dot: use circles if state names are all short

* spot/twaalgos/dot.cc: Check for state names sizes.
* tests/core/readsave.test: Test the change.
* tests/core/tgbagraph.test: Adjust.

spot/twaalgos/dot.cc

@@ -33,6 +33,7 @@
 #include <spot/twaalgos/sccinfo.hh>
 #include <cstdlib>
 #include <cstring>
+#include <algorithm>
 #include <ctype.h>
 
 
@@ -541,10 +542,19 @@ namespace spot
 	if (opt_shape_ == ShapeAuto)
 	  {
 	    if (sn_ || sprod_ || aut->num_states() > 100)
+	      {
 		opt_shape_ = ShapeEllipse;
-	    else
+		// If all state names are short, prefer circles.
+		if (sn_ && std::all_of(sn_->begin(), sn_->end(),
+				       [](const std::string& s)
+				       { return s.size() <= 2; }))
 		  opt_shape_ = ShapeCircle;
 	      }
+	    else
+	      {
+		opt_shape_ = ShapeCircle;
+	      }
+	  }
 	auto si =
 	  std::unique_ptr<scc_info>(opt_scc_ ? new scc_info(aut) : nullptr);
 

tests/core/readsave.test

@@ -538,6 +538,26 @@ EOF
 autfilt --dot=bao1 in | grep -v '>' >out
 diff out expected2
 
+cat >expected3 <<EOF
+digraph G {
+  rankdir=LR
+  node [shape="circle"]
+  I [label="", style=invis, width=0]
+  0 [label="6", peripheries=2]
+  u0 [label="...", shape=none, width=0, height=0]
+  1 [label="0", peripheries=2]
+  2 [label="1", peripheries=2]
+  3 [label="2", peripheries=2]
+  4 [label="3", peripheries=2]
+  u4 [label="...", shape=none, width=0, height=0]
+}
+EOF
+
+# States should be circled even if <5 causes all states to be named,
+# because the names are smaller then 2 characters anyway.
+ltl2tgba --det 'Ga | Gb | Gc' -d'<5' | grep -v '>' >out
+diff out expected3
+
 # Let's pretend that this is some used supplied input, as discussed in
 # the comments of https://github.com/adl/hoaf/issues/39
 

tests/core/tgbagraph.test

@@ -223,6 +223,7 @@ digraph G {
 }
 digraph G {
   rankdir=LR
+  node [shape="circle"]
   I [label="", style=invis, width=0]
   I -> 2
   0 [label="s1"]
@@ -231,6 +232,7 @@ digraph G {
 }
 digraph G {
   rankdir=LR
+  node [shape="circle"]
   I [label="", style=invis, width=0]
   I -> 0
   0 [label="s3"]