add ability to link to additional libraries for from_file processors

[tomeichlersmith]

I am updating ldmx-sw, here are the details.

What are the issues that this addresses?

I very quickly noticed that this stand-alone processor function can be updated to link to additional pre-compiled ldmx-sw libraries which is helpful in many circumstances. Specifically, I am working with a new graduate student who wished to have her analyzer user the detector ID classes in the DetDescr library and updating the compilation command to include -lDetDescr was all that was necessary.

The developments here are focused on allowing for the user to add other libraries to link. Pretty much any library that is system-findable (or installed with ldmx-sw) should be linkable in this way, although I haven't tested this thoroughly.

Check List

• I successfully compiled ldmx-sw with my developments
• I ran my developments and the following shows that they are successful.

[tomeichlersmith]

The complexity here is that some things work well without the additional linking because the libraries are loaded via other links. The example I've crafted below is the one I've first encountered, but may not be the simplest/minimal example.

cfg.py

We're just testing compilation and loading so I don't run over any events.

from LDMX.Framework import ldmxcfg
p = ldmxcfg.Process('ana')
p.sequence = [ ldmxcfg.Analyzer.from_file('MyAnalyzer.cxx') ]
p.inputFiles = [ ]
p.histogramFile = 'hist.root'

MyAnalyzer.cxx

#include "Framework/EventProcessor.h"

#include "DetDescr/EcalID.h"
#include "Ecal/Event/EcalHit.h"

class MyAnalyzer : public framework::Analyzer {
 public:
  MyAnalyzer(const std::string& name, framework::Process& p)
    : framework::Analyzer(name, p) {}
  ~MyAnalyzer() = default;
  void onProcessStart() final;
  void analyze(const framework::Event& event) final;
};

void MyAnalyzer::onProcessStart() {
  // this is where we will define the histograms we want to fill
  ldmx::EcalID id{0,0,0};
  auto [u, v] = id.getCellUV();
  std::cout << u << ", " << v << std::endl;
}

void MyAnalyzer::analyze(const framework::Event& event) {
  // this is where we will fill the histograms
}

DECLARE_ANALYZER(MyAnalyzer);

Note: In between runs, make sure to rm libMyAnalyzer.so to make sure that the re-compilation occurs.

on trunk

We get an undefined symbol error and library-load time.

tom@appa:~/code/ldmx/1366-from_file-needs$ denv fire cfg.py 
---- LDMXSW: Loading configuration --------
Processor source file /home/tom/code/ldmx/1366-from_file-needs/MyAnalyzer.cxx is newer than its compiled library /home/tom/code/ldmx/1366-from_file-needs/libMyAnalyzer.so (or library does not exist), recompiling...
done compiling /home/tom/code/ldmx/1366-from_file-needs/MyAnalyzer.cxx
Configuration Error [LibraryLoadFailure] : Error loading library '/home/tom/code/ldmx/1366-from_file-needs/libMyAnalyzer.so':/home/tom/code/ldmx/1366-from_file-needs/libMyAnalyzer.so: undefined symbol: _ZNK4ldmx6EcalID9getCellUVEv
  at /home/tom/code/ldmx/ldmx-sw/Framework/src/Framework/PluginFactory.cxx:94 in loadLibrary

on this branch without needs

i.e. the config is as shown above.
We get the same error.

tom@appa:~/code/ldmx/1366-from_file-needs$ denv fire cfg.py 
---- LDMXSW: Loading configuration --------
Processor source file /home/tom/code/ldmx/1366-from_file-needs/MyAnalyzer.cxx is newer than its compiled library /home/tom/code/ldmx/1366-from_file-needs/libMyAnalyzer.so (or library does not exist), recompiling...
done compiling /home/tom/code/ldmx/1366-from_file-needs/MyAnalyzer.cxx
Configuration Error [LibraryLoadFailure] : Error loading library '/home/tom/code/ldmx/1366-from_file-needs/libMyAnalyzer.so':/home/tom/code/ldmx/1366-from_file-needs/libMyAnalyzer.so: undefined symbol: _ZNK4ldmx6EcalID9getCellUVEv
  at /home/tom/code/ldmx/ldmx-sw/Framework/src/Framework/PluginFactory.cxx:94 in loadLibrary

on this branch with needs=['DetDescr']

i.e. the config above was changed with

3c3
< p.sequence = [ ldmxcfg.Analyzer.from_file('MyAnalyzer.cxx') ]
---
> p.sequence = [ ldmxcfg.Analyzer.from_file('MyAnalyzer.cxx', needs=['DetDescr']) ]

No error! 🎉

tom@appa:~/code/ldmx/1366-from_file-needs$ denv fire cfg.py 
---- LDMXSW: Loading configuration --------
Processor source file /home/tom/code/ldmx/1366-from_file-needs/MyAnalyzer.cxx is newer than its compiled library /home/tom/code/ldmx/1366-from_file-needs/libMyAnalyzer.so (or library does not exist), recompiling...
done compiling /home/tom/code/ldmx/1366-from_file-needs/MyAnalyzer.cxx
---- LDMXSW: Configuration load complete  --------
---- LDMXSW: Starting event processing --------
0, 0
---- LDMXSW: Event processing complete  --------

[tvami]

I ran the code on an existing analyzer I had which didnt have any needs, all looks good.