import semmle.code.cpp.exprs.Expr

/**

* An expression that is used to qualify some other expression.

*/

class Qualifier extends Expr {

Qualifier() {

exists(VariableAccess a | a.getQualifier() = this) or

exists(Call c | c.getQualifier() = this) or

exists(VacuousDestructorCall v | v.getQualifier() = this)

}

}

/**

* An expression that occurs in a void context, i.e. either as the toplevel expression of

* an expression statement or on the left hand side of the comma operator.

*

* Expressions that are explicitly cast to void are not considered to be in void context.

*/

class ExprInVoidContext extends Expr {

ExprInVoidContext() { exprInVoidContext(this) }

}

private predicate exprInVoidContext(Expr e) {

(

exists(ExprStmt s |

s = e.getParent() and

not exists(StmtExpr se | s = se.getStmt().(BlockStmt).getLastStmt())

)

or

exists(ConditionalExpr c | c.getThen() = e and c instanceof ExprInVoidContext)

or

exists(ConditionalExpr c | c.getElse() = e and c instanceof ExprInVoidContext)

or

exists(CommaExpr c | c.getLeftOperand() = e)

or

exists(CommaExpr c | c.getRightOperand() = e and c instanceof ExprInVoidContext)

or

exists(ForStmt for | for.getUpdate() = e)

) and

not e.getActualType() instanceof VoidType

}