Add tests to tests/ui/unnecessary_filter_map.rs

The tests currently fail, and are fixed by the next commit.

tests/ui/unnecessary_filter_map.rs

@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 fn main() {
     let _ = (0..4).filter_map(|x| if x > 1 { Some(x) } else { None });
     let _ = (0..4).filter_map(|x| {
@@ -19,3 +21,130 @@ fn main() {
 fn filter_map_none_changes_item_type() -> impl Iterator<Item = bool> {
     "".chars().filter_map(|_| None)
 }
+
+// https://github.com/rust-lang/rust-clippy/issues/4433#issue-483920107
+mod comment_483920107 {
+    enum Severity {
+        Warning,
+        Other,
+    }
+
+    struct ServerError;
+
+    impl ServerError {
+        fn severity(&self) -> Severity {
+            Severity::Warning
+        }
+    }
+
+    struct S {
+        warnings: Vec<ServerError>,
+    }
+
+    impl S {
+        fn foo(&mut self, server_errors: Vec<ServerError>) {
+            #[allow(unused_variables)]
+            let errors: Vec<ServerError> = server_errors
+                .into_iter()
+                .filter_map(|se| match se.severity() {
+                    Severity::Warning => {
+                        self.warnings.push(se);
+                        None
+                    },
+                    _ => Some(se),
+                })
+                .collect();
+        }
+    }
+}
+
+// https://github.com/rust-lang/rust-clippy/issues/4433#issuecomment-611006622
+mod comment_611006622 {
+    struct PendingRequest {
+        reply_to: u8,
+        token: u8,
+        expires: u8,
+        group_id: u8,
+    }
+
+    enum Value {
+        Null,
+    }
+
+    struct Node;
+
+    impl Node {
+        fn send_response(&self, _reply_to: u8, _token: u8, _value: Value) -> &Self {
+            self
+        }
+        fn on_error_warn(&self) -> &Self {
+            self
+        }
+    }
+
+    struct S {
+        pending_requests: Vec<PendingRequest>,
+    }
+
+    impl S {
+        fn foo(&mut self, node: Node, now: u8, group_id: u8) {
+            // "drain_filter"
+            self.pending_requests = self
+                .pending_requests
+                .drain(..)
+                .filter_map(|pending| {
+                    if pending.expires <= now {
+                        return None; // Expired, remove
+                    }
+
+                    if pending.group_id == group_id {
+                        // Matched - reuse strings and remove
+                        node.send_response(pending.reply_to, pending.token, Value::Null)
+                            .on_error_warn();
+                        None
+                    } else {
+                        // Keep waiting
+                        Some(pending)
+                    }
+                })
+                .collect();
+        }
+    }
+}
+
+// https://github.com/rust-lang/rust-clippy/issues/4433#issuecomment-621925270
+// This extrapolation doesn't reproduce the false positive. Additional context seems necessary.
+mod comment_621925270 {
+    struct Signature(u8);
+
+    fn foo(sig_packets: impl Iterator<Item = Result<Signature, ()>>) -> impl Iterator<Item = u8> {
+        sig_packets.filter_map(|res| match res {
+            Ok(Signature(sig_packet)) => Some(sig_packet),
+            _ => None,
+        })
+    }
+}
+
+// https://github.com/rust-lang/rust-clippy/issues/4433#issuecomment-1052978898
+mod comment_1052978898 {
+    #![allow(clippy::redundant_closure)]
+
+    pub struct S(u8);
+
+    impl S {
+        pub fn consume(self) {
+            println!("yum");
+        }
+    }
+
+    pub fn filter_owned() -> impl Iterator<Item = S> {
+        (0..10).map(|i| S(i)).filter_map(|s| {
+            if s.0 & 1 == 0 {
+                s.consume();
+                None
+            } else {
+                Some(s)
+            }
+        })
+    }
+}

tests/ui/unnecessary_filter_map.stderr

@@ -1,5 +1,5 @@
 error: this `.filter_map` can be written more simply using `.filter`
-  --> $DIR/unnecessary_filter_map.rs:2:13
+  --> $DIR/unnecessary_filter_map.rs:4:13
    |
 LL |     let _ = (0..4).filter_map(|x| if x > 1 { Some(x) } else { None });
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -7,7 +7,7 @@ LL |     let _ = (0..4).filter_map(|x| if x > 1 { Some(x) } else { None });
    = note: `-D clippy::unnecessary-filter-map` implied by `-D warnings`
 
 error: this `.filter_map` can be written more simply using `.filter`
-  --> $DIR/unnecessary_filter_map.rs:3:13
+  --> $DIR/unnecessary_filter_map.rs:5:13
    |
 LL |       let _ = (0..4).filter_map(|x| {
    |  _____________^
@@ -19,7 +19,7 @@ LL | |     });
    | |______^
 
 error: this `.filter_map` can be written more simply using `.filter`
-  --> $DIR/unnecessary_filter_map.rs:9:13
+  --> $DIR/unnecessary_filter_map.rs:11:13
    |
 LL |       let _ = (0..4).filter_map(|x| match x {
    |  _____________^
@@ -29,7 +29,7 @@ LL | |     });
    | |______^
 
 error: this `.filter_map` can be written more simply using `.map`
-  --> $DIR/unnecessary_filter_map.rs:14:13
+  --> $DIR/unnecessary_filter_map.rs:16:13
    |
 LL |     let _ = (0..4).filter_map(|x| Some(x + 1));
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^