aaron.ballman added a reviewer: sammccall.
aaron.ballman added a subscriber: sammccall.
aaron.ballman added a comment.
In general, I'm happy with this. Adding @sammccall in case I've missed anything
regarding the AST matcher internals or design concerns.
================
Comment at: clang/include/clang/ASTMatchers/ASTMatchers.h:4629-4630
+/// matches `[x](){}`.
+AST_MATCHER_P(LambdaCapture, refersToVarDecl, internal::Matcher<VarDecl>,
+ InnerMatcher) {
+ auto *capturedVar = Node.getCapturedVar();
----------------
jcking1034 wrote:
> aaron.ballman wrote:
> > jcking1034 wrote:
> > > ymandel wrote:
> > > > aaron.ballman wrote:
> > > > > The name here is a bit unclear -- whether it is the matcher matching
> > > > > `int x;` or the `x` from the capture is not clear from the name. The
> > > > > comment suggests it's matching `x` from the capture, but I think it's
> > > > > actually matching the `int x;` variable declaration.
> > > > >
> > > > > Being clear on what's matched here is important when we think about
> > > > > initializers:
> > > > > ```
> > > > > void foo() {
> > > > > int x = 12;
> > > > > auto f = [x = 100](){};
> > > > > }
> > > > > ```
> > > > > and
> > > > > ```
> > > > > lambdaExpr(hasAnyCapture(lambdaCapture(refersToVarDecl(hasName("x"),
> > > > > hasInitializer(integerLiteral(equals(100))))))
> > > > > ```
> > > > > Would you expect this to match? (This might be a good test case to
> > > > > add.)
> > > > In a similar vein, do we want a separate matcher on the name of the
> > > > capture itself? e.g. an overload of `hasName`? And what about matchers
> > > > for the initializers? Those don't have to land in this patch, but do
> > > > you think those would be doable?
> > > I would expect @aaron.ballman's initializer example to match, and I added
> > > a similar test case to the one described. I think that if a capture does
> > > not have an initializer, then `refersToVarDecl` will match on the
> > > variable declaration before the lambda. However, if a capture does have
> > > an initializer, that initializer itself seems to be represented as a
> > > `VarDecl` in the AST, which is the `VarDecl` that gets matched.
> > >
> > > For that reason, I think we may not need to have a separate matcher on
> > > the name of the capture itself. Additionally, since captures with/without
> > > initializers are both represented the same way, there may not be a good
> > > way to distinguish between them, so matchers for initializers may not be
> > > possible.
> > > I think that if a capture does not have an initializer, then
> > > refersToVarDecl will match on the variable declaration before the lambda.
> > > However, if a capture does have an initializer, that initializer itself
> > > seems to be represented as a VarDecl in the AST, which is the VarDecl
> > > that gets matched.
> >
> > Oof, that'd be confusing! :-(
> >
> > > For that reason, I think we may not need to have a separate matcher on
> > > the name of the capture itself.
> >
> > Er, but there are init captures where you can introduce a whole new
> > declaration. I think we do want to be able to match on that, right? e.g.,
> > ```
> > [x = 12](){ return x; }();
> > ```
> >
> > > Additionally, since captures with/without initializers are both
> > > represented the same way, there may not be a good way to distinguish
> > > between them, so matchers for initializers may not be possible.
> >
> > That's a bummer! :-( If this turns out to be a limitation, we should
> > probably document it as such.
> For the example you've provided, these can be matched with the
> `refersToVarDecl` matcher, as seen in the test
> `LambdaCaptureTest_BindsToCaptureWithInitializer`. I've gone ahead and
> updated the documentation to include an example with an initializer.
>
> Having that limitation with initializer representation is definitely a
> concern, though. Looking through the [[
> https://clang.llvm.org/doxygen/LambdaCapture_8h_source.html | source ]] for
> the `LambdaCapture` class, the documentation for the `DeclAndBits` (line
> 42-48) suggests that there isn't a distinguishment between the two cases.
> However, do you think it's feasible to update the classes related to
> `LambdaCapture` obtain and store this information (possibly through updating
> the `LambdaCaptureKind` enum, updating the constructor/fields of the class,
> etc)?
> However, do you think it's feasible to update the classes related to
> LambdaCapture obtain and store this information (possibly through updating
> the LambdaCaptureKind enum, updating the constructor/fields of the class,
> etc)?
I think that would make sense (thought perhaps as an orthogonal patch). That we
don't track init captures seems like a deficiency of the AST to me.
Repository:
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https://reviews.llvm.org/D112491/new/
https://reviews.llvm.org/D112491
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