Auto merge of #7330 - xFrednet:0000-refactor-map-identity, r=flip1995

Refactoring identity function lints

I've noticed that we have several lints that all check for identity functions and each used their own check implementation. I moved the `is_expr_identity_function` function to `clippy_utils` and adapted all lints to reuse that one function. This should make the addition of new lints like this also easier in the future.

I've also moved the `map_identity` lint into the `methods` module. It's probably the best to review this PR by checking each commit individually. And that's it, have a great day :upside_down_face:

changelog: none

13 files changed, 178 insertions, 204 deletions

diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index e7dd3952b3a..c6d9b378603 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -254,7 +254,6 @@ mod manual_strip;
 mod manual_unwrap_or;
 mod map_clone;
 mod map_err_ignore;
-mod map_identity;
 mod map_unit_fn;
 mod match_on_vec_items;
 mod matches;
@@ -705,7 +704,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         manual_unwrap_or::MANUAL_UNWRAP_OR,
         map_clone::MAP_CLONE,
         map_err_ignore::MAP_ERR_IGNORE,
-        map_identity::MAP_IDENTITY,
         map_unit_fn::OPTION_MAP_UNIT_FN,
         map_unit_fn::RESULT_MAP_UNIT_FN,
         match_on_vec_items::MATCH_ON_VEC_ITEMS,
@@ -765,6 +763,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         methods::MANUAL_STR_REPEAT,
         methods::MAP_COLLECT_RESULT_UNIT,
         methods::MAP_FLATTEN,
+        methods::MAP_IDENTITY,
         methods::MAP_UNWRAP_OR,
         methods::NEW_RET_NO_SELF,
         methods::OK_EXPECT,
@@ -1260,7 +1259,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(manual_strip::MANUAL_STRIP),
         LintId::of(manual_unwrap_or::MANUAL_UNWRAP_OR),
         LintId::of(map_clone::MAP_CLONE),
-        LintId::of(map_identity::MAP_IDENTITY),
         LintId::of(map_unit_fn::OPTION_MAP_UNIT_FN),
         LintId::of(map_unit_fn::RESULT_MAP_UNIT_FN),
         LintId::of(matches::INFALLIBLE_DESTRUCTURING_MATCH),
@@ -1301,6 +1299,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(methods::MANUAL_SATURATING_ARITHMETIC),
         LintId::of(methods::MANUAL_STR_REPEAT),
         LintId::of(methods::MAP_COLLECT_RESULT_UNIT),
+        LintId::of(methods::MAP_IDENTITY),
         LintId::of(methods::NEW_RET_NO_SELF),
         LintId::of(methods::OK_EXPECT),
         LintId::of(methods::OPTION_AS_REF_DEREF),
@@ -1586,7 +1585,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(loops::WHILE_LET_LOOP),
         LintId::of(manual_strip::MANUAL_STRIP),
         LintId::of(manual_unwrap_or::MANUAL_UNWRAP_OR),
-        LintId::of(map_identity::MAP_IDENTITY),
         LintId::of(map_unit_fn::OPTION_MAP_UNIT_FN),
         LintId::of(map_unit_fn::RESULT_MAP_UNIT_FN),
         LintId::of(matches::MATCH_AS_REF),
@@ -1601,6 +1599,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(methods::ITER_COUNT),
         LintId::of(methods::MANUAL_FILTER_MAP),
         LintId::of(methods::MANUAL_FIND_MAP),
+        LintId::of(methods::MAP_IDENTITY),
         LintId::of(methods::OPTION_AS_REF_DEREF),
         LintId::of(methods::OPTION_FILTER_MAP),
         LintId::of(methods::SEARCH_IS_SOME),
@@ -2039,7 +2038,6 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         single_char_binding_names_threshold,
     });
     store.register_late_pass(|| box macro_use::MacroUseImports::default());
-    store.register_late_pass(|| box map_identity::MapIdentity);
     store.register_late_pass(|| box pattern_type_mismatch::PatternTypeMismatch);
     store.register_late_pass(|| box stable_sort_primitive::StableSortPrimitive);
     store.register_late_pass(|| box repeat_once::RepeatOnce);
diff --git a/clippy_lints/src/map_identity.rs b/clippy_lints/src/map_identity.rs
deleted file mode 100644
index 41cda23510e..00000000000
--- a/clippy_lints/src/map_identity.rs
+++ /dev/null
@@ -1,126 +0,0 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::ty::is_type_diagnostic_item;
-use clippy_utils::{is_adjusted, is_qpath_def_path, is_trait_method, match_var, paths, remove_blocks};
-use if_chain::if_chain;
-use rustc_errors::Applicability;
-use rustc_hir::{Body, Expr, ExprKind, Pat, PatKind, QPath, StmtKind};
-use rustc_lint::{LateContext, LateLintPass};
-use rustc_session::{declare_lint_pass, declare_tool_lint};
-use rustc_span::sym;
-
-declare_clippy_lint! {
-    /// **What it does:** Checks for instances of `map(f)` where `f` is the identity function.
-    ///
-    /// **Why is this bad?** It can be written more concisely without the call to `map`.
-    ///
-    /// **Known problems:** None.
-    ///
-    /// **Example:**
-    ///
-    /// ```rust
-    /// let x = [1, 2, 3];
-    /// let y: Vec<_> = x.iter().map(|x| x).map(|x| 2*x).collect();
-    /// ```
-    /// Use instead:
-    /// ```rust
-    /// let x = [1, 2, 3];
-    /// let y: Vec<_> = x.iter().map(|x| 2*x).collect();
-    /// ```
-    pub MAP_IDENTITY,
-    complexity,
-    "using iterator.map(|x| x)"
-}
-
-declare_lint_pass!(MapIdentity => [MAP_IDENTITY]);
-
-impl<'tcx> LateLintPass<'tcx> for MapIdentity {
-    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
-        if expr.span.from_expansion() {
-            return;
-        }
-
-        if_chain! {
-            if let Some([caller, func]) = get_map_argument(cx, expr);
-            if is_expr_identity_function(cx, func);
-            then {
-                span_lint_and_sugg(
-                    cx,
-                    MAP_IDENTITY,
-                    expr.span.trim_start(caller.span).unwrap(),
-                    "unnecessary map of the identity function",
-                    "remove the call to `map`",
-                    String::new(),
-                    Applicability::MachineApplicable
-                )
-            }
-        }
-    }
-}
-
-/// Returns the arguments passed into map() if the expression is a method call to
-/// map(). Otherwise, returns None.
-fn get_map_argument<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<&'a [Expr<'a>]> {
-    if_chain! {
-        if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
-        if args.len() == 2 && method.ident.name == sym::map;
-        let caller_ty = cx.typeck_results().expr_ty(&args[0]);
-        if is_trait_method(cx, expr, sym::Iterator)
-            || is_type_diagnostic_item(cx, caller_ty, sym::result_type)
-            || is_type_diagnostic_item(cx, caller_ty, sym::option_type);
-        then {
-            Some(args)
-        } else {
-            None
-        }
-    }
-}
-
-/// Checks if an expression represents the identity function
-/// Only examines closures and `std::convert::identity`
-fn is_expr_identity_function(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
-    match expr.kind {
-        ExprKind::Closure(_, _, body_id, _, _) => is_body_identity_function(cx, cx.tcx.hir().body(body_id)),
-        ExprKind::Path(ref path) => is_qpath_def_path(cx, path, expr.hir_id, &paths::CONVERT_IDENTITY),
-        _ => false,
-    }
-}
-
-/// Checks if a function's body represents the identity function
-/// Looks for bodies of the form `|x| x`, `|x| return x`, `|x| { return x }` or `|x| {
-/// return x; }`
-fn is_body_identity_function(cx: &LateContext<'_>, func: &Body<'_>) -> bool {
-    let params = func.params;
-    let body = remove_blocks(&func.value);
-
-    // if there's less/more than one parameter, then it is not the identity function
-    if params.len() != 1 {
-        return false;
-    }
-
-    match body.kind {
-        ExprKind::Path(QPath::Resolved(None, _)) => match_expr_param(cx, body, params[0].pat),
-        ExprKind::Ret(Some(ret_val)) => match_expr_param(cx, ret_val, params[0].pat),
-        ExprKind::Block(block, _) => {
-            if_chain! {
-                if block.stmts.len() == 1;
-                if let StmtKind::Semi(expr) | StmtKind::Expr(expr) = block.stmts[0].kind;
-                if let ExprKind::Ret(Some(ret_val)) = expr.kind;
-                then {
-                    match_expr_param(cx, ret_val, params[0].pat)
-                } else {
-                    false
-                }
-            }
-        },
-        _ => false,
-    }
-}
-
-/// Returns true iff an expression returns the same thing as a parameter's pattern
-fn match_expr_param(cx: &LateContext<'_>, expr: &Expr<'_>, pat: &Pat<'_>) -> bool {
-    if let PatKind::Binding(_, _, ident, _) = pat.kind {
-        match_var(expr, ident.name) && !(cx.typeck_results().hir_owner == expr.hir_id.owner && is_adjusted(cx, expr))
-    } else {
-        false
-    }
-}
diff --git a/clippy_lints/src/methods/filter_map_identity.rs b/clippy_lints/src/methods/filter_map_identity.rs
index 403fe8d3546..d1b5e945dfd 100644
--- a/clippy_lints/src/methods/filter_map_identity.rs
+++ b/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,
+        );
     }
 }
diff --git a/clippy_lints/src/methods/flat_map_identity.rs b/clippy_lints/src/methods/flat_map_identity.rs
index 25f8434cb94..6f911d79d0b 100644
--- a/clippy_lints/src/methods/flat_map_identity.rs
+++ b/clippy_lints/src/methods/flat_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, 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;
@@ -15,36 +14,15 @@ pub(super) fn check<'tcx>(
     flat_map_arg: &'tcx hir::Expr<'_>,
     flat_map_span: Span,
 ) {
-    if is_trait_method(cx, expr, sym::Iterator) {
-        let apply_lint = |message: &str| {
-            span_lint_and_sugg(
-                cx,
-                FLAT_MAP_IDENTITY,
-                flat_map_span.with_hi(expr.span.hi()),
-                message,
-                "try",
-                "flatten()".to_string(),
-                Applicability::MachineApplicable,
-            );
-        };
-
-        if_chain! {
-            if let hir::ExprKind::Closure(_, _, body_id, _, _) = flat_map_arg.kind;
-            let body = cx.tcx.hir().body(body_id);
-
-            if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
-            if let hir::ExprKind::Path(hir::QPath::Resolved(_, path)) = body.value.kind;
-
-            if path.segments.len() == 1;
-            if path.segments[0].ident.name == binding_ident.name;
-
-            then {
-                apply_lint("called `flat_map(|x| x)` on an `Iterator`");
-            }
-        }
-
-        if is_expr_path_def_path(cx, flat_map_arg, &paths::CONVERT_IDENTITY) {
-            apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
-        }
+    if is_trait_method(cx, expr, sym::Iterator) && is_expr_identity_function(cx, flat_map_arg) {
+        span_lint_and_sugg(
+            cx,
+            FLAT_MAP_IDENTITY,
+            flat_map_span.with_hi(expr.span.hi()),
+            "use of `flat_map` with an identity function",
+            "try",
+            "flatten()".to_string(),
+            Applicability::MachineApplicable,
+        );
     }
 }
diff --git a/clippy_lints/src/methods/map_identity.rs b/clippy_lints/src/methods/map_identity.rs
new file mode 100644
index 00000000000..538a12566e3
--- /dev/null
+++ b/clippy_lints/src/methods/map_identity.rs
@@ -0,0 +1,38 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::{is_expr_identity_function, is_trait_method};
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_span::{source_map::Span, sym};
+
+use super::MAP_IDENTITY;
+
+pub(super) fn check(
+    cx: &LateContext<'_>,
+    expr: &hir::Expr<'_>,
+    caller: &hir::Expr<'_>,
+    map_arg: &hir::Expr<'_>,
+    _map_span: Span,
+) {
+    let caller_ty = cx.typeck_results().expr_ty(caller);
+
+    if_chain! {
+        if is_trait_method(cx, expr, sym::Iterator)
+            || is_type_diagnostic_item(cx, caller_ty, sym::result_type)
+            || is_type_diagnostic_item(cx, caller_ty, sym::option_type);
+        if is_expr_identity_function(cx, map_arg);
+        if let Some(sugg_span) = expr.span.trim_start(caller.span);
+        then {
+            span_lint_and_sugg(
+                cx,
+                MAP_IDENTITY,
+                sugg_span,
+                "unnecessary map of the identity function",
+                "remove the call to `map`",
+                String::new(),
+                Applicability::MachineApplicable,
+            )
+        }
+    }
+}
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index c8ae972f18c..d4f8cef4f37 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -35,6 +35,7 @@ mod manual_saturating_arithmetic;
 mod manual_str_repeat;
 mod map_collect_result_unit;
 mod map_flatten;
+mod map_identity;
 mod map_unwrap_or;
 mod ok_expect;
 mod option_as_ref_deref;
@@ -1562,6 +1563,29 @@ declare_clippy_lint! {
 }
 
 declare_clippy_lint! {
+    /// **What it does:** Checks for instances of `map(f)` where `f` is the identity function.
+    ///
+    /// **Why is this bad?** It can be written more concisely without the call to `map`.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// let x = [1, 2, 3];
+    /// let y: Vec<_> = x.iter().map(|x| x).map(|x| 2*x).collect();
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// let x = [1, 2, 3];
+    /// let y: Vec<_> = x.iter().map(|x| 2*x).collect();
+    /// ```
+    pub MAP_IDENTITY,
+    complexity,
+    "using iterator.map(|x| x)"
+}
+
+declare_clippy_lint! {
     /// **What it does:** Checks for the use of `.bytes().nth()`.
     ///
     /// **Why is this bad?** `.as_bytes().get()` is more efficient and more
@@ -1728,6 +1752,7 @@ impl_lint_pass!(Methods => [
     FILTER_NEXT,
     SKIP_WHILE_NEXT,
     FILTER_MAP_IDENTITY,
+    MAP_IDENTITY,
     MANUAL_FILTER_MAP,
     MANUAL_FIND_MAP,
     OPTION_FILTER_MAP,
@@ -2058,6 +2083,7 @@ fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Optio
                         _ => {},
                     }
                 }
+                map_identity::check(cx, expr, recv, m_arg, span);
             },
             ("map_or", [def, map]) => option_map_or_none::check(cx, expr, recv, def, map),
             ("next", []) => {
diff --git a/clippy_utils/src/lib.rs b/clippy_utils/src/lib.rs
index 93212f97cb7..d3efd32d727 100644
--- a/clippy_utils/src/lib.rs
+++ b/clippy_utils/src/lib.rs
@@ -1401,6 +1401,60 @@ pub fn is_must_use_func_call(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     did.map_or(false, |did| must_use_attr(cx.tcx.get_attrs(did)).is_some())
 }
 
+/// Checks if an expression represents the identity function
+/// Only examines closures and `std::convert::identity`
+pub fn is_expr_identity_function(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    /// Returns true if the expression is a binding to the given pattern
+    fn is_expr_pat_binding(cx: &LateContext<'_>, expr: &Expr<'_>, pat: &Pat<'_>) -> bool {
+        if let PatKind::Binding(_, _, ident, _) = pat.kind {
+            if match_var(expr, ident.name) {
+                return !(cx.typeck_results().hir_owner == expr.hir_id.owner && is_adjusted(cx, expr));
+            }
+        }
+
+        false
+    }
+
+    /// Checks if a function's body represents the identity function. Looks for bodies of the form:
+    /// * `|x| x`
+    /// * `|x| return x`
+    /// * `|x| { return x }`
+    /// * `|x| { return x; }`
+    fn is_body_identity_function(cx: &LateContext<'_>, func: &Body<'_>) -> bool {
+        let body = remove_blocks(&func.value);
+
+        let value_pat = if let [value_param] = func.params {
+            value_param.pat
+        } else {
+            return false;
+        };
+
+        match body.kind {
+            ExprKind::Path(QPath::Resolved(None, _)) => is_expr_pat_binding(cx, body, value_pat),
+            ExprKind::Ret(Some(ret_val)) => is_expr_pat_binding(cx, ret_val, value_pat),
+            ExprKind::Block(block, _) => {
+                if_chain! {
+                    if let &[block_stmt] = &block.stmts;
+                    if let StmtKind::Semi(expr) | StmtKind::Expr(expr) = block_stmt.kind;
+                    if let ExprKind::Ret(Some(ret_val)) = expr.kind;
+                    then {
+                        is_expr_pat_binding(cx, ret_val, value_pat)
+                    } else {
+                        false
+                    }
+                }
+            },
+            _ => false,
+        }
+    }
+
+    match expr.kind {
+        ExprKind::Closure(_, _, body_id, _, _) => is_body_identity_function(cx, cx.tcx.hir().body(body_id)),
+        ExprKind::Path(ref path) => is_qpath_def_path(cx, path, expr.hir_id, &paths::CONVERT_IDENTITY),
+        _ => false,
+    }
+}
+
 /// Gets the node where an expression is either used, or it's type is unified with another branch.
 pub fn get_expr_use_or_unification_node(tcx: TyCtxt<'tcx>, expr: &Expr<'_>) -> Option<Node<'tcx>> {
     let map = tcx.hir();
diff --git a/tests/ui/filter_map_identity.fixed b/tests/ui/filter_map_identity.fixed
index 23ce28d8e9b..a5860aa49b3 100644
--- a/tests/ui/filter_map_identity.fixed
+++ b/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();
 }
diff --git a/tests/ui/filter_map_identity.rs b/tests/ui/filter_map_identity.rs
index e698df13eea..7e998b9cdf7 100644
--- a/tests/ui/filter_map_identity.rs
+++ b/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);
 }
diff --git a/tests/ui/filter_map_identity.stderr b/tests/ui/filter_map_identity.stderr
index 596a6320608..43c9fdca4fb 100644
--- a/tests/ui/filter_map_identity.stderr
+++ b/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
 
diff --git a/tests/ui/flat_map_identity.fixed b/tests/ui/flat_map_identity.fixed
index dfe3bd47e13..1f4b880ef5b 100644
--- a/tests/ui/flat_map_identity.fixed
+++ b/tests/ui/flat_map_identity.fixed
@@ -1,6 +1,6 @@
 // run-rustfix
 
-#![allow(unused_imports)]
+#![allow(unused_imports, clippy::needless_return)]
 #![warn(clippy::flat_map_identity)]
 
 use std::convert;
@@ -11,4 +11,7 @@ fn main() {
 
     let iterator = [[0, 1], [2, 3], [4, 5]].iter();
     let _ = iterator.flatten();
+
+    let iterator = [[0, 1], [2, 3], [4, 5]].iter();
+    let _ = iterator.flatten();
 }
diff --git a/tests/ui/flat_map_identity.rs b/tests/ui/flat_map_identity.rs
index 393b9569255..de14a06d4e6 100644
--- a/tests/ui/flat_map_identity.rs
+++ b/tests/ui/flat_map_identity.rs
@@ -1,6 +1,6 @@
 // run-rustfix
 
-#![allow(unused_imports)]
+#![allow(unused_imports, clippy::needless_return)]
 #![warn(clippy::flat_map_identity)]
 
 use std::convert;
@@ -11,4 +11,7 @@ fn main() {
 
     let iterator = [[0, 1], [2, 3], [4, 5]].iter();
     let _ = iterator.flat_map(convert::identity);
+
+    let iterator = [[0, 1], [2, 3], [4, 5]].iter();
+    let _ = iterator.flat_map(|x| return x);
 }
diff --git a/tests/ui/flat_map_identity.stderr b/tests/ui/flat_map_identity.stderr
index e4686ae5a54..e776c9fdf51 100644
--- a/tests/ui/flat_map_identity.stderr
+++ b/tests/ui/flat_map_identity.stderr
@@ -1,4 +1,4 @@
-error: called `flat_map(|x| x)` on an `Iterator`
+error: use of `flat_map` with an identity function
   --> $DIR/flat_map_identity.rs:10:22
    |
 LL |     let _ = iterator.flat_map(|x| x);
@@ -6,11 +6,17 @@ LL |     let _ = iterator.flat_map(|x| x);
    |
    = note: `-D clippy::flat-map-identity` implied by `-D warnings`
 
-error: called `flat_map(std::convert::identity)` on an `Iterator`
+error: use of `flat_map` with an identity function
   --> $DIR/flat_map_identity.rs:13:22
    |
 LL |     let _ = iterator.flat_map(convert::identity);
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `flatten()`
 
-error: aborting due to 2 previous errors
+error: use of `flat_map` with an identity function
+  --> $DIR/flat_map_identity.rs:16:22
+   |
+LL |     let _ = iterator.flat_map(|x| return x);
+   |                      ^^^^^^^^^^^^^^^^^^^^^^ help: try: `flatten()`
+
+error: aborting due to 3 previous errors