[cfe-dev] check an AST node's parent node ?

[Kim Gräsman]

Hi kevinlynx,

Not a direct answer to your question, but...

On Tue, Jan 8, 2013 at 7:48 AM, kevinlynx <kevinlynx at gmail.com> wrote:
> In my coding standard checking tool, it limits comma expression usage,
> except in a for statment, i.e:
>
>     x++, x+=1; // this will be marked as invalid usage
>     for (x = 0, y = 0; ...) // but this comma expression is valid
>
> I can implement `VisitBinComma`, this function will be called when parsed
> comma expression. But how to know if this comma expression is in a for
> statment ?

... you can use -ast-dump to see what the AST for a representative
sample looks like:

--
// commaop.cpp
int main() {
  int x = 0;

  x++, x += 1;

  for (int x = 0, y = 0; x < 10; ++x, --y)
    ;
}
--

--
$ clang -cc1 -ast-dump commaop.cpp
(TranslationUnitDecl 0x600960 <<invalid sloc>>
  (TypedefDecl 0x600c50 <<invalid sloc>> __builtin_va_list 'char *')
  (FunctionDecl 0x600cc0 <D:\temp\commaop.cpp:2:1, line:9:1> main 'int (void)'
    (CompoundStmt 0x601050 <line:2:12, line:9:1>
      (DeclStmt 0x600db0 <line:3:3, col:12>
        (VarDecl 0x600d60 <col:3, col:11> x 'int'
          (IntegerLiteral 0x600d90 <col:11> 'int' 0)))
      (BinaryOperator 0x600e48 <line:5:3, col:13> 'int' lvalue ','
        (UnaryOperator 0x600dd8 <col:3, col:4> 'int' postfix '++'
          (DeclRefExpr 0x600dc0 <col:3> 'int' lvalue Var 0x600d60 'x' 'int'))
        (CompoundAssignOperator 0x600e28 <col:8, col:13> 'int' lvalue
'+=' ComputeLHSTy='int' ComputeResultTy='int'
          (DeclRefExpr 0x600dec <col:8> 'int' lvalue Var 0x600d60 'x' 'int')
          (IntegerLiteral 0x600e08 <col:13> 'int' 1)))
      (ForStmt 0x601028 <line:7:3, line:8:5>
        (DeclStmt 0x600f30 <line:7:8, col:24>
          (VarDecl 0x600e70 <col:8, col:16> x 'int'
            (IntegerLiteral 0x600ea0 <col:16> 'int' 0))
          (VarDecl 0x600ed0 <col:8, col:23> y 'int'
            (IntegerLiteral 0x600f00 <col:23> 'int' 0)))
        (<<<NULL>>>)
        (BinaryOperator 0x600f88 <col:26, col:30> '_Bool' '<'
          (ImplicitCastExpr 0x600f78 <col:26> 'int' <LValueToRValue>
            (DeclRefExpr 0x600f40 <col:26> 'int' lvalue Var 0x600e70 'x' 'int'))
          (IntegerLiteral 0x600f58 <col:30> 'int' 10))
        (BinaryOperator 0x601000 <col:34, col:41> 'int' lvalue ','
          (UnaryOperator 0x600fb8 <col:34, col:36> 'int' lvalue prefix '++'
            (DeclRefExpr 0x600fa0 <col:36> 'int' lvalue Var 0x600e70 'x' 'int'))
          (UnaryOperator 0x600fe8 <col:39, col:41> 'int' lvalue prefix '--'
            (DeclRefExpr 0x600fcc <col:41> 'int' lvalue Var 0x600ed0
'y' 'int')))
        (NullStmt 0x601018 <line:8:5>)))))
--

It doesn't look like the comma in the for statement declaration is
represented in the AST, but maybe you can trigger on the fact that
there are multiple VarDecls under the DeclStmt?

      (ForStmt 0x601028 <line:7:3, line:8:5>
        (DeclStmt 0x600f30 <line:7:8, col:24>
          (VarDecl 0x600e70 <col:8, col:16> x 'int'
            (IntegerLiteral 0x600ea0 <col:16> 'int' 0))
          (VarDecl 0x600ed0 <col:8, col:23> y 'int'
            (IntegerLiteral 0x600f00 <col:23> 'int' 0)))

- Kim