From 3d99f1f2c2a08f771ba54102348f71381b840f5e Mon Sep 17 00:00:00 2001
From: Swastik Baranwal <swstkbaranwal@gmail.com>
Date: Thu, 13 Apr 2023 11:08:21 +0530
Subject: [PATCH] checker: disallow struct int to ptr outside unsafe (#17923)

---
 cmd/tools/vpm.v                               |  2 +-
 doc/docs.md                                   |  4 +--
 .../sokol/particles/modules/particle/system.v |  4 +--
 vlib/builtin/sorted_map.v                     |  4 +--
 vlib/db/mysql/stmt.c.v                        |  2 +-
 vlib/db/sqlite/sqlite.v                       | 10 +++----
 vlib/db/sqlite/stmt.v                         |  2 +-
 vlib/db/sqlite/vfs_lowlevel.v                 |  2 +-
 vlib/dlmalloc/dlmalloc.v                      |  2 +-
 vlib/net/address.v                            |  2 +-
 vlib/net/common.v                             |  2 +-
 vlib/net/mbedtls/ssl_connection.v             |  2 +-
 vlib/net/openssl/openssl_compiles_test.v      |  2 +-
 vlib/net/openssl/ssl_connection.v             |  2 +-
 vlib/net/unix/common.v                        |  2 +-
 vlib/os/os_nix.c.v                            |  2 +-
 vlib/sqlite/sqlite.v                          | 10 +++----
 vlib/sqlite/vfs_lowlevel.v                    |  2 +-
 vlib/term/ui/input_nix.c.v                    |  2 +-
 vlib/term/ui/input_windows.c.v                |  2 +-
 vlib/term/ui/termios_nix.c.v                  |  4 +--
 vlib/toml/tests/toml_bom_test.v               |  2 +-
 vlib/v/ast/table.v                            |  2 +-
 vlib/v/checker/checker.v                      | 27 ++++++++++++++++++-
 ...struct_ptr_cast_int_outside_unsafe_err.out | 18 +++++++++++++
 .../struct_ptr_cast_int_outside_unsafe_err.vv |  8 ++++++
 .../tests/struct_ptr_cast_zero_err.out        | 18 +++++++++++++
 .../checker/tests/struct_ptr_cast_zero_err.vv |  8 ++++++
 vlib/v/gen/js/js.v                            |  2 +-
 vlib/v/parser/parser.v                        |  2 +-
 vlib/v/pkgconfig/main.v                       |  2 +-
 vlib/v/tests/cast_to_alias_test.v             |  4 +--
 vlib/v/token/keywords_matcher_trie.v          |  2 +-
 vlib/v/util/util.v                            |  4 +--
 vlib/vweb/tests/middleware_test.v             |  4 +--
 vlib/vweb/tests/vweb_test.v                   |  2 +-
 36 files changed, 124 insertions(+), 47 deletions(-)
 create mode 100644 vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.out
 create mode 100644 vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv
 create mode 100644 vlib/v/checker/tests/struct_ptr_cast_zero_err.out
 create mode 100644 vlib/v/checker/tests/struct_ptr_cast_zero_err.vv

diff --git a/cmd/tools/vpm.v b/cmd/tools/vpm.v
index 2838b91b0a..d1739c394b 100644
--- a/cmd/tools/vpm.v
+++ b/cmd/tools/vpm.v
@@ -704,7 +704,7 @@ const (
 )
 
 fn init_settings() {
-	mut s := &VpmSettings(0)
+	mut s := &VpmSettings(unsafe { nil })
 	unsafe {
 		s = settings
 	}
diff --git a/doc/docs.md b/doc/docs.md
index 264be94fc1..4a79fb0d6c 100644
--- a/doc/docs.md
+++ b/doc/docs.md
@@ -6188,12 +6188,12 @@ fn my_callback(arg voidptr, howmany int, cvalues &&char, cnames &&char) int {
 }
 
 fn main() {
-	db := &C.sqlite3(0) // this means `sqlite3* db = 0`
+	db := &C.sqlite3(unsafe { nil }) // this means `sqlite3* db = 0`
 	// passing a string literal to a C function call results in a C string, not a V string
 	C.sqlite3_open(c'users.db', &db)
 	// C.sqlite3_open(db_path.str, &db)
 	query := 'select count(*) from users'
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	// Note: You can also use the `.str` field of a V string,
 	// to get its C style zero terminated representation
 	C.sqlite3_prepare_v2(db, &char(query.str), -1, &stmt, 0)
diff --git a/examples/sokol/particles/modules/particle/system.v b/examples/sokol/particles/modules/particle/system.v
index dba4081976..c6035cc443 100644
--- a/examples/sokol/particles/modules/particle/system.v
+++ b/examples/sokol/particles/modules/particle/system.v
@@ -28,7 +28,7 @@ pub fn (mut s System) init(sc SystemConfig) {
 }
 
 pub fn (mut s System) update(dt f64) {
-	mut p := &Particle(0)
+	mut p := &Particle(unsafe { nil })
 	mut moved := 0
 	for i := 0; i < s.pool.len; i++ {
 		p = s.pool[i]
@@ -70,7 +70,7 @@ pub fn (mut s System) reset() {
 pub fn (mut s System) explode(x f32, y f32) {
 	mut reserve := 500
 	center := vec.Vec2[f64]{x, y}
-	mut p := &Particle(0)
+	mut p := &Particle(unsafe { nil })
 	mut moved := 0
 	for i := 0; i < s.bin.len && reserve > 0; i++ {
 		p = s.bin[i]
diff --git a/vlib/builtin/sorted_map.v b/vlib/builtin/sorted_map.v
index 941bd37b98..04bd6d2d57 100644
--- a/vlib/builtin/sorted_map.v
+++ b/vlib/builtin/sorted_map.v
@@ -70,7 +70,7 @@ fn new_node() &mapnode {
 fn (mut m SortedMap) set(key string, value voidptr) {
 	mut node := m.root
 	mut child_index := 0
-	mut parent := &mapnode(0)
+	mut parent := &mapnode(unsafe { nil })
 	for {
 		if node.len == max_len {
 			if parent == unsafe { nil } {
@@ -228,7 +228,7 @@ fn (mut n mapnode) remove_key(k string) bool {
 			n.fill(idx)
 		}
 
-		mut node := &mapnode(0)
+		mut node := &mapnode(unsafe { nil })
 		if flag && idx > n.len {
 			node = unsafe { &mapnode(n.children[idx - 1]) }
 		} else {
diff --git a/vlib/db/mysql/stmt.c.v b/vlib/db/mysql/stmt.c.v
index 4e6233e23b..162db2981c 100644
--- a/vlib/db/mysql/stmt.c.v
+++ b/vlib/db/mysql/stmt.c.v
@@ -63,7 +63,7 @@ fn C.mysql_stmt_next_result(&C.MYSQL_STMT) int
 fn C.mysql_stmt_store_result(&C.MYSQL_STMT) int
 
 pub struct Stmt {
-	stmt  &C.MYSQL_STMT = &C.MYSQL_STMT(0)
+	stmt  &C.MYSQL_STMT = &C.MYSQL_STMT(unsafe { nil })
 	query string
 mut:
 	binds []C.MYSQL_BIND
diff --git a/vlib/db/sqlite/sqlite.v b/vlib/db/sqlite/sqlite.v
index 7a95cc9ff5..ec6e254f55 100644
--- a/vlib/db/sqlite/sqlite.v
+++ b/vlib/db/sqlite/sqlite.v
@@ -127,7 +127,7 @@ fn C.sqlite3_changes(&C.sqlite3) int
 
 // connect Opens the connection with a database.
 pub fn connect(path string) !DB {
-	db := &C.sqlite3(0)
+	db := &C.sqlite3(unsafe { nil })
 	code := C.sqlite3_open(&char(path.str), &db)
 	if code != 0 {
 		return &SQLError{
@@ -182,7 +182,7 @@ pub fn (db &DB) get_affected_rows_count() int {
 
 // q_int returns a single integer value, from the first column of the result of executing `query`
 pub fn (db &DB) q_int(query string) int {
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	defer {
 		C.sqlite3_finalize(stmt)
 	}
@@ -195,7 +195,7 @@ pub fn (db &DB) q_int(query string) int {
 
 // q_string returns a single string value, from the first column of the result of executing `query`
 pub fn (db &DB) q_string(query string) string {
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	defer {
 		C.sqlite3_finalize(stmt)
 	}
@@ -210,7 +210,7 @@ pub fn (db &DB) q_string(query string) string {
 // Result codes: https://www.sqlite.org/rescode.html
 [manualfree]
 pub fn (db &DB) exec(query string) ([]Row, int) {
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	defer {
 		C.sqlite3_finalize(stmt)
 	}
@@ -278,7 +278,7 @@ pub fn (db &DB) error_message(code int, query string) IError {
 // Use it, in case you don't expect any row results, but still want a result code.
 // e.g. for queries like these: `INSERT INTO ... VALUES (...)`
 pub fn (db &DB) exec_none(query string) int {
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	C.sqlite3_prepare_v2(db.conn, &char(query.str), query.len, &stmt, 0)
 	code := C.sqlite3_step(stmt)
 	C.sqlite3_finalize(stmt)
diff --git a/vlib/db/sqlite/stmt.v b/vlib/db/sqlite/stmt.v
index 74ebc3be82..4e96fc0618 100644
--- a/vlib/db/sqlite/stmt.v
+++ b/vlib/db/sqlite/stmt.v
@@ -8,7 +8,7 @@ fn C.sqlite3_bind_text(&C.sqlite3_stmt, int, &char, int, voidptr) int
 // Only for V ORM
 fn (db &DB) init_stmt(query string) (&C.sqlite3_stmt, int) {
 	// println('init_stmt("$query")')
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	err := C.sqlite3_prepare_v2(db.conn, &char(query.str), query.len, &stmt, 0)
 	return stmt, err
 }
diff --git a/vlib/db/sqlite/vfs_lowlevel.v b/vlib/db/sqlite/vfs_lowlevel.v
index db8abfe486..09c64dd19f 100644
--- a/vlib/db/sqlite/vfs_lowlevel.v
+++ b/vlib/db/sqlite/vfs_lowlevel.v
@@ -149,7 +149,7 @@ pub enum OpenModeFlag {
 // connect_full Opens connection to sqlite database. It gives more control than `open`.
 // Flags give control over readonly and create decisions. Specific VFS can be chosen.
 pub fn connect_full(path string, mode_flags []OpenModeFlag, vfs_name string) !DB {
-	db := &C.sqlite3(0)
+	db := &C.sqlite3(unsafe { nil })
 
 	mut flags := 0
 
diff --git a/vlib/dlmalloc/dlmalloc.v b/vlib/dlmalloc/dlmalloc.v
index 3e7527d032..342cb0336c 100644
--- a/vlib/dlmalloc/dlmalloc.v
+++ b/vlib/dlmalloc/dlmalloc.v
@@ -1355,7 +1355,7 @@ fn (mut dl Dlmalloc) segment_holding(ptr voidptr) &Segment {
 		}
 		sp = sp.next
 	}
-	return &Segment(0)
+	return &Segment(unsafe { nil })
 }
 
 // realloc behaves as libc realloc, but operates within the given space
diff --git a/vlib/net/address.v b/vlib/net/address.v
index 99c52377ea..f5b34f3035 100644
--- a/vlib/net/address.v
+++ b/vlib/net/address.v
@@ -194,7 +194,7 @@ pub fn resolve_ipaddrs(addr string, family AddrFamily, typ SocketType) ![]Addr {
 	hints.ai_socktype = int(typ)
 	hints.ai_flags = C.AI_PASSIVE
 
-	results := &C.addrinfo(0)
+	results := &C.addrinfo(unsafe { nil })
 
 	sport := '${port}'
 
diff --git a/vlib/net/common.v b/vlib/net/common.v
index 5bc9247556..14b8efc70a 100644
--- a/vlib/net/common.v
+++ b/vlib/net/common.v
@@ -70,7 +70,7 @@ fn @select(handle int, test Select, timeout time.Duration) !bool {
 	// infinite timeout is signaled by passing null as the timeout to
 	// select
 	if timeout == net.infinite_timeout {
-		timeval_timeout = &C.timeval(0)
+		timeval_timeout = &C.timeval(unsafe { nil })
 	}
 
 	match test {
diff --git a/vlib/net/mbedtls/ssl_connection.v b/vlib/net/mbedtls/ssl_connection.v
index 963422d612..f353216b31 100644
--- a/vlib/net/mbedtls/ssl_connection.v
+++ b/vlib/net/mbedtls/ssl_connection.v
@@ -379,7 +379,7 @@ fn @select(handle int, test Select, timeout time.Duration) !bool {
 	// infinite timeout is signaled by passing null as the timeout to
 	// select
 	if timeout == net.infinite_timeout {
-		timeval_timeout = &C.timeval(0)
+		timeval_timeout = &C.timeval(unsafe { nil })
 	}
 
 	match test {
diff --git a/vlib/net/openssl/openssl_compiles_test.v b/vlib/net/openssl/openssl_compiles_test.v
index aac82c34e7..17f2598d0c 100644
--- a/vlib/net/openssl/openssl_compiles_test.v
+++ b/vlib/net/openssl/openssl_compiles_test.v
@@ -5,7 +5,7 @@ struct Abc {
 }
 
 fn test_printing_struct_with_reference_field_of_type_ssl_ctx() {
-	a := Abc{&C.SSL_CTX(123)}
+	a := unsafe { Abc{&C.SSL_CTX(123)} }
 	dump(a)
 	sa := a.str()
 	assert sa.contains('&C.SSL_CTX(0x7b)')
diff --git a/vlib/net/openssl/ssl_connection.v b/vlib/net/openssl/ssl_connection.v
index 7ca3c0f6bf..d82a198c11 100644
--- a/vlib/net/openssl/ssl_connection.v
+++ b/vlib/net/openssl/ssl_connection.v
@@ -436,7 +436,7 @@ fn @select(handle int, test Select, timeout time.Duration) !bool {
 	// infinite timeout is signaled by passing null as the timeout to
 	// select
 	if timeout == net.infinite_timeout {
-		timeval_timeout = &C.timeval(0)
+		timeval_timeout = &C.timeval(unsafe { nil })
 	}
 
 	match test {
diff --git a/vlib/net/unix/common.v b/vlib/net/unix/common.v
index ec9da8faf1..3ce379d145 100644
--- a/vlib/net/unix/common.v
+++ b/vlib/net/unix/common.v
@@ -42,7 +42,7 @@ fn @select(handle int, test Select, timeout time.Duration) !bool {
 	// infinite timeout is signaled by passing null as the timeout to
 	// select
 	if timeout == unix.infinite_timeout {
-		timeval_timeout = &C.timeval(0)
+		timeval_timeout = &C.timeval(unsafe { nil })
 	}
 
 	match test {
diff --git a/vlib/os/os_nix.c.v b/vlib/os/os_nix.c.v
index fe09e2b2ad..ed1f5e89f0 100644
--- a/vlib/os/os_nix.c.v
+++ b/vlib/os/os_nix.c.v
@@ -272,7 +272,7 @@ pub fn ls(path string) ![]string {
 	if isnil(dir) {
 		return error('ls() couldnt open dir "${path}"')
 	}
-	mut ent := &C.dirent(0)
+	mut ent := &C.dirent(unsafe { nil })
 	// mut ent := &C.dirent{!}
 	for {
 		ent = C.readdir(dir)
diff --git a/vlib/sqlite/sqlite.v b/vlib/sqlite/sqlite.v
index 77e1ca5610..664957ef8d 100644
--- a/vlib/sqlite/sqlite.v
+++ b/vlib/sqlite/sqlite.v
@@ -126,7 +126,7 @@ fn C.sqlite3_changes(&C.sqlite3) int
 
 // connect Opens the connection with a database.
 pub fn connect(path string) !DB {
-	db := &C.sqlite3(0)
+	db := &C.sqlite3(unsafe { nil })
 	code := C.sqlite3_open(&char(path.str), &db)
 	if code != 0 {
 		return &SQLError{
@@ -181,7 +181,7 @@ pub fn (db &DB) get_affected_rows_count() int {
 
 // Returns a single cell with value int.
 pub fn (db &DB) q_int(query string) int {
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	defer {
 		C.sqlite3_finalize(stmt)
 	}
@@ -194,7 +194,7 @@ pub fn (db &DB) q_int(query string) int {
 
 // Returns a single cell with value string.
 pub fn (db &DB) q_string(query string) string {
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	defer {
 		C.sqlite3_finalize(stmt)
 	}
@@ -209,7 +209,7 @@ pub fn (db &DB) q_string(query string) string {
 // Result codes: https://www.sqlite.org/rescode.html
 [manualfree]
 pub fn (db &DB) exec(query string) ([]Row, int) {
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	defer {
 		C.sqlite3_finalize(stmt)
 	}
@@ -276,7 +276,7 @@ pub fn (db &DB) error_message(code int, query string) IError {
 // In case you don't expect any row results, but still want a result code.
 // e.g. INSERT INTO ... VALUES (...)
 pub fn (db &DB) exec_none(query string) int {
-	stmt := &C.sqlite3_stmt(0)
+	stmt := &C.sqlite3_stmt(unsafe { nil })
 	C.sqlite3_prepare_v2(db.conn, &char(query.str), query.len, &stmt, 0)
 	code := C.sqlite3_step(stmt)
 	C.sqlite3_finalize(stmt)
diff --git a/vlib/sqlite/vfs_lowlevel.v b/vlib/sqlite/vfs_lowlevel.v
index 78d5814c82..d21c1e1297 100644
--- a/vlib/sqlite/vfs_lowlevel.v
+++ b/vlib/sqlite/vfs_lowlevel.v
@@ -149,7 +149,7 @@ pub enum OpenModeFlag {
 // connect_full Opens connection to sqlite database. It gives more control than `open`.
 // Flags give control over readonly and create decisions. Specific VFS can be chosen.
 pub fn connect_full(path string, mode_flags []OpenModeFlag, vfs_name string) !DB {
-	db := &C.sqlite3(0)
+	db := &C.sqlite3(unsafe { nil })
 
 	mut flags := 0
 
diff --git a/vlib/term/ui/input_nix.c.v b/vlib/term/ui/input_nix.c.v
index f74b450aec..8e8e84e6df 100644
--- a/vlib/term/ui/input_nix.c.v
+++ b/vlib/term/ui/input_nix.c.v
@@ -11,7 +11,7 @@ mut:
 	read_all_bytes bool = true
 }
 
-const ctx_ptr = &Context(0)
+const ctx_ptr = &Context(unsafe { nil })
 
 // init initializes the terminal console with Config `cfg`.
 pub fn init(cfg Config) &Context {
diff --git a/vlib/term/ui/input_windows.c.v b/vlib/term/ui/input_windows.c.v
index 6972f2308f..d8ba7f408e 100644
--- a/vlib/term/ui/input_windows.c.v
+++ b/vlib/term/ui/input_windows.c.v
@@ -8,7 +8,7 @@ import time
 
 const buf_size = 64
 
-const ctx_ptr = &Context(0)
+const ctx_ptr = &Context(unsafe { nil })
 
 const stdin_at_startup = u32(0)
 
diff --git a/vlib/term/ui/termios_nix.c.v b/vlib/term/ui/termios_nix.c.v
index 75c2126995..1d88cff2d1 100644
--- a/vlib/term/ui/termios_nix.c.v
+++ b/vlib/term/ui/termios_nix.c.v
@@ -255,7 +255,7 @@ fn (mut ctx Context) parse_events() {
 		if nr_iters > 100 {
 			ctx.shift(1)
 		}
-		mut event := &Event(0)
+		mut event := &Event(unsafe { nil })
 		if ctx.read_buf[0] == 0x1b {
 			e, len := escape_sequence(ctx.read_buf.bytestr())
 			event = e
@@ -420,7 +420,7 @@ fn escape_sequence(buf_ string) (&Event, int) {
 	if buf.len > 2 && buf[1] == `<` {
 		split := buf[2..].split(';')
 		if split.len < 3 {
-			return &Event(0), 0
+			return &Event(unsafe { nil }), 0
 		}
 
 		typ, x, y := split[0].int(), split[1].int(), split[2].int()
diff --git a/vlib/toml/tests/toml_bom_test.v b/vlib/toml/tests/toml_bom_test.v
index e47f8e88cb..fba1dd706d 100644
--- a/vlib/toml/tests/toml_bom_test.v
+++ b/vlib/toml/tests/toml_bom_test.v
@@ -4,7 +4,7 @@ import toml.to
 import toml.ast
 
 const empty_toml_document = toml.Doc{
-	ast: &ast.Root(0)
+	ast: &ast.Root(unsafe { nil })
 }
 
 const (
diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index 5d91a130e4..045d151e95 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -102,7 +102,7 @@ pub fn new_table() &Table {
 	return t
 }
 
-__global global_table = &Table(0)
+__global global_table = &Table(unsafe { nil })
 
 pub fn set_global_table(t &Table) {
 	global_table = t
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index aac14ace1c..67e3316c5f 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -2836,6 +2836,30 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 		if from_sym.kind == .alias {
 			from_type = (from_sym.info as ast.Alias).parent_type.derive_add_muls(from_type)
 		}
+		if mut node.expr is ast.IntegerLiteral {
+			if node.expr.val.int() == 0 && !c.pref.translated && !c.file.is_translated {
+				c.error('cannot null cast a struct pointer, use &${to_sym.name}(unsafe { nil })',
+					node.pos)
+			} else if !c.inside_unsafe && !c.pref.translated && !c.file.is_translated {
+				c.error('cannot cast int to a struct pointer outside `unsafe`', node.pos)
+			}
+		} else if mut node.expr is ast.Ident {
+			match mut node.expr.obj {
+				ast.GlobalField, ast.ConstField, ast.Var {
+					if mut node.expr.obj.expr is ast.IntegerLiteral {
+						if node.expr.obj.expr.val.int() == 0 && !c.pref.translated
+							&& !c.file.is_translated {
+							c.error('cannot null cast a struct pointer, use &${to_sym.name}(unsafe { nil })',
+								node.pos)
+						} else if !c.inside_unsafe && !c.pref.translated && !c.file.is_translated {
+							c.error('cannot cast int to a struct pointer outside `unsafe`',
+								node.pos)
+						}
+					}
+				}
+				else {}
+			}
+		}
 		if from_type == ast.voidptr_type_idx && !c.inside_unsafe {
 			// TODO make this an error
 			c.warn('cannot cast voidptr to a struct outside `unsafe`', node.pos)
@@ -3611,9 +3635,10 @@ fn (mut c Checker) lock_expr(mut node ast.LockExpr) ast.Type {
 }
 
 fn (mut c Checker) unsafe_expr(mut node ast.UnsafeExpr) ast.Type {
+	prev_unsafe := c.inside_unsafe
 	c.inside_unsafe = true
 	t := c.expr(node.expr)
-	c.inside_unsafe = false
+	c.inside_unsafe = prev_unsafe
 	return t
 }
 
diff --git a/vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.out b/vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.out
new file mode 100644
index 0000000000..059072a44f
--- /dev/null
+++ b/vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.out
@@ -0,0 +1,18 @@
+vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv:6:5: error: cannot cast int to a struct pointer outside `unsafe`
+    4 | a := 1
+    5 |
+    6 | _ = &Context(a)
+      |     ~~~~~~~~~~~
+    7 | _ = &Context(b)
+    8 | _ = &Context(1)
+vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv:7:5: error: cannot cast int to a struct pointer outside `unsafe`
+    5 |
+    6 | _ = &Context(a)
+    7 | _ = &Context(b)
+      |     ~~~~~~~~~~~
+    8 | _ = &Context(1)
+vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv:8:5: error: cannot cast int to a struct pointer outside `unsafe`
+    6 | _ = &Context(a)
+    7 | _ = &Context(b)
+    8 | _ = &Context(1)
+      |     ~~~~~~~~~~~
diff --git a/vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv b/vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv
new file mode 100644
index 0000000000..3bbe0f58c6
--- /dev/null
+++ b/vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv
@@ -0,0 +1,8 @@
+struct Context {}
+
+const b = 1
+a := 1
+
+_ = &Context(a)
+_ = &Context(b)
+_ = &Context(1)
diff --git a/vlib/v/checker/tests/struct_ptr_cast_zero_err.out b/vlib/v/checker/tests/struct_ptr_cast_zero_err.out
new file mode 100644
index 0000000000..ee9fda1898
--- /dev/null
+++ b/vlib/v/checker/tests/struct_ptr_cast_zero_err.out
@@ -0,0 +1,18 @@
+vlib/v/checker/tests/struct_ptr_cast_zero_err.vv:6:5: error: cannot null cast a struct pointer, use &Context(unsafe { nil })
+    4 | b := 0
+    5 |
+    6 | _ = &Context(0)
+      |     ~~~~~~~~~~~
+    7 | _ = &Context(a)
+    8 | _ = &Context(b)
+vlib/v/checker/tests/struct_ptr_cast_zero_err.vv:7:5: error: cannot null cast a struct pointer, use &Context(unsafe { nil })
+    5 |
+    6 | _ = &Context(0)
+    7 | _ = &Context(a)
+      |     ~~~~~~~~~~~
+    8 | _ = &Context(b)
+vlib/v/checker/tests/struct_ptr_cast_zero_err.vv:8:5: error: cannot null cast a struct pointer, use &Context(unsafe { nil })
+    6 | _ = &Context(0)
+    7 | _ = &Context(a)
+    8 | _ = &Context(b)
+      |     ~~~~~~~~~~~
diff --git a/vlib/v/checker/tests/struct_ptr_cast_zero_err.vv b/vlib/v/checker/tests/struct_ptr_cast_zero_err.vv
new file mode 100644
index 0000000000..4597d54a4d
--- /dev/null
+++ b/vlib/v/checker/tests/struct_ptr_cast_zero_err.vv
@@ -0,0 +1,8 @@
+struct Context {}
+
+const a = 0
+b := 0
+
+_ = &Context(0)
+_ = &Context(a)
+_ = &Context(b)
diff --git a/vlib/v/gen/js/js.v b/vlib/v/gen/js/js.v
index 2b57264435..491a84bd93 100644
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@@ -428,7 +428,7 @@ pub fn (mut g JsGen) enter_namespace(name string) {
 }
 
 pub fn (mut g JsGen) escape_namespace() {
-	g.ns = &Namespace(0)
+	g.ns = &Namespace(unsafe { nil })
 	g.inside_builtin = false
 }
 
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index 4435da4251..1a5de77e3e 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -179,7 +179,7 @@ pub fn (mut p Parser) free_scanner() {
 	unsafe {
 		if p.scanner != 0 {
 			p.scanner.free()
-			p.scanner = &scanner.Scanner(0)
+			p.scanner = &scanner.Scanner(nil)
 		}
 	}
 }
diff --git a/vlib/v/pkgconfig/main.v b/vlib/v/pkgconfig/main.v
index 5c3f5a253d..2e2faad695 100644
--- a/vlib/v/pkgconfig/main.v
+++ b/vlib/v/pkgconfig/main.v
@@ -78,7 +78,7 @@ pub fn (mut m Main) run() !string {
 	}
 	// m.opt = options
 	opt := m.opt
-	mut pc := &PkgConfig(0)
+	mut pc := &PkgConfig(unsafe { nil })
 	mut res := m.res
 	for arg in opt.args {
 		mut pcdep := load(arg, options) or {
diff --git a/vlib/v/tests/cast_to_alias_test.v b/vlib/v/tests/cast_to_alias_test.v
index 9592b8f667..80556a43dd 100644
--- a/vlib/v/tests/cast_to_alias_test.v
+++ b/vlib/v/tests/cast_to_alias_test.v
@@ -41,11 +41,11 @@ struct Foo {
 type Alias = Foo
 
 fn test_cast_to_alias_of_ref_struct() {
-	foo := &Foo(0)
+	foo := &Foo(unsafe { nil })
 	println(typeof(foo).name)
 	assert typeof(foo).name == '&Foo'
 
-	bar := &Alias(0)
+	bar := &Alias(unsafe { nil })
 	println(typeof(bar).name)
 	assert typeof(bar).name == '&Alias'
 }
diff --git a/vlib/v/token/keywords_matcher_trie.v b/vlib/v/token/keywords_matcher_trie.v
index 517a823944..0cc74c7d27 100644
--- a/vlib/v/token/keywords_matcher_trie.v
+++ b/vlib/v/token/keywords_matcher_trie.v
@@ -67,7 +67,7 @@ pub fn new_keywords_matcher_trie[T](kw_map map[string]T) KeywordsMatcherTrie {
 		nodes: []&TrieNode{cap: 20}
 	}
 	for _ in 0 .. 20 {
-		km.nodes << &TrieNode(0)
+		km.nodes << &TrieNode(unsafe { nil })
 	}
 	for k, v in kw_map {
 		km.add_word(k, int(v))
diff --git a/vlib/v/util/util.v b/vlib/v/util/util.v
index 2b5bbcdc7e..89e9acd000 100644
--- a/vlib/v/util/util.v
+++ b/vlib/v/util/util.v
@@ -297,7 +297,7 @@ mut:
 
 [unsafe]
 pub fn cached_read_source_file(path string) !string {
-	mut static cache := &SourceCache(0)
+	mut static cache := &SourceCache(unsafe { nil })
 	if cache == unsafe { nil } {
 		cache = &SourceCache{}
 	}
@@ -308,7 +308,7 @@ pub fn cached_read_source_file(path string) !string {
 	if path.len == 0 {
 		unsafe { cache.sources.free() }
 		unsafe { free(cache) }
-		cache = &SourceCache(0)
+		cache = &SourceCache(unsafe { nil })
 		return error('memory source file cache cleared')
 	}
 
diff --git a/vlib/vweb/tests/middleware_test.v b/vlib/vweb/tests/middleware_test.v
index ff468fd3e0..78c2a6d753 100644
--- a/vlib/vweb/tests/middleware_test.v
+++ b/vlib/vweb/tests/middleware_test.v
@@ -267,7 +267,7 @@ struct SimpleTcpClientConfig {
 }
 
 fn simple_tcp_client(config SimpleTcpClientConfig) !string {
-	mut client := &net.TcpConn(0)
+	mut client := &net.TcpConn(unsafe { nil })
 	mut tries := 0
 	for tries < config.retries {
 		tries++
@@ -308,7 +308,7 @@ ${config.content}'
 }
 
 fn simple_tcp_client_post_json(config SimpleTcpClientConfig) !string {
-	mut client := &net.TcpConn(0)
+	mut client := &net.TcpConn(unsafe { nil })
 	mut tries := 0
 	for tries < config.retries {
 		tries++
diff --git a/vlib/vweb/tests/vweb_test.v b/vlib/vweb/tests/vweb_test.v
index 0ee17190eb..183478b6a8 100644
--- a/vlib/vweb/tests/vweb_test.v
+++ b/vlib/vweb/tests/vweb_test.v
@@ -266,7 +266,7 @@ struct SimpleTcpClientConfig {
 }
 
 fn simple_tcp_client(config SimpleTcpClientConfig) !string {
-	mut client := &net.TcpConn(0)
+	mut client := &net.TcpConn(unsafe { nil })
 	mut tries := 0
 	for tries < config.retries {
 		tries++