fix charset encoding error with merge. Fixes #207

compiler/test/TestImportedModulesOrderAndOptions.kt

@@ -210,6 +210,28 @@ sub printit(str arg) {
         compileText(C64Target(), optimize=false, src, outputDir, writeAssembly=false) shouldNotBe null
     }
 
+    test("merge works with charset encoding") {
+        val src = """
+main {
+    sub start() {
+        cx16.r0L = KEY_0
+        cx16.r1L = KEY_9
+        when cx16.r0L {
+            KEY_0 to KEY_9 -> {}
+            else -> {}
+        }
+    }
+}
+
+main {
+    %option merge
+
+    const ubyte KEY_0 = 'A'
+    const ubyte KEY_9 = 'B'
+}"""
+        compileText(C64Target(), optimize=false, src, outputDir, writeAssembly=false) shouldNotBe null
+    }
+
     test("merge override existing subroutine") {
         val src="""
 %import textio

compiler/test/ast/TestProg8Parser.kt

@@ -618,11 +618,13 @@ class TestProg8Parser: FunSpec( {
         val char1 = CharLiteral.create('A', Encoding.PETSCII, Position.DUMMY)
         val char2 = CharLiteral.create('z', Encoding.SCREENCODES, Position.DUMMY)
         val char3 = CharLiteral.create('_', Encoding.ISO, Position.DUMMY)
+        val char4 = CharLiteral.create('_', Encoding.DEFAULT, Position.DUMMY)
 
         val program = Program("test", DummyFunctions, DummyMemsizer, AsciiStringEncoder)
-        char1.constValue(program).number.toInt() shouldBe 65
-        char2.constValue(program).number.toInt() shouldBe 122
-        char3.constValue(program).number.toInt() shouldBe 95
+        char1.constValue(program)?.number?.toInt() shouldBe 65
+        char2.constValue(program)?.number?.toInt() shouldBe 122
+        char3.constValue(program)?.number?.toInt() shouldBe 95
+        char4.constValue(program) shouldBe null
     }
 
     test("testLiteralValueComparisons") {

compilerAst/src/prog8/ast/AstToplevel.kt

@@ -381,9 +381,9 @@ open class Module(final override val statements: MutableList<Statement>,
     fun accept(visitor: AstWalker, parent: Node) = visitor.visit(this, parent)
 
     val textEncoding: Encoding by lazy {
-        val encoding = (statements.singleOrNull { it is Directive && it.directive == "%encoding" } as? Directive)
+        val encoding = statements.singleOrNull { it is Directive && it.directive == "%encoding" } as? Directive
         if(encoding!=null)
-            Encoding.entries.first { it.prefix==encoding.args[0].string }
+            Encoding.entries.firstOrNull { it.prefix==encoding.args[0].string } ?: program.encoding.defaultEncoding       // invalid encoding will be noticed by ast checker error message
         else
             program.encoding.defaultEncoding
     }

compilerAst/src/prog8/ast/expressions/AstExpressions.kt

@@ -1037,7 +1037,9 @@ class CharLiteral private constructor(val value: Char,
     override fun copy() =
         CharLiteral(value, encoding, position)
     override fun referencesIdentifier(nameInSource: List<String>) = false
-    override fun constValue(program: Program): NumericLiteral {
+    override fun constValue(program: Program): NumericLiteral? {
+        if(encoding== Encoding.DEFAULT) // will be determined at a later stage, hopefully
+            return null
         val bytevalue = program.encoding.encodeString(value.toString(), encoding).single()
         return NumericLiteral(BaseDataType.UBYTE, bytevalue.toDouble(), position)
     }
@@ -1611,6 +1613,8 @@ class ContainmentCheck(var element: Expression,
                 is StringLiteral -> {
                     if(elementConst.type.isByte) {
                         val stringval = iterable as StringLiteral
+                        if(stringval.encoding== Encoding.DEFAULT)   // will be set at a later stage, hopefully
+                            return null
                         val exists = program.encoding.encodeString(stringval.value, stringval.encoding).contains(elementConst.number.toInt().toUByte() )
                         return NumericLiteral.fromBoolean(exists, position)
                     }