cgen: fix code generated for optional comptime var (#16854)

vlib/v/gen/c/cgen.v

@@ -4247,6 +4247,22 @@ fn (mut g Gen) ident(node ast.Ident) {
 	}
 	mut is_auto_heap := false
 	if node.info is ast.IdentVar {
+		if node.obj is ast.Var {
+			if !g.is_assign_lhs && node.obj.is_comptime_field {
+				if g.comptime_for_field_type.has_flag(.optional) {
+					if g.inside_opt_or_res {
+						g.write('${name}')
+					} else {
+						g.write('/*opt*/')
+						styp := g.base_type(g.comptime_for_field_type)
+						g.write('(*(${styp}*)${name}.data)')
+					}
+				} else {
+					g.write('${name}')
+				}
+				return
+			}
+		}
 		// x ?int
 		// `x = 10` => `x.data = 10` (g.right_is_opt == false)
 		// `x = new_opt()` => `x = new_opt()` (g.right_is_opt == true)

vlib/v/tests/optional_compvar_types_test.v

@@ -0,0 +1,34 @@
+struct FixedStruct1 {
+	a int
+	b string
+}
+
+struct FixedStruct2 {
+	c ?int
+	d ?string
+}
+
+struct Writer {}
+
+fn write1[T](val T) {
+	println(val)
+}
+
+fn (wr &Writer) write2[T](val T) {
+	println(val)
+}
+
+fn encode_struct[T](val T) bool {
+	wr := Writer{}
+	$for field in T.fields {
+		value := val.$(field.name)
+		write1(value)
+		wr.write2(value)
+	}
+	return true
+}
+
+fn test_main() {
+	assert encode_struct(FixedStruct1{}) == true
+	assert encode_struct(FixedStruct2{}) == true
+}

vlib/v/tests/optional_compvar_val_test.v

@@ -0,0 +1,60 @@
+struct FixedStruct1 {
+	a int
+	b ?int
+	c ?int = 4
+}
+
+// struct FixedStruct2 {
+//     b ?int
+// }
+
+struct Encoder {}
+
+struct Writer {}
+
+fn write1[T](val T) {
+	println(val)
+}
+
+fn (wr &Writer) write2[T](val T) {
+	println(val)
+}
+
+fn encode_struct[T](val T) map[string][]string {
+	wr := Writer{}
+	mut out := map[string][]string{}
+	$if T is $Struct {
+		$for field in T.fields {
+			value := val.$(field.name)
+			$if field.typ is ?int {
+				// work if comment lines 27 and 28
+				write1(value)
+				wr.write2(value)
+				out[field.name] << '${value}'
+			} $else {
+				write1(value)
+				wr.write2(value)
+				out[field.name] << value.str()
+			}
+			// This work well
+			$if field.is_optional {
+				write1(value)
+				wr.write2(value)
+				out[field.name] << '${value}'
+			} $else {
+				write1(value)
+				wr.write2(value)
+				out[field.name] << value.str()
+			}
+		}
+	}
+	return out
+}
+
+fn test_main() {
+	// cgen error: cannot convert 'struct _option_int' to 'int'
+	out := encode_struct(FixedStruct1{})
+	assert out['a'] == ['0', '0']
+	assert out['b'] == ['0', '0']
+	assert out['c'] == ['4', '4']
+}