checker: fix infix arithmetic on explicit struct pointers

vlib/v/checker/infix.v

@@ -198,6 +198,10 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 		}
 	}
 	mut return_type := left_type
+	left_is_explicit_ptr := left_type.is_any_kind_of_pointer() && !node.left.is_auto_deref_var()
+		&& left_final_sym.kind != .voidptr
+	right_is_explicit_ptr := right_type.is_any_kind_of_pointer() && !node.right.is_auto_deref_var()
+		&& right_final_sym.kind != .voidptr
 
 	if node.op != .key_is {
 		match mut node.left {
@@ -459,7 +463,8 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 				c.error('infix `${node.op}` is not defined for pointer values', left_right_pos)
 			}
 
-			if !c.pref.translated && left_sym.kind in [.array, .array_fixed, .map, .struct] {
+			if !c.pref.translated && !left_is_explicit_ptr
+				&& left_sym.kind in [.array, .array_fixed, .map, .struct] {
 				if left_sym.has_method_with_generic_parent(op_str) {
 					if method := left_sym.find_method_with_generic_parent(op_str) {
 						return_type = method.return_type
@@ -477,7 +482,8 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 							left_right_pos)
 					}
 				}
-			} else if !c.pref.translated && right_sym.kind in [.array, .array_fixed, .map, .struct] {
+			} else if !c.pref.translated && !right_is_explicit_ptr
+				&& right_sym.kind in [.array, .array_fixed, .map, .struct] {
 				if right_sym.has_method_with_generic_parent(op_str) {
 					if method := right_sym.find_method_with_generic_parent(op_str) {
 						return_type = method.return_type
@@ -949,7 +955,7 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 			c.error('infix expr: cannot use `${error_right_sym.name}` (right expression) as `${error_left_sym.name}`',
 				left_right_pos)
 		} else if left_type.is_ptr() {
-			for_ptr_op := c.table.type_is_for_pointer_arithmetic(left_type)
+			for_ptr_op := left_is_explicit_ptr || c.table.type_is_for_pointer_arithmetic(left_type)
 			if left_sym.language == .v && !c.pref.translated && !c.inside_unsafe && !for_ptr_op
 				&& right_type.is_int() {
 				sugg := ' (you can use it inside an `unsafe` block)'

vlib/v/checker/tests/pointer_ops.out

@@ -61,13 +61,6 @@ vlib/v/checker/tests/pointer_ops.vv:15:3: error: infix `%` is not defined for po
       |         ~~~~~~~
    16 |     }
    17 | }
-vlib/v/checker/tests/pointer_ops.vv:15:3: error: mismatched types `&Foo` and `int literal`
-   13 |         _ = p[3]
-   14 |         mut foo := &Foo{}
-   15 |         foo % 3
-      |         ~~~~~~~
-   16 |     }
-   17 | }
 vlib/v/checker/tests/pointer_ops.vv:22:7: error: `+` cannot be used with `voidptr`
    20 |     unsafe {
    21 |         mut p := nil
@@ -131,10 +124,3 @@ vlib/v/checker/tests/pointer_ops.vv:30:3: error: infix `%` is not defined for po
       |         ~~~~~~~
    31 |     }
    32 | }
-vlib/v/checker/tests/pointer_ops.vv:30:3: error: mismatched types `&Foo` and `int literal`
-   28 |         _ = p[3]
-   29 |         mut foo := &Foo{}
-   30 |         foo % 3
-      |         ~~~~~~~
-   31 |     }
-   32 | }

vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.out

@@ -26,3 +26,31 @@ vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.vv:12:6: warnin
       |         ~~~~~
    13 |     _ := q
    14 |     _ := v
+vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.vv:23:11: warning: pointer arithmetic is only allowed in `unsafe` blocks
+   21 | fn test_struct_ptr_infix() {
+   22 |     v := Foo{}
+   23 |     mut q := &v - 1
+      |              ~~~~~~
+   24 |     q = q + 3
+   25 |     _ := q
+vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.vv:24:6: warning: pointer arithmetic is only allowed in `unsafe` blocks
+   22 |     v := Foo{}
+   23 |     mut q := &v - 1
+   24 |     q = q + 3
+      |         ~~~~~
+   25 |     _ := q
+   26 |     _ := v
+vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.vv:32:11: warning: pointer arithmetic is only allowed in `unsafe` blocks
+   30 |     v := Foo{}
+   31 |     p := &v
+   32 |     mut q := &p - 1
+      |              ~~~~~~
+   33 |     q = q + 3
+   34 |     _ := q
+vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.vv:33:6: warning: pointer arithmetic is only allowed in `unsafe` blocks
+   31 |     p := &v
+   32 |     mut q := &p - 1
+   33 |     q = q + 3
+      |         ~~~~~
+   34 |     _ := q
+   35 |     _ := p

vlib/v/checker/tests/unsafe_pointer_arithmetic_should_be_checked.vv

@@ -13,3 +13,24 @@ fn test_ptr_infix() {
 	_ := q
 	_ := v
 }
+
+struct Foo {
+	x int
+}
+
+fn test_struct_ptr_infix() {
+	v := Foo{}
+	mut q := &v - 1
+	q = q + 3
+	_ := q
+	_ := v
+}
+
+fn test_ptr_to_struct_ptr_infix() {
+	v := Foo{}
+	p := &v
+	mut q := &p - 1
+	q = q + 3
+	_ := q
+	_ := p
+}

vlib/v/tests/pointers/ptr_arithmetic_test.v

@@ -68,3 +68,28 @@ fn test_ptr_arithmetic_over_struct() {
 	}
 	assert pa == unsafe { &a[0] }
 }
+
+fn test_ptr_infix_arithmetic_over_struct() {
+	mut a := [3]Abc{}
+	a[0].x = 10
+	a[1].x = 100
+	a[2].x = 1000
+	unsafe {
+		pa := &a[0]
+		next := pa + 1
+		assert next.x == 100
+		last := next + 1
+		assert last.x == 1000
+		back := last - 2
+		assert back.x == 10
+
+		refs := [&a[0], &a[1], &a[2]]
+		ppa := &refs[0]
+		next_ptr := ppa + 1
+		assert (*next_ptr).x == 100
+		last_ptr := next_ptr + 1
+		assert (*last_ptr).x == 1000
+		back_ptr := last_ptr - 2
+		assert (*back_ptr).x == 10
+	}
+}