vfmt: do not error on `field [fsize]Type`, where `fsize` is from another .v file

vlib/v/fmt/tests/fixed_size_array_type_keep.vv

@@ -12,3 +12,17 @@ fn foo() [1]f32 {
 fn main() {
 	_ := [5]string{init: 'abc'}
 }
+
+// NB: secret_key_size is missing here on purpose
+// vfmt should leave it as is, assuming it is comming
+// from another .v file
+
+struct VerifyKey {
+	public_key [public_key_size]byte
+}
+
+struct SigningKey {
+	secret_key [secret_key_size]byte
+pub:
+	verify_key VerifyKey
+}

vlib/v/parser/parse_type.v

@@ -26,7 +26,14 @@ pub fn (mut p Parser) parse_array_type() ast.Type {
 							size_expr.pos)
 					}
 				} else {
-					p.error_with_pos('non-constant array bound `$size_expr.name`', size_expr.pos)
+					if p.pref.is_fmt {
+						// for vfmt purposes, pretend the constant does exist, it may have
+						// been defined in another .v file:
+						fixed_size = 1
+					} else {
+						p.error_with_pos('non-constant array bound `$size_expr.name`',
+							size_expr.pos)
+					}
 				}
 			}
 			else {