Bug 1707462 - expose Windows' localized file display names through XPCOM, r=mhowell

Differential Revision: https://phabricator.services.mozilla.com/D143480

xpcom/io/FileDescriptorFile.cpp

@@ -94,6 +94,10 @@ FileDescriptorFile::GetNativeLeafName(nsACString& aLeafName) {
   return mFile->GetNativeLeafName(aLeafName);
 }
 
+NS_IMETHODIMP FileDescriptorFile::GetDisplayName(nsAString& aLeafName) {
+  return mFile->GetDisplayName(aLeafName);
+}
+
 nsresult FileDescriptorFile::GetTarget(nsAString& aRetVal) {
   return mFile->GetTarget(aRetVal);
 }

xpcom/io/nsIFile.idl

@@ -116,6 +116,18 @@ interface nsIFile : nsISupports
     attribute AString leafName;
     [noscript] attribute ACString nativeLeafName;
 
+    /**
+     * The leaf name as displayed in OS-provided file pickers and similar UI.
+     * On Windows and macOS, 'real' leaf names of some directories can be
+     * in English, but the OS will show a different, translated name to users
+     * using a different locale. So folders like "Downloads", "Desktop" and
+     * "Documents" might not normally appear to users with that (English) name,
+     * but with an OS-localized translation. This API will return such a
+     * translation if it exists, or the leafName if it doesn't.
+     * On Linux, this will always be the same as `leafName`.
+     */
+    readonly attribute AString displayName;
+
     /**
      *  copyTo[Native]
      *

xpcom/io/nsLocalFileUnix.cpp

@@ -666,6 +666,11 @@ nsLocalFile::SetNativeLeafName(const nsACString& aLeafName) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsLocalFile::GetDisplayName(nsAString& aLeafName) {
+  return GetLeafName(aLeafName);
+}
+
 nsCString nsLocalFile::NativePath() { return mPath; }
 
 nsresult nsIFile::GetNativePath(nsACString& aResult) {

xpcom/io/nsLocalFileWin.cpp

@@ -1615,6 +1615,25 @@ nsLocalFile::SetLeafName(const nsAString& aLeafName) {
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsLocalFile::GetDisplayName(nsAString& aLeafName) {
+  aLeafName.Truncate();
+
+  if (mWorkingPath.IsEmpty()) {
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+  }
+  SHFILEINFOW sfi = {};
+  DWORD_PTR result = ::SHGetFileInfoW(mWorkingPath.get(), 0, &sfi, sizeof(sfi),
+                                      SHGFI_DISPLAYNAME);
+  // If we found a display name, return that:
+  if (result) {
+    aLeafName.Assign(sfi.szDisplayName);
+    return NS_OK;
+  }
+  // Nope - fall back to the regular leaf name.
+  return GetLeafName(aLeafName);
+}
+
 NS_IMETHODIMP
 nsLocalFile::GetPath(nsAString& aResult) {
   MOZ_ASSERT_IF(