[bug #62852] Combination of "eqn" and "tbl" in compatibility mode errors

[G. Branden Robinson]

Update of bug #62852 (project groff):

                Category:                    None => Preprocessor eqn       
                  Status:                    None => Confirmed              
             Assigned to:                    None => gbranden               

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Follow-up Comment #1:

This affects groff 1.22.4 and, I suspect, every earlier version going back to
groff 1.22.2.

I believe the problem to be this.

The -C flag turns on AT&T compatibility mode in both tbl and eqn.  In the
latter, this disables special interpretation of the eqn input "delim on". 
Instead of re-enabling delimiters that have been shut off with "delim off", it
assigns opening and closing delimiters of 'o' and 'n' respectively, just as
AT&T eqn would have.

However, even with -C specified, tbl expects "delim on" to work in the GNU eqn
way.  GNU tbl brackets portions of the groff input it writes in "delim
off"/"delim on" pairs to avoid interference from eqn with the output of
formatting-time diagnostics.

For example, we have the following in Git HEAD.


$ sed -n '2190,2207p' src/preproc/tbl/table.cpp
  if ((!(flags & NOWARN)) && (!(flags & EXPAND))) {
    // Protect characters in diagnostic message (especially :, [, ])
    // from being interpreted by eqn.
    prints(".ig\n"
           ".EQ\n"
           "delim off\n"
           ".EN\n"
           "..\n");
    entry_list->set_location();
    prints(".tmc \\n[.F]:\\n[.c]: warning:\n"
           ".tm1 \" table wider than line length minus indentation\n");
    prints(".ig\n"
           ".EQ\n"
           "delim on\n"
           ".EN\n"
           "..\n");
    prints(".nr " EXPAND_REG " 0\n");
  }


I think the discarded special recognition of "delim on" in eqn's compatibility
mode is going to have to go.  Even in AT&T documents, I suspect the number of
documents using "o" and "n" as _delimiters_ is low to zero.

So I propose to disable this feature, losing an aspect of AT&T eqn
compatibility that I believe to be negligible.


diff --git a/src/preproc/eqn/lex.cpp b/src/preproc/eqn/lex.cpp
index 115617b1d..51c5af246 100644
--- a/src/preproc/eqn/lex.cpp
+++ b/src/preproc/eqn/lex.cpp
@@ -1079,7 +1079,7 @@ void do_delim()
       end_delim_saved = end_delim;
       start_delim = end_delim = '\0';
     }
-    else if (c == 'o' && d == 'n' && !compatible_flag) {
+    else if (c == 'o' && d == 'n') {
       start_delim = start_delim_saved;
       end_delim = end_delim_saved;
     }


Here's a simpler reproducer and its behavior with groff 1.22.4 and a patched
Git HEAD.


$ groff -Cetz EXPERIMENTS/eqn-tbl-compatibility-mode.roff
eqn:EXPERIMENTS/eqn-tbl-compatibility-mode.roff:122: '\' ignored because
followed by newline
eqn:EXPERIMENTS/eqn-tbl-compatibility-mode.roff:123: unquoted escape
eqn:EXPERIMENTS/eqn-tbl-compatibility-mode.roff:36: '\' ignored because
followed by newline
eqn:EXPERIMENTS/eqn-tbl-compatibility-mode.roff:87: '\' ignored because
followed by newline
eqn:EXPERIMENTS/eqn-tbl-compatibility-mode.roff:8: '\' ignored because
followed by newline
eqn:EXPERIMENTS/eqn-tbl-compatibility-mode.roff:8: '\' ignored because
followed by newline
troff: EXPERIMENTS/eqn-tbl-compatibility-mode.roff:36: '\&' is not allowed in
a name
troff: EXPERIMENTS/eqn-tbl-compatibility-mode.roff:82: '\&' is not allowed in
a name
troff: EXPERIMENTS/eqn-tbl-compatibility-mode.roff:82: warning: numeric
expression expected (got '\&')
troff: EXPERIMENTS/eqn-tbl-compatibility-mode.roff:87: '\&' is not allowed in
a name
troff: EXPERIMENTS/eqn-tbl-compatibility-mode.roff:8: '\&' is not allowed in a
name
troff: EXPERIMENTS/eqn-tbl-compatibility-mode.roff:8: warning: numeric
expression expected (got '\&')
$ ./build/test-groff -Cetz EXPERIMENTS/eqn-tbl-compatibility-mode.roff
$ 


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