parseaut: allow the univ-branch diagnostics to be ignored

* spot/parseaut/parseaut.yy: Check the SPOT_HOA_TOLERANT variable.
* tests/core/ltl3ba.test, tests/core/parseaut.test: Adjust test cases.
* NEWS, bin/man/spot-x.x: Mention SPOT_HOA_TOLERANT.

NEWS

@@ -181,6 +181,11 @@ New in spot 2.3.5.dev (not yet released)
     been adjusted to these new semantics, see "Backward-incompatible
     changes" below.
 
+  - The parser for HOA now recognize and verifies correct use of the
+    "univ-branch" property.  This is known to be a problem with option
+    -H1 of ltl3ba 1.1.2 and ltl3dra 0.2.3, so the environment variable
+    SPOT_HOA_TOLERANT can be set to disable the diagnostic.
+
   Python:
 
   - The 'spot.gen' package exports the functions from libspotgen.

bin/man/spot-x.x

@@ -91,6 +91,14 @@ The contents of this variable is added to any dot output, immediately
 before the first state is output.  This makes it easy to override
 global attributes of the graph.
 
+.TP
+\fBSPOT_HOA_TOLERANT\fR
+If this variable is set, a few sanity checks performed by the HOA
+parser are skipped.  The tests in questions correspond to issues
+in third-party tools that output incorrect HOA (e.g., declaring
+the automaton with property "univ-branch" when no universal branching
+is actually used)
+
 .TP
 \fBSPOT_SATLOG\fR
 If set to a filename, the SAT-based minimization routines will append

spot/parseaut/parseaut.yy

@@ -1110,18 +1110,25 @@ body: states
               error(p.loc, "... despite 'properties: !deterministic'");
               det_warned = true;
             }
-        if (res.universal.is_true() && !det_warned)
+        static bool tolerant = getenv("SPOT_HOA_TOLERANT");
+        if (res.universal.is_true() && !det_warned && !tolerant)
           if (auto p = res.prop_is_true("exist-branch"))
             {
               error(@1, "automaton has no existential branching...");
-              error(p.loc, "... despite 'properties: exist-branch'");
+              error(p.loc, "... despite 'properties: exist-branch'\n"
+                    "note: If this is an issue you cannot fix, you may disable "
+                    "this diagnostic\n      by defining the SPOT_HOA_TOLERANT "
+                    "environment variable.");
               det_warned = true;
             }
-        if (res.existential.is_true() && !det_warned)
+        if (res.existential.is_true() && !det_warned && !tolerant)
           if (auto p = res.prop_is_true("univ-branch"))
             {
               error(@1, "automaton is has no universal branching...");
-              error(p.loc, "... despite 'properties: univ-branch'");
+              error(p.loc, "... despite 'properties: univ-branch'\n"
+                    "note: If this is an issue you cannot fix, you may disable "
+                    "this diagnostic\n      by defining the SPOT_HOA_TOLERANT "
+                    "environment variable.");
               det_warned = true;
             }
       }

tests/core/ltl3ba.test

@@ -29,7 +29,11 @@ set -e
 (ltl3ba -v) || exit 77
 
 # The -H1 option will output alternating automata, so this tests
-# ltlcross's support in this area.
+# ltlcross's support in this area.  However ltl3ba 1.1.3 incorrectly
+# output "univ-branch" for all automata produced by -H1, causing
+# error messages from Spot's parser unless SPOT_HOA_TOLERANT is set.
+SPOT_HOA_TOLERANT=1
+export SPOT_HOA_TOLERANT
 # Using '_x' as first formula makes sure that ltlcross automatically
 # relabels the input formula when the atomic propositions are not
 # compatible with Spin's syntax.

tests/core/parseaut.test

@@ -783,12 +783,16 @@ input:62.1-64.6: automaton has existential branching...
 input:57.13-25: ... despite 'properties: !exist-branch'
 input:58.9-64.6: automaton is has no universal branching...
 input:57.27-37: ... despite 'properties: univ-branch'
+note: If this is an issue you cannot fix, you may disable this diagnostic
+      by defining the SPOT_HOA_TOLERANT environment variable.
 input:68.1-10: conjunct initial state despite...
 input:71.26-37: ... property: !univ-branch
 input:91.6-8: universal branch used despite previous declaration...
 input:85.26-37: ... here
 input:86.9-91.8: automaton has no existential branching...
 input:85.13-24: ... despite 'properties: exist-branch'
+note: If this is an issue you cannot fix, you may disable this diagnostic
+      by defining the SPOT_HOA_TOLERANT environment variable.
 input:106.6-9: we can read HOA v1 but this file uses v1.1; $t
 input:108.1-10: conjunct initial state despite...
 input:111.13-25: ... property: deterministic