[bug #64212] [PATCH] give troff a string register naming the next trap

[G. Branden Robinson]

URL:
  <https://savannah.gnu.org/bugs/?64212>

                 Summary: [PATCH] give troff a string register naming the next
trap
                   Group: GNU roff
               Submitter: gbranden
               Submitted: Thu 18 May 2023 09:58:26 AM UTC
                Category: Core
                Severity: 1 - Wish
              Item Group: Feature change
                  Status: Need Info
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None


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Follow-up Comments:


-------------------------------------------------------
Date: Thu 18 May 2023 09:58:26 AM UTC By: G. Branden Robinson <gbranden>
This was, uh, "inspired" by the ongoing headache that is bug #57538.

I found it annoying that you can get the _distance_ to the next trap but not
its _name_, when internally, the formatter has ready access to this
information.

So here's a patch adding a new read-only, string-valued register that tells
you the name of the next trap you will spring if you are in the top level.

An empty string is interpolated if you are in a diversion (there is only at
most one trap in a diversion; it has no name) or if, somehow, there is no next
trap at the top level, but that...should be impossible?

Anyway, it worked to tell me what I wanted.  It didn't cause a Eureka moment,
though.


diff --git a/src/roff/troff/div.cpp b/src/roff/troff/div.cpp
index f4dc06f33..679575f99 100644
--- a/src/roff/troff/div.cpp
+++ b/src/roff/troff/div.cpp
@@ -250,6 +250,11 @@ vunits macro_diversion::distance_to_next_trap()
     return vunits(INT_MAX - vresolution);
 }
 
+const char *macro_diversion::get_next_trap_name()
+{
+  return "";
+}
+
 void macro_diversion::transparent_output(unsigned char c)
 {
   mac->append(c);
@@ -372,6 +377,16 @@ vunits top_level_diversion::distance_to_next_trap()
     return d - vertical_position;
 }
 
+const char *top_level_diversion::get_next_trap_name()
+{
+  vunits next_trap_pos;
+  trap *next_trap = find_next_trap(&next_trap_pos);
+  if (0 /* nullptr */ == next_trap)
+    return "";
+  else
+    return next_trap->nm.contents();
+}
+
 void top_level_diversion::output(node *nd, int retain_size,
                                 vunits vs, vunits post_vs, hunits width)
 {
@@ -1059,6 +1074,16 @@ const char *diversion_name_reg::get_string()
   return curdiv->get_diversion_name();
 }
 
+class next_trap_name_reg : public reg {
+public:
+  const char *get_string();
+};
+
+const char *next_trap_name_reg::get_string()
+{
+  return curdiv->get_next_trap_name();
+}
+
 class page_number_reg : public general_reg {
 public:
   page_number_reg();
@@ -1194,6 +1219,7 @@ void init_div_requests()
   register_dictionary.define(".pe", new page_ejecting_reg);
   register_dictionary.define(".pn", new next_page_number_reg);
   register_dictionary.define(".t", new distance_to_next_trap_reg);
+  register_dictionary.define(".trap", new next_trap_name_reg);
   register_dictionary.define(".trunc",
       new constant_vunits_reg(&truncated_space));
   register_dictionary.define(".vpt",
diff --git a/src/roff/troff/div.h b/src/roff/troff/div.h
index 15c7807a5..6180caa0b 100644
--- a/src/roff/troff/div.h
+++ b/src/roff/troff/div.h
@@ -57,6 +57,7 @@ public:
   vunits get_vertical_position() { return vertical_position; }
   vunits get_high_water_mark() { return high_water_mark; }
   virtual vunits distance_to_next_trap() = 0;
+  virtual const char * get_next_trap_name() = 0;
   void need(vunits);
   const char *get_diversion_name() { return nm.contents(); }
   virtual void set_diversion_trap(symbol, vunits) = 0;
@@ -84,6 +85,7 @@ public:
   void vjustify(symbol);
 #endif /* COLUMN */
   vunits distance_to_next_trap();
+  const char *get_next_trap_name();
   void set_diversion_trap(symbol, vunits);
   void clear_diversion_trap();
   void copy_file(const char *filename);
@@ -125,6 +127,7 @@ public:
   hunits get_page_offset() { return page_offset; }
   vunits get_page_length() { return page_length; }
   vunits distance_to_next_trap();
+  const char *get_next_trap_name();
   void add_trap(symbol nm, vunits pos);
   void change_trap(symbol nm, vunits pos);
   void remove_trap(symbol);


Does anybody want this?







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