recordDecl() AST matcher

[Manuel Klimek via cfe-commits]

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
>
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