Reuse is_expr_identity_function for filter_map_identity

clippy_lints/src/methods/filter_map_identity.rs

@@ -1,6 +1,5 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::{is_expr_path_def_path, is_trait_method, path_to_local_id, paths};
-use if_chain::if_chain;
+use clippy_utils::{is_expr_identity_function, is_trait_method};
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_lint::LateContext;
@@ -9,32 +8,15 @@ use rustc_span::{source_map::Span, sym};
 use super::FILTER_MAP_IDENTITY;
 
 pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, filter_map_arg: &hir::Expr<'_>, filter_map_span: Span) {
-    if is_trait_method(cx, expr, sym::Iterator) {
-        let apply_lint = |message: &str| {
-            span_lint_and_sugg(
-                cx,
-                FILTER_MAP_IDENTITY,
-                filter_map_span.with_hi(expr.span.hi()),
-                message,
-                "try",
-                "flatten()".to_string(),
-                Applicability::MachineApplicable,
-            );
-        };
-
-        if_chain! {
-            if let hir::ExprKind::Closure(_, _, body_id, _, _) = filter_map_arg.kind;
-            let body = cx.tcx.hir().body(body_id);
-
-            if let hir::PatKind::Binding(_, binding_id, ..) = body.params[0].pat.kind;
-            if path_to_local_id(&body.value, binding_id);
-            then {
-                apply_lint("called `filter_map(|x| x)` on an `Iterator`");
-            }
-        }
-
-        if is_expr_path_def_path(cx, filter_map_arg, &paths::CONVERT_IDENTITY) {
-            apply_lint("called `filter_map(std::convert::identity)` on an `Iterator`");
-        }
+    if is_trait_method(cx, expr, sym::Iterator) && is_expr_identity_function(cx, filter_map_arg) {
+        span_lint_and_sugg(
+            cx,
+            FILTER_MAP_IDENTITY,
+            filter_map_span.with_hi(expr.span.hi()),
+            "use of `filter_map` with an identity function",
+            "try",
+            "flatten()".to_string(),
+            Applicability::MachineApplicable,
+        );
     }
 }

tests/ui/filter_map_identity.fixed

@@ -1,6 +1,6 @@
 // run-rustfix
 
-#![allow(unused_imports)]
+#![allow(unused_imports, clippy::needless_return)]
 #![warn(clippy::filter_map_identity)]
 
 fn main() {
@@ -13,4 +13,7 @@ fn main() {
     use std::convert::identity;
     let iterator = vec![Some(1), None, Some(2)].into_iter();
     let _ = iterator.flatten();
+
+    let iterator = vec![Some(1), None, Some(2)].into_iter();
+    let _ = iterator.flatten();
 }

tests/ui/filter_map_identity.rs

@@ -1,6 +1,6 @@
 // run-rustfix
 
-#![allow(unused_imports)]
+#![allow(unused_imports, clippy::needless_return)]
 #![warn(clippy::filter_map_identity)]
 
 fn main() {
@@ -13,4 +13,7 @@ fn main() {
     use std::convert::identity;
     let iterator = vec![Some(1), None, Some(2)].into_iter();
     let _ = iterator.filter_map(identity);
+
+    let iterator = vec![Some(1), None, Some(2)].into_iter();
+    let _ = iterator.filter_map(|x| return x);
 }

tests/ui/filter_map_identity.stderr

@@ -1,4 +1,4 @@
-error: called `filter_map(|x| x)` on an `Iterator`
+error: use of `filter_map` with an identity function
   --> $DIR/filter_map_identity.rs:8:22
    |
 LL |     let _ = iterator.filter_map(|x| x);
@@ -6,17 +6,23 @@ LL |     let _ = iterator.filter_map(|x| x);
    |
    = note: `-D clippy::filter-map-identity` implied by `-D warnings`
 
-error: called `filter_map(std::convert::identity)` on an `Iterator`
+error: use of `filter_map` with an identity function
   --> $DIR/filter_map_identity.rs:11:22
    |
 LL |     let _ = iterator.filter_map(std::convert::identity);
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `flatten()`
 
-error: called `filter_map(std::convert::identity)` on an `Iterator`
+error: use of `filter_map` with an identity function
   --> $DIR/filter_map_identity.rs:15:22
    |
 LL |     let _ = iterator.filter_map(identity);
    |                      ^^^^^^^^^^^^^^^^^^^^ help: try: `flatten()`
 
-error: aborting due to 3 previous errors
+error: use of `filter_map` with an identity function
+  --> $DIR/filter_map_identity.rs:18:22
+   |
+LL |     let _ = iterator.filter_map(|x| return x);
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `flatten()`
+
+error: aborting due to 4 previous errors