royjacobson added inline comments.
================
Comment at: clang/bindings/python/clang/cindex.py:1530
+
+ def record_needs_implicit_default_constructor(self):
+ """Returns True if the cursor refers to a C++ record declaration
----------------
anderslanglands wrote:
> royjacobson wrote:
> > anderslanglands wrote:
> > > royjacobson wrote:
> > > > aaron.ballman wrote:
> > > > > aaron.ballman wrote:
> > > > > > I don't think we should expose any of the "needs" functions like
> > > > > > this -- those are internal implementation details of the class and
> > > > > > I don't think we want to calcify that into something we have to
> > > > > > support forever. As we add members to a class, we recalculate
> > > > > > whether the added member causes us to delete defaulted special
> > > > > > members (among other things), and the "needs" functions are
> > > > > > basically used when the class is completed to handle lazily created
> > > > > > special members. I'm pretty sure that lazy creation is not mandated
> > > > > > by the standard, which is why I think the "needs" functions are
> > > > > > more of an implementation detail.
> > > > > CC @erichkeane and @royjacobson as folks who have been in this same
> > > > > area of the compiler to see if they agree or disagree with my
> > > > > assessment there.
> > > > I think so. The 'needs_*' functions query `DeclaredSpecialMembers` and
> > > > I'm pretty sure it's modified when we add the implicit definitions in
> > > > the class completion code. So this looks a bit suspicious. Is this API
> > > > //meant// to be used with incomplete classes?
> > > > For complete classes I think looking up the default/move/copy
> > > > constructor and calling `isImplicit()` is the way to do it.
> > > >
> > > > About the 'is deleted' API - can't the same be done for those functions
> > > > as well so we have a smaller API?
> > > >
> > > > If this //is// meant to be used with incomplete classes for efficiency
> > > > that would be another thing, I guess.
> > > >
> > > So the intended use case here is I'm using libclang to parse an existing
> > > C++ libray's headers and generate a C interface to it. To do that I need
> > > to know if I need to generate default constructors etc, which the needs*
> > > methods do for me (I believe). The alternative is I have to check
> > > manually whether all the constructors/assignment operators exist, then
> > > implement the implicit declaration rules myself correctly for each
> > > version of the standard, which I'd rather avoid.
> > >
> > > Would putting a note in the doc comment about the behaviour differing
> > > when the class is being constructed as originally suggested work for
> > > everyone?
> > Why is the `__is_default_constructible` builtin type trait not enough? Do
> > you have different behavior for user provided and implicit default
> > constructors?
> >
> Can I evaluate that from libclang somewhow? I can't modify the C++ libraries
> I'm wrapping.
>
> Basically, given:
> ```
> struct Foo { /* ... */ };
> ```
>
> I want to generate:
>
> ```
> typedef struct Foo_t;
>
> Foo_t* Foo_ctor();
> Foo_t* Foo_copy_ctor(Foo_t*);
> /* etc... */
> Foo_dtor(Foo_t*);
> ```
>
> In order to know which ones to generate for an arbitrary struct that may or
> may not have any combination of ctor/assignments defined, I need to know
> which ones exist and follow the implicit generation rules for the ones that
> don't. I can do this myself with a whole bunch of version-dependent logic,
> but I'd rather just rely on libclang since it already knows all this much
> better than I do.
I looked a bit, and it seems they aren't, and that generally libclang doesn't
really know about Sema, so exporting the type traits is not that easy :/
I'm not sure what's the best way forward here, but I don't like the idea of
exporting those half baked internal API calls when there are actual
standardized and implemented type traits that perform the same goal.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D135557/new/
https://reviews.llvm.org/D135557
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