[cfe-dev] API for auto type deduction in libclang

[Richard Smith]

On Tue Jan 28 2014 at 3:43:30 AM, Kevin Funk <krf at gmx.de> wrote:

> Am Sonntag, 26. Januar 2014, 13:00:24 schrieb Jacob Carlborg:
> > On 2014-01-25 22:03, Kevin Funk wrote:
> > > That doesn't work for me.
> > >
> > > For testing we have a small wrapper binary that basically creates a
> > > CXTranslationUnit and then traverses through the AST via
> > > clang_visitChildren().
> > >
> > > During the call to 'visit' it does the following (amongst other
> things):
> > > - auto location = clang_getCursorLocation(cursor)
> > > - auto type = clang_getCursorType(cursor)
> > > - auto typeString = clang_getTypeSpelling(type)
> > > - now: auto canonicalTypeString =
> > >
> > >      clang_getTypeSpelling(clang_getCanonicalType(type))
> > >
> > > It outputs all the values of those variabes to stdout, and when I pass
> > > "auto i = 5;" to it I get:
> > >
> > > """
> > > decl: "auto (canonical type: auto) i " of kind VarDecl (9) in
> > > stdin.cpp at 1:6
> > >
> > >    "int (canonical type: int) " of kind IntegerLiteral (106) in
> > >    stdin.cpp at 1:10
> > >
> > > """
> > >
> > > So the 'canonical type' of VarDecl still resolves to 'auto', instead of
> > > 'int'. Sorry, if we're doing something completely wrong, but I don't
> seem
> > > to get this working as you suggest.
> >
> > Ok, I see, you're using clang_getTypeSpelling. I created my tool before
> > clang_getTypeSpelling was available. For aggregates, typedefs and a
> > couple of other types I'm using the following code[1]:
> >
> > auto cursor = clang_getTypeDeclaration(type);
> > auto str = clang_getCursorSpelling(cursor);
> >
> > For basic types like "int", "char" and so on, the above will return an
> > empty string. For those types I use a big switch statement on the type
> > kind and just returns a string representation [2].
> >
> > [1]
> > https://github.com/jacob-carlborg/dstep/blob/master/
> dstep/translator/Type.d#
> > L43
> >
> > [2]
> > https://github.com/jacob-carlborg/dstep/blob/master/
> dstep/translator/Type.d#
> > L248
>
> Unfortunately, your source code doesn't help me, nor can I get it to work
> using any combination of getTypeDeclaration, getCursorSpelling, and the
> ones I
> referred to earlier...
>
> I wonder if there's some bug in Clang's type printers I'm experiencing
> here.
>
> Let's do some testing:
> Test file: test.cpp, containing 'auto i = 5;'
>
> $ clang -cc1 -std=c++11 -ast-dump test.cpp
> (...)
> `-VarDecl 0x1c2e5b0 <test.cpp:1:1, col:10> i 'int':'int'
>   `-IntegerLiteral 0x1c2e608 <col:10> 'int' 5
>
> => What I'd expect! ('auto' => 'int')
>
> Next try: My clang-standalone-parser (basically emulating 'clang -cc1
> -dump')
> but using libclang only [1]:
>
> $ ./clang-standalone-parser -std=c++11 test.cpp
> test.cpp:1:6 (5, 0-10) kind: VarDecl type: auto display name: i (...)
>   test.cpp:1:10 (9, 9-10) kind: IntegerLiteral type: int
>
> => Not what I'd expect, 'auto' is not deduced
>
> And the odd part here is: Breaking on the symbol
> 'clang::AutoType::getDeducedType()' for both clang and
> clang-standalone-parser
> shows that *both* versions actually call that function when trying to find
> a
> string representation for the type 'auto'. But with
> clang-standalone-parser,
> 'clang::AutoType::getDeducedType()' always returns an null QualType.
>
> Can someone make any sense out of this? Bug in Clang/LLVM? Note that the
> backtrace towards the call of getDeducedType is slightly different for the
> two
> versions (see attached file). Maybe this is the reason?
>

I would expect that clang's dumper is using VarDecl->getType() and your
standalone tool is using VarDecl->getTypeSourceInfo(). The former produces
the type of the variable (which is 'int'); the latter produces the
type-as-written (which is 'auto').

FWIW, we've been considering changing this for variables, but even if we
did, the problem would persist for functions with 'auto' return types.


> Any help greatly appreciated!
>
> Greets
>
> [1] http://quickgit.kde.org/?p=kdev-clang.git&a=blob&h=
> dbad9e8942cc5e20fd005677fc32a5a0b54977ae&hb=1fa9eca7a9a58404c3ef687fcfa638
> 00d459cff5&f=tests%2Fclang-standalone-parser.c
>
> Compiling is simple:
> $ clang clang-standalone-parser.c -I/path/to/llvm/include
> -L/path/to/llvm/lib
> -lclang -Wl,-rpath,'/path/to/llvm/lib' -o clang-standalone-parser
>
> --
> Kevin Funk_______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
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