checker: prepare for the is_changed check

examples/tetris/tetris.v

@@ -362,7 +362,7 @@ fn (mut g Game) draw_ui() {
 		if g.state == .gameover {
 			g.gg.draw_rect(0, win_height / 2 - text_size, win_width,
 		 								5 * text_size, ui_color)
-			g.ft.draw_text(1, win_height / 2 + 0 * text_size, 'Game Over', over_cfg)
+			g.gg.draw_text(1, win_height / 2 + 0 * text_size, 'Game Over', over_cfg)
 			g.ft.draw_text(1, win_height / 2 + 2 * text_size, 'Space to restart', over_cfg)
 		} else if g.state == .paused {
 			g.gg.draw_rect(0, win_height / 2 - text_size, win_width,

vlib/v/ast/ast.v

@@ -287,14 +287,15 @@ pub struct Stmt {
 */
 pub struct Var {
 pub:
-	name    string
-	expr    Expr
-	is_mut  bool
-	is_arg  bool // fn args should not be autofreed
+	name       string
+	expr       Expr
+	is_mut     bool
+	is_arg     bool // fn args should not be autofreed
 pub mut:
-	typ     table.Type
-	pos     token.Position
-	is_used bool
+	typ        table.Type
+	pos        token.Position
+	is_used    bool
+	is_changed bool // to detect mutable vars that are never changed
 }
 
 pub struct GlobalDecl {

vlib/v/checker/checker.v

@@ -59,8 +59,23 @@ pub fn (mut c Checker) check(ast_file ast.File) {
 	for stmt in ast_file.stmts {
 		c.stmt(stmt)
 	}
+	// Check scopes
+	// TODO
+	/*
+	for i, obj in c.file.global_scope.objects {
+		match obj {
+			ast.Var {
+				if it.is_mut && !it.is_changed {
+					c.warn('`$it.name` is declared as mutable, but it was never changed', it.pos)
+				}
+			}
+			else {}
+		}
+	}
+	*/
 }
 
+// not used right now
 pub fn (mut c Checker) check2(ast_file ast.File) []errors.Error {
 	c.file = ast_file
 	for stmt in ast_file.stmts {
@@ -583,7 +598,8 @@ fn (mut c Checker) fail_if_immutable(expr ast.Expr) {
 					c.error('`$it.name` is immutable, declare it with `mut` to make it mutable',
 						it.pos)
 				}
-			} else if it.name in c.const_names {          
+				v.is_changed = true
+			} else if it.name in c.const_names {
 				c.error('cannot modify constant `$it.name`', it.pos)
 			}
 		}

vlib/v/parser/parser.v

@@ -12,9 +12,9 @@ import v.util
 import v.errors
 import os
 import runtime
-//import sync
 import time
 
+// import sync
 pub struct Parser {
 	file_name         string // "/home/user/hello.v"
 	file_name_dir     string // "/home/user"
@@ -173,7 +173,6 @@ fn (mut q Queue) run() {
 	}
 }
 */
-
 pub fn parse_files(paths []string, table &table.Table, pref &pref.Preferences, global_scope &ast.Scope) []ast.File {
 	// println('nr_cpus= $nr_cpus')
 	$if macos {
@@ -234,6 +233,7 @@ pub fn (mut p Parser) open_scope() {
 }
 
 pub fn (mut p Parser) close_scope() {
+	// TODO move this to checker since is_changed is set there?
 	if !p.pref.is_repl && !p.scanner.is_fmt {
 		for _, obj in p.scope.objects {
 			match obj {
@@ -245,6 +245,12 @@ pub fn (mut p Parser) close_scope() {
 							p.warn_with_pos('unused variable: `$it.name`', it.pos)
 						}
 					}
+					/*
+					if it.is_mut && !it.is_changed {
+						p.warn_with_pos('`$it.name` is declared as mutable, but it was never changed',
+							it.pos)
+					}
+					*/
 				}
 				else {}
 			}
@@ -1486,7 +1492,7 @@ fn (mut p Parser) type_decl() ast.TypeDecl {
 	} else {
 		table.Language.v
 	}
-	p.table.register_type_symbol(table.TypeSymbol{
+	p.table.register_type_symbol({
 		kind: .alias
 		name: p.prepend_mod(name)
 		parent_idx: pid