checker: always trigger error for anon fns without a body block (#16358)

vlib/v/checker/fn.v

@@ -410,6 +410,9 @@ fn (mut c Checker) anon_fn(mut node ast.AnonFn) ast.Type {
 		c.inside_anon_fn = keep_inside_anon
 		c.cur_anon_fn = keep_anon_fn
 	}
+	if node.decl.no_body {
+		c.error('anonymous function must declare a body', node.decl.pos)
+	}
 	for param in node.decl.params {
 		if param.name.len == 0 {
 			c.error('use `_` to name an unused parameter', param.pos)

vlib/v/checker/struct.v

@@ -450,15 +450,6 @@ pub fn (mut c Checker) struct_init(mut node ast.StructInit) ast.Type {
 							field.pos)
 					}
 				}
-				if field_type_sym.kind == .function && field_type_sym.language == .v {
-					pos := field.expr.pos()
-					if mut field.expr is ast.AnonFn {
-						if field.expr.decl.no_body {
-							c.error('cannot initialize the fn field with anonymous fn that does not have a body',
-								pos)
-						}
-					}
-				}
 				node.fields[i].typ = expr_type
 				node.fields[i].expected_type = field_info.typ
 

vlib/v/checker/tests/anon_fn_without_body.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/anon_fn_without_body.vv:4:10: error: anonymous function must declare a body
+    2 |
+    3 | fn main() {
+    4 |     func := fn () int
+      |             ~~~~~~~~~
+    5 |
+    6 |     println(func())

vlib/v/checker/tests/anon_fn_without_body.vv

@@ -0,0 +1,7 @@
+module main
+
+fn main() {
+	func := fn () int
+
+	println(func())
+}

vlib/v/checker/tests/globals/global_anon_fn_without_body.out

@@ -0,0 +1,3 @@
+vlib/v/checker/tests/globals/global_anon_fn_without_body.vv:1:14: error: anonymous function must declare a body
+    1 | __global f = fn ()
+      |              ~~~~~

vlib/v/checker/tests/globals/global_anon_fn_without_body.vv

@@ -0,0 +1 @@
+__global f = fn ()

vlib/v/checker/tests/struct_field_init_with_nobody_anon_fn_err.out

@@ -1,4 +1,4 @@
-vlib/v/checker/tests/struct_field_init_with_nobody_anon_fn_err.vv:7:7: error: cannot initialize the fn field with anonymous fn that does not have a body
+vlib/v/checker/tests/struct_field_init_with_nobody_anon_fn_err.vv:7:7: error: anonymous function must declare a body
     5 | fn main() {
     6 |     _ = App{
     7 |         cb: fn(x int)  // Note the missing `{}` (the function body) here