[cfe-dev] Performing a path-sensitive check only when a function return value is ignored

[Artem Dergachev via cfe-dev]

For implementing your approach, i'd suggest something like that (untested!):

void YourChecker::checkPreCall(const CallEvent &Call, CheckerContext &C) 
const {
   const CallExpr *CE = dyn_cast_or_null<CallExpr>(Call.getOriginExpr());
   if (!CE)
     return;
   // Find the parent statement of the call expression, which should be 
somewhere in the caller's body.
   const Stmt *Parent = 
C.getLocationContext()->getCurrentStackFrame()->getParent()->getParentMap().getParent(CE);
   if (!isa<CompoundStmt>(Parent)) // Return value not discarded?
     return;
   // Proceed with your checks.
}

However, you might also consider the path-sensitive approach to finding 
discarded/unchecked return values. That is, if the return value was 
saved into a variable, it might have still been discarded, so a 
syntax-only check is not enough, you'd need to see how the value flows. 
For that, you'd need to subscribe to checkDeadSymbols, and see if upon 
the death of the symbol there are no range constraints on it; then, if 
the value was truly unchecked, you can throw the warning on the original 
call expression. But that's more complicated.
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