hoa: fix segfault when input has initial alternation

* src/hoaparse/hoaparse.yy: Do not check initial alternating state
number until we support alternation.
* src/tests/hoaparse.test: Add a test case.

src/hoaparse/hoaparse.yy

@@ -428,7 +428,7 @@ header-item: "States:" INT
 	       }
 	     res.states = std::max(res.states, (int) $2);
 	   }
-           | "Start:" state-conj-2
+           | "Start:" init-state-conj-2
 	     {
 	       error(@2, "alternation is not yet supported");
 	       YYABORT;
@@ -587,6 +587,11 @@ header-spec: | header-spec BOOLEAN
 state-conj-2: checked-state-num '&' checked-state-num
             | state-conj-2 '&' checked-state-num
 
+	      // Currently we do not check the number of these states
+	      // since we do not support alternation.
+init-state-conj-2: state-num '&' state-num
+            | init-state-conj-2 '&' state-num
+
 label-expr: 't'
 	    {
 	      $$ = bddtrue.id();

src/tests/hoaparse.test

@@ -1672,3 +1672,62 @@ input:13.9: state 2 has no definition
 input:17.7: state 5 has no definition
 input:14.9: state 8 has no definition
 EOF
+
+
+# This input caused a segfault at some point.
+# Not supporting alternation is not an excuse for segfaulting.
+cat >input <<EOF
+HOA: v1
+tool: "ltl3ba" "1.1.2"
+States: 12
+Start: 8&6&2
+Start: 8&4&2
+Start: 8&6&0
+Start: 8&4&0
+acc-name: co-Buchi
+Acceptance: 1 Fin(0)
+AP: 4 "p2" "c1" "p1" "c2"
+properties: trans-labels explicit-labels state-acc univ-branch very-weak
+--BODY--
+State: 0 "X (G(c2))"
+ [t] 1
+State: 1 "G(c2)"
+ [(3)] 1
+State: 2 "FG(c1)" {0}
+ [(1)] 3
+ [t] 2
+State: 3 "G(c1)"
+ [(1)] 3
+State: 4 "X (F!((c2)))"
+ [t] 5
+State: 5 "F!((c2))" {0}
+ [(!3)] 11
+ [t] 5
+State: 6 "GF!((c1))"
+ [(!1)] 6
+ [t] 7&6
+State: 7 "F!((c1))" {0}
+ [(!1)] 11
+ [t] 7
+State: 8 "((!((c1)) U (!((c1)) && !((p1)))) R F!((p2)))"
+ [(!0 & !1 & !2)] 11
+ [(!1 & !2)] 10
+ [(!0 & !1)] 9
+ [(!1)] 10&9
+ [(!0)] 8
+ [t] 10&8
+State: 9 "(!((c1)) U (!((c1)) && !((p1))))" {0}
+ [(!1 & !2)] 11
+ [(!1)] 9
+State: 10 "F!((p2))" {0}
+ [(!0)] 11
+ [t] 10
+State: 11 "t"
+ [t] 11
+--END--
+EOF
+
+expecterr input <<EOF
+input:4.8-12: alternation is not yet supported
+autfilt: failed to read automaton from input
+EOF