Add default file extension for the file dialog in Windows.

Author: xStrom

druid-shell/src/dialog.rs

@@ -35,6 +35,7 @@ pub enum FileDialogType {
 pub struct FileDialogOptions {
     pub show_hidden: bool,
     pub allowed_types: Option<Vec<FileSpec>>,
+    pub default_type: Option<FileSpec>,
     // we don't want a library user to be able to construct this type directly
     __non_exhaustive: (),
     // multi selection
@@ -49,7 +50,7 @@ pub struct FileDialogOptions {
 /// struct.
 ///
 /// [`COMDLG_FILTERSPEC`]: https://docs.microsoft.com/en-ca/windows/win32/api/shtypes/ns-shtypes-comdlg_filterspec
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub struct FileSpec {
     /// A human readable name, describing this filetype.
     ///
@@ -85,11 +86,19 @@ impl FileDialogOptions {
         self
     }
 
-    /// Set the filetypes the user is allowed to select.
+    /// Set the file types the user is allowed to select.
     pub fn allowed_types(mut self, types: Vec<FileSpec>) -> Self {
         self.allowed_types = Some(types);
         self
     }
+
+    /// Set the default file type.
+    /// If it's `None` or not present in [`allowed_types`](#method.allowed_types)
+    /// then the first entry in [`allowed_types`](#method.allowed_types) will be used as default.
+    pub fn default_type(mut self, default_type: FileSpec) -> Self {
+        self.default_type = Some(default_type);
+        self
+    }
 }
 
 impl FileSpec {

druid-shell/src/platform/windows/dialog.rs

@@ -39,6 +39,8 @@ use crate::dialog::{FileDialogOptions, FileDialogType, FileSpec};
 use std::ffi::OsString;
 use std::ptr::null_mut;
 
+use std::convert::TryInto;
+
 // TODO: remove these when they get added to winapi
 DEFINE_GUID! {CLSID_FileOpenDialog,
 0xDC1C_5A9C, 0xE88A, 0x4DDE, 0xA5, 0xA1, 0x60, 0xF8, 0x2A, 0x20, 0xAE, 0xF7}
@@ -117,9 +119,24 @@ pub(crate) unsafe fn get_file_dialog_path(
             .collect::<Vec<_>>()
     });
 
+    // Having Some in raw_spec means that we can safely unwrap options.allowed_types.
+    // Be careful when moving the unwraps out of this block or changing how raw_spec is made.
     if let Some(spec) = &raw_spec {
-        as_result(file_dialog.SetFileTypes(spec.len() as u32, spec.as_ptr()))?;
-        as_result(file_dialog.SetFileTypeIndex(1))?;
+        // We also want to make sure that options.allowed_types wasn't Some(zero-length vector)
+        if !spec.is_empty() {
+            as_result(file_dialog.SetFileTypes(spec.len() as u32, spec.as_ptr()))?;
+
+            let index = match (&options.default_type, &options.allowed_types) {
+                (Some(typ), Some(typs)) => typs.iter().position(|t| t == typ).unwrap_or(0),
+                _ => 0,
+            };
+
+            let default_allowed_type = options.allowed_types.as_ref().unwrap().get(index).unwrap();
+            let default_extension = default_allowed_type.extensions.first().unwrap_or(&"");
+
+            as_result(file_dialog.SetFileTypeIndex((index + 1).try_into().unwrap()))?;
+            as_result(file_dialog.SetDefaultExtension(default_extension.to_wide().as_ptr()))?;
+        }
     }
 
     as_result(file_dialog.SetOptions(flags))?;