recordDecl() AST matcher

[Manuel Klimek via cfe-commits]

On Mon, Sep 14, 2015, 8:40 AM Aaron Ballman <aaron at aaronballman.com> wrote:

> On Sat, Sep 12, 2015 at 11:06 PM, Manuel Klimek <klimek at google.com> wrote:
> >
> >
> > On Sat, Sep 12, 2015, 9:25 PM Aaron Ballman <aaron at aaronballman.com>
> wrote:
> >>
> >> On Sat, Sep 12, 2015 at 8:22 AM, Manuel Klimek <klimek at google.com>
> wrote:
> >> >
> >> >
> >> > On Fri, Sep 11, 2015 at 10:39 PM Aaron Ballman <
> aaron at aaronballman.com>
> >> > wrote:
> >> >>
> >> >> On Fri, Sep 11, 2015 at 4:30 PM, Richard Smith <
> richard at metafoo.co.uk>
> >> >> wrote:
> >> >> > I don't think CXXRecordDecl is an anachronism, so much as an
> >> >> > implementation
> >> >> > detail; it makes sense to use a smaller class when in C mode, as we
> >> >> > don't
> >> >> > need most of the features and complexity that CXXRecordDecl brings
> >> >> > with
> >> >> > it.
> >> >> > But... as a user of clang matchers, I don't think I'd want to care
> >> >> > about
> >> >> > the
> >> >> > difference, and it'd be more convenient if I could nest (say) a
> >> >> > hasMethod
> >> >> > matcher within a recordDecl matcher, since it's completely obvious
> >> >> > what
> >> >> > that
> >> >> > should mean. If I have a matcher that says:
> >> >> >
> >> >> >   recordDecl(or(hasMethod(...), hasField(...)))
> >> >> >
> >> >> > I would expect that to work in both C and C++ (and the only way it
> >> >> > could
> >> >> > match in C would be on a record with the specified field, since the
> >> >> > hasMethod matcher would always fail).
> >> >>
> >> >> Okay, so then it sounds like we want recordDecl to *mean* RecordDecl,
> >> >> but we want the traversal and narrowing matchers that currently take
> a
> >> >> CXXRecordDecl to instead take a RecordDecl and handle the CXX part
> >> >> transparently? This means we would not need to add a cxxRecordDecl()
> >> >> matcher, but could still access CXX-only functionality (like access
> >> >> control, base classes, etc) through recordDecl()?
> >> >
> >> >
> >> > I'm against that proposal. I think we have tried to make the matchers
> >> > more
> >> > "user friendly" in the past, and all those attempts have failed
> >> > miserably;
> >> > in the end, users will do ast-dump to see what they want to match, and
> >> > then
> >> > be confused when the matchers do follow the AST 99% of the time, but
> try
> >> > to
> >> > be smart 1% of the time.
> >> > I think given that we want to keep CXXRecordDecl, the right solution
> is
> >> > to
> >> > have a cxxRecordDecl() matcher.
> >>
> >> Personally, I think this makes the most sense, at least to me. The
> >> recommendation I've always heard (and given) is to use -ast-dump and
> >> write matchers from there. (Consequently, the more I work with type
> >> traversal matchers, the more I wish we had -ast-dump-types to give
> >> even *more* information for writing matchers.)
> >>
> >> But the question still remains, what do we do with recordDecl? Right
> >> now, it means CXXRecordDecl instead of RecordDecl. If we change it to
> >> mean RecordDecl instead, there's a chance we'll break existing,
> >> reasonable code. Are we okay with that risk? If we're at least
> >> conceptually okay with it, I could make the change locally and see
> >> just how much of our own code breaks, and report back. But if that
> >> turns out to be problematic, do we want to deprecate recordDecl and
> >> replace it with structDecl as our fallback position? Or is there a
> >> better solution?
> >>
> >> Basically, I see a few ways to solve this (and there may be other ways
> >> I'm not thinking about yet):
> >>
> >> 1) Undocument/deprecate recordDecl, add structDecl, unionDecl, and
> >> cxxRecordDecl. This does not match the AST because we have no
> >> StructDecl or UnionDecl types. The more I think about this option, the
> >> less I like it. It's easy to implement, but seems hard to relate to
> >> the AST.
> >> 2) Make recordDecl match RecordDecl, don't touch other matchers. Add
> >> way to distinguish unions from structs (e.g., isUnion(), isStruct()),
> >> add cxxRecordDecl. This matches the AST most closely, but may break
> >> code. I think that I prefer this approach, but it depends heavily on
> >> what "may break code" looks like in practice.
> >> 3) Make recordDecl match RecordDecl, fix other matchers that currently
> >> take CXXRecordDecl to instead take RecordDecl and handle sensibly when
> >> possible. Add a way to distinguish unions from structs, add
> >> cxxRecordDecl. This doesn't match the AST because we will have
> >> matchers taking a RecordDecl when the AST would require a
> >> CXXRecordDecl, but is likely to break less code.
> >
> >
> > That sums it up. My preferences are 2, 3, 1 in that order :)
>
> I've attached a patch that implements #2, but it comes with ~85 errors
> from C++ matchers that use recordDecl to mean cxxRecordDecl.
>
> http://pastebin.com/bxkRcqBV
>
> If this is an acceptable failure rate, I can also update the failing
> matchers to use cxxRecordDecl instead of recordDecl where applicable.
> Doing some spot-checking of the failing code, the failures are ones we
> anticipated, such as:
>
> constructorDecl(ofClass(recordDecl(
> hasDeclaration(recordDecl(hasMethod(hasName("begin")),
> hasMethod(hasName("end"))))
> etc
>

+Daniel for another opinion. I think this is fine, but I'd  prefer not to
end up in a meme :)

~Aaron
>
> >
> >>
> >> ~Aaron
> >>
> >>
> >> > Richard: if CXXRecordDecl was really an implementation detail, it
> would
> >> > be
> >> > hidden behind a RecordDecl class, as an implementation detail. The
> >> > reasons
> >> > why we don't want it to be an implementation detail in the code
> >> > (performance, data structure size) don't matter - in the end, it's in
> >> > the
> >> > AST API.
> >> >
> >> >>
> >> >>
> >> >> ~Aaron
> >> >>
> >> >> >
> >> >> > On Fri, Sep 11, 2015 at 6:30 AM, Manuel Klimek <klimek at google.com>
> >> >> > wrote:
> >> >> >>
> >> >> >> Richard! We need an informed opinion :D
> >> >> >>
> >> >> >> On Fri, Sep 11, 2015 at 3:07 PM Aaron Ballman
> >> >> >> <aaron at aaronballman.com>
> >> >> >> wrote:
> >> >> >>>
> >> >> >>> Ping?
> >> >> >>>
> >> >> >>> On Tue, Sep 8, 2015 at 9:26 AM, Manuel Klimek <klimek at google.com
> >
> >> >> >>> wrote:
> >> >> >>> > On Tue, Sep 8, 2015 at 3:23 PM Aaron Ballman
> >> >> >>> > <aaron at aaronballman.com>
> >> >> >>> > wrote:
> >> >> >>> >>
> >> >> >>> >> On Tue, Sep 8, 2015 at 9:18 AM, Manuel Klimek
> >> >> >>> >> <klimek at google.com>
> >> >> >>> >> wrote:
> >> >> >>> >> > On Tue, Sep 8, 2015 at 2:23 PM Aaron Ballman
> >> >> >>> >> > <aaron at aaronballman.com>
> >> >> >>> >> > wrote:
> >> >> >>> >> >>
> >> >> >>> >> >> On Tue, Sep 8, 2015 at 5:40 AM, Manuel Klimek
> >> >> >>> >> >> <klimek at google.com>
> >> >> >>> >> >> wrote:
> >> >> >>> >> >> > Yea, we had that discussion a few times, and I can never
> >> >> >>> >> >> > remember
> >> >> >>> >> >> > why
> >> >> >>> >> >> > we
> >> >> >>> >> >> > ended up in the state we're in.
> >> >> >>> >> >> > We definitely had a time where we switched to just using
> >> >> >>> >> >> > the
> >> >> >>> >> >> > exact
> >> >> >>> >> >> > same
> >> >> >>> >> >> > name
> >> >> >>> >> >> > as the node's class name for the matchers.
> >> >> >>> >> >> > I *think* we didn't do it for cxxRecordDecl, because
> >> >> >>> >> >> > Richard
> >> >> >>> >> >> > said
> >> >> >>> >> >> > that's
> >> >> >>> >> >> > a
> >> >> >>> >> >> > relic we should get rid of anyway, but I'm not sure.
> >> >> >>> >> >>
> >> >> >>> >> >> FWIW, I think the state we're in is the worst of all
> worlds.
> >> >> >>> >> >> It's
> >> >> >>> >> >> not
> >> >> >>> >> >> intuitive that recordDecl() doesn't match a struct in C
> mode,
> >> >> >>> >> >> and
> >> >> >>> >> >> as
> >> >> >>> >> >> it stands, there is no way to match a struct or union
> >> >> >>> >> >> declaration
> >> >> >>> >> >> in C
> >> >> >>> >> >> at all.
> >> >> >>> >> >
> >> >> >>> >> >
> >> >> >>> >> > Agreed. Best intentions. Worst possible outcome. That's
> >> >> >>> >> > software
> >> >> >>> >> > development
> >> >> >>> >> > :)
> >> >> >>> >> >
> >> >> >>> >> >> >
> >> >> >>> >> >> > On Fri, Sep 4, 2015 at 8:32 PM Aaron Ballman
> >> >> >>> >> >> > <aaron at aaronballman.com>
> >> >> >>> >> >> > wrote:
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> It turns out that the recordDecl() AST matcher doesn't
> >> >> >>> >> >> >> match
> >> >> >>> >> >> >> RecordDecl objects; instead, it matches CXXRecordDecl
> >> >> >>> >> >> >> objects.
> >> >> >>> >> >> >> This
> >> >> >>> >> >> >> is... unfortunate... as it makes writing AST matchers
> more
> >> >> >>> >> >> >> complicated
> >> >> >>> >> >> >> because of having to translate between
> >> >> >>> >> >> >> recordDecl()/CXXRecordDecl.
> >> >> >>> >> >> >> It
> >> >> >>> >> >> >> also makes it impossible to match a struct or union
> >> >> >>> >> >> >> declaration
> >> >> >>> >> >> >> in C
> >> >> >>> >> >> >> or ObjC. However, given how prevalent recordDecl()'s use
> >> >> >>> >> >> >> is
> >> >> >>> >> >> >> in
> >> >> >>> >> >> >> the
> >> >> >>> >> >> >> wild (I'm guessing), changing it at this point would be
> a
> >> >> >>> >> >> >> Bad
> >> >> >>> >> >> >> Thing.
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> For people trying to write AST matchers for languages
> like
> >> >> >>> >> >> >> C
> >> >> >>> >> >> >> or
> >> >> >>> >> >> >> ObjC,
> >> >> >>> >> >> >> I would like to propose adding:
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> structDecl()
> >> >> >>> >> >> >> unionDecl()
> >> >> >>> >> >> >> tagDecl()
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> These will match nicely with the existing enumDecl() AST
> >> >> >>> >> >> >> matcher.
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> Additionally, I would like to add cxxRecordDecl() to
> match
> >> >> >>> >> >> >> CXXRecordDecl objects. While it duplicates the
> >> >> >>> >> >> >> functionality
> >> >> >>> >> >> >> exposed
> >> >> >>> >> >> >> by recordDecl(), it more clearly matches the intention
> of
> >> >> >>> >> >> >> which
> >> >> >>> >> >> >> AST
> >> >> >>> >> >> >> node it corresponds to.
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> Finally, I would like to undocument recordDecl() and
> >> >> >>> >> >> >> change
> >> >> >>> >> >> >> our
> >> >> >>> >> >> >> existing documentation and AST matcher uses to use
> >> >> >>> >> >> >> cxxRecordDecl/structDecl() instead. Maybe someday we can
> >> >> >>> >> >> >> deprecate
> >> >> >>> >> >> >> recordDecl() more officially.
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> I'm open to other ideas if there are better ways to move
> >> >> >>> >> >> >> forward. If
> >> >> >>> >> >> >> you think changing the meaning of recordDecl() is
> >> >> >>> >> >> >> acceptable,
> >> >> >>> >> >> >> I
> >> >> >>> >> >> >> can
> >> >> >>> >> >> >> also go that route (though I would still propose adding
> >> >> >>> >> >> >> unionDecl()
> >> >> >>> >> >> >> and cxxRecordDecl() in that case).
> >> >> >>> >> >> >
> >> >> >>> >> >> >
> >> >> >>> >> >> > I think changing recordDecl is acceptable. I believe very
> >> >> >>> >> >> > few
> >> >> >>> >> >> > tools
> >> >> >>> >> >> > will
> >> >> >>> >> >> > actually start doing wrong things because of it. I'd like
> >> >> >>> >> >> > more
> >> >> >>> >> >> > opinions
> >> >> >>> >> >> > first, though :)
> >> >> >>> >> >>
> >> >> >>> >> >> I was giving this more thought over the long weekend, and I
> >> >> >>> >> >> think
> >> >> >>> >> >> you
> >> >> >>> >> >> may be right. I think changing recordDecl() to mean
> >> >> >>> >> >> RecordDecl
> >> >> >>> >> >> will
> >> >> >>> >> >> fix more code than it breaks, so long as we take a holistic
> >> >> >>> >> >> approach
> >> >> >>> >> >> to the change and see which narrowing and traversal
> matchers
> >> >> >>> >> >> we
> >> >> >>> >> >> need
> >> >> >>> >> >> to fix up at the same time. When I tried to think of AST
> >> >> >>> >> >> matchers
> >> >> >>> >> >> that
> >> >> >>> >> >> mean CXXRecordDecl but *not* RecordDecl, they were horribly
> >> >> >>> >> >> contrived
> >> >> >>> >> >> because you usually are matching on additional selection
> >> >> >>> >> >> criteria
> >> >> >>> >> >> that
> >> >> >>> >> >> is specific to C++ (such as hasMethod() or isDerivedFrom())
> >> >> >>> >> >> which
> >> >> >>> >> >> would cause the match to continue to fail, as expected.
> Code
> >> >> >>> >> >> that
> >> >> >>> >> >> uses
> >> >> >>> >> >> recordDecl() to mean RecordDecl will suddenly start to
> match
> >> >> >>> >> >> in
> >> >> >>> >> >> more
> >> >> >>> >> >> cases, but that's likely to be a bug fix more than a
> breaking
> >> >> >>> >> >> change.
> >> >> >>> >> >> To the best of my understanding, the only breaking cases
> >> >> >>> >> >> would
> >> >> >>> >> >> be
> >> >> >>> >> >> where you wrote recordDecl(), meant CXXRecordDecl, had no
> >> >> >>> >> >> further
> >> >> >>> >> >> narrowing or traversal matchers, and were compiling in C
> >> >> >>> >> >> mode;
> >> >> >>> >> >> with
> >> >> >>> >> >> the result being additional unexpected matches.
> >> >> >>> >> >
> >> >> >>> >> >
> >> >> >>> >> > Ah, there's one thing that can break: the compile can break:
> >> >> >>> >> > recordDecl(hasMethod(...)) will *not* compile (it'll work in
> >> >> >>> >> > the
> >> >> >>> >> > dynamic
> >> >> >>> >> > matchers and fail as you suggest, but the in-C++ DSL does
> more
> >> >> >>> >> > static
> >> >> >>> >> > type
> >> >> >>> >> > checking).
> >> >> >>> >> > I don't think that's super bad though.
> >> >> >>> >> >
> >> >> >>> >> >>
> >> >> >>> >> >> So perhaps it would make sense to:
> >> >> >>> >> >>
> >> >> >>> >> >> 1) Make recordDecl() mean RecordDecl
> >> >> >>> >> >> 2) Do a comprehensive review of matchers that take a
> >> >> >>> >> >> CXXRecordDecl
> >> >> >>> >> >> and
> >> >> >>> >> >> see if they should instead take a RecordDecl
> >> >> >>> >> >> 3) Add unionDecl() as a node matcher (or should we add
> >> >> >>> >> >> isUnion()
> >> >> >>> >> >> and
> >> >> >>> >> >> isStruct() as narrowing matchers?)
> >> >> >>> >> >> 4) Add tagDecl() as a node matcher, but not add
> >> >> >>> >> >> cxxRecordDecl()
> >> >> >>> >> >
> >> >> >>> >> >
> >> >> >>> >> > Why not add cxxRecordDecl()? I think we need it if we want
> >> >> >>> >> > narrowing
> >> >> >>> >> > matchers on CXXRecordDecl?
> >> >> >>> >>
> >> >> >>> >> If Richard thinks CXXRecordDecl is an anachronism, I figured
> we
> >> >> >>> >> didn't
> >> >> >>> >> want to expose it. Instead, we could make hasMethod (et al)
> >> >> >>> >> accept
> >> >> >>> >> a
> >> >> >>> >> RecordDecl and do the type checking for the caller. Then
> >> >> >>> >> recordDecl(hasMethod(...)) continues to compile and work, and
> >> >> >>> >> when
> >> >> >>> >> hasMethod is given a RecordDecl instead of a CXXRecordDecl, it
> >> >> >>> >> simply
> >> >> >>> >> matches nothing. But you bring up a good point about the C++
> DSL
> >> >> >>> >> being
> >> >> >>> >> a problem still, I hadn't considered that.
> >> >> >>> >
> >> >> >>> >
> >> >> >>> > First I want Richard to confirm that. I have a very bad memory,
> >> >> >>> > so I
> >> >> >>> > might
> >> >> >>> > as well misremember :)
> >> >> >>> >
> >> >> >>> >>
> >> >> >>> >>
> >> >> >>> >> ~Aaron
> >> >> >>> >>
> >> >> >>> >> >
> >> >> >>> >> >>
> >> >> >>> >> >>
> >> >> >>> >> >> ~Aaron
> >> >> >>> >> >>
> >> >> >>> >> >> >
> >> >> >>> >> >> >>
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> Thanks!
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> ~Aaron
> >> >> >
> >> >> >
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20150914/b087c5bf/attachment-0001.html>