checker: do not allow &u8(0), force nil like we do with &Type(0)

doc/docs.md

@@ -1599,11 +1599,11 @@ println('Your OS is ${current_os}.')
 > This section is valid when .v files are not in the project's root directory.
 
 Modules names in .v files, must match the name of their directory.
- 
-A .v file `./abc/source.v` must start with `module abc`. All .v files in this directory 
+
+A .v file `./abc/source.v` must start with `module abc`. All .v files in this directory
 belong to the same module `abc`. They should also start with `module abc`.
 
-If you have `abc/def/`, and .v files in both folders, you can `import abc`, but you will have 
+If you have `abc/def/`, and .v files in both folders, you can `import abc`, but you will have
 to `import abc.def` too, to get to the symbols in the subfolder. It is independent.
 
 In `module name` statement, name never repeats directory's hierarchy, but only its directory.
@@ -1637,7 +1637,7 @@ fn main() {
 
 A function, located in `abc/def/source.v`, is called with `def.func()`, not `abc.def.func()`
 
-This always implies a *single prefix*, whatever sub-module depth. This behavior flattens 
+This always implies a *single prefix*, whatever sub-module depth. This behavior flattens
 modules/sub-modules hierarchy. Should you have two modules with the same name in different
 directories, then you should use Module import aliasing (see below).
 
@@ -1963,7 +1963,7 @@ println(typ)
 ```
 
 A match statement also can match the variant types of a `sumtype`. Note that
-in that case, the match is exhaustive, since all variant types are mentioned 
+in that case, the match is exhaustive, since all variant types are mentioned
 explicitly, so there is no need for an `else{}` branch.
 
 ```v nofmt
@@ -4730,12 +4730,12 @@ fn main() {
 
 ### Difference Between Channels and Shared Objects
 
-**Purpose**: 
+**Purpose**:
 - Channels: Used for message passing between threads, ensuring safe communication.
 - Shared objects: Used for direct data sharing and modification between threads.
 
-**Synchronization**: 
-- Channels: Implicit (via channel operations) 
+**Synchronization**:
+- Channels: Implicit (via channel operations)
 - Shared objects:  Explicit (via `rlock`/`lock` blocks)
 
 ## JSON
@@ -5836,20 +5836,20 @@ pub mut:
 
 Function/method deprecations:
 
-Functions are deprecated before they are finally removed to give users time to migrate their code. 
-Adding a date is preferable in most cases. An immediate change, without a deprecation date, may be 
-used for functions that are found to be conceptually broken and obsoleted by much better 
-functionality. Other than that setting a date is advisable to grant users a grace period. 
+Functions are deprecated before they are finally removed to give users time to migrate their code.
+Adding a date is preferable in most cases. An immediate change, without a deprecation date, may be
+used for functions that are found to be conceptually broken and obsoleted by much better
+functionality. Other than that setting a date is advisable to grant users a grace period.
 
-Deprecated functions cause warnings, which cause errors if built with `-prod`. To avoid immediate 
-CI breakage, it is advisable to set a future date, ahead of the date when the code is merged. This 
-gives people who actively developed V projects, the chance to see the deprecation notice at least 
-once and fix the uses. Setting a date in the next 30 days, assumes they would have compiled their 
+Deprecated functions cause warnings, which cause errors if built with `-prod`. To avoid immediate
+CI breakage, it is advisable to set a future date, ahead of the date when the code is merged. This
+gives people who actively developed V projects, the chance to see the deprecation notice at least
+once and fix the uses. Setting a date in the next 30 days, assumes they would have compiled their
 projects manually at least once, within that time. For small changes, this should be plenty
-of time. For complex changes, this time may need to be longer. 
+of time. For complex changes, this time may need to be longer.
 
-Different V projects and maintainers may reasonably choose different deprecation policies. 
-Depending on the type and impact of the change, you may want to consult with them first, before 
+Different V projects and maintainers may reasonably choose different deprecation policies.
+Depending on the type and impact of the change, you may want to consult with them first, before
 deprecating a function.
 
 
@@ -7710,7 +7710,7 @@ fn main() {
 	C.sqlite3_finalize(stmt)
 	println('There are ${nr_users} users in the database.')
 
-	error_msg := &char(0)
+	error_msg := &char(unsafe { nil })
 	query_all_users := 'select * from users'
 	rc := C.sqlite3_exec(db, &char(query_all_users.str), my_callback, voidptr(7), &error_msg)
 	if rc != C.SQLITE_OK {
@@ -8193,7 +8193,7 @@ exists the file will be overridden. If you want to rebuild each time and not kee
 instead use `#!/usr/bin/env -S v -raw-vsh-tmp-prefix tmp run`.
 
 Note: there is a small shell script `cmd/tools/vrun`, that can be useful for systems, that have an
-env program (`/usr/bin/env`), that still does not support an `-S` option (like BusyBox). 
+env program (`/usr/bin/env`), that still does not support an `-S` option (like BusyBox).
 See https://github.com/vlang/v/blob/master/cmd/tools/vrun for more details.
 
 # Appendices

examples/c_interop_wkhtmltopdf.v

@@ -72,7 +72,7 @@ fn main() {
 	error_code := C.wkhtmltopdf_http_error_code(converter)
 	println('wkhtmltopdf_http_error_code: ${error_code}')
 	if result {
-		pdata := &char(0)
+		pdata := &char(unsafe { nil })
 		ppdata := &pdata
 		size := C.wkhtmltopdf_get_output(converter, voidptr(ppdata))
 		println('wkhtmltopdf_get_output: ${size} bytes')

examples/sokol/01_cubes/cube.v

@@ -37,7 +37,7 @@ fn create_texture(w int, h int, buf &u8) (gfx.Image, gfx.Sampler) {
 		height:      h
 		num_mipmaps: 0
 		// usage: .dynamic
-		label:         &char(0)
+		label:         &char(unsafe { nil })
 		d3d11_texture: 0
 	}
 	// comment, if .dynamic is enabled

examples/sokol/02_cubes_glsl/cube_glsl.v

@@ -61,7 +61,7 @@ fn create_texture(w int, h int, buf &u8) (gfx.Image, gfx.Sampler) {
 		height:      h
 		num_mipmaps: 0
 		// usage: .dynamic
-		label:         &char(0)
+		label:         &char(unsafe { nil })
 		d3d11_texture: 0
 	}
 	// comment if .dynamic is enabled

examples/sokol/03_march_tracing_glsl/rt_glsl.v

@@ -64,7 +64,7 @@ fn create_texture(w int, h int, buf &u8) (gfx.Image, gfx.Sampler) {
 		// usage: .dynamic
 		//		wrap_u: .clamp_to_edge
 		//		wrap_v: .clamp_to_edge
-		label:         &char(0)
+		label:         &char(unsafe { nil })
 		d3d11_texture: 0
 	}
 	// comment if .dynamic is enabled

examples/sokol/05_instancing_glsl/rt_glsl.v

@@ -75,7 +75,7 @@ fn create_texture(w int, h int, buf byteptr) (gfx.Image, gfx.Sampler) {
 		//usage: .dynamic
 //		wrap_u:        .clamp_to_edge
 //		wrap_v:        .clamp_to_edge
-		label:         &char(0)
+		label:         &char(unsafe { nil })
 		d3d11_texture: 0
 	}
 	// vfmt on

examples/sokol/06_obj_viewer/modules/obj/rend.v

@@ -29,7 +29,7 @@ pub fn create_texture(w int, h int, buf &u8) (gfx.Image, gfx.Sampler) {
 		// usage: .dynamic
 		// wrap_u: .clamp_to_edge
 		// wrap_v: .clamp_to_edge
-		label:         &char(0)
+		label:         &char(unsafe { nil })
 		d3d11_texture: 0
 	}
 	// comment if .dynamic is enabled

examples/viewer/view.v

@@ -119,7 +119,7 @@ fn create_texture(w int, h int, buf &u8) (gfx.Image, gfx.Sampler) {
 		height:      h
 		num_mipmaps: 0
 		// usage: .dynamic
-		label:         &u8(0)
+		label:         &u8(unsafe { nil })
 		d3d11_texture: 0
 	}
 	// comment if .dynamic is enabled

vlib/builtin/backtraces_windows.c.v

@@ -87,7 +87,7 @@ fn print_backtrace_skipping_top_frames_msvc(skipframes int) bool {
 		si.f_max_name_len = sizeof(SymbolInfoContainer) - sizeof(SymbolInfo) - 1
 		fname := &char(&si.f_name)
 		mut sline64 := Line64{
-			f_file_name: &u8(0)
+			f_file_name: &u8(unsafe { nil })
 		}
 		sline64.f_size_of_struct = sizeof(Line64)
 

vlib/builtin/builtin.c.v

@@ -438,9 +438,9 @@ pub fn malloc(n isize) &u8 {
 	if n < 0 {
 		_memory_panic(@FN, n)
 	} else if n == 0 {
-		return &u8(0)
+		return &u8(unsafe { nil })
 	}
-	mut res := &u8(0)
+	mut res := &u8(unsafe { nil })
 	$if prealloc {
 		return unsafe { prealloc_malloc(n) }
 	} $else $if gcboehm ? {
@@ -476,7 +476,7 @@ pub fn malloc_noscan(n isize) &u8 {
 	if n < 0 {
 		_memory_panic(@FN, n)
 	}
-	mut res := &u8(0)
+	mut res := &u8(unsafe { nil })
 	$if prealloc {
 		return unsafe { prealloc_malloc(n) }
 	} $else $if gcboehm ? {
@@ -529,7 +529,7 @@ pub fn malloc_uncollectable(n isize) &u8 {
 		_memory_panic(@FN, n)
 	}
 
-	mut res := &u8(0)
+	mut res := &u8(unsafe { nil })
 	$if prealloc {
 		return unsafe { prealloc_malloc(n) }
 	} $else $if gcboehm ? {
@@ -561,7 +561,7 @@ pub fn v_realloc(b &u8, n isize) &u8 {
 	$if trace_realloc ? {
 		C.fprintf(C.stderr, c'v_realloc %6d\n', n)
 	}
-	mut new_ptr := &u8(0)
+	mut new_ptr := &u8(unsafe { nil })
 	$if prealloc {
 		unsafe {
 			new_ptr = malloc(n)
@@ -613,7 +613,7 @@ pub fn realloc_data(old_data &u8, old_size int, new_size int) &u8 {
 			return new_ptr
 		}
 	}
-	mut nptr := &u8(0)
+	mut nptr := &u8(unsafe { nil })
 	$if gcboehm ? {
 		nptr = unsafe { C.GC_REALLOC(old_data, new_size) }
 	} $else {
@@ -636,7 +636,7 @@ pub fn vcalloc(n isize) &u8 {
 	if n < 0 {
 		_memory_panic(@FN, n)
 	} else if n == 0 {
-		return &u8(0)
+		return &u8(unsafe { nil })
 	}
 	$if prealloc {
 		return unsafe { prealloc_calloc(n) }
@@ -645,7 +645,7 @@ pub fn vcalloc(n isize) &u8 {
 	} $else {
 		return unsafe { C.calloc(1, n) }
 	}
-	return &u8(0) // not reached, TODO: remove when V's checker is improved
+	return &u8(unsafe { nil }) // not reached, TODO: remove when V's checker is improved
 }
 
 // special versions of the above that allocate memory which is not scanned
@@ -673,7 +673,7 @@ pub fn vcalloc_noscan(n isize) &u8 {
 	} $else {
 		return unsafe { vcalloc(n) }
 	}
-	return &u8(0) // not reached, TODO: remove when V's checker is improved
+	return &u8(unsafe { nil }) // not reached, TODO: remove when V's checker is improved
 }
 
 // free allows for manually freeing memory allocated at the address `ptr`.

vlib/builtin/builtin_windows.c.v

@@ -172,7 +172,7 @@ pub fn winapi_lasterr_str() string {
 		// handle this case special since `FormatMessageW()` might not work anymore
 		return 'insufficient memory'
 	}
-	mut msgbuf := &u16(0)
+	mut msgbuf := &u16(unsafe { nil })
 	res := C.FormatMessageW(format_message_allocate_buffer | format_message_from_system | format_message_ignore_inserts,
 		0, err_msg_id, 0, voidptr(&msgbuf), 0, 0)
 	err_msg := if res == 0 {

vlib/builtin/isnil_test.v

@@ -1,5 +1,5 @@
 fn test_isnil_byteptr() {
-	pb := &u8(0)
+	pb := &u8(unsafe { nil })
 	assert isnil(pb)
 }
 
@@ -9,7 +9,7 @@ fn test_isnil_voidptr() {
 }
 
 fn test_isnil_charptr() {
-	pc := &char(0)
+	pc := &char(unsafe { nil })
 	assert isnil(pc)
 }
 

vlib/builtin/js/map_test.js.v

@@ -200,8 +200,8 @@ fn test_various_map_value() {
 	m14['test'] = voidptr(0)
 	assert m14['test'] == voidptr(0)
 	mut m15 := map[string]&byte{}
-	m15['test'] = &u8(0)
-	assert m15['test'] == &u8(0)
+	m15['test'] = &u8(unsafe { nil })
+	assert m15['test'] == &u8(unsafe { nil })
 	mut m16 := map[string]i64{}
 	m16['test'] = i64(0)
 	assert m16['test'] == i64(0)

vlib/builtin/linux_bare/memory_managment.v

@@ -10,7 +10,8 @@ fn mm_alloc(size u64) (&u8, Errno) {
 	map_flags := unsafe { MapFlags(int(MapFlags.map_private) | int(MapFlags.map_anonymous)) }
 	// END CONSTS
 
-	a, e := sys_mmap(&u8(0), size + sizeof(u64), mem_prot, map_flags, -1, 0)
+	a, e := sys_mmap(&u8(unsafe { nil }), size + sizeof(u64), mem_prot, map_flags, -1,
+		0)
 	if e == .enoerror {
 		unsafe {
 			mut ap := &u64(a)
@@ -19,7 +20,7 @@ fn mm_alloc(size u64) (&u8, Errno) {
 			return x2, e
 		}
 	}
-	return &u8(0), e
+	return &u8(unsafe { nil }), e
 }
 
 fn mm_free(addr &u8) Errno {
@@ -38,7 +39,7 @@ fn system_alloc(_ voidptr, size usize) (voidptr, usize, u32) {
 	map_flags := unsafe { MapFlags(int(MapFlags.map_private) | int(MapFlags.map_anonymous)) }
 	// END CONSTS
 
-	a, e := sys_mmap(&u8(0), u64(size), mem_prot, map_flags, -1, 0)
+	a, e := sys_mmap(&u8(unsafe { nil }), u64(size), mem_prot, map_flags, -1, 0)
 
 	if e == .enoerror {
 		return a, size, 0

vlib/builtin/linux_bare/old/mm_bare.v

@@ -19,7 +19,7 @@ pub fn mm_alloc(size u64) (&u8, Errno) {
 		*ap = pages
 		return &u8(a + 4), e
 	}
-	return &u8(0), e
+	return &u8(unsafe { nil }), e
 }
 
 pub fn mm_free(addr &u8) Errno {

vlib/builtin/map.c.v

@@ -19,7 +19,8 @@ fn fast_string_eq(a string, b string) bool {
 
 fn map_hash_string(pkey voidptr) u64 {
 	key := *unsafe { &string(pkey) }
-	return C.wyhash(key.str, u64(key.len), 0, &u64(C._wyp))
+	// XTODO remove voidptr cast once virtual C.consts can be declared
+	return C.wyhash(key.str, u64(key.len), 0, &u64(voidptr(C._wyp)))
 }
 
 fn map_hash_int_1(pkey voidptr) u64 {

vlib/builtin/map_test.v

@@ -213,8 +213,8 @@ fn test_various_map_value() {
 	m14['test'] = unsafe { nil }
 	assert unsafe { m14['test'] } == unsafe { nil }
 	mut m15 := map[string]&u8{}
-	m15['test'] = &u8(0)
-	assert unsafe { m15['test'] } == &u8(0)
+	m15['test'] = &u8(unsafe { nil })
+	assert unsafe { m15['test'] } == &u8(unsafe { nil })
 	mut m16 := map[string]i64{}
 	m16['test'] = i64(0)
 	assert m16['test'] == i64(0)

vlib/clipboard/x11/clipboard.c.v

@@ -409,7 +409,7 @@ fn read_property(d &C.Display, w Window, p Atom) Property {
 	actual_format := 0
 	nitems := u64(0)
 	bytes_after := u64(0)
-	ret := &u8(0)
+	ret := &u8(unsafe { nil })
 	mut read_bytes := 1024
 	for {
 		if ret != 0 {

vlib/compress/szip/szip.c.v

@@ -205,7 +205,7 @@ pub fn (mut zentry Zip) create_entry(name string) ! {
 // NOTE: remember to release the memory allocated for an output buffer.
 // for large entries, please take a look at zip_entry_extract function.
 pub fn (mut zentry Zip) read_entry() !voidptr {
-	mut buf := &u8(0)
+	mut buf := &u8(unsafe { nil })
 	mut bsize := usize(0)
 	res := C.zip_entry_read(zentry, unsafe { &voidptr(&buf) }, &bsize)
 	if res == -1 {

vlib/db/mysql/orm.c.v

@@ -45,7 +45,7 @@ pub fn (db DB) select(config orm.SelectConfig, data orm.QueryData, where orm.Que
 			.type_string, .type_var_string, .type_blob, .type_tiny_blob, .type_medium_blob,
 			.type_long_blob {
 				// Memory will be allocated later dynamically depending on the length of the value.
-				data_pointers << &u8(0)
+				data_pointers << &u8(unsafe { nil })
 			}
 			else {
 				return error('\'${unsafe { FieldType(field.type) }}\' is not yet implemented. Please create a new issue at https://github.com/vlang/v/issues/new')

vlib/db/pg/orm.v

@@ -176,7 +176,7 @@ fn pg_stmt_match(mut types []u32, mut vals []&char, mut lens []int, mut formats
 		}
 		orm.Null {
 			types << u32(0) // we do not know col type, let server infer
-			vals << &char(0) // NULL pointer indicates NULL
+			vals << &char(unsafe { nil }) // NULL pointer indicates NULL
 			lens << int(0) // ignored
 			formats << 0 // ignored
 		}

vlib/db/pg/pg.c.v

@@ -392,14 +392,14 @@ pub fn (db DB) copy_expert(query string, mut file io.ReaderWriter) !int {
 			}
 		}
 
-		code := C.PQputCopyEnd(db.conn, &char(0))
+		code := C.PQputCopyEnd(db.conn, &char(unsafe { nil }))
 
 		if code != 1 {
 			return error('pg copy error: Failed to finish copy command, code: ${code}')
 		}
 	} else if status == .copy_out {
 		for {
-			address := &char(0)
+			address := &char(unsafe { nil })
 			n_bytes := C.PQgetCopyData(db.conn, &address, 0)
 			if n_bytes > 0 {
 				mut local_buf := []u8{len: n_bytes}

vlib/db/sqlite/sqlite.c.v

@@ -224,7 +224,7 @@ pub fn (db &DB) q_string(query string) !string {
 		return db.error_message(code, query)
 	}
 	val := unsafe { &u8(C.sqlite3_column_text(stmt, 0)) }
-	return if val != &u8(0) { unsafe { tos_clone(val) } } else { '' }
+	return if val != &u8(unsafe { nil }) { unsafe { tos_clone(val) } } else { '' }
 }
 
 // exec_map executes the query on the given `db`, and returns an array of maps of strings, or an error on failure
@@ -254,7 +254,7 @@ pub fn (db &DB) exec_map(query string) ![]map[string]string {
 			val := unsafe { &u8(C.sqlite3_column_text(stmt, i)) }
 			col_char := unsafe { &u8(C.sqlite3_column_name(stmt, i)) }
 			col := unsafe { col_char.vstring() }
-			if val == &u8(0) {
+			if val == &u8(unsafe { nil }) {
 				row[col] = ''
 			} else {
 				row[col] = unsafe { tos_clone(val) }
@@ -294,7 +294,7 @@ pub fn (db &DB) exec(query string) ![]Row {
 		mut row := Row{}
 		for i in 0 .. nr_cols {
 			val := unsafe { &u8(C.sqlite3_column_text(stmt, i)) }
-			if val == &u8(0) {
+			if val == &u8(unsafe { nil }) {
 				row.vals << ''
 			} else {
 				row.vals << unsafe { val.vstring() }
@@ -388,7 +388,7 @@ pub fn (db &DB) exec_param_many(query string, params []string) ![]Row {
 		mut row := Row{}
 		for i in 0 .. nr_cols {
 			val := unsafe { &u8(C.sqlite3_column_text(stmt, i)) }
-			if val == &u8(0) {
+			if val == &u8(unsafe { nil }) {
 				row.vals << ''
 			} else {
 				row.vals << unsafe { val.vstring() }

vlib/db/sqlite/stmt.c.v

@@ -71,7 +71,7 @@ fn (stmt &Stmt) get_text(idx int) ?string {
 		return none
 	} else {
 		b := &char(C.sqlite3_column_text(stmt.stmt, idx))
-		if b == &char(0) {
+		if b == &char(unsafe { nil }) {
 			return ''
 		}
 		return unsafe { b.vstring() }

vlib/fontstash/fontstash.c.v

@@ -204,7 +204,7 @@ pub fn (s &Context) set_font(font_id int) {
 // The function returns the `x` coordinate of the resulting render.
 @[inline]
 pub fn (s &Context) draw_text(x f32, y f32, text string) f32 {
-	return C.fonsDrawText(s, x, y, &char(text.str), &char(0))
+	return C.fonsDrawText(s, x, y, &char(text.str), &char(unsafe { nil }))
 }
 
 // text_bounds fills the `bounds` argument with the pixel dimensions
@@ -218,7 +218,7 @@ pub fn (s &Context) draw_text(x f32, y f32, text string) f32 {
 // `bounds[3]` is the `y` coordinate of the bottom-right point.
 @[inline]
 pub fn (s &Context) text_bounds(x f32, y f32, text string, bounds &f32) f32 {
-	return C.fonsTextBounds(s, x, y, &char(text.str), &char(0), bounds)
+	return C.fonsTextBounds(s, x, y, &char(text.str), &char(unsafe { nil }), bounds)
 }
 
 // line_bounds fills `miny` and `maxy` with the values of the `minimum`

vlib/gg/image.c.v

@@ -307,7 +307,7 @@ pub fn (ctx &Context) draw_image_with_config(config DrawImageConfig) {
 					return
 				}
 				if img.width == 0 {
-					println('w=0')
+					println('gg: draw_image() width=0')
 					return
 				}
 				if !os.exists(img.path) {

vlib/hash/wyhash.c.v

@@ -9,7 +9,7 @@ fn C.wyhash64(u64, u64) u64
 // wyhash_c returns a hash given a byte string `key`, its `len`, and a `seed`.
 @[inline]
 pub fn wyhash_c(key &u8, len u64, seed u64) u64 {
-	return C.wyhash(key, len, seed, &u64(C._wyp))
+	return C.wyhash(key, len, seed, &u64(voidptr(C._wyp)))
 }
 
 // wyhash64_c returns a hash given two u64 values `a` and `b`.

vlib/os/environment.c.v

@@ -85,6 +85,9 @@ pub fn unsetenv(name string) int {
 // See: https://docs.microsoft.com/bg-bg/windows/win32/api/processenv/nf-processenv-getenvironmentstrings
 // os.environ returns a map of all the current environment variables
 
+// TODO how to declare Virtual C globals?
+// const C.environ &&char
+
 pub fn environ() map[string]string {
 	mut res := map[string]string{}
 	$if windows {
@@ -102,7 +105,7 @@ pub fn environ() map[string]string {
 		}
 		C.FreeEnvironmentStringsW(estrings)
 	} $else {
-		start := &&char(C.environ)
+		start := &&char(voidptr(C.environ))
 		mut i := 0
 		for {
 			x := unsafe { start[i] }

vlib/os/os.c.v

@@ -579,7 +579,7 @@ pub fn get_raw_line() string {
 		}
 	} $else {
 		max := usize(0)
-		buf := unsafe { &u8(0) }
+		buf := &u8(unsafe { nil })
 		nr_chars := unsafe { C.getline(voidptr(&buf), &max, C.stdin) }
 		str := unsafe { tos(buf, if nr_chars < 0 { 0 } else { nr_chars }) }
 		ret := str.clone()
@@ -624,7 +624,7 @@ pub fn get_raw_stdin() []u8 {
 		}
 	} $else {
 		max := usize(0)
-		buf := unsafe { &u8(0) }
+		buf := &u8(unsafe { nil })
 		nr_chars := unsafe { C.getline(voidptr(&buf), &max, C.stdin) }
 		return array{
 			element_size: 1
@@ -995,7 +995,7 @@ pub fn execvp(cmdpath string, cmdargs []string) ! {
 	for i in 0 .. cmdargs.len {
 		cargs << &char(cmdargs[i].str)
 	}
-	cargs << &char(0)
+	cargs << &char(unsafe { nil })
 	mut res := int(0)
 	$if windows {
 		res = C._execvp(&char(cmdpath.str), cargs.data)
@@ -1026,8 +1026,8 @@ pub fn execve(cmdpath string, cmdargs []string, envs []string) ! {
 	for i in 0 .. envs.len {
 		cenvs << &char(envs[i].str)
 	}
-	cargv << &char(0)
-	cenvs << &char(0)
+	cargv << &char(unsafe { nil })
+	cenvs << &char(unsafe { nil })
 	mut res := int(0)
 	$if windows {
 		res = C._execve(&char(cmdpath.str), cargv.data, cenvs.data)

vlib/os/os_windows.c.v

@@ -293,9 +293,9 @@ pub fn execute(cmd string) Result {
 // user provided escape sequences.
 @[unsafe]
 pub fn raw_execute(cmd string) Result {
-	mut child_stdin := &u32(0)
-	mut child_stdout_read := &u32(0)
-	mut child_stdout_write := &u32(0)
+	mut child_stdin := &u32(unsafe { nil })
+	mut child_stdout_read := &u32(unsafe { nil })
+	mut child_stdout_write := &u32(unsafe { nil })
 	mut sa := SecurityAttributes{}
 	sa.n_length = sizeof(C.SECURITY_ATTRIBUTES)
 	sa.b_inherit_handle = true
@@ -609,8 +609,8 @@ pub fn disk_usage(path string) !DiskUsage {
 	mut available := u64(0)
 	mut ret := false
 	if path == '.' || path == '' {
-		ret = C.GetDiskFreeSpaceExA(&char(0), &free_bytes_available_to_caller, &total,
-			&available)
+		ret = C.GetDiskFreeSpaceExA(&char(unsafe { nil }), &free_bytes_available_to_caller,
+			&total, &available)
 	} else {
 		ret = C.GetDiskFreeSpaceExA(&char(path.str), &free_bytes_available_to_caller,
 			&total, &available)

vlib/os/process_windows.c.v

@@ -32,10 +32,10 @@ fn failed_cfn_report_error(ok bool, label string) {
 
 fn close_valid_handle(p voidptr) {
 	h := &&u32(p)
-	if *h != &u32(0) {
+	if *h != &u32(unsafe { nil }) {
 		C.CloseHandle(*h)
 		unsafe {
-			*h = &u32(0)
+			*h = &u32(nil)
 		}
 	}
 }
@@ -231,7 +231,7 @@ fn (mut p Process) win_read_string(idx int, _maxbytes int) (string, int) {
 	if unsafe { wdata == 0 } {
 		return '', 0
 	}
-	mut rhandle := &u32(0)
+	mut rhandle := &u32(unsafe { nil })
 	if idx == 1 {
 		rhandle = wdata.child_stdout_read
 	}
@@ -263,7 +263,7 @@ fn (mut p Process) win_is_pending(idx int) bool {
 	if unsafe { wdata == 0 } {
 		return false
 	}
-	mut rhandle := &u32(0)
+	mut rhandle := &u32(unsafe { nil })
 	if idx == 1 {
 		rhandle = wdata.child_stdout_read
 	}
@@ -285,7 +285,7 @@ fn (mut p Process) win_slurp(idx int) string {
 	if unsafe { wdata == 0 } {
 		return ''
 	}
-	mut rhandle := &u32(0)
+	mut rhandle := &u32(unsafe { nil })
 	if idx == 1 {
 		rhandle = wdata.child_stdout_read
 	}

vlib/sokol/gfx/gfx_structs.c.v

@@ -49,7 +49,7 @@ pub mut:
 	sample_count              int
 	blend_color               Color
 	alpha_to_coverage_enabled bool
-	label                     &char = &char(0)
+	label                     &char = &char(unsafe { nil })
 }
 
 pub type PipelineDesc = C.sg_pipeline_desc

vlib/sokol/sapp/screenshot.c.v

@@ -29,7 +29,7 @@ pub fn screenshot_window() &Screenshot {
 pub fn (mut ss Screenshot) free() {
 	unsafe {
 		free(ss.pixels)
-		ss.pixels = &u8(0)
+		ss.pixels = &u8(nil)
 	}
 }
 

vlib/sync/channels.c.v

@@ -69,8 +69,8 @@ pub fn new_channel[T](n u32) &Channel {
 fn new_channel_st(n u32, st u32) &Channel {
 	wsem := if n > 0 { n } else { 1 }
 	rsem := if n > 0 { u32(0) } else { 1 }
-	rbuf := if n > 0 { unsafe { malloc(int(n * st)) } } else { &u8(0) }
-	sbuf := if n > 0 { vcalloc_noscan(int(n * 2)) } else { &u8(0) }
+	rbuf := if n > 0 { unsafe { malloc(int(n * st)) } } else { &u8(unsafe { nil }) }
+	sbuf := if n > 0 { vcalloc_noscan(int(n * 2)) } else { &u8(unsafe { nil }) }
 	mut ch := Channel{
 		objsize:          st
 		cap:              n
@@ -92,8 +92,8 @@ fn new_channel_st_noscan(n u32, st u32) &Channel {
 	$if gcboehm_opt ? {
 		wsem := if n > 0 { n } else { 1 }
 		rsem := if n > 0 { u32(0) } else { 1 }
-		rbuf := if n > 0 { unsafe { malloc_noscan(int(n * st)) } } else { &u8(0) }
-		sbuf := if n > 0 { vcalloc_noscan(int(n * 2)) } else { &u8(0) }
+		rbuf := if n > 0 { unsafe { malloc_noscan(int(n * st)) } } else { &u8(unsafe { nil }) }
+		sbuf := if n > 0 { vcalloc_noscan(int(n * 2)) } else { &u8(unsafe { nil }) }
 		mut ch := Channel{
 			objsize:          st
 			cap:              n

vlib/toml/parser/parser.v

@@ -914,7 +914,7 @@ pub fn (mut p Parser) double_array_of_tables(mut table map[string]ast.Value) ! {
 	first := DottedKey([dotted_key[0]]) // The array that holds the entries
 	last := DottedKey([dotted_key[1]]) // The key the parsed array data should be added to
 
-	mut t_arr := &[]ast.Value(0)
+	mut t_arr := &[]ast.Value(unsafe { nil })
 	mut t_map := ast.Value(ast.Null{})
 
 	unsafe {

vlib/v/checker/checker.v

@@ -3594,6 +3594,17 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 		c.error('cannot cast type `${ft}` to `${tt}`', node.pos)
 	}
 
+	// if from_type == ast.voidptr_type_idx && !c.inside_unsafe && !c.pref.translated
+	// Do not allow `&u8(unsafe { nil })` etc, force nil or voidptr cast
+	if from_type.is_number() && to_type.is_ptr() && !c.inside_unsafe && !c.pref.translated
+		&& !c.file.is_translated {
+		if from_sym.language != .c {
+			// TODO make an error
+			c.warn('cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`',
+				node.pos)
+		}
+	}
+
 	// T(0) where T is array or map
 	if node.typ.has_flag(.generic) && to_sym.kind in [.array, .map, .array_fixed]
 		&& node.expr.is_literal() {

vlib/v/checker/tests/cast_expr_T_type_err.out

@@ -1,13 +1,13 @@
-vlib/v/checker/tests/cast_expr_T_type_err.vv:4:9: error: unknown type `A`
-    2 | 
+vlib/v/checker/tests/cast_expr_T_type_err.vv:4:6: error: unknown type `A`
+    2 |
     3 | fn main() {
     4 |     _ = A(0)
       |         ~~~~
-    5 |     _ = &A(0)
+    5 |     _ = &A(unsafe { nil })
     6 | }
-vlib/v/checker/tests/cast_expr_T_type_err.vv:5:9: error: unknown type `A`
+vlib/v/checker/tests/cast_expr_T_type_err.vv:5:6: error: unknown type `A`
     3 | fn main() {
     4 |     _ = A(0)
-    5 |     _ = &A(0)
-      |         ~~~~~
+    5 |     _ = &A(unsafe { nil })
+      |         ~~~~~~~~~~~~~~~~~~
     6 | }

vlib/v/checker/tests/cast_expr_T_type_err.vv

@@ -1,6 +1,6 @@
 module main
 
 fn main() {
-    _ = A(0)
-    _ = &A(0)
+	_ = A(0)
+	_ = &A(unsafe { nil })
 }

vlib/v/checker/tests/fixed_array_conv.out

@@ -3,17 +3,17 @@ vlib/v/checker/tests/fixed_array_conv.vv:3:5: notice: left-side of assignment ex
     2 | mut p := unsafe { nil }
     3 | p = arr
       |     ~~~
-    4 | mut ip := &int(0)
+    4 | mut ip := &int(unsafe { nil })
     5 | ip = arr
 vlib/v/checker/tests/fixed_array_conv.vv:5:6: notice: left-side of assignment expects a mutable reference, but variable `arr` is immutable, declare it with `mut` to make it mutable or clone it
     3 | p = arr
-    4 | mut ip := &int(0)
+    4 | mut ip := &int(unsafe { nil })
     5 | ip = arr
       |      ~~~
     6 | _ = &int(arr)
     7 | _ = p
 vlib/v/checker/tests/fixed_array_conv.vv:6:5: warning: cannot cast a fixed array (use e.g. `&arr[0]` instead)
-    4 | mut ip := &int(0)
+    4 | mut ip := &int(unsafe { nil })
     5 | ip = arr
     6 | _ = &int(arr)
       |     ~~~~~~~~~
@@ -24,25 +24,25 @@ vlib/v/checker/tests/fixed_array_conv.vv:3:3: error: mismatched types `voidptr`
     2 | mut p := unsafe { nil }
     3 | p = arr
       |   ^
-    4 | mut ip := &int(0)
+    4 | mut ip := &int(unsafe { nil })
     5 | ip = arr
 vlib/v/checker/tests/fixed_array_conv.vv:3:5: error: cannot assign to `p`: expected `voidptr`, not `[2]int`
     1 | arr := [2, 3]!
     2 | mut p := unsafe { nil }
     3 | p = arr
       |     ~~~
-    4 | mut ip := &int(0)
+    4 | mut ip := &int(unsafe { nil })
     5 | ip = arr
 vlib/v/checker/tests/fixed_array_conv.vv:5:4: error: mismatched types `&int` and `[2]int`
     3 | p = arr
-    4 | mut ip := &int(0)
+    4 | mut ip := &int(unsafe { nil })
     5 | ip = arr
       |    ^
     6 | _ = &int(arr)
     7 | _ = p
 vlib/v/checker/tests/fixed_array_conv.vv:5:6: error: cannot assign to `ip`: expected `&int`, not `[2]int`
     3 | p = arr
-    4 | mut ip := &int(0)
+    4 | mut ip := &int(unsafe { nil })
     5 | ip = arr
       |      ~~~
     6 | _ = &int(arr)

vlib/v/checker/tests/fixed_array_conv.vv

@@ -1,7 +1,7 @@
 arr := [2, 3]!
 mut p := unsafe { nil }
 p = arr
-mut ip := &int(0)
+mut ip := &int(unsafe { nil })
 ip = arr
 _ = &int(arr)
 _ = p

vlib/v/checker/tests/globals/cast_expr_T_type_err.out

@@ -1,3 +1,10 @@
+vlib/v/checker/tests/globals/cast_expr_T_type_err.vv:5:8: warning: cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`
+    3 | __global (
+    4 |     fo = A(0)
+    5 |     fo1 = &A(0)
+      |           ~~~~~
+    6 | )
+    7 |
 vlib/v/checker/tests/globals/cast_expr_T_type_err.vv:4:7: error: unknown type `A`
     2 | 
     3 | __global (

vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.out

@@ -1,3 +1,21 @@
+vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv:7:5: warning: cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`
+    5 | a := 1
+    6 | 
+    7 | _ = &Context(a)
+      |     ~~~~~~~~~~~
+    8 | _ = &Context(b)
+    9 | _ = &Context(1)
+vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv:8:5: warning: cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`
+    6 | 
+    7 | _ = &Context(a)
+    8 | _ = &Context(b)
+      |     ~~~~~~~~~~~
+    9 | _ = &Context(1)
+vlib/v/checker/tests/struct_ptr_cast_int_outside_unsafe_err.vv:9:5: warning: cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`
+    7 | _ = &Context(a)
+    8 | _ = &Context(b)
+    9 | _ = &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 | a := 1
     6 | 

vlib/v/checker/tests/struct_ptr_cast_zero_err.out

@@ -1,3 +1,21 @@
+vlib/v/checker/tests/struct_ptr_cast_zero_err.vv:7:5: warning: cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`
+    5 | b := 0
+    6 | 
+    7 | _ = &Context(0)
+      |     ~~~~~~~~~~~
+    8 | _ = &Context(a)
+    9 | _ = &Context(b)
+vlib/v/checker/tests/struct_ptr_cast_zero_err.vv:8:5: warning: cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`
+    6 | 
+    7 | _ = &Context(0)
+    8 | _ = &Context(a)
+      |     ~~~~~~~~~~~
+    9 | _ = &Context(b)
+vlib/v/checker/tests/struct_ptr_cast_zero_err.vv:9:5: warning: cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`
+    7 | _ = &Context(0)
+    8 | _ = &Context(a)
+    9 | _ = &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 | b := 0
     6 | 

vlib/v/checker/tests/unsafe_generic_call_test.out

@@ -1 +1,8 @@
+vlib/v/checker/tests/unsafe_generic_call_test.vv:8:15: warning: cannot cast a number to a type reference, use `nil` or a voidptr cast first: `&Type(voidptr(123))`
+    6 | 
+    7 | fn test_main() {
+    8 |     pointers := [&int(1234)]
+      |                  ~~~~~~~~~~
+    9 |     length := 1
+   10 |     array := unsafe { arrays.carray_to_varray[&Blah](pointers, length) }
 [&Blah{}]

vlib/v/embed_file/embed_file.v

@@ -26,11 +26,11 @@ pub fn (mut ed EmbedFileData) free() {
 		ed.compression_type.free()
 		if ed.free_compressed {
 			free(ed.compressed)
-			ed.compressed = &u8(0)
+			ed.compressed = &u8(nil)
 		}
 		if ed.free_uncompressed {
 			free(ed.uncompressed)
-			ed.uncompressed = &u8(0)
+			ed.uncompressed = &u8(nil)
 		}
 	}
 }

vlib/v/fmt/tests/pointer_casts_keep.vv

@@ -13,10 +13,10 @@ fn main() {
 		dump(voidptr(ppb))
 		dump(voidptr(pppb))
 		dump(voidptr(ppppb))
-		pc := &char(0)
-		ppc := &&char(0)
-		pppc := &&&char(0)
-		ppppc := &&&&char(0)
+		pc := &char(nil)
+		ppc := &&char(nil)
+		pppc := &&&char(nil)
+		ppppc := &&&&char(nil)
 		dump(voidptr(pc))
 		dump(voidptr(ppc))
 		dump(voidptr(pppc))

vlib/v/gen/c/cgen.v

@@ -96,7 +96,7 @@ mut:
 	is_assign_lhs             bool // inside left part of assign expr (for array_set(), etc)
 	is_void_expr_stmt         bool // ExprStmt whose result is discarded
 	is_arraymap_set           bool // map or array set value state
-	is_amp                    bool // for `&Foo{}` to merge PrefixExpr `&` and StructInit `Foo{}`; also for `&u8(0)` etc
+	is_amp                    bool // for `&Foo{}` to merge PrefixExpr `&` and StructInit `Foo{}`; also for `&u8(unsafe { nil })` etc
 	is_sql                    bool // Inside `sql db{}` statement, generating sql instead of C (e.g. `and` instead of `&&` etc)
 	is_shared                 bool // for initialization of hidden mutex in `[rw]shared` literals
 	is_vlines_enabled         bool // is it safe to generate #line directives when -g is passed

vlib/v/tests/aliases/alias_char_type_reference_test.v

@@ -1,8 +1,8 @@
 type ALchar = char
 
 fn test_alias_char_type_reference() {
-	c1 := &char(0)
-	c2 := &ALchar(0)
+	c1 := &char(unsafe { nil })
+	c2 := &ALchar(unsafe { nil })
 	println('${typeof(c1).name} ${c1}')
 	assert '${c1}' == '0'
 	println('${typeof(c2).name} ${c2}')

vlib/v/tests/builtin_strings_and_interpolation/string_interpolation_test.v

@@ -96,7 +96,7 @@ fn test_inttypes_string_interpolation() {
 	i := -1622999040 // -0x60BD 0000
 	ui := u32(3421958087) // 0xCBF6 EFC7
 	vp := voidptr(ui)
-	mut bp := &u8(0)
+	mut bp := &u8(unsafe { nil })
 	$if x64 {
 		bp = &u8(15541149836) // 0x3 9E53 208C
 	} $else {

vlib/v/tests/multiret_with_ptrtype_test.v

@@ -3,7 +3,7 @@ fn multi_voidptr_ret() (voidptr, bool) {
 }
 
 fn multi_byteptr_ret() (&u8, bool) {
-	return &u8(0), true
+	return &u8(unsafe { nil }), true
 }
 
 fn test_multi_ptrtype_ret() {

vlib/v/trace_calls/tracing_calls.c.v

@@ -2,12 +2,12 @@
 module trace_calls
 
 @[markused]
-__global g_stack_base = &u8(0)
+__global g_stack_base = &u8(unsafe { nil })
 __global g_start_time = u64(0)
 
 @[markused]
 pub fn on_call(fname string) {
-	mut volatile pfbase := unsafe { &u8(0) }
+	mut volatile pfbase := &u8(unsafe { nil })
 	volatile fbase := u8(0)
 	ns := current_time() - g_start_time
 	mut ssize := u64(0)

vlib/x/ttf/render_sokol_cpu.v

@@ -131,7 +131,7 @@ pub fn (mut tf_skl TTF_render_Sokol) create_texture() {
 		height:      h
 		num_mipmaps: 0
 		// usage: .dynamic
-		label:         &char(0)
+		label:         &char(unsafe { nil })
 		d3d11_texture: 0
 	}
 	// comment for dynamic