Allow empty assignment in for-loop

For loops with no assignment are no longer syntax errors. For example,
this is now valid:

    for ( ; i < 10; i++) { ... }

Corresponding changes to lsl.{lexer,parser} in r99 in opensim-libs.

Fixes Mantis #2501. Fixes Mantis #2884.

OpenSim/Region/ScriptEngine/Shared/CodeTools/CSCodeGenerator.cs

@@ -671,9 +671,15 @@ namespace OpenSim.Region.ScriptEngine.Shared.CodeTools
 
             retstr += GenerateIndented("for (", fl);
 
+            // It's possible that we don't have an assignment, in which case
+            // the child will be null and we only print the semicolon.
             // for ( x = 0 ; x < 10 ; x++ )
             //       ^^^^^^^
-            retstr += GenerateForLoopStatement((ForLoopStatement) fl.kids.Pop());
+            ForLoopStatement s = (ForLoopStatement) fl.kids.Pop();
+            if (null != s)
+            {
+                retstr += GenerateForLoopStatement(s);
+            }
             retstr += Generate("; ");
             // for ( x = 0 ; x < 10 ; x++ )
             //               ^^^^^^^^

OpenSim/Region/ScriptEngine/Shared/CodeTools/LSL2CSCodeTransformer.cs

@@ -92,10 +92,22 @@ namespace OpenSim.Region.ScriptEngine.Shared.CodeTools
 
             for (int i = 0; i < s.kids.Count; i++)
             {
-                if (!(s is Assignment || s is ArgumentDeclarationList) && s.kids[i] is Declaration)
-                    AddImplicitInitialization(s, i);
+                // It's possible that a child is null, for instance when the
+                // assignment part in a for-loop is left out, ie:
+                //
+                //     for ( ; i < 10; i++)
+                //     {
+                //         ...
+                //     }
+                //
+                // We need to check for that here.
+                if (null != s.kids[i])
+                {
+                    if (!(s is Assignment || s is ArgumentDeclarationList) && s.kids[i] is Declaration)
+                        AddImplicitInitialization(s, i);
 
-                TransformNode((SYMBOL) s.kids[i]);
+                    TransformNode((SYMBOL) s.kids[i]);
+                }
             }
         }
 

OpenSim/Region/ScriptEngine/Shared/CodeTools/Tests/CSCodeGeneratorTest.cs

@@ -1515,6 +1515,31 @@ default
             Assert.AreEqual(expected, output);
         }
 
+        [Test]
+        public void TestForLoopWithNoAssignment()
+        {
+            string input = @"default
+{
+    state_entry()
+    {
+        integer x = 4;
+        for (; 1<0; x += 2);
+    }
+}";
+
+            string expected =
+                "\n        public void default_event_state_entry()" +
+                "\n        {" +
+                "\n            LSL_Types.LSLInteger x = new LSL_Types.LSLInteger(4);" +
+                "\n            for (; new LSL_Types.LSLInteger(1) < new LSL_Types.LSLInteger(0); x += new LSL_Types.LSLInteger(2))" +
+                "\n                ;" +
+                "\n        }\n";
+
+            CSCodeGenerator cg = new CSCodeGenerator();
+            string output = cg.Convert(input);
+            Assert.AreEqual(expected, output);
+        }
+
         [Test]
         public void TestAssignmentInIfWhileDoWhile()
         {

OpenSim/Region/ScriptEngine/Shared/CodeTools/lsl.lexer.cs

@@ -18785,6 +18785,7 @@ public override TOKEN OldAction(Lexer yym,ref string yytext,int action, ref bool
    case 946: { ((LSLTokens)yym).str += yytext; }
       break;
    case 1010: { yym.yy_begin("YYINITIAL"); ((LSLTokens)yym).yytext = ((LSLTokens)yym).str; ((LSLTokens)yym).str = String.Empty; return new STRING_CONSTANT(yym); }
+      break;
    case 1015: { yym.yy_begin("COMMENT"); }
       break;
    case 1027: { yym.yy_begin("YYINITIAL"); }