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

Author: medvednikov

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`.