cgen: fix fn_with_mut_args (fix #7139) (#8446)

vlib/v/checker/checker.v

@@ -68,6 +68,7 @@ mut:
 	cur_orm_ts                       table.TypeSymbol
 	error_details                    []string
 	for_in_mut_val_name              string
+	fn_mut_arg_names                 []string
 	vmod_file_content                string       // needed for @VMOD_FILE, contents of the file, *NOT its path**
 	vweb_gen_types                   []table.Type // vweb route checks
 	prevent_sum_type_unwrapping_once bool   // needed for assign new values to sum type, stopping unwrapping then
@@ -2579,7 +2580,7 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 				assign_stmt.pos)
 		}
 		left_is_ptr := left_type.is_ptr() || left_sym.is_pointer()
-		if left_is_ptr && c.for_in_mut_val_name != left.str() {
+		if left_is_ptr && c.for_in_mut_val_name != left.str() && left.str() !in c.fn_mut_arg_names {
 			if !c.inside_unsafe && assign_stmt.op !in [.assign, .decl_assign] {
 				// ptr op=
 				c.warn('pointer arithmetic is only allowed in `unsafe` blocks', assign_stmt.pos)
@@ -5512,8 +5513,17 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			}
 		}
 	}
+	for param in node.params {
+		if param.is_mut {
+			c.fn_mut_arg_names << param.name
+		}
+	}
 	c.fn_scope = node.scope
 	c.stmts(node.stmts)
+
+	if c.fn_mut_arg_names.len > 0 {
+		c.fn_mut_arg_names.clear()
+	}
 	returns := c.returns || has_top_return(node.stmts)
 	if node.language == .v && !node.no_body && node.return_type != table.void_type && !returns
 		&& node.name !in ['panic', 'exit'] {

vlib/v/gen/cgen.v

@@ -118,6 +118,7 @@ mut:
 	// strs_to_free          []string // strings.Builder
 	inside_call           bool
 	for_in_mut_val_name   string
+	fn_mut_arg_names      []string
 	has_main              bool
 	inside_const          bool
 	comp_for_method       string      // $for method in T.methods {}
@@ -1990,7 +1991,7 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 			} else {
 				g.out.go_back_to(pos)
 				is_var_mut := !is_decl && left is ast.Ident
-					&& g.for_in_mut_val_name == (left as ast.Ident).name
+					&& (g.for_in_mut_val_name == (left as ast.Ident).name || (left as ast.Ident).name in g.fn_mut_arg_names)
 				addr := if is_var_mut { '' } else { '&' }
 				g.writeln('')
 				g.write('memcpy($addr')
@@ -2061,8 +2062,8 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 					g.prevent_sum_type_unwrapping_once = true
 				}
 				if !is_fixed_array_copy || is_decl {
-					if !is_decl && left is ast.Ident
+					if !is_decl && var_type != table.string_type_idx && left is ast.Ident
-						&& g.for_in_mut_val_name == (left as ast.Ident).name {
+						&& (g.for_in_mut_val_name == (left as ast.Ident).name || (left as ast.Ident).name in g.fn_mut_arg_names) {
 						g.write('*')
 					}
 					g.expr(left)

vlib/v/gen/fn.v

@@ -126,6 +126,11 @@ fn (mut g Gen) gen_fn_decl(it ast.FnDecl, skip bool) {
 		g.definitions.write(fn_header)
 		g.write(fn_header)
 	}
+	for param in it.params {
+		if param.is_mut {
+			g.fn_mut_arg_names << param.name
+		}
+	}
 	arg_start_pos := g.out.len
 	fargs, fargtypes := g.fn_args(it.params, it.is_variadic)
 	arg_str := g.out.after(arg_start_pos)
@@ -170,7 +175,11 @@ fn (mut g Gen) gen_fn_decl(it ast.FnDecl, skip bool) {
 	prev_defer_stmts := g.defer_stmts
 	g.defer_stmts = []
 	g.stmts(it.stmts)
-	//
+	// clear g.fn_mut_arg_names
+	if g.fn_mut_arg_names.len > 0 {
+		g.fn_mut_arg_names.clear()
+	}
+
 	if it.return_type == table.void_type {
 		g.write_defer_stmts_when_needed()
 	}

vlib/v/gen/str.v

@@ -343,14 +343,16 @@ fn (mut g Gen) gen_expr_to_string(expr ast.Expr, etype table.Type) {
 	} else if sym_has_str_method
 		|| sym.kind in [.array, .array_fixed, .map, .struct_, .multi_return, .sum_type, .interface_] {
 		is_ptr := typ.is_ptr()
+		is_var_mut := expr is ast.Ident
+			&& ((expr as ast.Ident).name == g.for_in_mut_val_name || (expr as ast.Ident).name in g.fn_mut_arg_names)
 		str_fn_name := g.gen_str_for_type(typ)
-		if is_ptr {
+		if is_ptr && !is_var_mut {
 			g.write('_STR("&%.*s\\000", 2, ')
 		}
 		g.write('${str_fn_name}(')
 		if str_method_expects_ptr && !is_ptr {
 			g.write('&')
-		} else if !str_method_expects_ptr && is_ptr {
+		} else if (!str_method_expects_ptr && is_ptr) || is_var_mut {
 			g.write('*')
 		}
 		if expr is ast.ArrayInit {
@@ -361,7 +363,7 @@ fn (mut g Gen) gen_expr_to_string(expr ast.Expr, etype table.Type) {
 		}
 		g.expr(expr)
 		g.write(')')
-		if is_ptr {
+		if is_ptr && !is_var_mut {
 			g.write(')')
 		}
 	} else {

vlib/v/tests/fn_mut_args_test.v

@@ -0,0 +1,23 @@
+fn func(mut a []int) {
+	a = [1, 2, 3, 4]
+	println('inside fn: $a')
+	assert '$a' == '[1, 2, 3, 4]'
+}
+
+fn test_fn_mut_args_of_array() {
+	mut a := [1, 2, 3]
+	func(mut a)
+	println('inside main: $a')
+	assert '$a' == '[1, 2, 3, 4]'
+}
+
+fn init_map(mut n map[string]int) {
+	n = {'one': 1}
+}
+
+fn test_fn_mut_args_of_map() {
+	mut m := map[string]int{}
+	init_map(mut m)
+	println(m)
+	assert m == {'one': 1}
+}