[Bug 1903548] Re: nauty-biplabg gives "sorry, this program doesn't support digraphs yet"

[Mathew Hodson]

** Tags added: patch

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Title:
  nauty-biplabg gives "sorry, this program doesn't support digraphs yet"

Status in nauty package in Ubuntu:
  Fix Released
Status in nauty source package in Focal:
  New

Bug description:
  [Impact]
  Running nauty-biplabg in focal always results in an error.  In particular, it always complains that a digraph has been input even if this is not the case.

  This is due to the following code in nauty:

  int
  main(int argc, char *argv[])
  {
          char *infilename,*outfilename;
          FILE *infile,*outfile;
          boolean badargs,quiet;
  	int j,m,n,argnum;
  	int codetype,outcode;
  	graph *g;
  	nauty_counter nin,nout;
          char *arg,sw;
  	double t;

  [...snip...]

          NODIGRAPHSYET(codetype);

  	if (infilename && infilename[0] == '-') infilename = NULL;
  	infile = opengraphfile(infilename,&codetype,FALSE,1);
  	if (!infile) exit(1);
  	if (!infilename) infilename = "stdin";

  The NODIGRAPHSYET macro is defined in a header file and is responsible
  for our error message:

  #define NODIGRAPHSYET(code) if (((code)&DIGRAPH6)) \
    gt_abort(">E Sorry, this program doesn't support digraphs yet.\n")

  The variable codetype is not initialized until the call to
  opengraphfile, so if we're unlucky, it might find that DIGRAPH6 bit in
  whatever piece of memory it's pointing to at the time.

  This bug results in build failures when building the computer algebra
  software Macaulay2 in focal, as one of its packages calls nauty-
  biplabg when building examples and running tests.  See
  https://github.com/Macaulay2/M2/issues/1408.

  This has been fixed in nauty version 2.7 (which is in groovy and
  hirsute already) by moving the call to NODIGRAPHSYET a few lines
  lower.  See the attached patch.

  [Test Case]
  (focal-amd64)root at nimmie:~# nauty-biplabg 
  >A biplabg
  >E Sorry, this program doesn't support digraphs yet.

  [Where problems could occur]
  None known.  The attached patch is very small.

  Further information:
  (focal-amd64)root at nimmie:~# lsb_release -rd
  Description:	Ubuntu 20.04 LTS
  Release:	20.04
  (focal-amd64)root at nimmie:~# apt-cache policy nauty
  nauty:
    Installed: 2.6r10+ds-1ubuntu1
    Candidate: 2.6r10+ds-1ubuntu1
    Version table:
   *** 2.6r10+ds-1ubuntu1 500
          500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
          100 /var/lib/dpkg/status

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