checker: disallow casting to bool, use `some_int != 0` instead (#6138)

vlib/os/inode.v

@@ -58,38 +58,38 @@ pub fn inode(path string) FileMode {
 		return FileMode{
 			typ: typ
 			owner: FilePermission{
-				read: bool(attr.st_mode & u32(C.S_IREAD))
-				write: bool(attr.st_mode & u32(C.S_IWRITE))
-				execute: bool(attr.st_mode & u32(C.S_IEXEC))
+				read: (attr.st_mode & u32(C.S_IREAD)) != 0
+				write: (attr.st_mode & u32(C.S_IWRITE)) != 0
+				execute: (attr.st_mode & u32(C.S_IEXEC)) != 0
 			}
 			group: FilePermission{
-				read: bool(attr.st_mode & u32(C.S_IREAD))
-				write: bool(attr.st_mode & u32(C.S_IWRITE))
-				execute: bool(attr.st_mode & u32(C.S_IEXEC))
+				read: (attr.st_mode & u32(C.S_IREAD)) != 0
+				write: (attr.st_mode & u32(C.S_IWRITE)) != 0
+				execute: (attr.st_mode & u32(C.S_IEXEC)) != 0
 			}
 			others: FilePermission{
-				read: bool(attr.st_mode & u32(C.S_IREAD))
-				write: bool(attr.st_mode & u32(C.S_IWRITE))
-				execute: bool(attr.st_mode & u32(C.S_IEXEC))
+				read: (attr.st_mode & u32(C.S_IREAD)) != 0
+				write: (attr.st_mode & u32(C.S_IWRITE)) != 0
+				execute: (attr.st_mode & u32(C.S_IEXEC)) != 0
 			}
 		}
 	} $else {
 		return FileMode{
 			typ: typ
 			owner: FilePermission{
-				read: bool(attr.st_mode & u32(C.S_IRUSR))
-				write: bool(attr.st_mode & u32(C.S_IWUSR))
-				execute: bool(attr.st_mode & u32(C.S_IXUSR))
+				read: (attr.st_mode & u32(C.S_IRUSR)) != 0
+				write: (attr.st_mode & u32(C.S_IWUSR)) != 0
+				execute: (attr.st_mode & u32(C.S_IXUSR)) != 0
 			}
 			group: FilePermission{
-				read: bool(attr.st_mode & u32(C.S_IRGRP))
-				write: bool(attr.st_mode & u32(C.S_IWGRP))
-				execute: bool(attr.st_mode & u32(C.S_IXGRP))
+				read: (attr.st_mode & u32(C.S_IRGRP)) != 0
+				write: (attr.st_mode & u32(C.S_IWGRP)) != 0
+				execute: (attr.st_mode & u32(C.S_IXGRP)) != 0
 			}
 			others: FilePermission{
-				read: bool(attr.st_mode & u32(C.S_IROTH))
-				write: bool(attr.st_mode & u32(C.S_IWOTH))
-				execute: bool(attr.st_mode & u32(C.S_IXOTH))
+				read: (attr.st_mode & u32(C.S_IROTH)) != 0
+				write: (attr.st_mode & u32(C.S_IWOTH)) != 0
+				execute: (attr.st_mode & u32(C.S_IXOTH)) != 0
 			}
 		}
 	}

vlib/v/checker/checker.v

@@ -2356,6 +2356,8 @@ pub fn (mut c Checker) expr(node ast.Expr) table.Type {
 					type_name := c.table.type_to_str(node.expr_type)
 					c.error('cannot cast `$type_name` to struct', node.pos)
 				}
+			} else if node.typ == table.bool_type {
+				c.error('cannot cast to bool - use e.g. `some_int != 0` instead', node.pos)
 			}
 			if node.has_arg {
 				c.expr(node.arg)

vlib/v/checker/tests/cast_err.out

@@ -0,0 +1,20 @@
+vlib/v/checker/tests/cast_err.v:3:11: error: cannot cast to bool - use e.g. `some_int != 0` instead
+    1 | fn test_bool_cast() {
+    2 |     v := 3
+    3 |     _ = bool(v)
+      |              ^
+    4 |     _ = bool(&v)
+    5 |     _ = bool([2])
+vlib/v/checker/tests/cast_err.v:4:11: error: cannot cast to bool - use e.g. `some_int != 0` instead
+    2 |     v := 3
+    3 |     _ = bool(v)
+    4 |     _ = bool(&v)
+      |              ^
+    5 |     _ = bool([2])
+    6 | }
+vlib/v/checker/tests/cast_err.v:5:11: error: cannot cast to bool - use e.g. `some_int != 0` instead
+    3 |     _ = bool(v)
+    4 |     _ = bool(&v)
+    5 |     _ = bool([2])
+      |              ~~~
+    6 | }

vlib/v/checker/tests/cast_err.vv

@@ -0,0 +1,6 @@
+fn test_bool_cast() {
+	v := 3
+	_ = bool(v)
+	_ = bool(&v)
+	_ = bool([2])
+}

vlib/v/tests/conversions_test.v

@@ -0,0 +1,16 @@
+fn test_conv_to_bool() {
+	v := 0
+	mut b := v != 0
+	assert !b
+	b = u64(&v) != 0
+	assert b
+	// check true -> 1
+	assert int(b) == 1
+	
+	// branchless tests (can be important for manual optimization)
+	arr := [7,8]!!
+	e := arr[int(b)]
+	assert e == 8
+	b = e < 0
+	assert arr[int(b)] == 7
+}