1463907 - Clean up redundant uses of do_QueryInterface

Status: RESOLVED DUPLICATE of bug 1493226

(Developer Infrastructure :: Source Code Analysis, enhancement)

Description

[Adrian Wielgosik [:adrian17]]

I've noticed that the codebase has a small amount of seemingly-redundant (casting to the same type or base type) interface conversions. It seems like some of them were caused by recent interface refactors and removals.

For example, what used to be

nsIDOMNode* aDestinationNode;
...
nsCOMPtr<nsINode> node = do_QueryInterface(aDestinationNode);

After bug 1449147 became

nsINode* aDestinationNode;
...
nsCOMPtr<nsINode> node = do_QueryInterface(aDestinationNode);

Which is clearly unnecessary.

I've written a simple Clang checker that detects such QI uses. I'll attach the patch (not for review, I don't think it should go into the repo?) and output. While I don't think it has false positives, some cases of QI to related type are intentional. Still, it should be a useful tool for cleaning such code.

Comment 1

[Adrian Wielgosik [:adrian17]]

Attachment: Prototype Clang checker that finds possibly-redundant QI

Comment 2

[Adrian Wielgosik [:adrian17]]

Attachment: detected QI warnings, extracted from build log

Comment 3

[Andrew McCreight [:mccr8]]

I'm working on a patch for this, including fixes, in bug 1493226. I enforce it via a static_assert rather than a static analysis.