[PATCH] D80623: WIP: Add an API to simplify setting TraversalKind in clang-tidy matchers

Tue Dec 22 10:14:36 PST 2020

aaron.ballman added inline comments.

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Comment at: clang/include/clang/ASTMatchers/ASTMatchFinder.h:118
+    /// behavior of clang-tidy.
+    virtual llvm::Optional<ast_type_traits::TraversalKind>
+    getCheckTraversalKind() const;
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steveire wrote:
> aaron.ballman wrote:
> > steveire wrote:
> > > sammccall wrote:
> > > > I don't really get why this would be optional.
> > > > A check's implementation isn't really going to be robust to "whatever the default is", it's going to be tested against one or the other.
> > > > So None isn't really a sensible return value - can't the base class simply return the actual default?
> > > ASTMatchFinder doesn't know the ASTContext, so it can't access the default. That's why I made it an optional.
> > The fact that it's optional is a bit weird. Given that this is a temporary API, I see two approaches: hold our nose because the ugliness shouldn't be long-lived, or have the default be specified in two places with comments saying "don't forget to update over here if you change this value" so we can get rid of the `Optional<>` here. WDYT?
> My preference is to keep the optional. Having multiple places to update makes it likely they'll get out of sync.
Then I think it's fine to leave it as `Optional<>` given that it's a temporary API for easing the transition. @sammccall, are you okay with that?

In terms of eventually removing this API, what's your plan? I noticed we can't do something nice like slapping a `[[deprecated]]` attribute on the declaration and have overriders get a notification that the method they're overriding is deprecated. Will we just pull the API entirely and force users to react to the code breakage?

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  https://reviews.llvm.org/D80623/new/

https://reviews.llvm.org/D80623