cgen: fix array map with it selector expr, used as an it method closure (#17968)

vlib/v/checker/checker.v

@@ -1471,6 +1471,7 @@ fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 		node.has_hidden_receiver = true
 		method.name = ''
 		fn_type := ast.new_type(c.table.find_or_register_fn_type(method, false, true))
+		node.typ = fn_type
 		return fn_type
 	}
 	if sym.kind !in [.struct_, .aggregate, .interface_, .sum_type] {

vlib/v/checker/fn.v

@@ -2444,8 +2444,16 @@ fn (mut c Checker) array_builtin_method_call(mut node ast.CallExpr, left_type as
 		c.check_map_and_filter(true, elem_typ, node)
 		arg_sym := c.table.sym(arg_type)
 		ret_type := match arg_sym.info {
-			ast.FnType { arg_sym.info.func.return_type }
-			else { arg_type }
+			ast.FnType {
+				if node.args[0].expr is ast.SelectorExpr {
+					arg_type
+				} else {
+					arg_sym.info.func.return_type
+				}
+			}
+			else {
+				arg_type
+			}
 		}
 		node.return_type = c.table.find_or_register_array(c.unwrap_generic(ret_type))
 		if node.return_type.has_flag(.shared_f) {

vlib/v/gen/c/array.v

@@ -421,12 +421,24 @@ fn (mut g Gen) gen_array_map(node ast.CallExpr) {
 	ret_sym := g.table.sym(node.return_type)
 	inp_sym := g.table.sym(node.receiver_type)
 	ret_info := ret_sym.info as ast.Array
-	ret_elem_type := g.typ(ret_info.elem_type)
+	mut ret_elem_type := g.typ(ret_info.elem_type)
 	inp_info := inp_sym.info as ast.Array
 	inp_elem_type := g.typ(inp_info.elem_type)
 	if inp_sym.kind != .array {
 		verror('map() requires an array')
 	}
+
+	mut closure_var_decl := ''
+	if node.args[0].expr is ast.SelectorExpr {
+		if node.args[0].expr.typ != ast.void_type {
+			var_sym := g.table.sym(node.args[0].expr.typ)
+			if var_sym.info is ast.FnType {
+				ret_elem_type = 'voidptr'
+				closure_var_decl = g.fn_var_signature(var_sym.info.func.return_type, var_sym.info.func.params.map(it.typ),
+					'ti')
+			}
+		}
+	}
 	g.empty_line = true
 	noscan := g.check_noscan(ret_info.elem_type)
 	has_infix_left_var_name := g.write_prepared_tmp_value(tmp, node, ret_typ, '{0}')
@@ -473,7 +485,11 @@ fn (mut g Gen) gen_array_map(node ast.CallExpr) {
 			g.expr(node.args[0].expr)
 		}
 		else {
+			if closure_var_decl != '' {
+				g.write('${closure_var_decl} = ')
+			} else {
 				g.write('${ret_elem_type} ti = ')
+			}
 			g.expr(node.args[0].expr)
 		}
 	}

vlib/v/tests/map_with_selector_test.v

@@ -0,0 +1,9 @@
+fn test_main() {
+	k := [10, 20, 30]
+	println(k.map(it.hex()))
+	dump(k.map(it.hex))
+	a := k.map(it.hex)
+	assert dump(a[0]()) == 'a'
+	assert dump(a[1]()) == '14'
+	assert dump(a[2]()) == '1e'
+}