[eg] deprecate cfortran and Hepevt headers that are implementation details

[ferdymercury]

It's urgent to avoid a sure collision with Debian when doing make install

libcfitsio-dev installs cfortran.h on the same destination as ROOT.

[pcanal]

I understand the challenge with cfortran.h being duplicated across product.

That said, Hepevt.h is part of the TGenerator interface and defined/declare the default layout a fortran implemented generator can/should use to leverage the default implementation available within TGenerator.

So this PR (underlying feature) is not a technical/straight-forward cleanup but rather a real feature deprecation: "no longer supporting Fortran based generator".

So this deserve a larger discussion and the conclusion might be to recommend this PR, to delay this PR or to expand this PR to deprecate a larger set of functionality.

[ferdymercury]

That said, Hepevt.h is part of the TGenerator interface

Why so?

It's only used by TGenerator.cxx but not by TGenerator.h

Or you mean someone was using

#include "TGenerator.h"
#include "Hepevt.h"

directly in some downstream code? and then binding those in some way ?

[pcanal]

directly in some downstream code? and then binding those in some way ?

yes (via the 'magic' of common blocks)

Per the documentation:

If the generator code stores event data in the /HEPEVT/ common block 
Then the default implementation of ImportParticles should suffice.   
The common block /HEPEVT/ is structed like                           
                                                                     
\verbatim
  // C                                                            
  typedef struct {                                                   
     Int_t    nevhep;           // Event number                      
     Int_t    nhep;             // # of particles                    
     Int_t    isthep[4000];     // Status flag of i'th particle      
     Int_t    idhep[4000];      // PDG # of particle                 
     Int_t    jmohep[4000][2];  // 1st & 2nd mother particle #       
     Int_t    jdahep[4000][2];  // 1st & 2nd daughter particle #     
     Double_t phep[4000][5];    // 4-momentum and 1 word             
     Double_t vhep[4000][4];    // 4-position of production          
  } HEPEVT_DEF;                                                      
                                                                     
                                                                     
  C Fortran                                                          
        COMMON/HEPEVT/NEVHEP,NHEP,ISTHEP(4000),IDHEP(4000),          
      +    JMOHEP(2,4000),JDAHEP(2,4000),PHEP(5,4000),VHEP(4,4000)   
        INTEGER NEVHEP,NHEP,ISTHEP,IDHEP,JMOHEP,JDAHEP               
        DOUBLE PRECISION PHEP,VHEP                                   
\endverbatim

[ferdymercury]

yes (via the 'magic' of common blocks)

wouldn't it make then more sense to copy-paste HepEvt.h into TGenerator.h rather than having a separate header? And then remove HepEvt.h Otherwise it can also be 'magically' broken if only includes TGenerator.h, right?

[github-actions]

Test Results

    22 files      22 suites   3d 11h 35m 13s ⏱️
 3 879 tests  3 879 ✅ 0 💤 0 ❌
76 263 runs  76 263 ✅ 0 💤 0 ❌

Results for commit 818bf64.