%merge: let mergers record a typing-symbol, rather than a type

Symbols are richer than types, and in M4 it is my simpler (and more
common) to deal with symbols rather than types.  So let's associate
mergers to a symbol rather than a type name.

* src/reader.h (merger_list): Replace the 'type' member by a symbol
member.
* src/reader.c (record_merge_function_type): Take a symbol as
argument, rather than a type name.
* src/output.c (merger_output): Adjust.

src/output.c

@@ -554,14 +554,12 @@ merger_output (FILE *out)
   int n;
   merger_list* p;
   for (n = 1, p = merge_functions; p != NULL; n += 1, p = p->next)
-    {
-      if (p->type[0] == '\0')
-        fprintf (out, "  case %d: *yy0 = %s (*yy0, *yy1); break;\n",
-                 n, p->name);
-      else
-        fprintf (out, "  case %d: yy0->%s = %s (*yy0, *yy1); break;\n",
-                 n, p->type, p->name);
-    }
+    if (p->sym && p->sym->content->type_name)
+      fprintf (out, "  case %d: yy0->%s = %s (*yy0, *yy1); break;\n",
+               n, p->sym->content->type_name, p->name);
+    else
+      fprintf (out, "  case %d: *yy0 = %s (*yy0, *yy1); break;\n",
+               n, p->name);
   fputs ("]])\n\n", out);
 }
 

src/reader.c

@@ -42,7 +42,7 @@ static void check_and_convert_grammar (void);
 
 static symbol_list *grammar = NULL;
 symbol_list *start_symbols = NULL;
-merger_list *merge_functions;
+merger_list *merge_functions = NULL;
 
 /* Was %union seen?  */
 bool union_seen = false;
@@ -114,27 +114,27 @@ get_merge_function (uniqstr name)
       syms->next->name = uniqstr_new (name);
       /* After all symbol type declarations have been parsed, packgram invokes
          record_merge_function_type to set the type.  */
-      syms->next->type = NULL;
+      syms->next->sym = NULL;
       syms->next->next = NULL;
       merge_functions = head.next;
     }
   return n;
 }
 
-/*-------------------------------------------------------------------------.
-| For the existing merging function with index MERGER, record the result   |
-| type as TYPE as required by the lhs of the rule whose %merge declaration |
-| is at DECLARATION_LOC.                                                   |
-`-------------------------------------------------------------------------*/
+/*-------------------------------------------------------------------.
+| For the existing merging function with index MERGER, record that   |
+| the result type is that of SYM, as required by the lhs (i.e., SYM) |
+| of the rule whose %merge declaration is at DECLARATION_LOC.        |
+`-------------------------------------------------------------------*/
 
 static void
-record_merge_function_type (int merger, uniqstr type, location declaration_loc)
+record_merge_function_type (int merger, symbol *sym, location declaration_loc)
 {
   if (merger <= 0)
     return;
 
-  if (type == NULL)
-    type = uniqstr_new ("");
+  uniqstr type
+    = sym->content->type_name ? sym->content->type_name : uniqstr_new ("");
 
   merger_list *merge_function;
   int merger_find = 1;
@@ -143,17 +143,18 @@ record_merge_function_type (int merger, uniqstr type, location declaration_loc)
        merge_function = merge_function->next)
     merger_find += 1;
   aver (merge_function != NULL && merger_find == merger);
-  if (merge_function->type != NULL && !UNIQSTR_EQ (merge_function->type, type))
+  if (merge_function->sym && merge_function->sym->content->type_name
+      && !UNIQSTR_EQ (merge_function->sym->content->type_name, type))
     {
       complain (&declaration_loc, complaint,
                 _("result type clash on merge function %s: "
                 "<%s> != <%s>"),
                 quote (merge_function->name), type,
-                merge_function->type);
+                merge_function->sym->content->type_name);
       subcomplain (&merge_function->type_declaration_loc, complaint,
                    _("previous declaration"));
     }
-  merge_function->type = uniqstr_new (type);
+  merge_function->sym = sym;
   merge_function->type_declaration_loc = declaration_loc;
 }
 
@@ -668,7 +669,7 @@ packgram (void)
   for (symbol_list *p = grammar; p; p = p->next)
     {
       symbol_list *lhs = p;
-      record_merge_function_type (lhs->merger, lhs->content.sym->content->type_name,
+      record_merge_function_type (lhs->merger, lhs->content.sym,
                                   lhs->merger_declaration_loc);
       /* If the midrule's $$ is set or its $n is used, remove the '$' from the
          symbol name so that it's a user-defined symbol so that the default

src/reader.h

@@ -31,7 +31,10 @@ typedef struct merger_list
 {
   struct merger_list* next;
   uniqstr name;
-  uniqstr type;
+  /* One symbol whose type is the one used by all the symbols on which
+     this merging function is used.  */
+  symbol *sym;
+  /* Where SYM was bound to this merging function.  */
   location type_declaration_loc;
 } merger_list;