all: make 0 => unsafe { nil } an error, not a notice

doc/docs.md

@@ -6707,16 +6707,16 @@ struct Node {
 }
 
 // Reference fields must be initialized unless an initial value is declared.
-// Zero (0) is OK but use with caution, it's a nil pointer.
+// Nil is OK but use with caution, it's a nil pointer.
 foo := Node{
-	a: 0
+	a: unsafe { nil }
 }
 bar := Node{
 	a: &foo
 }
 baz := Node{
-	a: 0
-	b: 0
+	a: unsafe { nil }
+	b: unsafe { nil }
 }
 qux := Node{
 	a: &foo

vlib/v/README.md

@@ -51,7 +51,7 @@ and a new scope is created:
 import v.ast
 
 scope := ast.Scope{
-	parent: 0
+	parent: unsafe { nil }
 }
 ```
 after that, you can parse your files.

vlib/v/checker/struct.v

@@ -760,7 +760,7 @@ or use an explicit `unsafe{ a[..] }`, if you do not want a copy of the slice.',
 						&& !got_type.is_any_kind_of_pointer() && !exp_type.has_flag(.option)
 						&& !(init_field.expr is ast.UnsafeExpr && init_field.expr.expr.str() == '0') {
 						if init_field.expr.str() == '0' {
-							c.note('assigning `0` to a reference field is only allowed in `unsafe` blocks',
+							c.error('assigning `0` to a reference field is only allowed in `unsafe` blocks',
 								init_field.pos)
 						} else {
 							c.error('reference field must be initialized with reference',

vlib/v/checker/tests/struct_ref_fields_init_0_err.out

@@ -1,11 +1,11 @@
-vlib/v/checker/tests/struct_ref_fields_init_0_err.vv:6:10: notice: assigning `0` to a reference field is only allowed in `unsafe` blocks
+vlib/v/checker/tests/struct_ref_fields_init_0_err.vv:6:10: error: assigning `0` to a reference field is only allowed in `unsafe` blocks
     4 | 
     5 | fn main() {
     6 |     _ = Foo{0}
       |             ^
     7 |     _ = Foo{
     8 |         foo: 0
-vlib/v/checker/tests/struct_ref_fields_init_0_err.vv:8:3: notice: assigning `0` to a reference field is only allowed in `unsafe` blocks
+vlib/v/checker/tests/struct_ref_fields_init_0_err.vv:8:3: error: assigning `0` to a reference field is only allowed in `unsafe` blocks
     6 |     _ = Foo{0}
     7 |     _ = Foo{
     8 |         foo: 0

vlib/v/parser/tests/invalid_struct_decl_script_err.out

@@ -3,10 +3,10 @@ vlib/v/parser/tests/invalid_struct_decl_script_err.vv:1:1: notice: script mode s
       | ~~~~~
     2 | 
     3 | struct Abc {
-vlib/v/parser/tests/invalid_struct_decl_script_err.vv:3:1: error: all definitions must occur before code in script mode
+vlib/v/parser/tests/invalid_struct_decl_script_err.vv:3:8: error: all definitions must occur before code in script mode
     1 | mynum := 10
     2 | 
     3 | struct Abc {
-      | ~~~~~~
+      |        ~~~
     4 |     x int
     5 | }

vlib/v/parser/v_parser_test.v

@@ -41,7 +41,7 @@ fn test_eval() {
 	vpref := &pref.Preferences{}
 	mut scope := &ast.Scope{
 		start_pos: 0
-		parent: 0
+		parent: unsafe { nil }
 	}
 	mut stmts := []ast.Stmt{}
 	for input in inputs {

vlib/v/tests/builtin_strings_and_interpolation/str_gen_test.v

@@ -209,7 +209,7 @@ fn test_struct_with_struct_pointer() {
 }
 
 fn test_struct_with_nil() {
-	w := Wrapper4{0}
+	w := Wrapper4{unsafe { nil }}
 	assert '${w}' == 'Wrapper4{\n    foo: &nil\n}'
 	assert w.str() == 'Wrapper4{\n    foo: &nil\n}'
 }

vlib/v/tests/builtin_strings_and_interpolation/string_interpolation_struct_test.v

@@ -60,14 +60,14 @@ mut:
 }
 
 fn test_stack_circular_elem_auto_str() {
-	mut elem := Circular{0}
+	mut elem := Circular{unsafe { nil }}
 	elem.next = &elem
 	s := '${elem}'.replace('\n', '|')
 	assert s == 'Circular{|    next: &<circular>|}'
 }
 
 fn test_heap_circular_elem_auto_str() {
-	mut elem := &Circular{0}
+	mut elem := &Circular{unsafe { nil }}
 	elem.next = elem
 	s := '${elem}'.replace('\n', '|')
 	assert s == '&Circular{|    next: &<circular>|}'

vlib/v/tests/builtin_strings_and_interpolation/string_ref_struct_test.v

@@ -1,13 +1,7 @@
 struct Node {
 	val   int
-	left  &Node
-	right &Node
-}
-
-fn test_string_ref_struct() {
-	n := Node{123, 0, 0}
-	println(n.left)
-	assert '${n.left}' == '&nil'
+	left  &Node = unsafe { nil }
+	right &Node = unsafe { nil }
 }
 
 fn test_string_ref_struct_with_nil_instead_of_0() {

vlib/v/tests/generics/generic_fn_assign_generics_struct_test.v

@@ -38,7 +38,7 @@ fn new[T]() &Node[T] {
 }
 
 fn (mut n Node[T]) add(val T) {
-	node := &Node[T]{val, 0}
+	node := &Node[T]{val, unsafe { nil }}
 	n.next = node
 }
 

vlib/v/tests/generics/generics_assign_reference_generic_struct_test.v

@@ -14,8 +14,8 @@ pub fn list_new[T]() List[T] {
 }
 
 pub fn (mut l List[T]) add(value T) {
-	mut node := &ListNode[T]{value, 0}
-	if unsafe { l.head == 0 } {
+	mut node := &ListNode[T]{value, unsafe { nil }}
+	if unsafe { l.head == nil } {
 		l.head = node
 	} else {
 		node.next = l.head

vlib/v/tests/generics/generics_return_generics_struct_test.v

@@ -136,8 +136,8 @@ fn (mut node ListNode[T]) test() &ListNode[T] {
 }
 
 fn test_generics_return_generic_struct_field() {
-	mut node1 := &ListNode[int]{100, 0}
-	mut node2 := &ListNode[int]{200, 0}
+	mut node1 := &ListNode[int]{100, unsafe { nil }}
+	mut node2 := &ListNode[int]{200, unsafe { nil }}
 	node1.next = node2
 	ret := node1.test()
 	println(ret)

vlib/v/tests/generics/generics_return_recursive_generics_struct_test.v

@@ -1,13 +1,12 @@
 struct Node[T] {
 mut:
 	val  T
-	next &Node[T]
+	next &Node[T] = unsafe { nil }
 }
 
 fn make_node[T](val []T) Node[T] {
 	return Node[T]{
 		val: val[0]
-		next: 0
 	}
 }
 

vlib/v/tests/generics/generics_with_generics_struct_init_test.v

@@ -15,7 +15,7 @@ fn create[T](arr []T) &List[T] {
 	assert arr.len > 0
 	mut n := &ListNode[T]{
 		val:  arr[0]
-		next: 0
+		next: unsafe { nil }
 	}
 	mut l := &List[T]{
 		first: n

vlib/v/tests/sumtypes/sumtype_test.v

@@ -50,7 +50,7 @@ fn test_sum_type_match() {
 		baz: &IntAndStr{
 			foo: 3
 			bar: 'hello'
-			baz: 0
+			baz: unsafe { nil }
 		}
 	}) == 'This is the string representation of "5_hi_hello"'
 	assert as_string(true) == 'This is the string representation of "true"'
@@ -532,7 +532,7 @@ fn sumtype_match_with_string_interpolation(code int) string {
 				baz: &IntAndStr{
 					foo: 3
 					bar: 'hello'
-					baz: 0
+					baz: unsafe { nil }
 				}
 			})
 			match bar {