add LR(0) output

[Akim Demaille]

commit e346210c038bc5c6ab2aca99e04f8452181406e1
Author: Akim Demaille <address@hidden>
Date:   Sun Jan 27 18:29:17 2019 +0100

    add LR(0) output
    
    This should not be used to generate parsers.  My point is actually to
    facilitate debugging (when tweaking the generation of the LR(0)
    automaton for instance, not carying -yet- about lookaheads).
    
    * src/reader.c (prepare_percent_define_front_end_variables): Add lr(0).
    * src/conflicts.c (set_conflicts): Be robust to reds not having
    lookaheads at all.
    * src/ielr.c (LrType, lr_type_get): Adjust.
    (ielr): Implement support for LR(0).
    * src/lalr.c (lalr_free): Don't free LA when it's not computed.

diff --git a/src/conflicts.c b/src/conflicts.c
index c849e898..734b8c15 100644
--- a/src/conflicts.c
+++ b/src/conflicts.c
@@ -369,13 +369,16 @@ set_conflicts (state *s, symbol **errors)
     s->solved_conflicts_xml = obstack_finish0 (&solved_conflicts_xml_obstack);
 
   /* Loop over all rules which require lookahead in this state.  Check
-     for conflicts not resolved above.  */
-  for (int i = 0; i < reds->num; ++i)
-    {
-      if (!bitset_disjoint_p (reds->lookahead_tokens[i], lookahead_set))
-        conflicts[s->number] = 1;
-      bitset_or (lookahead_set, lookahead_set, reds->lookahead_tokens[i]);
-    }
+     for conflicts not resolved above.
+
+     reds->lookahead_tokens can be NULL if the LR type is LR(0).  */
+  if (reds->lookahead_tokens)
+    for (int i = 0; i < reds->num; ++i)
+      {
+        if (!bitset_disjoint_p (reds->lookahead_tokens[i], lookahead_set))
+          conflicts[s->number] = 1;
+        bitset_or (lookahead_set, lookahead_set, reds->lookahead_tokens[i]);
+      }
 }
 
 
diff --git a/src/ielr.c b/src/ielr.c
index fe1217b1..47ce38c3 100644
--- a/src/ielr.c
+++ b/src/ielr.c
@@ -36,7 +36,36 @@
 #include "symtab.h"
 
 /** Records the value of the \%define variable lr.type.  */
-typedef enum { LR_TYPE__LALR, LR_TYPE__IELR, LR_TYPE__CANONICAL_LR } LrType;
+typedef enum
+  {
+   LR_TYPE__LR0,
+   LR_TYPE__LALR,
+   LR_TYPE__IELR,
+   LR_TYPE__CANONICAL_LR
+  } LrType;
+
+/* The user's requested LR type.  */
+static LrType
+lr_type_get (void)
+{
+  char *type = muscle_percent_define_get ("lr.type");
+  LrType res;
+  if (STREQ (type, "lr(0)"))
+    res = LR_TYPE__LR0;
+  else if (STREQ (type, "lalr"))
+    res = LR_TYPE__LALR;
+  else if (STREQ (type, "ielr"))
+    res = LR_TYPE__IELR;
+  else if (STREQ (type, "canonical-lr"))
+    res = LR_TYPE__CANONICAL_LR;
+  else
+    {
+      aver (false);
+      abort ();
+    }
+  free (type);
+  return res;
+}
 
 /**
  * \post:
@@ -1052,46 +1081,39 @@ ielr_split_states (bitsetv follow_kernel_items, bitsetv 
always_follows,
 }
 
 
-/* The user's requested LR type.  */
-static LrType
-lr_type_get (void)
-{
-  char *type = muscle_percent_define_get ("lr.type");
-  LrType res;
-  if (STREQ (type, "lalr"))
-    res = LR_TYPE__LALR;
-  else if (STREQ (type, "ielr"))
-    res = LR_TYPE__IELR;
-  else if (STREQ (type, "canonical-lr"))
-    res = LR_TYPE__CANONICAL_LR;
-  else
-    {
-      aver (false);
-      abort ();
-    }
-  free (type);
-  return res;
-}
-
-
 void
 ielr (void)
 {
   LrType lr_type = lr_type_get ();
 
   /* Phase 0: LALR(1).  */
-  timevar_push (tv_lalr);
-  if (lr_type == LR_TYPE__CANONICAL_LR)
-    set_goto_map ();
-  else
-    lalr ();
-  if (lr_type == LR_TYPE__LALR)
+  switch (lr_type)
     {
+    case LR_TYPE__LR0:
+      timevar_push (tv_lalr);
+      set_goto_map ();
+      timevar_pop (tv_lalr);
+      return;
+
+    case LR_TYPE__CANONICAL_LR:
+      timevar_push (tv_lalr);
+      set_goto_map ();
+      timevar_pop (tv_lalr);
+      break;
+
+    case LR_TYPE__LALR:
+      timevar_push (tv_lalr);
+      lalr ();
       bitsetv_free (goto_follows);
       timevar_pop (tv_lalr);
       return;
+
+    case LR_TYPE__IELR:
+      timevar_push (tv_lalr);
+      lalr ();
+      timevar_pop (tv_lalr);
+      break;
     }
-  timevar_pop (tv_lalr);
 
   {
     bitsetv follow_kernel_items;
diff --git a/src/reader.c b/src/reader.c
index 075d6c7a..dbc834a4 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -754,11 +754,12 @@ prepare_percent_define_front_end_variables (void)
 
   /* Check %define front-end variables.  */
   {
-    static char const * const values[] = {
-      "lr.type", "lalr", "ielr", "canonical-lr", NULL,
-      "lr.default-reduction", "most", "consistent", "accepting", NULL,
-      NULL
-    };
+    static char const * const values[] =
+      {
+       "lr.type", "lr(0)", "lalr", "ielr", "canonical-lr", NULL,
+       "lr.default-reduction", "most", "consistent", "accepting", NULL,
+       NULL
+      };
     muscle_percent_define_check_values (values);
   }
 }