checker, cgen: fix codegen for option fntype

vlib/v/checker/checker.v

@@ -1197,6 +1197,18 @@ fn (mut c Checker) check_expr_option_or_result_call(expr ast.Expr, ret_type ast.
 					expr_ret_type = unaliased_ret_type
 				}
 			}
+			// var with option function
+			if expr.is_fn_var && expr.fn_var_type.has_option_or_result()
+				&& expr.or_block.kind == .absent {
+				ret_sym := c.table.sym(expr.fn_var_type)
+				if expr.fn_var_type.has_flag(.option) {
+					c.error('type `?${ret_sym.name}` is an Option, it must be unwrapped first',
+						expr.pos)
+				} else {
+					c.error('type `?${ret_sym.name}` is an Result, it must be unwrapped first',
+						expr.pos)
+				}
+			}
 			if expr_ret_type.has_option_or_result() {
 				if expr.or_block.kind == .absent {
 					ret_sym := c.table.sym(expr_ret_type)

vlib/v/checker/tests/option_fn_var_err.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/option_fn_var_err.vv:18:9: error: type `?DataFn` is an Option, it must be unwrapped first
+   16 | fn main() {
+   17 |     req := find_func('vlang')
+   18 |     fun := req('options')
+      |            ~~~~~~~~~~~~~~
+   19 |     println(fun)
+   20 | }

vlib/v/checker/tests/option_fn_var_err.vv

@@ -0,0 +1,20 @@
+module main
+
+type DataFn = fn (name string) string
+
+fn which_lang(name string) string {
+	return name
+}
+
+fn find_func(name string) ?DataFn {
+	return match name {
+		'vlang' { which_lang }
+		else { none }
+	}
+}
+
+fn main() {
+	req := find_func('vlang')
+	fun := req('options')
+	println(fun)
+}

vlib/v/gen/c/match.v

@@ -92,10 +92,10 @@ fn (mut g Gen) match_expr(node ast.MatchExpr) {
 		cur_line = g.go_before_last_stmt().trim_left(' \t')
 		tmp_var = g.new_tmp_var()
 		mut func_decl := ''
-		if g.table.final_sym(node.return_type).kind == .function {
-			func_sym := g.table.final_sym(node.return_type)
-			if func_sym.info is ast.FnType {
-				def := g.fn_var_signature(func_sym.info.func.return_type, func_sym.info.func.params.map(it.typ),
+		ret_final_sym := g.table.final_sym(node.return_type)
+		if !node.return_type.has_option_or_result() && ret_final_sym.kind == .function {
+			if ret_final_sym.info is ast.FnType {
+				def := g.fn_var_signature(ret_final_sym.info.func.return_type, ret_final_sym.info.func.params.map(it.typ),
 					tmp_var)
 				func_decl = '${def} = &${g.typ(node.return_type)};'
 			}

vlib/v/tests/options/option_fn_var_test.v

@@ -0,0 +1,21 @@
+module main
+
+type DataFn = fn (name string) string
+
+fn which_lang(name string) string {
+	return name
+}
+
+fn find_func(name string) ?DataFn {
+	return match name {
+		'vlang' { which_lang }
+		else { none }
+	}
+}
+
+fn test_main() {
+	req := find_func('vlang')?
+	fun := req('options')
+	println(fun)
+	assert fun == 'options'
+}