checker: allow ptr++/ptr-- in unsafe{}, for any kind of pointer, except voidptr

vlib/v/checker/checker.v

@@ -4680,15 +4680,16 @@ fn (c &Checker) has_return(stmts []ast.Stmt) ?bool {
 pub fn (mut c Checker) postfix_expr(mut node ast.PostfixExpr) table.Type {
 	typ := c.expr(node.expr)
 	typ_sym := c.table.get_type_symbol(typ)
-	if !typ_sym.is_number() && typ_sym.kind !in [.byteptr, .charptr] {
+	is_non_void_pointer := (typ.is_ptr() || typ.is_pointer()) && typ_sym.kind != .voidptr
+	if !c.inside_unsafe && is_non_void_pointer {
+		c.warn('pointer arithmetic is only allowed in `unsafe` blocks', node.pos)
+	}
+	if !(typ_sym.is_number() || (c.inside_unsafe && is_non_void_pointer)) {
 		c.error('invalid operation: $node.op.str() (non-numeric type `$typ_sym.name`)',
 			node.pos)
 	} else {
 		node.auto_locked, _ = c.fail_if_immutable(node.expr)
 	}
-	if !c.inside_unsafe && (typ.is_ptr() || typ_sym.is_pointer()) {
-		c.warn('pointer arithmetic is only allowed in `unsafe` blocks', node.pos)
-	}
 	return typ
 }
 

vlib/v/embed_file/embed_file.v

@@ -79,7 +79,7 @@ pub fn find_index_entry_by_path(start voidptr, path string) &EmbedFileIndexEntry
 	mut x := &EmbedFileIndexEntry(start)
 	for !(x.path == path || isnil(x.data)) {
 		unsafe {
-			x = &EmbedFileIndexEntry(u64(x) + sizeof(EmbedFileIndexEntry))
+			x++
 		}
 	}
 	$if debug_embed_file_in_prod ? {

vlib/v/tests/ptr_arithmetic_test.v

@@ -1,4 +1,4 @@
-fn test_ptr_arithmetic(){
+fn test_ptr_arithmetic() {
 	unsafe {
 		// Do NOT move this outside unsafe{}.
 		// It causes too much churn in CI when new checks are implemented.
@@ -28,7 +28,43 @@ fn test_ptr_arithmetic_over_byteptr() {
 	assert q == byteptr(9)
 	s := unsafe { q - 1 }
 	assert s == byteptr(8)
-
-	unsafe {q++ q++ q--}
+	unsafe {
+		q++
+		q++
+		q--
+	}
 	assert q == byteptr(10)
 }
+
+struct Abc {
+mut:
+	x int
+	y int
+	z int
+}
+
+fn test_ptr_arithmetic_over_struct() {
+	mut a := [3]Abc{}
+	a[0].x = 10
+	a[1].x = 100
+	a[2].x = 1000
+	mut pa := &a[0]
+	assert pa == &a[0]
+	unsafe {
+		assert pa.x == 10
+		pa++
+		assert u64(pa) - u64(&a[0]) == sizeof(Abc)
+		assert pa.x == 100
+		pa++
+		assert u64(pa) - u64(&a[0]) == 2 * sizeof(Abc)
+		assert pa.x == 1000
+		pa--
+		assert pa.x == 100
+		pa--
+		assert pa.x == 10
+		pa += 2
+		assert pa.x == 1000
+		pa -= 2
+	}
+	assert pa == &a[0]
+}