fixed crash when loopvar in for loop wasn't defined

compiler/res/prog8lib/cx16/gfx2.p8

@@ -137,7 +137,7 @@ gfx2 {
             }
             0, 128 -> {
                 ; 1 bpp mode
-                ; TODO optimize this to plot 8 pixels at once while possible
+                ; TODO optimize this to plot 8 pixels at once while possible, note: do mind the stipple setting
                 repeat length {
                     gfx2.plot(x, y, color)
                     x++
@@ -147,7 +147,7 @@ gfx2 {
     }
 
     sub vertical_line(uword x, uword y, uword height, ubyte color) {
-        ; TODO optimize this to use vera special increment mode
+        ; TODO optimize this to use vera special increment mode, note: do mind the stipple setting
         repeat height {
             plot(x, y, color)
             y++

compiler/src/prog8/optimizer/ConstantFoldingOptimizer.kt

@@ -226,7 +226,8 @@ internal class ConstantFoldingOptimizer(private val program: Program) : AstWalke
         val rangeTo = iterableRange.to as? NumericLiteralValue
         if(rangeFrom==null || rangeTo==null) return noModifications
 
-        val loopvar = forLoop.loopVar.targetVarDecl(program.namespace)!!
+        val loopvar = forLoop.loopVar.targetVarDecl(program.namespace) ?: throw UndefinedSymbolError(forLoop.loopVar)
+
         val stepLiteral = iterableRange.step as? NumericLiteralValue
         when(loopvar.datatype) {
             DataType.UBYTE -> {

docs/source/todo.rst

@@ -2,7 +2,6 @@
 TODO
 ====
 
-- nice error msg for float as for loop var
 - implement gfx2's rect, fillrect, horizontal_line and vertical_line in graphics modules as well. (and optimize bresenham line to use vert/horiz line if possible)
 - detect variables that are written but never read - mark those as unused too and remove them, such as uword unused = memory("unused222", 20) - also remove the memory slab allocation
 - hoist all variable declarations up to the subroutine scope *before* even the constant folding takes place (to avoid undefined symbol errors when referring to a variable from another nested scope in the subroutine)

examples/test.p8

@@ -9,15 +9,6 @@ main {
 
     sub start () {
 
-        word ww
-        float y_f
-        float fl
-        for ww in -300 to 300 {         ; TODO fix crash if ww is not defined
-            fl = ww as float
-            floats.print_f(fl)
-            txt.chrout(' ')
-        }
-
         test_stack.test()
 
     }