(Potential) False positive: "caller does not check return value"

[mjeronimo]

Using the jpl ruleset, this rule indicates that the code does not check the return value. However, the calls return the return a duration and are then used in a boolean expression. Not sure what checking could happen on the return values.

Also, the rule complains about this:

  return rmw_time_total_nsec(left) == rmw_time_total_nsec(right);

but not this:

  rmw_duration_t d1 = rmw_time_total_nsec(left);
  rmw_duration_t d2 = rmw_time_total_nsec(right);
  return d1 == d2;

Which are semantically equivalent.

To reproduce:

  cobra -C++ -comments -f jpl t.c

Where t.c contains:

#include "rmw/time.h"
#include "rcutils/time.h"

RMW_PUBLIC
RMW_WARN_UNUSED
bool
rmw_time_equal(const rmw_time_t left, const rmw_time_t right)
{
  return rmw_time_total_nsec(left) == rmw_time_total_nsec(right);
}

RMW_PUBLIC
RMW_WARN_UNUSED
rmw_duration_t
rmw_time_total_nsec(const rmw_time_t time)
{
  static const uint64_t max_sec = INT64_MAX / RCUTILS_S_TO_NS(1);
  if (time.sec > max_sec) {
    // Seconds not representable in nanoseconds
    return INT64_MAX;
  }

  const int64_t sec_as_nsec = RCUTILS_S_TO_NS(time.sec);
  if (time.nsec > (uint64_t)(INT64_MAX - sec_as_nsec)) {
    // overflow
    return INT64_MAX;
  }
  return sec_as_nsec + time.nsec;
}

Results in:

=== R13: declare data objects at smallest possible level of scope
    globals used in one scope only:   0
    globals used in one file  only:   4
    bool    used in only file /root/src/spaceros_ws/src/rmw/rmw/src/t.c
    RMW_PUBLIC  used in only file /root/src/spaceros_ws/src/rmw/rmw/src/t.c
    RMW_WARN_UNUSED used in only file /root/src/spaceros_ws/src/rmw/rmw/src/t.c
    rmw_duration_t  used in only file /root/src/spaceros_ws/src/rmw/rmw/src/t.c
=== R14f: caller does not check return value: 1
t.c:9:
  1:      9    return rmw_time_total_nsec(left) == rmw_time_total_nsec(right);
=== R14g: caller does not check return value: 1
t.c:9:
  1:      9    return rmw_time_total_nsec(left) == rmw_time_total_nsec(right);
=== R16: Nr of statements: 6
=== R16: Nr of assertions: 0
=== R16: the minimum number of assertions is 2% = 0
1 errors

[nimble-code]

Updated the implementation of Rule 14 (d,e,f,and g) to remove this false positive. The checker verified if the result of the fct call was used in an assignment, or in a condition (indicated by the call appearing inside round braces). The example used a condition without the round braces. The fix now checks if the fct call is preceded or followed by a boolean operator as well, to address this case. thanks for the report and the example!