fix tra_to_tba()

Fixes #324, reported by Tobias Meggendorfer and František Blahoudek.

* spot/twa/acc.hh (rs_pairs_view::paired_with): Rename as...
(rs_pairs_view::paired_with_fin):... this and adjust the code.
* spot/twaalgos/remfin.cc: Use paired_with_fin instead of
paired_with, and do it once per pair.
* tests/core/remfin.test: Add a test case.
* NEWS: Mention the issue.

NEWS

@@ -18,6 +18,13 @@ New in spot 2.5.0.dev (not yet released)
     as Fin(0)|(Fin(1)&Inf(2)) instead.  Likewise for
     is_generalized_streett
 
+  - the conversion from Rabin to Büchi was broken on Rabin-like
+    acceptance condition where one pair used Fin(x) and another pair
+    used Inf(x) with the same x.  Unfortunately, this situation could
+    also occur as a side effect of simplifying the acceptance
+    condition (by merging identical set) prior to running the
+    conversion to Büchi.
+
 New in spot 2.5 (2018-01-20)
 
   Build:

spot/twa/acc.hh

@@ -1397,19 +1397,12 @@ namespace spot
         });
     }
 
-    acc_cond::mark_t paired_with(unsigned mark) const
+    acc_cond::mark_t paired_with_fin(unsigned mark) const
     {
       acc_cond::mark_t res = 0U;
       for (const auto& p: pairs_)
-      {
-        if (visible(p.fin) && visible(p.inf))
-          {
-            if (p.fin.has(mark))
-              res |= p.inf;
-            if (p.inf.has(mark))
-              res |= p.fin;
-          }
-      }
+        if (p.fin.has(mark) && visible(p.fin) && visible(p.inf))
+          res |= p.inf;
       return res;
     }
 

spot/twaalgos/remfin.cc

@@ -312,7 +312,7 @@ namespace spot
 
               for (const auto& e: si.edges_of(scc))
                 {
-                  bool acc{e.acc & scc_infs_alone};
+                  bool acc = (e.acc & scc_infs_alone) != 0;
                   res->new_acc_edge(e.src, e.dst, e.cond, acc);
                 }
 
@@ -320,6 +320,7 @@ namespace spot
 
               for (auto r: scc_pairs.fins().sets())
                 {
+                  acc_cond::mark_t pairinf = scc_pairs.paired_with_fin(r);
                   unsigned base = res->new_states(states.size());
                   for (auto s: states)
                       state_map[s] = base++;
@@ -329,9 +330,7 @@ namespace spot
                         continue;
                       auto src = state_map[e.src];
                       auto dst = state_map[e.dst];
-                      bool cacc = fins_alone.has(r)
-                                ? true
-                                : ((scc_pairs.paired_with(r) & e.acc) != 0);
+                      bool cacc = fins_alone.has(r) || (pairinf & e.acc) != 0;
                       res->new_acc_edge(src, dst, e.cond, cacc);
                       // We need only one non-deterministic jump per
                       // cycle.  As an approximation, we only do

tests/core/remfin.test

@@ -1504,6 +1504,27 @@ run 0 autfilt -H --tgba test1 > output
 cat output
 diff -u output expected-tgba
 
+# Issue #324.
+cat > 324 <<EOF
+HOA: v1
+States: 2
+Start: 1
+AP: 2 "a" "b"
+acc-name: Rabin 3
+Acceptance: 6 (Fin(0) & Inf(1)) | (Fin(2) & Inf(3)) | (Fin(4) & Inf(5))
+properties: trans-labels explicit-labels trans-acc deterministic
+--BODY--
+State: 0
+[!0&!1] 0 {0 4}
+[!0&1] 0 {0 3 4}
+[0&!1] 0 {2 5}
+[0&1] 0 {1 2 5}
+State: 1
+[0] 0
+--END--
+EOF
+autfilt --remove-fin 324 > out
+test 2 = `autfilt -c --reject-word='a;cycle{!a&!b}' 324 out`
 
 # Add 10 small random automata for the next case
 randaut -A'random 6' -Q10 -n10 3 -Hl >> test1