[bug #64061] pdfpic.tmac requires non-standard sed feature

[G. Branden Robinson]

Follow-up Comment #18, bug #64061 (project groff):

Updated fix on branch (does not expand test cases as mused about in comment
#17).


commit 15ca5031a84d98a195403de89bf33a0b96c032a7
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
Date:   Mon Apr 17 16:41:33 2023 -0500

    [pdfpic]: Fix Savannah #64061.
    
    * tmac/pdfpic.tmac: Refactor to make comprehensible some woefully
      undocumented cleverness and improve efficiency.
    
      (PDFPIC): Break out flaming-hoop-leaping "clever" bit of `sy` usage
      into its own macro, calling from here and relocating its requests from
      here...
    
      (pdfpic@get-image-dimensions): ...to here.  When using `sy` request to
      collect and munge output of pdfinfo(1), (a) disable the escape
      character while defining the macro; (b) construct the command in a
      roff string, appending to it in discrete, hopefully comprehensible
      chunks; (c) disable the escape character during macro interpretation
      wherever possible (most of it); (d) retain doubled backslashes so that
      they survive subsequent string interpolation; (e) stop using grep(1)
      in the pipeline when sed(1) is perfectly capable of performing its own
      input filtering; (f) invoke sed with '-n' option and emit output only
      upon a successful substitution; (g) replace unportable(!) POSIX BRE
      character class '[:digit:]' in substitution match text with '[0-9]';
      and most importantly (h) replace multi-line sed 's' replacement text
      (see below for the reason we can't use it) with single roff control
      line employing the groff extension escape sequence `\R` to assign
      multiple registers.  Annotate portability and escaping challenges.
      Tested on GNU/Linux, macOS 12, and (with simulated pdfinfo(1) output)
      Solaris 11.
    
    There is a problem with trying to embed true newlines into the arguments
    of a `sy` request.  The C++ function that GNU troff uses to assemble the
    command string (character by character) _does not recognize C/C++ string
    literal escape sequences_.  This means that you _cannot_ embed "\n" in
    `sy`'s arguments and have it survive, as a newline character, into the
    command string passed to the standard C library's system(3) function.
    ("A\nB" gets encoded as 'A', '\\', 'n', 'B', not 'A', '\n', 'B'.)
    Unfortunately, this appears to be AT&T troff-compatible behavior.  But
    it means that you _cannot_ portably construct multi-line replacement
    text for sed's 's' command.  (Other sed commands like 'a', 'c', and 'i'
    will be similarly affected.)  See Savannah #64071.
    
    * PROBLEMS: Drop item.
    
    Fixes <https://savannah.gnu.org/bugs/?64061>.  Thanks to Bruno Haible
    for the report, and to him and Ralph Corderoy for the discussion of
    portable and efficient sed constructs.


And for grins...


commit 8de67a3bf1163b18ce8bfce54075fca8a6fd379b
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
Date:   Wed Apr 26 04:36:05 2023 -0500

    [pdfpic]: Refactor (`sy` -> `pso`).
    
    * tmac/pdfpic.tmac: Migrate gathering of image dimensions from `sy` and
      a temporary file to `pso`.
    
      (pdfpic@cleanup): Drop `pdfpic*temporary-file` string.
    
      (pdfpic@get-image-dimensions): Remove redirection.  Invoke `pso`, not
      `sy`.
    
      (PDFPIC): Stop constructing `pdfpic*temporary-file` string.  Stop
      testing `systat` register.  Stop sourcing and deleting temporary file.
    
    We keep the temporary directory handling because we will need it for the
    `PSPIC` fallback logic, but it also promises to be really painful to fix
    that before we have more formatter support for string traversal.  See
    <https://savannah.gnu.org/bugs/index.php?64114>.




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