better warning + don't remove non-trivial initializer expression for unused variables

Author: irmen

codeOptimizers/src/prog8/optimizer/UnusedCodeRemover.kt

@@ -120,12 +120,26 @@ class UnusedCodeRemover(private val program: Program,
                         if(singleUse is AssignTarget) {
                             val assignment = singleUse.parent as Assignment
                             if(assignment.origin==AssignmentOrigin.VARINIT) {
-                                if(!decl.definingModule.isLibrary)
-                                    errors.warn("removing unused variable '${decl.name}'", decl.position)
-                                return listOf(
-                                    IAstModification.Remove(decl, parent as IStatementContainer),
-                                    IAstModification.Remove(assignment, assignment.parent as IStatementContainer)
-                                )
+                                if(assignment.value.isSimple) {
+                                    // remove the vardecl
+                                    if(!decl.definingModule.isLibrary)
+                                        errors.warn("removing unused variable '${decl.name}'", decl.position)
+                                    return listOf(
+                                        IAstModification.Remove(decl, parent as IStatementContainer),
+                                        IAstModification.Remove(assignment, assignment.parent as IStatementContainer)
+                                    )
+                                } else if(assignment.value is IFunctionCall) {
+                                    // replace the unused variable's initializer function call by a void
+                                    errors.warn("replaced unused variable '${decl.name}' with void call, maybe this can be removed altogether", decl.position)
+                                    val fcall = assignment.value as IFunctionCall
+                                    val voidCall = FunctionCallStatement(fcall.target, fcall.args, true, fcall.position)
+                                    return listOf(
+                                        IAstModification.ReplaceNode(decl, voidCall, parent),
+                                        IAstModification.Remove(assignment, assignment.parent as IStatementContainer)
+                                    )
+                                } else {
+                                    errors.warn("variable '${decl.name}' is unused but has non-trivial initialization assignment. Leaving this in but maybe it can be removed altogether", decl.position)
+                                }
                             }
                         }
                     }