From acc85be5ae9fb311447aa3350e08fb6dd452a374 Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Sat, 17 Oct 2020 22:32:30 +0530
Subject: [PATCH] checker: disallow type casting to `none` (#6635)

---
 vlib/v/checker/checker.v                    |  3 +
 vlib/v/checker/tests/none_type_cast_err.out | 75 +++++++++++++++++++++
 vlib/v/checker/tests/none_type_cast_err.vv  | 13 ++++
 3 files changed, 91 insertions(+)
 create mode 100644 vlib/v/checker/tests/none_type_cast_err.out
 create mode 100644 vlib/v/checker/tests/none_type_cast_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index f6b3bdd173..606c5f8547 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2670,6 +2670,9 @@ pub fn (mut c Checker) expr(node ast.Expr) table.Type {
 				}
 			} else if node.typ == table.bool_type {
 				c.error('cannot cast to bool - use e.g. `some_int != 0` instead', node.pos)
+			} else if node.expr_type == table.none_type {
+				type_name := c.table.type_to_str(node.typ)
+				c.error('cannot cast `none` to `$type_name`', node.pos)
 			}
 			if node.has_arg {
 				c.expr(node.arg)
diff --git a/vlib/v/checker/tests/none_type_cast_err.out b/vlib/v/checker/tests/none_type_cast_err.out
new file mode 100644
index 0000000000..2d25d700d7
--- /dev/null
+++ b/vlib/v/checker/tests/none_type_cast_err.out
@@ -0,0 +1,75 @@
+vlib/v/checker/tests/none_type_cast_err.vv:2:14: error: cannot cast `none` to `string`
+    1 | fn main() {
+    2 |     _ := string(none)
+      |                 ~~~~
+    3 |     _ := int(none)
+    4 |     _ := i8(none)
+vlib/v/checker/tests/none_type_cast_err.vv:3:11: error: cannot cast `none` to `int`
+    1 | fn main() {
+    2 |     _ := string(none)
+    3 |     _ := int(none)
+      |              ~~~~
+    4 |     _ := i8(none)
+    5 |     _ := i16(none)
+vlib/v/checker/tests/none_type_cast_err.vv:4:10: error: cannot cast `none` to `i8`
+    2 |     _ := string(none)
+    3 |     _ := int(none)
+    4 |     _ := i8(none)
+      |             ~~~~
+    5 |     _ := i16(none)
+    6 |     _ := i64(none)
+vlib/v/checker/tests/none_type_cast_err.vv:5:11: error: cannot cast `none` to `i16`
+    3 |     _ := int(none)
+    4 |     _ := i8(none)
+    5 |     _ := i16(none)
+      |              ~~~~
+    6 |     _ := i64(none)
+    7 |     _ := u16(none)
+vlib/v/checker/tests/none_type_cast_err.vv:6:11: error: cannot cast `none` to `i64`
+    4 |     _ := i8(none)
+    5 |     _ := i16(none)
+    6 |     _ := i64(none)
+      |              ~~~~
+    7 |     _ := u16(none)
+    8 |     _ := u32(none)
+vlib/v/checker/tests/none_type_cast_err.vv:7:11: error: cannot cast `none` to `u16`
+    5 |     _ := i16(none)
+    6 |     _ := i64(none)
+    7 |     _ := u16(none)
+      |              ~~~~
+    8 |     _ := u32(none)
+    9 |     _ := u64(none)
+vlib/v/checker/tests/none_type_cast_err.vv:8:11: error: cannot cast `none` to `u32`
+    6 |     _ := i64(none)
+    7 |     _ := u16(none)
+    8 |     _ := u32(none)
+      |              ~~~~
+    9 |     _ := u64(none)
+   10 |     _ := rune(none)
+vlib/v/checker/tests/none_type_cast_err.vv:9:11: error: cannot cast `none` to `u64`
+    7 |     _ := u16(none)
+    8 |     _ := u32(none)
+    9 |     _ := u64(none)
+      |              ~~~~
+   10 |     _ := rune(none)
+   11 |     _ := f32(none)
+vlib/v/checker/tests/none_type_cast_err.vv:10:12: error: cannot cast `none` to `rune`
+    8 |     _ := u32(none)
+    9 |     _ := u64(none)
+   10 |     _ := rune(none)
+      |               ~~~~
+   11 |     _ := f32(none)
+   12 |     _ := f64(none)
+vlib/v/checker/tests/none_type_cast_err.vv:11:11: error: cannot cast `none` to `f32`
+    9 |     _ := u64(none)
+   10 |     _ := rune(none)
+   11 |     _ := f32(none)
+      |              ~~~~
+   12 |     _ := f64(none)
+   13 | }
+vlib/v/checker/tests/none_type_cast_err.vv:12:11: error: cannot cast `none` to `f64`
+   10 |     _ := rune(none)
+   11 |     _ := f32(none)
+   12 |     _ := f64(none)
+      |              ~~~~
+   13 | }
diff --git a/vlib/v/checker/tests/none_type_cast_err.vv b/vlib/v/checker/tests/none_type_cast_err.vv
new file mode 100644
index 0000000000..953b36965e
--- /dev/null
+++ b/vlib/v/checker/tests/none_type_cast_err.vv
@@ -0,0 +1,13 @@
+fn main() {
+	_ := string(none)
+	_ := int(none)
+	_ := i8(none)
+	_ := i16(none)
+	_ := i64(none)
+	_ := u16(none)
+	_ := u32(none)
+	_ := u64(none)
+	_ := rune(none)
+	_ := f32(none)
+	_ := f64(none)
+}