types: Fix table() resulting in table_type->IsSet() == true

typename(table()) apparently always resulted in a set[] type
being rendered. Make the yield type of an unspecified table
ANY so that type->IsSet() ends up false.

While at it, also render unspecified types as table(), set() and
vector() rather than vector of void, set[] or table[] of any which
IMO should help to figure out what's going.

src/Expr.cc

@@ -3181,7 +3181,7 @@ TableConstructorExpr::TableConstructorExpr(ListExprPtr constructor_list,
     }
     else {
         if ( op->AsListExpr()->Exprs().empty() )
-            SetType(make_intrusive<TableType>(make_intrusive<TypeList>(base_type(TYPE_ANY)), nullptr));
+            SetType(make_intrusive<TableType>(make_intrusive<TypeList>(base_type(TYPE_ANY)), base_type(TYPE_ANY)));
         else {
             SetType(init_type(op));
 

src/Type.cc

@@ -320,11 +320,19 @@ int IndexType::MatchesIndex(detail::ListExpr* const index) const {
 
 void IndexType::DoDescribe(ODesc* d) const {
     Type::DoDescribe(d);
-    if ( ! d->IsBinary() )
-        d->Add("[");
 
     const auto& its = GetIndexTypes();
 
+    // Deal with unspecified table/set.
+    if ( its.empty() ) {
+        if ( ! d->IsBinary() )
+            d->Add("()");
+        return;
+    }
+
+    if ( ! d->IsBinary() )
+        d->Add("[");
+
     for ( auto i = 0u; i < its.size(); ++i ) {
         if ( ! d->IsBinary() && i > 0 )
             d->Add(",");
@@ -1763,6 +1771,11 @@ int VectorType::MatchesIndex(detail::ListExpr* const index) const {
 bool VectorType::IsUnspecifiedVector() const { return yield_type->Tag() == TYPE_VOID; }
 
 void VectorType::DoDescribe(ODesc* d) const {
+    if ( IsUnspecifiedVector() && d->IsReadable() ) {
+        d->Add("vector()");
+        return;
+    }
+
     if ( d->IsReadable() )
         d->AddSP("vector of");
     else

testing/btest/Baseline/language.unspecified/output

@@ -0,0 +1,4 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+set()
+table()
+vector()

testing/btest/language/unspecified.zeek

@@ -0,0 +1,7 @@
+# @TEST-DOC: Test representation of unspecified table, set and vector
+# @TEST-EXEC: zeek -b %INPUT >output
+# @TEST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff output
+
+print type_name(set());
+print type_name(table());
+print type_name(vector());