all: do not allow uninitialized function pointers

vlib/cli/command.v

@@ -18,9 +18,9 @@ pub mut:
 	description     string
 	man_description string
 	version         string
-	pre_execute     FnCommandCallback
-	execute         FnCommandCallback
-	post_execute    FnCommandCallback
+	pre_execute     FnCommandCallback = unsafe { nil }
+	execute         FnCommandCallback = unsafe { nil }
+	post_execute    FnCommandCallback = unsafe { nil }
 	disable_help    bool
 	disable_man     bool
 	disable_version bool

vlib/datatypes/bloom_filter.v

@@ -4,13 +4,22 @@ module datatypes
 
 [heap]
 struct BloomFilter[T] {
-	hash_func     fn (T) u32 // hash function, input [T] , output u32
-	table_size    int        // every entry is one-bit, packed into `table`
-	num_functions int        // 1~16
+	// TODO V bug
+	hash_func fn (T) u32 = unsafe { nil } // hash function, input [T] , output u32
+	// hash_func     fn (T) u32 = empty_cb // hash function, input [T] , output u32
+	table_size    int // every entry is one-bit, packed into `table`
+	num_functions int // 1~16
 mut:
 	table []u8
 }
 
+/*
+TODO maybe allow pointing to generic fns?
+fn empty_cb[T](x T) u32 {
+	panic('empty BloomFilter.hash_func callback')
+}
+*/
+
 const (
 	// Salt values(random values).  These salts are XORed with the output of the hash function to give multiple unique hashes.
 	salts = [

vlib/eventbus/eventbus.v

@@ -19,8 +19,8 @@ mut:
 
 struct EventHandler[T] {
 	name     T
-	handler  EventHandlerFn
-	receiver voidptr = unsafe { nil }
+	handler  EventHandlerFn = unsafe { nil }
+	receiver voidptr        = unsafe { nil }
 	once     bool
 }
 

vlib/fontstash/fontstash_structs.c.v

@@ -6,15 +6,15 @@ pub struct C.FONSparams {
 	flags   char
 	userPtr voidptr
 	// int (*renderCreate)(void* uptr, int width, int height)
-	renderCreate fn (uptr voidptr, width int, height int) int
+	renderCreate fn (uptr voidptr, width int, height int) int = unsafe { nil }
 	// int (*renderResize)(void* uptr, int width, int height)
-	renderResize fn (uptr voidptr, width int, height int) int
+	renderResize fn (uptr voidptr, width int, height int) int = unsafe { nil }
 	// void (*renderUpdate)(void* uptr, int* rect, const unsigned char* data)
-	renderUpdate fn (uptr voidptr, rect &int, data &u8)
+	renderUpdate fn (uptr voidptr, rect &int, data &u8) = unsafe { nil }
 	// void (*renderDraw)(void* uptr, const float* verts, const float* tcoords, const unsigned int* colors, int nverts)
-	renderDraw fn (uptr voidptr, verts &f32, tcoords &f32, colors &u32, nverts int)
+	renderDraw fn (uptr voidptr, verts &f32, tcoords &f32, colors &u32, nverts int) = unsafe { nil }
 	// void (*renderDelete)(void* uptr)
-	renderDelete fn (uptr voidptr)
+	renderDelete fn (uptr voidptr) = unsafe { nil }
 }
 
 pub struct C.FONSquad {

vlib/regex/regex.v

@@ -248,7 +248,7 @@ mut:
 	// counters for quantifier check (repetitions)
 	rep int
 	// validator function pointer
-	validator FnValidator
+	validator FnValidator = unsafe { nil }
 	// groups variables
 	group_neg bool // negation flag for the group, 0 => no negation > 0 => negataion
 	group_rep int  // repetition of the group
@@ -376,7 +376,7 @@ fn (mut re RE) reset_src() {
 ******************************************************************************/
 struct BslsStruct {
 	ch        rune        // meta char
-	validator FnValidator // validator function pointer
+	validator FnValidator = unsafe { nil } // validator function pointer
 }
 
 const (
@@ -463,7 +463,7 @@ mut:
 	cc_type   int         // type of cc token
 	ch0       rune        // first char of the interval a-b  a in this case
 	ch1       rune        // second char of the interval a-b b in this case
-	validator FnValidator // validator function pointer
+	validator FnValidator = unsafe { nil } // validator function pointer
 }
 
 enum CharClass_parse_state {

vlib/sokol/gfx/gfx_allocator_and_logger.c.v

@@ -5,14 +5,14 @@ import sokol.memory
 [typedef]
 pub struct C.sg_allocator {
 pub mut:
-	alloc     memory.FnAllocatorAlloc
-	free      memory.FnAllocatorFree
+	alloc     memory.FnAllocatorAlloc = unsafe { nil }
+	free      memory.FnAllocatorFree  = unsafe { nil }
 	user_data voidptr
 }
 
 [typedef]
 pub struct C.sg_logger {
 pub mut:
-	log_cb    memory.FnLogCb
+	log_cb    memory.FnLogCb = unsafe { nil }
 	user_data voidptr
 }

vlib/sokol/gfx/gfx_structs.c.v

@@ -46,17 +46,17 @@ pub type GLContextDesc = C.sg_gl_context_desc
 
 struct C.sg_metal_context_desc {
 	device                   voidptr
-	renderpass_descriptor_cb fn () voidptr
-	drawable_cb              fn () voidptr
+	renderpass_descriptor_cb fn () voidptr = unsafe { nil }
+	drawable_cb              fn () voidptr = unsafe { nil }
 }
 
 pub type MetalContextDesc = C.sg_metal_context_desc
 
 struct C.sg_d3d11_context_desc {
 	device                voidptr
 	device_context        voidptr
-	render_target_view_cb fn () voidptr
-	depth_stencil_view_cb fn () voidptr
+	render_target_view_cb fn () voidptr = unsafe { nil }
+	depth_stencil_view_cb fn () voidptr = unsafe { nil }
 }
 
 pub type D3D11ContextDesc = C.sg_d3d11_context_desc

vlib/sokol/sapp/sapp_allocator_and_logger.c.v

@@ -5,14 +5,14 @@ import sokol.memory
 [typedef]
 pub struct C.sapp_allocator {
 pub mut:
-	alloc     memory.FnAllocatorAlloc
-	free      memory.FnAllocatorFree
+	alloc     memory.FnAllocatorAlloc = unsafe { nil }
+	free      memory.FnAllocatorFree  = unsafe { nil }
 	user_data voidptr
 }
 
 [typedef]
 pub struct C.sapp_logger {
 pub mut:
-	log_cb    memory.FnLogCb
+	log_cb    memory.FnLogCb = unsafe { nil }
 	user_data voidptr
 }

vlib/sokol/sapp/sapp_structs.c.v

@@ -37,18 +37,19 @@ pub type IconDesc = C.sapp_icon_desc
 [typedef]
 pub struct C.sapp_desc {
 pub:
-	init_cb    fn () // these are the user-provided callbacks without user data
-	frame_cb   fn ()
-	cleanup_cb fn ()
-	event_cb   fn (&Event) //&sapp_event)
-	fail_cb    fn (&u8)
+	// these are the user-provided callbacks without user data
+	init_cb    fn ()       = unsafe { nil }
+	frame_cb   fn ()       = unsafe { nil }
+	cleanup_cb fn ()       = unsafe { nil }
+	event_cb   fn (&Event) = unsafe { nil } // &sapp_event
+	fail_cb    fn (&u8)    = unsafe { nil }
 
 	user_data           voidptr // these are the user-provided callbacks with user data
-	init_userdata_cb    fn (voidptr)
-	frame_userdata_cb   fn (voidptr)
-	cleanup_userdata_cb fn (voidptr)
-	event_userdata_cb   fn (&Event, voidptr)
-	fail_userdata_cb    fn (&char, voidptr)
+	init_userdata_cb    fn (voidptr) = unsafe { nil }
+	frame_userdata_cb   fn (voidptr) = unsafe { nil }
+	cleanup_userdata_cb fn (voidptr) = unsafe { nil }
+	event_userdata_cb   fn (&Event, voidptr) = unsafe { nil }
+	fail_userdata_cb    fn (&char, voidptr)  = unsafe { nil }
 
 	width                        int      // the preferred width of the window / canvas
 	height                       int      // the preferred height of the window / canvas

vlib/sokol/sfons/sfons_funcs.c.v

@@ -6,8 +6,8 @@ import sokol.memory
 [typedef]
 pub struct C.sfons_allocator_t {
 pub:
-	alloc     memory.FnAllocatorAlloc
-	free      memory.FnAllocatorFree
+	alloc     memory.FnAllocatorAlloc = unsafe { nil }
+	free      memory.FnAllocatorFree  = unsafe { nil }
 	user_data voidptr
 }
 

vlib/sokol/sgl/sgl_allocator_and_logger.c.v

@@ -5,14 +5,14 @@ import sokol.memory
 [typedef]
 pub struct C.sgl_allocator_t {
 pub mut:
-	alloc     memory.FnAllocatorAlloc
-	free      memory.FnAllocatorFree
+	alloc     memory.FnAllocatorAlloc = unsafe { nil }
+	free      memory.FnAllocatorFree  = unsafe { nil }
 	user_data voidptr
 }
 
 [typedef]
 pub struct C.sgl_logger_t {
 pub mut:
-	log_cb    memory.FnLogCb
+	log_cb    memory.FnLogCb = unsafe { nil }
 	user_data voidptr
 }

vlib/sync/pool/pool.v

@@ -24,9 +24,15 @@ mut:
 
 pub type ThreadCB = fn (mut p PoolProcessor, idx int, task_id int) voidptr
 
+fn empty_cb(mut p PoolProcessor, idx int, task_id int) voidptr {
+	unsafe {
+		return nil
+	}
+}
+
 pub struct PoolProcessorConfig {
 	maxjobs  int
-	callback ThreadCB
+	callback ThreadCB = empty_cb
 }
 
 // new_pool_processor returns a new PoolProcessor instance.

vlib/toml/ast/walker/walker.v

@@ -15,7 +15,7 @@ pub interface Modifier {
 pub type InspectorFn = fn (value &ast.Value, data voidptr) !
 
 struct Inspector {
-	inspector_callback InspectorFn
+	inspector_callback InspectorFn = unsafe { nil }
 mut:
 	data voidptr
 }

vlib/v/ast/walker/walker.v

@@ -10,8 +10,12 @@ mut:
 
 pub type InspectorFn = fn (node &ast.Node, data voidptr) bool
 
+fn empty_callback(node &ast.Node, data voidptr) bool {
+	panic('empty ast.walker')
+}
+
 struct Inspector {
-	inspector_callback InspectorFn
+	inspector_callback InspectorFn = empty_callback
 mut:
 	data voidptr
 }

vlib/v/checker/struct.v

@@ -70,6 +70,19 @@ fn (mut c Checker) struct_decl(mut node ast.StructDecl) {
 					}
 				}
 			}
+			// Do not allow uninitialized `fn` fields, or force `?fn`
+			// (allow them in `C.` structs)
+			if !c.is_builtin_mod && node.language == .v {
+				sym := c.table.sym(field.typ)
+				if sym.kind == .function {
+					if !field.typ.has_flag(.option) && !field.has_default_expr
+						&& field.attrs.filter(it.name == 'required').len == 0 {
+						error_msg := 'uninitialized `fn` struct fields are not allowed, since they can result in segfaults; use `?fn` or initialize the field with `=` (if you absolutely want to have unsafe function pointers, use `= unsafe { nil }`)'
+						c.note(error_msg, field.pos)
+					}
+				}
+			}
+
 			if field.has_default_expr {
 				c.expected_type = field.typ
 				field.default_expr_typ = c.expr(mut field.default_expr)

vlib/v/checker/tests/duplicate_field_method_err.vv

@@ -1,5 +1,5 @@
-struct St{
-	attr fn()
+struct St {
+	attr fn () = unsafe { nil }
 }
 
 fn (s St) attr() {}

vlib/v/checker/tests/fn_check_for_matching_option_result_in_fields.out

@@ -1,7 +1,13 @@
+vlib/v/checker/tests/fn_check_for_matching_option_result_in_fields.vv:2:2: notice: uninitialized `fn` struct fields are not allowed, since they can result in segfaults; use `?fn` or initialize the field with `=` (if you absolutely want to have unsafe function pointers, use `= unsafe { nil }`)
+    1 | struct Abc {
+    2 |     f fn (voidptr)
+      |     ~~~~~~~~~~~~~~
+    3 | }
+    4 |
 vlib/v/checker/tests/fn_check_for_matching_option_result_in_fields.vv:7:3: error: cannot assign to field `f`: expected `fn (voidptr)`, not `fn (voidptr) ?`
     5 | fn main() {
     6 |     a := Abc{
     7 |         f: fn (data voidptr) ? {}
       |         ~~~~~~~~~~~~~~~~~~~~~~~~~
     8 |     }
-    9 |     println(a)
+    9 |     println(a)

vlib/v/checker/tests/generics_struct_init_err.out

@@ -1,3 +1,10 @@
+vlib/v/checker/tests/generics_struct_init_err.vv:14:2: notice: uninitialized `fn` struct fields are not allowed, since they can result in segfaults; use `?fn` or initialize the field with `=` (if you absolutely want to have unsafe function pointers, use `= unsafe { nil }`)
+   12 | 
+   13 | struct FnHolder2[T] {
+   14 |     func fn (int) int
+      |     ~~~~~~~~~~~~~~~~~
+   15 | }
+   16 |
 vlib/v/checker/tests/generics_struct_init_err.vv:67:8: error: could not infer generic type `T` in generic struct `FnHolder2[T]`
    65 |     ret = holder_call_22(neg, 5)
    66 |     assert ret == -5
@@ -6,14 +13,14 @@ vlib/v/checker/tests/generics_struct_init_err.vv:67:8: error: could not infer ge
    68 |     assert ret == -6
    69 | }
 vlib/v/checker/tests/generics_struct_init_err.vv:22:7: error: generic struct init must specify type parameter, e.g. Foo[T]
-   20 |
+   20 | 
    21 | fn holder_call_1[T](func T, a int) int {
    22 |     h := FnHolder1{func}
       |          ~~~~~~~~~~~~~~~
    23 |     return h.call(a)
    24 | }
 vlib/v/checker/tests/generics_struct_init_err.vv:27:7: error: generic struct init must specify type parameter, e.g. Foo[T]
-   25 |
+   25 | 
    26 | fn holder_call_2[T](func T, a int) int {
    27 |     h := FnHolder2{func}
       |          ~~~~~~~~~~~~~~~
@@ -34,14 +41,14 @@ vlib/v/checker/tests/generics_struct_init_err.vv:39:7: error: generic struct ini
    40 |     return h.call(a)
    41 | }
 vlib/v/checker/tests/generics_struct_init_err.vv:44:9: error: generic struct init must specify type parameter, e.g. Foo[T]
-   42 |
+   42 | 
    43 | fn holder_call_12[T](func T, a int) int {
    44 |     return FnHolder1{func}.call(a)
       |            ~~~~~~~~~~~~~~~
    45 | }
    46 |
 vlib/v/checker/tests/generics_struct_init_err.vv:48:9: error: generic struct init must specify type parameter, e.g. Foo[T]
-   46 |
+   46 | 
    47 | fn holder_call_22[T](func T, a int) int {
    48 |     return FnHolder2{func}.call(a)
       |            ~~~~~~~~~~~~~~~

vlib/v/checker/tests/method_call_arg_no_mut_err.vv

@@ -9,7 +9,7 @@ struct Alarm {
 struct Clock {
 mut:
 	arr       []Alarm
-	alarm_fkt Fkt
+	alarm_fkt Fkt = unsafe { nil }
 }
 
 fn fkt(mut a Alarm) {

vlib/v/checker/tests/option_fn_err.vv

@@ -13,7 +13,7 @@ const (
 )
 
 struct Data {
-	f fn (int)
+	f fn (int) = unsafe { nil }
 mut:
 	value int  = bar(0)
 	opt   ?int = bar(0)

vlib/v/checker/tests/struct_field_init_with_nobody_anon_fn_err.vv

@@ -1,5 +1,5 @@
 struct App {
-	cb fn(x int) // the function signature doesn't make a difference
+	cb fn(x int) = unsafe { nil } // the function signature doesn't make a difference
 }
 
 fn main() {

vlib/v/checker/tests/struct_field_type_err.vv

@@ -2,8 +2,8 @@ struct Data {
 mut:
 	n    int
 	b    bool
-	f1   fn (voidptr)
-	f2   fn (...voidptr)
+	f1   fn (voidptr) [required]
+	f2   fn (...voidptr) [required]
 	data &Data
 }
 

vlib/v/checker/tests/unknown_type_in_anon_fn.out

@@ -1,7 +1,7 @@
 vlib/v/checker/tests/unknown_type_in_anon_fn.vv:5:10: error: unknown type `Another`
     3 | struct Struc{
     4 | mut:
-    5 |     f fn (s Another, i int)?
+    5 |     f fn (s Another, i int)? [required]
       |             ~~~~~~~
     6 | }
     7 |

vlib/v/checker/tests/unknown_type_in_anon_fn.vv

@@ -2,7 +2,7 @@ module main
 
 struct Struc{
 mut:
-	f fn (s Another, i int)?
+	f fn (s Another, i int)? [required]
 }
 
 fn main() {}