checker: arr1=arr2 warning

vlib/builtin/array_test.v

@@ -361,7 +361,10 @@ fn test_clone() {
 
 fn test_copy() {
 	a := [1, 2, 3]
-	b := [3, 4, 5]
+	b := a
+	assert b[0] == 1
+	assert b[1] == 2
+	assert b[2] == 3
 }
 
 fn test_mutli_array_clone() {

vlib/os/args.v

@@ -11,7 +11,7 @@ pub fn args_after(cut_word string) []string {
 	}
 	mut cargs := []string{}
 	if cut_word !in args {
-		cargs = args
+		cargs = args.clone()
 	} else {
 		mut found := false
 		cargs << args[0]
@@ -37,7 +37,7 @@ pub fn args_before(cut_word string) []string {
 	}
 	mut cargs := []string{}
 	if cut_word !in args {
-		cargs = args
+		cargs = args.clone()
 	} else {
 		cargs << args[0]
 		for a in args[1..] {

vlib/v/checker/checker.v

@@ -2209,6 +2209,11 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 			// TODO replace all c.pref.translated checks with `$if !translated` for performance
 			continue
 		}
+		if left_sym.kind == .array &&
+			assign_stmt.op == .assign && right_sym.kind == .array && left is ast.Ident && right is ast.Ident {
+			// Do not allow `a = b`, only `a = b.clone()`
+			c.warn('use `array2 = array1.clone()` instead of `array1 = array2`', assign_stmt.pos)
+		}
 		left_is_ptr := left_type.is_ptr() || left_sym.is_pointer()
 		if left_is_ptr {
 			if !c.inside_unsafe && assign_stmt.op !in [.assign, .decl_assign] {
@@ -2321,6 +2326,7 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 			}
 		}
 	}
+	// right_sym := c.table.get_type_symbol(right_type_unwrapped)
 }
 
 fn scope_register_it(mut s ast.Scope, pos token.Position, typ table.Type) {

vlib/v/parser/struct.v

@@ -97,7 +97,7 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 				}
 			}
 			if p.tok.kind == .rcbr {
-				end_comments = comments
+				end_comments = comments.clone()
 				break
 			}
 			if p.tok.kind == .key_pub {

vlib/v/vmod/vmod.v

@@ -154,7 +154,7 @@ fn (mut mcache ModFileCacher) get_files(cfolder string) []string {
 	mut files := []string{}
 	if os.exists(cfolder) && os.is_dir(cfolder) {
 		if listing := os.ls(cfolder) {
-			files = listing
+			files = listing.clone()
 		}
 	}
 	mcache.folder_files[cfolder] = files