Bug 984466 - change CallQueryInterface to assert in cases of trivial conversions; r=ehsan

dom/plugins/base/nsPluginDirServiceProvider.cpp

@@ -345,12 +345,14 @@ nsPluginDirServiceProvider::GetFile(const char *charProp, bool *persistant,
     }
   }
 
-  if (localFile && NS_SUCCEEDED(rv))
-    return CallQueryInterface(localFile, _retval);
-
+  if (NS_FAILED(rv)) {
     return rv;
   }
 
+  localFile.forget(_retval);
+  return NS_OK;
+}
+
 nsresult
 nsPluginDirServiceProvider::GetPLIDDirectories(nsISimpleEnumerator **aEnumerator)
 {

embedding/components/webbrowserpersist/src/nsWebBrowserPersist.cpp

@@ -1116,12 +1116,14 @@ nsresult nsWebBrowserPersist::GetLocalFileFromURI(nsIURI *aURI, nsIFile **aLocal
 
     nsCOMPtr<nsIFile> file;
     rv = fileURL->GetFile(getter_AddRefs(file));
-    if (NS_SUCCEEDED(rv))
-        rv = CallQueryInterface(file, aLocalFile);
-
+    if (NS_FAILED(rv)) {
         return rv;
     }
 
+    file.forget(aLocalFile);
+    return NS_OK;
+}
+
 nsresult nsWebBrowserPersist::AppendPathToURI(nsIURI *aURI, const nsAString & aPath) const
 {
     NS_ENSURE_ARG_POINTER(aURI);

modules/libpref/src/Preferences.cpp

@@ -720,7 +720,9 @@ Preferences::GetBranch(const char *aPrefRoot, nsIPrefBranch **_retval)
     rv = CallQueryInterface(prefBranch, _retval);
   } else {
     // special case caching the default root
-    rv = CallQueryInterface(sRootBranch, _retval);
+    nsCOMPtr<nsIPrefBranch> root(sRootBranch);
+    root.forget(_retval);
+    rv = NS_OK;
   }
   return rv;
 }
@@ -729,15 +731,18 @@ NS_IMETHODIMP
 Preferences::GetDefaultBranch(const char *aPrefRoot, nsIPrefBranch **_retval)
 {
   if (!aPrefRoot || !aPrefRoot[0]) {
-    return CallQueryInterface(sDefaultRootBranch, _retval);
+    nsCOMPtr<nsIPrefBranch> root(sDefaultRootBranch);
+    root.forget(_retval);
+    return NS_OK;
   }
 
   // TODO: - cache this stuff and allow consumers to share branches (hold weak references I think)
-  nsPrefBranch* prefBranch = new nsPrefBranch(aPrefRoot, true);
+  nsRefPtr<nsPrefBranch> prefBranch = new nsPrefBranch(aPrefRoot, true);
   if (!prefBranch)
     return NS_ERROR_OUT_OF_MEMORY;
 
-  return CallQueryInterface(prefBranch, _retval);
+  prefBranch.forget(_retval);
+  return NS_OK;
 }
 
 

profile/dirserviceprovider/src/nsProfileDirServiceProvider.cpp

@@ -232,13 +232,14 @@ nsProfileDirServiceProvider::GetFile(const char *prop, bool *persistant, nsIFile
     }
   }
 
-  
-  if (localFile && NS_SUCCEEDED(rv))
-    return CallQueryInterface(localFile, _retval);
-
+  if (NS_FAILED(rv)) {
     return rv;
   }
 
+  localFile.forget(_retval);
+  return NS_OK;
+}
+
 //*****************************************************************************
 // Protected methods
 //*****************************************************************************

toolkit/components/downloads/nsDownloadManager.cpp

@@ -3202,12 +3202,17 @@ nsDownload::GetTargetFile(nsIFile **aTargetFile)
   nsresult rv;
 
   nsCOMPtr<nsIFileURL> fileURL = do_QueryInterface(mTarget, &rv);
-  if (NS_FAILED(rv)) return rv;
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
 
   nsCOMPtr<nsIFile> file;
   rv = fileURL->GetFile(getter_AddRefs(file));
-  if (NS_SUCCEEDED(rv))
-    rv = CallQueryInterface(file, aTargetFile);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  file.forget(aTargetFile);
   return rv;
 }
 

toolkit/xre/nsAppRunner.cpp

@@ -2969,9 +2969,7 @@ XREMain::XRE_mainInit(bool* aExitFlag)
     if (NS_FAILED(rv))
       return 2;
 
-    rv = CallQueryInterface(greDir, &mAppData->xreDirectory);
-    if (NS_FAILED(rv))
-      return 2;
+    greDir.forget(&mAppData->xreDirectory);
   }
 
   if (!mAppData->directory) {

uriloader/exthandler/nsMIMEInfoImpl.cpp

@@ -265,13 +265,18 @@ nsMIMEInfoBase::GetLocalFileFromURI(nsIURI *aURI, nsIFile **aFile)
   nsresult rv;
 
   nsCOMPtr<nsIFileURL> fileUrl = do_QueryInterface(aURI, &rv);
-  if (NS_FAILED(rv)) return rv;
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
 
   nsCOMPtr<nsIFile> file;
   rv = fileUrl->GetFile(getter_AddRefs(file));
-  if (NS_FAILED(rv)) return rv;    
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
 
-  return CallQueryInterface(file, aFile);
+  file.forget(aFile);
+  return NS_OK;
 }
 
 NS_IMETHODIMP

widget/gtk/nsFilePicker.cpp

@@ -309,7 +309,8 @@ nsFilePicker::GetFile(nsIFile **aFile)
   rv = fileURL->GetFile(getter_AddRefs(file));
   NS_ENSURE_SUCCESS(rv, rv);
 
-  return CallQueryInterface(file, aFile);
+  file.forget(aFile);
+  return NS_OK;
 }
 
 NS_IMETHODIMP

widget/xpwidgets/nsBaseFilePicker.cpp

@@ -272,9 +272,11 @@ NS_IMETHODIMP nsBaseFilePicker::GetDisplayDirectory(nsIFile **aDirectory)
     return NS_OK;
   nsCOMPtr<nsIFile> directory;
   nsresult rv = mDisplayDirectory->Clone(getter_AddRefs(directory));
-  if (NS_FAILED(rv))
+  if (NS_FAILED(rv)) {
     return rv;
-  return CallQueryInterface(directory, aDirectory);
+  }
+  directory.forget(aDirectory);
+  return NS_OK;
 }
 
 NS_IMETHODIMP

xpcom/glue/nsISupportsUtils.h

@@ -11,6 +11,7 @@
 #include "nsError.h"
 #include "nsDebug.h"
 #include "nsISupportsImpl.h"
+#include "mozilla/TypeTraits.h"
 
 /**
  * Macro for adding a reference to an interface.
@@ -128,6 +129,12 @@ inline
 nsresult
 CallQueryInterface( T* aSource, DestinationType** aDestination )
 {
+    // We permit nsISupports-to-nsISupports here so that one can still obtain
+    // the canonical nsISupports pointer with CallQueryInterface.
+    static_assert(!mozilla::IsSame<T, DestinationType>::value ||
+                  mozilla::IsSame<DestinationType, nsISupports>::value,
+                  "don't use CallQueryInterface for compile-time-determinable casts");
+
     NS_PRECONDITION(aSource, "null parameter");
     NS_PRECONDITION(aDestination, "null parameter");
 

xpcom/io/nsDirectoryService.cpp

@@ -879,7 +879,8 @@ nsDirectoryService::GetFile(const char *prop, bool *persistent, nsIFile **_retva
     if (!localFile)
         return NS_ERROR_FAILURE;
 
-    return CallQueryInterface(localFile, _retval);
+    localFile.forget(_retval);
+    return NS_OK;
 }
 
 NS_IMETHODIMP

xpcom/io/nsLocalFileUnix.cpp

@@ -1370,11 +1370,14 @@ nsLocalFile::GetParent(nsIFile **aParent)
     // make buffer whole again
     *slashp = c;
 
-    if (NS_SUCCEEDED(rv) && localFile)
-        rv = CallQueryInterface(localFile, aParent);
+    if (NS_FAILED(rv)) {
         return rv;
     }
 
+    localFile.forget(aParent);
+    return NS_OK;
+}
+
 /*
  * The results of Exists, isWritable and isReadable are not cached.
  */

xpcom/io/nsLocalFileWin.cpp

@@ -2684,12 +2684,14 @@ nsLocalFile::GetParent(nsIFile * *aParent)
     nsCOMPtr<nsIFile> localFile;
     nsresult rv = NS_NewLocalFile(parentPath, mFollowSymlinks, getter_AddRefs(localFile));
 
-    if (NS_SUCCEEDED(rv) && localFile) {
-        return CallQueryInterface(localFile, aParent);
-    }
+    if (NS_FAILED(rv)) {
         return rv;
     }
 
+    localFile.forget(aParent);
+    return NS_OK;
+}
+
 NS_IMETHODIMP
 nsLocalFile::Exists(bool *_retval)
 {