refactor(AST): introduce AstVisitor trait (#1231)

* refactor(AST): introduce AstVisitor trait

The AST-Visitor trait allows generic visiting of AST-nodes. A default
Walking behavior is implemented for each AstStatement but it can be
altered by any implementor. When overriding a visit_XXX method, the
implementation can decide to continue with the default walking behavior
(by calling the walk function on the passed AstStatement-Struct, to skip it,
or to continue with an alternative walking bahavior.

removed unused AST element CastStatement

Author: riederm

compiler/plc_ast/src/ast.rs

@@ -600,7 +600,6 @@ pub enum AstStatement {
     DefaultValue(DefaultValue),
     // Literals
     Literal(AstLiteral),
-    CastStatement(CastStatement),
     MultipliedStatement(MultipliedStatement),
     // Expressions
     ReferenceExpr(ReferenceExpr),
@@ -735,9 +734,6 @@ impl Debug for AstNode {
             }
             AstStatement::ContinueStatement(..) => f.debug_struct("ContinueStatement").finish(),
             AstStatement::ExitStatement(..) => f.debug_struct("ExitStatement").finish(),
-            AstStatement::CastStatement(CastStatement { target, type_name }) => {
-                f.debug_struct("CastStatement").field("type_name", type_name).field("target", target).finish()
-            }
             AstStatement::ReferenceExpr(ReferenceExpr { access, base }) => {
                 f.debug_struct("ReferenceExpr").field("kind", access).field("base", base).finish()
             }

compiler/plc_ast/src/lib.rs

@@ -7,3 +7,4 @@ pub mod control_statements;
 pub mod literals;
 mod pre_processor;
 pub mod provider;
+pub mod visitor;

compiler/plc_ast/src/visitor.rs

@@ -846,20 +846,6 @@ fn generate_variable_length_array_bound_function<'ink>(
             let offset = if is_lower { (value - 1) as u64 * 2 } else { (value - 1) as u64 * 2 + 1 };
             llvm.i32_type().const_int(offset, false)
         }
-        AstStatement::CastStatement(data) => {
-            let ExpressionValue::RValue(value) = generator.generate_expression_value(&data.target)? else {
-                unreachable!()
-            };
-
-            if !value.is_int_value() {
-                return Err(Diagnostic::codegen_error(
-                    format!("Expected INT value, found {}", value.get_type()),
-                    location,
-                ));
-            };
-
-            value.into_int_value()
-        }
         // e.g. LOWER_BOUND(arr, idx + 3)
         _ => {
             let expression_value = generator.generate_expression(params[1])?;

src/builtins.rs

@@ -1751,7 +1751,6 @@ impl<'ink, 'b> ExpressionCodeGenerator<'ink, 'b> {
             }
             // if there is just one assignment, this may be an struct-initialization (TODO this is not very elegant :-/ )
             AstStatement::Assignment { .. } => self.generate_literal_struct(literal_statement),
-            AstStatement::CastStatement(data) => self.generate_expression_value(&data.target),
             _ => Err(cannot_generate_literal()),
         }
     }

src/codegen/generators/expression_generator.rs

@@ -5,6 +5,7 @@ use plc_ast::{
 use plc_source::source_location::SourceLocation;
 
 // Copyright (c) 2020 Ghaith Hachem and Mathias Rieder
+mod ast_visitor_tests;
 mod class_parser_tests;
 mod container_parser_tests;
 mod control_parser_tests;