From f07022212475e16754eb8b6c026f2ba564e47e5d Mon Sep 17 00:00:00 2001
From: shadowninja55 <49539636+shadowninja55@users.noreply.github.com>
Date: Wed, 7 Jul 2021 04:57:10 -0400
Subject: [PATCH] checker: prohibit option and `IError` in multi-return
 (#10689)

---
 vlib/v/checker/checker.v                        | 12 ++++++++++++
 vlib/v/checker/tests/ierror_in_return_tuple.out | 12 ++++++++++++
 vlib/v/checker/tests/ierror_in_return_tuple.vv  |  7 +++++++
 3 files changed, 31 insertions(+)
 create mode 100644 vlib/v/checker/tests/ierror_in_return_tuple.out
 create mode 100644 vlib/v/checker/tests/ierror_in_return_tuple.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 72750abd8f..143a4ce9e7 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -7458,6 +7458,18 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 				}
 			}
 		}
+		return_sym := c.table.get_type_symbol(node.return_type)
+		if return_sym.info is ast.MultiReturn {
+			for multi_type in return_sym.info.types {
+				if multi_type == ast.error_type {
+					c.error('type `IError` cannot be used in multi-return, return an option instead',
+						node.return_type_pos)
+				} else if multi_type.has_flag(.optional) {
+					c.error('option cannot be used in multi-return, return an option instead',
+						node.return_type_pos)
+				}
+			}
+		}
 	}
 	if node.return_type == ast.void_type {
 		for mut a in node.attrs {
diff --git a/vlib/v/checker/tests/ierror_in_return_tuple.out b/vlib/v/checker/tests/ierror_in_return_tuple.out
new file mode 100644
index 0000000000..60d648331f
--- /dev/null
+++ b/vlib/v/checker/tests/ierror_in_return_tuple.out
@@ -0,0 +1,12 @@
+vlib/v/checker/tests/ierror_in_return_tuple.vv:1:29: error: type `IError` cannot be used in multi-return, return an option instead
+    1 | fn return_ierror_in_tuple() (bool, IError) {
+      |                             ~~~~~~~~~~~~~~
+    2 |     return false, error('')
+    3 | }
+vlib/v/checker/tests/ierror_in_return_tuple.vv:5:29: error: option cannot be used in multi-return, return an option instead
+    3 | }
+    4 | 
+    5 | fn return_option_in_tuple() (bool, ?bool) {
+      |                             ~~~~~~~~~~~~~
+    6 |     return false, error('')
+    7 | }
diff --git a/vlib/v/checker/tests/ierror_in_return_tuple.vv b/vlib/v/checker/tests/ierror_in_return_tuple.vv
new file mode 100644
index 0000000000..47175283bb
--- /dev/null
+++ b/vlib/v/checker/tests/ierror_in_return_tuple.vv
@@ -0,0 +1,7 @@
+fn return_ierror_in_tuple() (bool, IError) {
+	return false, error('')
+}
+
+fn return_option_in_tuple() (bool, ?bool) {
+	return false, error('')
+}