellapi", "winnls"]
 
 [target.'cfg(target_os="macos")'.dependencies]
 block = "0.1.6"

druid-shell/src/backend/windows/application.rs

@@ -27,6 +27,8 @@ use winapi::shared::windef::{DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2, HCURSOR
 use winapi::shared::winerror::HRESULT_FROM_WIN32;
 use winapi::um::errhandlingapi::GetLastError;
 use winapi::um::shellscalingapi::PROCESS_PER_MONITOR_DPI_AWARE;
+use winapi::um::winnls::GetUserDefaultLocaleName;
+use winapi::um::winnt::LOCALE_NAME_MAX_LENGTH;
 use winapi::um::winuser::{
     DispatchMessageW, GetAncestor, GetMessageW, LoadIconW, PeekMessageW, PostMessageW,
     PostQuitMessage, RegisterClassW, TranslateAcceleratorW, TranslateMessage, GA_ROOT,
@@ -40,7 +42,7 @@ use crate::application::AppHandler;
 use super::accels;
 use super::clipboard::Clipboard;
 use super::error::Error;
-use super::util::{self, ToWide, CLASS_NAME, OPTIONAL_FUNCTIONS};
+use super::util::{self, FromWide, ToWide, CLASS_NAME, OPTIONAL_FUNCTIONS};
 use super::window::{self, DS_REQUEST_DESTROY};
 
 #[derive(Clone)]
@@ -194,7 +196,17 @@ impl Application {
     }
 
     pub fn get_locale() -> String {
-        //TODO ahem
-        "en-US".into()
+        let mut buf = [0u16; LOCALE_NAME_MAX_LENGTH];
+        let len_with_null =
+            unsafe { GetUserDefaultLocaleName(buf.as_mut_ptr(), buf.len() as _) as usize };
+        let locale = if len_with_null > 0 {
+            buf.get(..len_with_null - 1).and_then(FromWide::from_wide)
+        } else {
+            None
+        };
+        locale.unwrap_or_else(|| {
+            tracing::warn!("Failed to get user locale");
+            "en-US".into()
+        })
     }
 }