improve error message for undefined symbol in when choices

compiler/src/prog8/compiler/astprocessing/TypecastsAdder.kt

@@ -330,7 +330,7 @@ class TypecastsAdder(val program: Program, val options: CompilationOptions, val
             val values = whenChoice.values
             values?.toTypedArray()?.withIndex()?.forEach { (index, value) ->
                 val valueDt = value.inferType(program)
-                if(valueDt!=conditionDt) {
+                if(valueDt.isKnown && valueDt!=conditionDt) {
                     val castedValue = value.typecastTo(conditionDt.getOr(DataType.UNDEFINED), valueDt.getOr(DataType.UNDEFINED), true)
                     if(castedValue.first) {
                         castedValue.second.linkParents(whenChoice)

compiler/test/TestTypecasts.kt

@@ -839,4 +839,22 @@ main {
         compileText(VMTarget(), false, src, writeAssembly = true) shouldNotBe null
         compileText(C64Target(), false, src, writeAssembly = true) shouldNotBe null
     }
+
+    test("undefined symbol error instead of type cast error") {
+        val src="""
+main {
+    const ubyte foo = 0
+    ubyte bar = 0
+    sub start() {
+        when foo {
+            notdefined -> bar = 1
+            else -> bar = 2
+        }
+    }
+}"""
+        val errors = ErrorReporterForTests()
+        compileText(C64Target(), false, src, writeAssembly = false, errors = errors) shouldBe null
+        errors.errors.size shouldBe 2
+        errors.errors[1] shouldContain "undefined symbol"
+    }
 })

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

@@ -5,7 +5,6 @@ import prog8.ast.Node
 import prog8.ast.Program
 import prog8.ast.base.ExpressionError
 import prog8.ast.base.FatalAstException
-import prog8.ast.base.UndefinedSymbolError
 import prog8.ast.statements.*
 import prog8.ast.walk.AstWalker
 import prog8.ast.walk.IAstVisitor
@@ -1100,7 +1099,7 @@ data class IdentifierReference(val nameInSource: List<String>, override val posi
                 if(sub.parameters.any { it.name==nameInSource.last() })
                     return null
             }
-            throw UndefinedSymbolError(this)
+            return null
         }
         val vardecl = node as? VarDecl
         if(vardecl==null) {