checker,cgen: allow ?.str() on compile-time fields var (#16969)

vlib/v/checker/checker.v

@@ -3503,6 +3503,11 @@ fn (c &Checker) has_return(stmts []ast.Stmt) ?bool {
 	return none
 }
 
+pub fn (mut c Checker) is_comptime_var(node ast.Expr) bool {
+	return c.inside_comptime_for_field && node is ast.Ident
+		&& (node as ast.Ident).info is ast.IdentVar && ((node as ast.Ident).obj as ast.Var).is_comptime_field
+}
+
 fn (mut c Checker) postfix_expr(mut node ast.PostfixExpr) ast.Type {
 	typ := c.unwrap_generic(c.expr(node.expr))
 	typ_sym := c.table.sym(typ)
@@ -3511,6 +3516,14 @@ fn (mut c Checker) postfix_expr(mut node ast.PostfixExpr) ast.Type {
 		c.warn('pointer arithmetic is only allowed in `unsafe` blocks', node.pos)
 	}
 	if !(typ_sym.is_number() || ((c.inside_unsafe || c.pref.translated) && is_non_void_pointer)) {
+		if c.inside_comptime_for_field {
+			if c.is_comptime_var(node.expr) {
+				return c.comptime_fields_default_type
+			} else if node.expr is ast.ComptimeSelector {
+				return c.comptime_fields_default_type
+			}
+		}
+
 		typ_str := c.table.type_to_str(typ)
 		c.error('invalid operation: ${node.op.str()} (non-numeric type `${typ_str}`)',
 			node.pos)

vlib/v/checker/fn.v

@@ -1326,7 +1326,7 @@ fn (mut c Checker) method_call(mut node ast.CallExpr) ast.Type {
 	} else {
 		'unknown method or field: `${left_sym.name}.${method_name}`'
 	}
-	if left_type.has_flag(.option) {
+	if left_type.has_flag(.option) && method_name != 'str' {
 		c.error('option type cannot be called directly', node.left.pos())
 		return ast.void_type
 	} else if left_type.has_flag(.result) {

vlib/v/gen/c/fn.v

@@ -864,40 +864,41 @@ fn (mut g Gen) gen_to_str_method_call(node ast.CallExpr) bool {
 	if rec_type.has_flag(.shared_f) {
 		rec_type = rec_type.clear_flag(.shared_f).set_nr_muls(0)
 	}
-	if node.left is ast.ComptimeSelector {
-		key_str := g.get_comptime_selector_key_type(node.left)
+	left_node := if node.left is ast.PostfixExpr { node.left.expr } else { node.left }
+	if left_node is ast.ComptimeSelector {
+		key_str := g.get_comptime_selector_key_type(left_node)
 		if key_str != '' {
 			rec_type = g.comptime_var_type_map[key_str] or { rec_type }
-			g.gen_expr_to_string(node.left, rec_type)
+			g.gen_expr_to_string(left_node, rec_type)
 			return true
 		}
-	} else if node.left is ast.ComptimeCall {
-		if node.left.method_name == 'method' {
-			sym := g.table.sym(g.unwrap_generic(node.left.left_type))
+	} else if left_node is ast.ComptimeCall {
+		if left_node.method_name == 'method' {
+			sym := g.table.sym(g.unwrap_generic(left_node.left_type))
 			if m := sym.find_method(g.comptime_for_method) {
 				rec_type = m.return_type
-				g.gen_expr_to_string(node.left, rec_type)
+				g.gen_expr_to_string(left_node, rec_type)
 				return true
 			}
 		}
-	} else if node.left is ast.Ident {
-		if node.left.obj is ast.Var {
+	} else if left_node is ast.Ident {
+		if left_node.obj is ast.Var {
 			if g.comptime_var_type_map.len > 0 {
-				rec_type = node.left.obj.typ
-				g.gen_expr_to_string(node.left, rec_type)
+				rec_type = left_node.obj.typ
+				g.gen_expr_to_string(left_node, rec_type)
 				return true
-			} else if node.left.obj.smartcasts.len > 0 {
-				rec_type = g.unwrap_generic(node.left.obj.smartcasts.last())
+			} else if left_node.obj.smartcasts.len > 0 {
+				rec_type = g.unwrap_generic(left_node.obj.smartcasts.last())
 				cast_sym := g.table.sym(rec_type)
 				if cast_sym.info is ast.Aggregate {
 					rec_type = cast_sym.info.types[g.aggregate_type_idx]
 				}
-				g.gen_expr_to_string(node.left, rec_type)
+				g.gen_expr_to_string(left_node, rec_type)
 				return true
 			}
 		}
-	} else if node.left is ast.None {
-		g.gen_expr_to_string(node.left, ast.none_type)
+	} else if left_node is ast.None {
+		g.gen_expr_to_string(left_node, ast.none_type)
 		return true
 	}
 	g.get_str_fn(rec_type)

vlib/v/tests/call_to_str_on_option_test.v

@@ -0,0 +1,38 @@
+struct FixedStruct1 {
+	a int
+	b string
+	c ?int
+	d ?string
+}
+
+struct Encoder {}
+
+fn test_main() {
+	fixed := FixedStruct1{123, '456', 789, '321'}
+	// this work well
+	println(fixed.a.str())
+	println(fixed.c?.str())
+
+	println(fixed.b.int())
+	println(fixed.d?.int())
+
+	e := Encoder{}
+	// this not work
+	e.encode_struct(fixed)
+}
+
+fn (e &Encoder) encode_struct[T](val T) {
+	mut count := 0
+	$for field in T.fields {
+		mut value := val.$(field.name)
+		$if field.is_option {
+			if field.name in ['c', 'd'] {
+				assert true
+			}
+			println('>> ${value ?.str()}')
+			println(val.$(field.name) ?.str())
+			count += 1
+		}
+	}
+	assert count == 2
+}