clippy::filter_map_identity

compiler/rustc_hir/src/def.rs

@@ -476,7 +476,7 @@ impl<T> PerNS<Option<T>> {
 
     /// Returns an iterator over the items which are `Some`.
     pub fn present_items(self) -> impl Iterator<Item = T> {
-        IntoIter::new([self.type_ns, self.value_ns, self.macro_ns]).filter_map(|it| it)
+        IntoIter::new([self.type_ns, self.value_ns, self.macro_ns]).flatten()
     }
 }
 

compiler/rustc_parse/src/parser/item.rs

@@ -1107,8 +1107,7 @@ impl<'a> Parser<'a> {
                 e
             })?;
 
-        let enum_definition =
-            EnumDef { variants: variants.into_iter().filter_map(|v| v).collect() };
+        let enum_definition = EnumDef { variants: variants.into_iter().flatten().collect() };
         Ok((id, ItemKind::Enum(enum_definition, generics)))
     }
 

compiler/rustc_typeck/src/check/mod.rs

@@ -791,7 +791,7 @@ fn fn_sig_suggestion<'tcx>(
             })
         })
         .chain(std::iter::once(if sig.c_variadic { Some("...".to_string()) } else { None }))
-        .filter_map(|arg| arg)
+        .flatten()
         .collect::<Vec<String>>()
         .join(", ");
     let output = sig.output();