fix compiler crash on certain typecasting assignment

codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt

@@ -791,6 +791,20 @@ internal class AssignmentAsmGen(private val program: Program,
                 assignTypeCastedFloatFAC1("P8ZP_SCRATCH_W1", target.datatype)
                 assignVariableToRegister("P8ZP_SCRATCH_W1", target.register!!, target.datatype in SignedDatatypes)
             } else {
+                if(!(valueDt isAssignableTo targetDt)) {
+                    if(valueDt in WordDatatypes && targetDt in ByteDatatypes) {
+                        // word to byte, just take the lsb
+                        return assignCastViaLsbFunc(value, target)
+                    } else if(valueDt in WordDatatypes && targetDt in WordDatatypes) {
+                        // word to word, just assign
+                        assignExpressionToRegister(value, target.register!!, targetDt==DataType.BYTE || targetDt==DataType.WORD)
+                    } else if(valueDt in ByteDatatypes && targetDt in ByteDatatypes) {
+                        // byte to byte, just assign
+                        assignExpressionToRegister(value, target.register!!, targetDt==DataType.BYTE || targetDt==DataType.WORD)
+                    }
+                    else
+                        throw AssemblyError("can't cast $valueDt to $targetDt, this should have been checked in the astchecker")
+                }
                 assignExpressionToRegister(value, target.register!!, targetDt==DataType.BYTE || targetDt==DataType.WORD)
             }
             return

compiler/test/TestTypecasts.kt

@@ -16,6 +16,26 @@ import prog8tests.helpers.compileText
 
 class TestTypecasts: FunSpec({
 
+    test("word to byte casts") {
+        val text="""
+            %import textio
+            main {
+                sub func(ubyte arg) -> word {
+                    return arg-99
+                }
+            
+                sub start() {
+                    txt.print_ub(func(0) as ubyte)
+                    txt.print_uw(func(0) as ubyte)
+                    txt.print_w(func(0) as ubyte)
+                }
+            }"""
+        val result = compileText(C64Target(), false, text, writeAssembly = false)!!
+        val stmts = result.program.entrypoint.statements
+        stmts.size shouldBe 3
+
+    }
+
     test("add missing & to function arguments") {
         val text="""
             main  {

docs/source/todo.rst

@@ -3,7 +3,6 @@ TODO
 
 For next release
 ^^^^^^^^^^^^^^^^
-- fix compiler crash txt.print_w(value(99) as ubyte)    where value()->word
 - fix imageviewer compilation crash
 
 - petaxian is larger again after introduction of BOOL type (against main branch). WHY??? FIX.