From da9588c1a551bc8d3031a3854f9e0cf674d110a6 Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Tue, 15 Dec 2020 09:00:51 +0530
Subject: [PATCH] checker: fix struct cast (#7308)

---
 vlib/v/checker/checker.v                      |  4 ++
 vlib/v/checker/tests/struct_type_cast_err.out | 63 +++++++++++++++++++
 vlib/v/checker/tests/struct_type_cast_err.vv  | 15 +++++
 3 files changed, 82 insertions(+)
 create mode 100644 vlib/v/checker/tests/struct_type_cast_err.out
 create mode 100644 vlib/v/checker/tests/struct_type_cast_err.vv

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 26d7eb3453..0e03464f5d 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -3182,6 +3182,10 @@ pub fn (mut c Checker) cast_expr(mut node ast.CastExpr) table.Type {
 	} else if node.expr_type == table.none_type {
 		type_name := c.table.type_to_str(node.typ)
 		c.error('cannot cast `none` to `$type_name`', node.pos)
+	} else if from_type_sym.kind == .struct_ && !node.expr_type.is_ptr() && to_type_sym.kind !in
+		[.sum_type, .interface_] && !c.is_builtin_mod {
+		type_name := c.table.type_to_str(node.typ)
+		c.error('cannot cast `struct` to `$type_name`', node.pos)
 	}
 	if node.has_arg {
 		c.expr(node.arg)
diff --git a/vlib/v/checker/tests/struct_type_cast_err.out b/vlib/v/checker/tests/struct_type_cast_err.out
new file mode 100644
index 0000000000..cdf9f0c6b1
--- /dev/null
+++ b/vlib/v/checker/tests/struct_type_cast_err.out
@@ -0,0 +1,63 @@
+vlib/v/checker/tests/struct_type_cast_err.vv:5:10: error: cannot cast `struct` to `string`
+    3 | fn main() {
+    4 |     foo := Foo{}
+    5 |     _ := string(foo)
+      |          ~~~~~~~~~~~
+    6 |     _ := int(foo)
+    7 |     _ := u64(foo)
+vlib/v/checker/tests/struct_type_cast_err.vv:6:10: error: cannot cast `struct` to `int`
+    4 |     foo := Foo{}
+    5 |     _ := string(foo)
+    6 |     _ := int(foo)
+      |          ~~~~~~~~
+    7 |     _ := u64(foo)
+    8 |     _ := u32(foo)
+vlib/v/checker/tests/struct_type_cast_err.vv:7:10: error: cannot cast `struct` to `u64`
+    5 |     _ := string(foo)
+    6 |     _ := int(foo)
+    7 |     _ := u64(foo)
+      |          ~~~~~~~~
+    8 |     _ := u32(foo)
+    9 |     _ := rune(foo)
+vlib/v/checker/tests/struct_type_cast_err.vv:8:10: error: cannot cast `struct` to `u32`
+    6 |     _ := int(foo)
+    7 |     _ := u64(foo)
+    8 |     _ := u32(foo)
+      |          ~~~~~~~~
+    9 |     _ := rune(foo)
+   10 |     _ := byte(foo)
+vlib/v/checker/tests/struct_type_cast_err.vv:9:10: error: cannot cast `struct` to `rune`
+    7 |     _ := u64(foo)
+    8 |     _ := u32(foo)
+    9 |     _ := rune(foo)
+      |          ~~~~~~~~~
+   10 |     _ := byte(foo)
+   11 |     _ := i8(foo)
+vlib/v/checker/tests/struct_type_cast_err.vv:10:10: error: cannot cast type `Foo` to `byte`
+    8 |     _ := u32(foo)
+    9 |     _ := rune(foo)
+   10 |     _ := byte(foo)
+      |          ~~~~~~~~~
+   11 |     _ := i8(foo)
+   12 |     _ := i64(foo)
+vlib/v/checker/tests/struct_type_cast_err.vv:11:10: error: cannot cast `struct` to `i8`
+    9 |     _ := rune(foo)
+   10 |     _ := byte(foo)
+   11 |     _ := i8(foo)
+      |          ~~~~~~~
+   12 |     _ := i64(foo)
+   13 |     _ := int(foo)
+vlib/v/checker/tests/struct_type_cast_err.vv:12:10: error: cannot cast `struct` to `i64`
+   10 |     _ := byte(foo)
+   11 |     _ := i8(foo)
+   12 |     _ := i64(foo)
+      |          ~~~~~~~~
+   13 |     _ := int(foo)
+   14 | }
+vlib/v/checker/tests/struct_type_cast_err.vv:13:10: error: cannot cast `struct` to `int`
+   11 |     _ := i8(foo)
+   12 |     _ := i64(foo)
+   13 |     _ := int(foo)
+      |          ~~~~~~~~
+   14 | }
+   15 |
diff --git a/vlib/v/checker/tests/struct_type_cast_err.vv b/vlib/v/checker/tests/struct_type_cast_err.vv
new file mode 100644
index 0000000000..e800a5662b
--- /dev/null
+++ b/vlib/v/checker/tests/struct_type_cast_err.vv
@@ -0,0 +1,15 @@
+struct Foo{}
+
+fn main() {
+    foo := Foo{}
+    _ := string(foo)
+    _ := int(foo)
+    _ := u64(foo)
+    _ := u32(foo)
+    _ := rune(foo)
+    _ := byte(foo)
+    _ := i8(foo)
+    _ := i64(foo)
+    _ := int(foo)
+}
+