Bug 1409635 (part 2) - Fix up nsIPrefLocalizedString. r=froydnj.

nsIPrefLocalizedString is meant to be a wrapper for nsISupportsString,
basically identical but with a different identifier. But it's not a
sub-interface of nsISupportsString. Instead it (almost) duplicates
nsISupportsString's internals.

Specifically, nsISupportsString has `attribute AString data`, resulting in
these C++ methods:

> NS_IMETHOD GetData(nsAString& aData)
> NS_IMETHOD SetData(const nsAString& aData)

nsIPrefLocalizedString has `attribute wstring data`, resulting in these C++
methods:

> NS_IMETHOD GetData(char16_t** aData)
> NS_IMETHOD SetData(const char16_t* aData)

Then we have nsPrefLocalizedString, the concrete subclass of
nsIPrefLocalizedString. It implements the AString methods via
NS_FORWARD_NSISUPPORTSSTRING, which forwards to mUnicodeString. It also
implements the wstring methods explicitly, and they just call the AString
methods. It's all a bit of a mess.

(Both interfaces also have `wstring toString()`. The forwarding works more
smoothly for that method.)

This patch changes nsIPrefLocalizedString so it is a trivial sub-interface of
nsISupportsString. This change eliminates the need for the wstring methods, so
the patch removes them as well. The net result is we have less code, and fewer
conversions between C strings and Gecko strings. The patch also merges the
nsISupportsString and nsIPrefLocalizedString cases in
nsPrefBranch::SetComplexValue(), because they are now identical. (The
nsISupportsString and nsIPrefLocalizedString cases in
nsPrefBranch::GetComplexValue() remain distinct; indeed, that's the whole
reason for having them as separate interfaces.)

modules/libpref/Preferences.cpp

@@ -2263,23 +2263,19 @@ class nsPrefBranch final
 
 class nsPrefLocalizedString final
   : public nsIPrefLocalizedString
-  , public nsISupportsString
 {
 public:
   nsPrefLocalizedString();
 
   NS_DECL_ISUPPORTS
-  NS_FORWARD_NSISUPPORTSSTRING(mUnicodeString->)
   NS_FORWARD_NSISUPPORTSPRIMITIVE(mUnicodeString->)
+  NS_FORWARD_NSISUPPORTSSTRING(mUnicodeString->)
 
   nsresult Init();
 
 private:
   virtual ~nsPrefLocalizedString();
 
-  NS_IMETHOD GetData(char16_t**) override;
-  NS_IMETHOD SetData(const char16_t* aData) override;
-
   nsCOMPtr<nsISupportsString> mUnicodeString;
 };
 
@@ -2587,12 +2583,12 @@ nsPrefBranch::GetComplexValue(const char* aPrefName,
       nsAutoString utf16String;
       rv = GetDefaultFromPropertiesFile(pref.get(), utf16String);
       if (NS_SUCCEEDED(rv)) {
-        theString->SetData(utf16String.get());
+        theString->SetData(utf16String);
       }
     } else {
       rv = GetCharPref(aPrefName, getter_Copies(utf8String));
       if (NS_SUCCEEDED(rv)) {
-        theString->SetData(NS_ConvertUTF8toUTF16(utf8String).get());
+        theString->SetData(NS_ConvertUTF8toUTF16(utf8String));
       }
     }
 
@@ -2851,7 +2847,8 @@ nsPrefBranch::SetComplexValue(const char* aPrefName,
     return SetCharPrefInternal(aPrefName, descriptorString.get());
   }
 
-  if (aType.Equals(NS_GET_IID(nsISupportsString))) {
+  if (aType.Equals(NS_GET_IID(nsISupportsString)) ||
+      aType.Equals(NS_GET_IID(nsIPrefLocalizedString))) {
     nsCOMPtr<nsISupportsString> theString = do_QueryInterface(aValue);
 
     if (theString) {
@@ -2871,25 +2868,6 @@ nsPrefBranch::SetComplexValue(const char* aPrefName,
     return rv;
   }
 
-  if (aType.Equals(NS_GET_IID(nsIPrefLocalizedString))) {
-    nsCOMPtr<nsIPrefLocalizedString> theString = do_QueryInterface(aValue);
-
-    if (theString) {
-      nsString wideString;
-      rv = theString->GetData(getter_Copies(wideString));
-      if (NS_SUCCEEDED(rv)) {
-        // Check sanity of string length before any lengthy conversion
-        rv = CheckSanityOfStringLength(aPrefName, wideString);
-        if (NS_FAILED(rv)) {
-          return rv;
-        }
-        rv = SetCharPrefInternal(aPrefName,
-                                 NS_ConvertUTF16toUTF8(wideString).get());
-      }
-    }
-    return rv;
-  }
-
   NS_WARNING("nsPrefBranch::SetComplexValue - Unsupported interface type");
   return NS_NOINTERFACE;
 }
@@ -3241,33 +3219,6 @@ nsPrefLocalizedString::Init()
   return rv;
 }
 
-NS_IMETHODIMP
-nsPrefLocalizedString::GetData(char16_t** aRetVal)
-{
-  nsAutoString data;
-
-  nsresult rv = GetData(data);
-  if (NS_FAILED(rv)) {
-    return rv;
-  }
-
-  *aRetVal = ToNewUnicode(data);
-  if (!*aRetVal) {
-    return NS_ERROR_OUT_OF_MEMORY;
-  }
-
-  return NS_OK;
-}
-
-NS_IMETHODIMP
-nsPrefLocalizedString::SetData(const char16_t* aData)
-{
-  if (!aData) {
-    return SetData(EmptyString());
-  }
-  return SetData(nsDependentString(aData));
-}
-
 //----------------------------------------------------------------------------
 // nsRelativeFilePref
 //----------------------------------------------------------------------------
@@ -5018,7 +4969,7 @@ Preferences::GetLocalizedString(const char* aPref, nsAString& aResult)
     aPref, NS_GET_IID(nsIPrefLocalizedString), getter_AddRefs(prefLocalString));
   if (NS_SUCCEEDED(rv)) {
     NS_ASSERTION(prefLocalString, "Succeeded but the result is NULL");
-    prefLocalString->GetData(getter_Copies(aResult));
+    prefLocalString->GetData(aResult);
   }
   return rv;
 }
@@ -5498,7 +5449,7 @@ Preferences::GetDefaultLocalizedString(const char* aPref, nsAString& aResult)
     aPref, NS_GET_IID(nsIPrefLocalizedString), getter_AddRefs(prefLocalString));
   if (NS_SUCCEEDED(rv)) {
     NS_ASSERTION(prefLocalString, "Succeeded but the result is NULL");
-    prefLocalString->GetData(getter_Copies(aResult));
+    prefLocalString->GetData(aResult);
   }
   return rv;
 }

modules/libpref/nsIPrefLocalizedString.idl

@@ -4,6 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsISupports.idl"
+#include "nsISupportsPrimitives.idl"
 
 /**
  * The nsIPrefLocalizedString interface is simply a wrapper interface for
@@ -15,24 +16,8 @@
  * @see nsIPrefBranch
  * @see nsISupportsString
  */
-
 [scriptable, uuid(ae419e24-1dd1-11b2-b39a-d3e5e7073802)]
-interface nsIPrefLocalizedString : nsISupports
-{
-  /**
-   * Provides access to string data stored in this property.
-   *
-   * @throws Error An error occurred.
-   */
-  attribute wstring data;
-
-  /**
-   * Used to retrieve the contents of this object into a wide string.
-   *
-   * @return wstring The string containing the data stored within this object.
-   */
-  wstring toString();
-};
+interface nsIPrefLocalizedString : nsISupportsString {};
 
 %{C++