parser: fix mutability with chained fields

compiler/cgen.v

@@ -11,19 +11,20 @@ import time
 struct CGen {
 	out          os.File
 	out_path     string
-	typedefs     []string
+	//types        []string
-	type_aliases []string
-	includes     []string
-	thread_args  []string
 	thread_fns   []string
-	consts       []string
-	fns          []string
-	so_fns       []string
-	consts_init  []string
 	//buf          strings.Builder
 	is_user      bool
 mut:
 	lines        []string
+	typedefs     []string
+	type_aliases []string
+	includes     []string
+	thread_args  []string
+	consts       []string
+	fns          []string
+	so_fns       []string
+	consts_init  []string
 	pass         Pass
 	nogen           bool
 	tmp_line        string

compiler/parser.v

@@ -34,6 +34,8 @@ mut:
 	mod            string
 	inside_const   bool
 	expr_var       Var
+	has_immutable_field bool
+	first_immutable_field Var
 	assigned_type  string
 	expected_type  string
 	tmp_cnt        int
@@ -1405,6 +1407,7 @@ fn (p mut Parser) bterm() string {
 
 // also called on *, &, @, . (enum)
 fn (p mut Parser) name_expr() string {
+	p.has_immutable_field = false
 	ph := p.cgen.add_placeholder()
 	// amp
 	ptr := p.tok == .amp
@@ -1774,17 +1777,24 @@ fn (p mut Parser) dot(str_typ string, method_ph int) string {
 	if has_field {
 		struct_field := if typ.name != 'Option' { p.table.var_cgen_name(field_name) } else { field_name }
 		field := p.table.find_field(typ, struct_field)
+		if !field.is_mut && !p.has_immutable_field {
+			p.has_immutable_field = true
+			p.first_immutable_field = field
+		}
 		// Is the next token `=`, `+=` etc?  (Are we modifying the field?)
 		next := p.peek()
-		modifying := next.is_assign() || next == .inc || next == .dec
+		modifying := next.is_assign() || next == .inc || next == .dec ||
+			(field.typ.starts_with('array_') && next == .left_shift)
 		is_vi := p.fileis('vid')
-		if !p.builtin_mod && !p.pref.translated && modifying && !field.is_mut && !is_vi {
+		if !p.builtin_mod && !p.pref.translated && modifying && !is_vi
-			p.error('cannot modify immutable field `$struct_field` (type `$typ.name`)\n' +
+			&& p.has_immutable_field {
-				'declare the field with `mut:`
+			f := p.first_immutable_field
+			p.error('cannot modify immutable field `$f.name` (type `$f.parent_fn`)\n' +
+					'declare the field with `mut:`
 
-struct $typ.name {
+struct $f.parent_fn {
   mut:
-	$struct_field $field.typ
+	$f.name $f.typ
 }
 ')
 		}
@@ -1796,13 +1806,6 @@ struct $typ.name {
 			// println(field.access_mod)
 			p.error('cannot refer to unexported field `$struct_field` (type `$typ.name`)')
 		}
-		// if field.access_mod ==.public && p.peek() == .assign && !p.builtin_mod && p.mod != typ.mod {
-		// Don't allow `str.len = 0`
-		if field.access_mod == .public && !p.builtin_mod && p.mod != typ.mod {
-			if !field.is_mut && !p.pref.translated && modifying {
-				p.error('cannot modify public immutable field `$struct_field` (type `$typ.name`)')
-			}
-		}
 		p.gen(dot + struct_field)
 		p.next()
 		return field.typ

compiler/table.v

@@ -27,6 +27,7 @@ mut:
 
 struct GenTable {
 	fn_name string
+mut:
 	types []string
 }
 
@@ -423,6 +424,7 @@ fn (t mut Type) add_field(name, typ string, is_mut bool, attr string, access_mod
 		typ: typ
 		is_mut: is_mut
 		attr: attr
+		parent_fn: t.name   // Name of the parent type
 		access_mod: access_mod
 	}
 	t.fields << v

compiler/tests/repl/chained_fields.repl

@@ -0,0 +1,78 @@
+/*  1 */ struct A { mut: v int }
+/*  2 */ struct B {      a A }
+/*  3 */ struct C { mut: b B }
+/*  4 */ struct D { mut: c C }
+
+/*  5 */ struct E { mut: v []int }
+/*  6 */ struct F {      e []E }
+
+/*  7 */ mut s := 'hello world'
+/*( 8)*/ s.len = 0   // Error (field len immutable)
+
+/*  8 */ mut b := B{}
+/*( 9)*/ b.a.v = 1   // Error (field a immutable)
+/*( 9)*/ b.a = A{}   // Error (field a immutable)
+/*  9 */ b = B{A{2}} // Correct
+
+/* 10 */ mut c := C{}
+/* 11 */ c.b = B{}   // Correct
+/*(12)*/ c.b.a = A{} // Error (field a immutable)
+/*(12)*/ c.b.a.v = 1 // Error (field a immutable)
+
+/* 12 */ c2 := C{}
+/*(13)*/ c2.b = B{}  // Error (c2 immutable)
+/* 13 */ mut d := D{}
+/* 14 */ d.c.b = B{} // Correct
+
+/* 15 */ mut f := F{}
+/*(16)*/ f.e << E{}      // Error (field e immutable)
+/*(16)*/ f.e[0].v << 1   // Error (field e immutable)
+
+/* 16 */ e := E{}
+/*(17)*/ e.v << 1    // Error (e immutable)
+
+===output===
+.vrepl_temp.v:8:14: cannot modify immutable field `len` (type `string`)
+declare the field with `mut:`
+struct string {
+  mut:
+	len int
+}
+.vrepl_temp.v:9:14: cannot modify immutable field `a` (type `B`)
+declare the field with `mut:`
+struct B {
+  mut:
+	a A
+}
+.vrepl_temp.v:9:12: cannot modify immutable field `a` (type `B`)
+declare the field with `mut:`
+struct B {
+  mut:
+	a A
+}
+.vrepl_temp.v:12:14: cannot modify immutable field `a` (type `B`)
+declare the field with `mut:`
+struct B {
+  mut:
+	a A
+}
+.vrepl_temp.v:12:16: cannot modify immutable field `a` (type `B`)
+declare the field with `mut:`
+struct B {
+  mut:
+	a A
+}
+.vrepl_temp.v:13:15: `c2` is immutable.
+.vrepl_temp.v:16:12: cannot modify immutable field `e` (type `F`)
+declare the field with `mut:`
+struct F {
+  mut:
+	e []E
+}
+.vrepl_temp.v:16:17: cannot modify immutable field `e` (type `F`)
+declare the field with `mut:`
+struct F {
+  mut:
+	e []E
+}
+.vrepl_temp.v:17:17: `e` is immutable (can't <<)

vlib/builtin/array_test.v

@@ -214,6 +214,7 @@ struct Test2 {
 
 struct Test {
 	a string
+mut:
 	b []Test2
 }
 

vlib/freetype/freetype.v

@@ -63,10 +63,11 @@ struct Context {
 	line_vbo  u32
 	vbo       u32
 	chars     []Character
-	utf_runes []string
-	utf_chars []Character
 	face      C.FT_Face
 	scale     int // retina = 2 , normal = 1
+mut:
+	utf_runes []string
+	utf_chars []Character
 }
 
 struct C.Bitmap {

vlib/vweb/vweb.v

@@ -20,6 +20,7 @@ pub:
 	conn net.Socket 
 	form map[string]string 
 	// TODO Response 
+mut:
 	headers []string  // response headers 
 }