autfilt: support -n,--max-count

* src/bin/autfilt.cc: Implement this new option.
* src/tgbatest/readsave.test: Test it.

src/bin/autfilt.cc

@@ -98,6 +98,8 @@ static const argp_option options[] =
     { "lbtt", OPT_LBTT, "t", OPTION_ARG_OPTIONAL,
       "LBTT's format (add =t to force transition-based acceptance even"
       " on Büchi automata)", 0 },
+    { "max-count", 'n', "NUM", 0,
+      "output at most NUM automata", 0 },
     { "name", OPT_NAME, "FORMAT", OPTION_ARG_OPTIONAL,
       "set the name of the output automaton (default: %M)", 0 },
     { "quiet", 'q', 0, 0, "suppress all normal output", 0 },
@@ -193,6 +195,7 @@ static bool opt_is_deterministic = false;
 static bool opt_invert = false;
 static range opt_states = { 0, std::numeric_limits<int>::max() };
 static const char* opt_name = nullptr;
+static int opt_max_count = -1;
 
 static int
 to_int(const char* s)
@@ -204,6 +207,15 @@ to_int(const char* s)
   return res;
 }
 
+static int
+to_pos_int(const char* s)
+{
+  int res = to_int(s);
+  if (res < 0)
+    error(2, 0, "%d is not positive", res);
+  return res;
+}
+
 static int
 parse_opt(int key, char* arg, struct argp_state*)
 {
@@ -229,6 +241,9 @@ parse_opt(int key, char* arg, struct argp_state*)
     case 'M':
       type = spot::postprocessor::Monitor;
       break;
+    case 'n':
+      opt_max_count = to_pos_int(arg);
+      break;
     case 'q':
       format = Quiet;
       break;
@@ -550,6 +565,10 @@ namespace
 	  break;
 	}
       flush_cout();
+
+      if (opt_max_count >= 0 && match_count >= opt_max_count)
+	abort_run = true;
+
       return 0;
     }
 
@@ -568,7 +587,7 @@ namespace
 
       int err = 0;
 
-      for (;;)
+      while (!abort_run)
 	{
 	  pel.clear();
 	  auto haut = hp.parse(pel, dict);

src/tgbatest/readsave.test

@@ -106,12 +106,13 @@ run 0 $autfilt --hoa stdout > stdout2
 diff stdout stdout2
 
 # Find formula that can be translated into a 3-state automaton, and
-# exercise both %M and %m.
+# exercise both %M and %m.  The nonexistant file should never be
+# open, because the input stream is infinite and autfilt should
+# stop after 10 automata.
 $randltl -n -1 a b |
     $ltl2tgba -H -F - |
-    $autfilt --states=3 --name='%M, %S states' --stats='<%m>, %t' |
-    head -n 10 > output
-cat output
+    $autfilt -F- -F nonexistant --states=3 \
+	     --name='%M, %S states' --stats='<%m>, %t' -n 10 > output
 cat >expected <<EOF
 <F(b | GF!a), 3 states>, 13
 <XFb, 3 states>, 6