From 92630a2821762951a5220b4283242c69e80fa2b7 Mon Sep 17 00:00:00 2001
From: Nick Treleaven <n@trelsoft.com>
Date: Thu, 8 Oct 2020 23:48:39 +0100
Subject: [PATCH] checker: error if assigning to a function (#6581)

---
 vlib/v/checker/checker.v                         |  2 ++
 .../checker/tests/assign_multi_immutable_err.out | 16 +++++++++++++++-
 .../checker/tests/assign_multi_immutable_err.vv  | 16 +++++++++++++++-
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 3c0f706fc3..69b4407d59 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1944,6 +1944,8 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 					if assign_stmt.op !in [.assign, .decl_assign] {
 						c.error('cannot modify blank `_` identifier', left.pos)
 					}
+				} else if left.info !is ast.IdentVar {
+					c.error('cannot assign to $left.kind `$left.name`', left.pos)
 				} else {
 					if is_decl {
 						c.check_valid_snake_case(left.name, 'variable name', left.pos)
diff --git a/vlib/v/checker/tests/assign_multi_immutable_err.out b/vlib/v/checker/tests/assign_multi_immutable_err.out
index 44eb52dbe2..635e02059c 100644
--- a/vlib/v/checker/tests/assign_multi_immutable_err.out
+++ b/vlib/v/checker/tests/assign_multi_immutable_err.out
@@ -4,4 +4,18 @@ vlib/v/checker/tests/assign_multi_immutable_err.vv:4:2: error: `a` is immutable,
     4 |     a, b = 1, 2
       |     ^
     5 |
-    6 |     println('$a, $b')
\ No newline at end of file
+    6 |     println('$a, $b')
+vlib/v/checker/tests/assign_multi_immutable_err.vv:18:5: error: cannot assign to function `error`
+   16 |
+   17 | fn assign_fn() {
+   18 |     _, error = g()
+      |        ~~~~~
+   19 |     g = f()
+   20 | }
+vlib/v/checker/tests/assign_multi_immutable_err.vv:19:2: error: cannot assign to function `g`
+   17 | fn assign_fn() {
+   18 |     _, error = g()
+   19 |     g = f()
+      |     ^
+   20 | }
+   21 |
diff --git a/vlib/v/checker/tests/assign_multi_immutable_err.vv b/vlib/v/checker/tests/assign_multi_immutable_err.vv
index a0c4f0d82d..cfed449fdd 100644
--- a/vlib/v/checker/tests/assign_multi_immutable_err.vv
+++ b/vlib/v/checker/tests/assign_multi_immutable_err.vv
@@ -4,4 +4,18 @@ fn main() {
 	a, b = 1, 2
 
 	println('$a, $b')
-}
\ No newline at end of file
+}
+
+fn f() int {
+	return 2
+}
+
+fn g() (int, int) {
+  return 1, 2
+}
+
+fn assign_fn() {
+	_, error = g()
+	g = f()
+}
+