parser: deprecate %nterm

It has several weaknesses.
Reported by Rici Lake.
http://lists.gnu.org/archive/html/bug-bison/2018-10/msg00000.html

* src/scan-gram.l: here.

NEWS

@@ -10,12 +10,19 @@ GNU Bison NEWS
   - relative paths (allowing to relocate an installation of bison)
   - use gettext-h in gnulib instead of gettext
   - constexpr/noexcept in C++
+  - resolving %type/%nterm/%type inconsistencies
 
 ** Backward incompatible changes
 
   Support for DJGPP, which has been unmaintained and untested for years, is
   removed.
 
+** Deprecated features
+
+  The directive %nterm, an historical heritage from an ancestor of Bison,
+  was never officially documented.  Its use now triggers warnings.
+  Eventually, support will be removed.  Use %type instead.
+
 * Noteworthy changes in release 3.2.1 (2018-11-09) [stable]
 
 ** Bug fixes

src/scan-gram.l

@@ -240,7 +240,6 @@ eqopt    ([[:space:]]*=)?
   "%no-lines"                       return PERCENT_NO_LINES;
   "%nonassoc"                       return PERCENT_NONASSOC;
   "%nondeterministic-parser"        return PERCENT_NONDETERMINISTIC_PARSER;
-  "%nterm"                          return PERCENT_NTERM;
   "%output"                         return PERCENT_OUTPUT;
   "%param"                          RETURN_PERCENT_PARAM(both);
   "%parse-param"                    RETURN_PERCENT_PARAM(parse);
@@ -260,7 +259,7 @@ eqopt    ([[:space:]]*=)?
   "%verbose"                        return PERCENT_VERBOSE;
   "%yacc"                           return PERCENT_YACC;
 
-  /* deprecated */
+  /* Deprecated since Bison 2.7.90, 2012. */
   "%default"[-_]"prec"              DEPRECATED("%default-prec");
   "%error"[-_]"verbose"             DEPRECATED("%define parse.error verbose");
   "%expect"[-_]"rr"                 DEPRECATED("%expect-rr");
@@ -273,6 +272,12 @@ eqopt    ([[:space:]]*=)?
   "%pure"[-_]"parser"               DEPRECATED("%pure-parser");
   "%token"[-_]"table"               DEPRECATED("%token-table");
 
+  "%nterm"  {
+    /* Deprecated since Bison 3.3, but was a rather stealth feature.  */
+    deprecated_directive (loc, yytext, "%type");
+    return PERCENT_NTERM;
+  }
+
   "%"{id} {
     complain (loc, complaint, _("invalid directive: %s"), quote (yytext));
   }

tests/c++.at

@@ -210,7 +210,7 @@ AT_DATA_GRAMMAR([input.yy],
 [[%skeleton "lalr1.cc"
 %define api.value.automove
 %token <int> NUMBER "number"
-%nterm <int> exp
+%type <int> exp
 %%
 exp:
   "number"          { $$ = $1; $$; }
@@ -576,7 +576,7 @@ AT_DATA_GRAMMAR([[input.y]],
 }
 
 %token <int> NUMBER;
-%nterm <int> expr;
+%type <int> expr;
 %token EOI 0;
 %printer { yyo << $$; } <int>;
 %destructor { std::cerr << "destroy: " << $$ << '\n'; } <int>

tests/reduce.at

@@ -73,32 +73,20 @@ AT_DATA([[input.y]],
 [[%verbose
 %output "input.c"
 
-%nterm useless1
-%nterm useless2
-%nterm useless3
-%nterm useless4
-%nterm useless5
-%nterm useless6
-%nterm useless7
-%nterm useless8
-%nterm useless9
-
 %token useful
 %%
 exp: useful;
+useless1:
+useless2:
+useless3:
 ]])
 
 AT_BISON_CHECK([[input.y]], 0, [],
-[[input.y: warning: 9 nonterminals useless in grammar [-Wother]
-input.y:4.8-15: warning: nonterminal useless in grammar: useless1 [-Wother]
-input.y:5.8-15: warning: nonterminal useless in grammar: useless2 [-Wother]
-input.y:6.8-15: warning: nonterminal useless in grammar: useless3 [-Wother]
-input.y:7.8-15: warning: nonterminal useless in grammar: useless4 [-Wother]
-input.y:8.8-15: warning: nonterminal useless in grammar: useless5 [-Wother]
-input.y:9.8-15: warning: nonterminal useless in grammar: useless6 [-Wother]
-input.y:10.8-15: warning: nonterminal useless in grammar: useless7 [-Wother]
-input.y:11.8-15: warning: nonterminal useless in grammar: useless8 [-Wother]
-input.y:12.8-15: warning: nonterminal useless in grammar: useless9 [-Wother]
+[[input.y: warning: 3 nonterminals useless in grammar [-Wother]
+input.y: warning: 3 rules useless in grammar [-Wother]
+input.y:7.1-8: warning: nonterminal useless in grammar: useless1 [-Wother]
+input.y:8.1-8: warning: nonterminal useless in grammar: useless2 [-Wother]
+input.y:9.1-8: warning: nonterminal useless in grammar: useless3 [-Wother]
 ]])
 
 AT_CHECK([[sed -n '/^Grammar/q;/^$/!p' input.output]], 0,
@@ -106,12 +94,10 @@ AT_CHECK([[sed -n '/^Grammar/q;/^$/!p' input.output]], 0,
    useless1
    useless2
    useless3
-   useless4
-   useless5
-   useless6
-   useless7
-   useless8
-   useless9
+Rules useless in grammar
+    2 useless1: %empty
+    3 useless2: %empty
+    4 useless3: %empty
 ]])
 
 AT_CLEANUP

tests/synclines.at

@@ -344,7 +344,7 @@ AT_TEST([%destructor syncline],
 %union {
   int ival;
 }
-%nterm <ival> exp
+%type <ival> exp
 %%
 exp: '0' { $$ = 0; };
 %%
@@ -369,7 +369,7 @@ AT_TEST([%printer syncline],
 %union {
   int ival;
 }
-%nterm <ival> exp
+%type <ival> exp
 %%
 exp: '0' { $$ = 0; };
 %%