[bug #58153] input_stack::backtrace() over-suppresses output

[G. Branden Robinson]

Follow-up Comment #2, bug #58153 (project groff):


commit 6051dae0ed025521ec5a32f9c5e8ebffa7feaf36
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
Date:   Sat Apr 11 11:08:55 2020 +1000

    Empower backtracing in error/warning conditions.
    
    Enable backtracing across process/file boundaries when errors or
    non-ignored warnings are encountered.
    
    Experimentation reveals that .so, .mso, and .pso requests act as
    barriers to backtracing except when explicitly requested with the
    .backtrace request.  Judging by the git history, this behavior dates
    back to June 1991 or earlier.  This did not appear to be the intention
    according to a comment, which was only to suppress the output of
    backtrace output for the line corresponding to the top level itself.
    Unfortunately, that was not its only effect.
    
    This change does result in one additional line of output when -b is
    given and an error or (non-ignored) warning happens at the top level.
    However, I regard this as unobjectionable because (1) a backtrace was in
    fact explicitly requested; and (2) it seems a poor tradeoff to suppress
    most of the backtrace in all complicated and frustrating cases for the
    sake of one fewer line of backtrace output in a trivial one.
    
    Now, backtracing behaves the same no matter what triggers it.
    
    Fixes Savannah #58153.
    
    * src/roff/troff/input.cpp (file_iterator::backtrace): Call
      get_location() for its side effect of rewriting a filename of "-" to
      "<standard input>", for consistency with other diagnostic messages.
      (In this class, this member function always returns 1, so ignore the
      return value.)
    
      (input_stack::backtrace): Replace member function body with that
      of input_stack::backtrace_all().
    
      (input_stack::backtrace_all): Delete.
    
      (backtrace_request): Update the only call site of the above.
    
    * src/roff/groff/tests/regression_savannah_58153.sh:
    * src/roff/groff/groff.am: Add regression test.
    
    * src/roff/groff/tests/string_case_xform_errors.sh: Update regression
      test to not be confounded by additional line of backtrace output.
      Remove bashism along the way.
    
    * doc/groff.texi:
    * man/groff.7.man:
    * man/groff_diff.7.man: Update documentation.



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