all: support `volatile field Type` in struct declarations

vlib/v/ast/ast.v

@@ -267,6 +267,7 @@ pub:
 	default_val      string
 	is_mut           bool
 	is_global        bool
+	is_volatile      bool
 pub mut:
 	default_expr     Expr
 	default_expr_typ Type

vlib/v/fmt/struct.v

@@ -108,7 +108,8 @@ pub fn (mut f Fmt) struct_decl(node ast.StructDecl) {
 		after_type_comments := field.comments[(before_comments.len + between_comments.len)..]
 		// Handle comments before the field
 		f.comments_before_field(before_comments)
-		f.write('\t$field.name ')
+		volatile_prefix := if field.is_volatile { 'volatile ' } else { '' }
+		f.write('\t$volatile_prefix$field.name ')
 		// Handle comments between field name and type
 		before_len := f.line_len
 		f.comments(between_comments, iembed: true, has_nl: false)

vlib/v/gen/c/cgen.v

@@ -6343,7 +6343,8 @@ fn (mut g Gen) write_types(types []ast.TypeSymbol) {
 						}
 						type_name := g.typ(field.typ)
 						field_name := c_name(field.name)
-						g.type_definitions.writeln('\t$type_name $field_name;')
+						volatile_prefix := if field.is_volatile { 'volatile ' } else { '' }
+						g.type_definitions.writeln('\t$volatile_prefix$type_name $field_name;')
 					}
 				} else {
 					g.type_definitions.writeln('\tEMPTY_STRUCT_DECLARATION;')

vlib/v/gen/c/testdata/volatile.c.must_have

@@ -1,2 +1,4 @@
 volatile int *zzz = HEAP(int, (123));
 volatile int* pzzz = &(*(zzz));
+volatile int a_volatile_field;
+int a_non_volatile_field;

vlib/v/gen/c/testdata/volatile.out

@@ -1,2 +1,6 @@
 123
 &123
+Abc{
+    a_volatile_field: 0
+    a_non_volatile_field: 0
+}

vlib/v/gen/c/testdata/volatile.vv

@@ -1,4 +1,10 @@
+struct Abc {
+	volatile a_volatile_field     int
+	a_non_volatile_field int
+}
+
 mut volatile zzz := 123
 mut volatile pzzz := &zzz
 println(zzz)
 println(&int(voidptr(pzzz)))
+println(Abc{})

vlib/v/parser/struct.v

@@ -170,6 +170,11 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 				}
 			}
 			field_start_pos := p.tok.position()
+			mut is_field_volatile := false
+			if p.tok.kind == .key_volatile {
+				p.next()
+				is_field_volatile = true
+			}
 			is_embed := ((p.tok.lit.len > 1 && p.tok.lit[0].is_capital())
 				|| p.peek_tok.kind == .dot) && language == .v && p.peek_tok.kind != .key_fn
 			is_on_top := ast_fields.len == 0 && !(is_field_mut || is_field_global)
@@ -255,6 +260,7 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 					is_pub: is_embed || is_field_pub
 					is_mut: is_embed || is_field_mut
 					is_global: is_field_global
+					is_volatile: is_field_volatile
 				}
 			}
 			// save embeds as table fields too, it will be used in generation phase
@@ -270,6 +276,7 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 				is_pub: is_embed || is_field_pub
 				is_mut: is_embed || is_field_mut
 				is_global: is_field_global
+				is_volatile: is_field_volatile
 			}
 			p.attrs = []
 		}