[cfe-dev] Distinguishing between implicit and explicit bool to int casts

[David Blaikie via cfe-dev]

It's a bit of a quirk of Clang's AST representation, to be sure - but,
yeah, basically I think you have to check that there's no explicit cast
around the implicit cast to find the things you're looking for.

On Fri, May 13, 2016 at 11:50 AM, Michael Layzell <michael at thelayzells.com>
wrote:

> Indeed, there is a difference, but I don't understand why the implicit
> cast is occurring. I could theoretically look for the pattern of the no-op
> CStyleCastExpr around the ImplicitCastExpr, but that seems like a bit of a
> hack. The cast isn't really implicit in this situation I would think.
>
> On Mon, May 9, 2016 at 1:18 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>> In C++ at least, there seems to be a difference:
>>
>> |-VarDecl 0x7da9f60 <cast.cc:1:1, col:14> col:5 x 'int' cinit
>> | `-CStyleCastExpr 0x7daa040 <col:9, col:14> 'int' <NoOp>
>> |   `-ImplicitCastExpr 0x7daa028 <col:14> 'int' <IntegralCast>
>> |     `-CXXBoolLiteralExpr 0x7daa000 <col:14> '_Bool' true
>> `-VarDecl 0x7daa078 <line:2:1, col:9> col:5 y 'int' cinit
>>   `-ImplicitCastExpr 0x7daa0f0 <col:9> 'int' <IntegralCast>
>>     `-CXXBoolLiteralExpr 0x7daa0d8 <col:9> '_Bool' true
>>
>> One has a CStyleCastExpr, one doesn't.
>>
>> On Mon, May 9, 2016 at 1:15 PM, Michael Layzell via cfe-dev <
>> cfe-dev at lists.llvm.org> wrote:
>>
>>> I was trying to write a clang static analysis for detecting implicit
>>> bool to int casts. Namely, I wanted to allow forms like:
>>>
>>> int x = (int) true;
>>>
>>> But disallow forms like:
>>>
>>> int x = true;
>>>
>>> Unfortunately, it seems like both of these generate implicit cast AST
>>> nodes, namely I get the following AST tree for the explicitly casted form:
>>>
>>>     `-DeclStmt 0x7fae2407a118 <line:51:3, col:30>
>>>       `-VarDecl 0x7fae2407a050 <col:3, col:26> col:7 x 'int' cinit
>>>         `-CStyleCastExpr 0x7fae2407a0f0 <col:21, col:26> 'int' <NoOp>
>>>           `-ImplicitCastExpr 0x7fae2407a0d8 <col:26> 'int' <IntegralCast>
>>>             `-CXXBoolLiteralExpr 0x7fae2407a0b0 <col:26> '_Bool' true
>>>
>>> How should I distinguish between the two forms reliably, such that
>>> explicit casts are never matched, but implicit casts are matched, when an
>>> explicit cast still inserts an implicit cast, and then just becomes a NoOp?
>>>
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>>>
>>>
>>
>
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