Move box_vec to its own module

Author: Y-Nak

clippy_lints/src/types/box_vec.rs

@@ -0,0 +1,22 @@
+use rustc_hir::{self as hir, def_id::DefId, QPath};
+use rustc_lint::LateContext;
+use rustc_span::symbol::sym;
+
+use crate::utils::{is_ty_param_diagnostic_item, span_lint_and_help};
+
+use super::BOX_VEC;
+
+pub(super) fn check(cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, qpath: &QPath<'_>, def_id: DefId) {
+    if Some(def_id) == cx.tcx.lang_items().owned_box() {
+        if is_ty_param_diagnostic_item(cx, qpath, sym::vec_type).is_some() {
+            span_lint_and_help(
+                cx,
+                BOX_VEC,
+                hir_ty.span,
+                "you seem to be trying to use `Box<Vec<T>>`. Consider using just `Vec<T>`",
+                None,
+                "`Vec<T>` is already on the heap, `Box<Vec<T>>` makes an extra allocation",
+            );
+        }
+    }
+}

clippy_lints/src/types/mod.rs

@@ -1,5 +1,7 @@
 #![allow(rustc::default_hash_types)]
 
+mod box_vec;
+
 use std::borrow::Cow;
 use std::cmp::Ordering;
 use std::collections::BTreeMap;
@@ -346,6 +348,7 @@ impl Types {
                 let hir_id = hir_ty.hir_id;
                 let res = cx.qpath_res(qpath, hir_id);
                 if let Some(def_id) = res.opt_def_id() {
+                    box_vec::check(cx, hir_ty, qpath, def_id);
                     if Some(def_id) == cx.tcx.lang_items().owned_box() {
                         if let Some(span) = match_borrows_parameter(cx, qpath) {
                             let mut applicability = Applicability::MachineApplicable;
@@ -360,17 +363,6 @@ impl Types {
                             );
                             return; // don't recurse into the type
                         }
-                        if is_ty_param_diagnostic_item(cx, qpath, sym::vec_type).is_some() {
-                            span_lint_and_help(
-                                cx,
-                                BOX_VEC,
-                                hir_ty.span,
-                                "you seem to be trying to use `Box<Vec<T>>`. Consider using just `Vec<T>`",
-                                None,
-                                "`Vec<T>` is already on the heap, `Box<Vec<T>>` makes an extra allocation",
-                            );
-                            return; // don't recurse into the type
-                        }
                     } else if cx.tcx.is_diagnostic_item(sym::Rc, def_id) {
                         if let Some(ty) = is_ty_param_diagnostic_item(cx, qpath, sym::Rc) {
                             let mut applicability = Applicability::MachineApplicable;