cschreib-ibex
commented
1 week ago For people coming here with the same problem, this cannot be solved with // NOLINT commands, since this is not coming from clang-tidy but from the clang builtin analyzer. The only way that I know to silence these false positives is to add a pre-processor compilation guard, such as:
#include "jsoncons/json.hpp"
void test(jsoncons::json some_json, const std::string &some_string) {
#if !defined(__clang_analyzer__)
// The normal code.
some_json["test"] = some_string;
#else
// The code that the analyzer will see.
// Need so silence unused variable warnings...
static_cast<void>(some_json);
static_cast<void>(some_string);
#endif
}
Describe the proposed feature We use jsoncons in one of our project, for which we run clang static analysis on every build. Unfortunately, jsoncons has had a history of triggering false positives from clang's compile-time memory leak analyzer, and this has gotten worse in 0.178.0 (we just upgraded from 0.176.0).
What other libraries (C++ or other) have this feature?
nlohmann::jsonInclude a code fragment with sample data that illustrates the use of this feature Here's an example that triggers the false positive:
Here's the
compile_commands.jsonfile (adjust with your own paths):Running
clang-tidy-16 -p . test.cpp, we get the report shown in full in "Details" below. In summary, the analyzer is unable to keep track of the storage kind of a JSON variable across function calls; it clearly sees an JSON variable being initialised as an "object" (and sees the memory allocated for that), and then immediately after it goes down an unreachableswitchcase where the variable is a "string" (which thus fails to de-allocate the memory allocated for the object). I don't know if something can be done to help analysers track this better.This example reports no leak with
nlohmann::json.