Compilation error if the user does not own the code files

txssu · March 12, 2024, 11:54am

Hi,
Found this line in the compiler. The comment says:

# For each changed file, mark it as changed.
# If compilation fails mid-cycle, they will be picked next time around.

If I understand correctly, some files may change during compilation? Where do these changes come from? In what case can this happen?

Details: CI runs tests in a container, compiler tries to execute File.touch!("my_file.ex", timestamp) and gets an error because it is not the owner of the file. Everything used to work before, but at some point it stopped for some reason…

What can I do to find the cause of the problem?

al2o3cr · March 12, 2024, 2:07pm

The underlying BEAM code (on Unix-ish systems, anyways) always calls utime with a not-NULL pointer:

github.com

erlang/otp/blob/master/erts/emulator/nifs/unix/unix_prim_file.c#L841-L854


      
          posix_errno_t efile_set_time(const efile_path_t *path, Sint64 a_time, Sint64 m_time, Sint64 c_time) {
              struct utimbuf tval;
          
              tval.actime = (time_t)a_time;
              tval.modtime = (time_t)m_time;
          
              (void)c_time;
          
              if(utime((const char*)path->data, &tval) < 0) {
                  return errno;
              }
          
              return 0;
          }

but that’s been in the code for years and years, so it can’t be the reason for the recent change in behavior you observed.

The name of the function that’s calling touch (each_cycle) suggests that something may have changed in the dependency graph of your application. Comparing the output of mix xref between an older “known good” version and now could provide some insight.

txssu · March 12, 2024, 2:54pm

but that’s been in the code for years and years, so it can’t be the reason for the recent change in behavior you observed.

No, I didn’t mean that some behavior changed in touch or somewhere else outside my code. My question was that, according to the each_cycle function comment (if I understood correctly), some changes may be happening. But what kind of changes exactly? Are we talking about some files already compiled and some need to be updated? Why haven’t I encountered this error before? Why should the compiler execute `File.touch(“my_file.ex”, timestamp)? What changes caused this behavior?

The name of the function that’s calling touch (each_cycle) suggests that something may have changed in the dependency graph of your application. Comparing the output of mix xref between an older “known good” version and now could provide some insight.

The problem is also that the specific file that causes the error has not changed from version to version. This module was imported 4 times in an old working version. In the new version it is imported 5 times. I don’t see this as a problem and have no idea what could be wrong.

dimitarvp · March 12, 2024, 3:58pm

Hard to say with the info you’ve given, maybe the CI containers have gotten some upgrades that contributed to the problem? But as @al2o3cr said, your best bet is to try to have a before/after output of mix xref and compare.