fix clippy::{filter_map_identiy, map_identity, manual_flatten}

Author: matthiaskrgr

Diff for: compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs

@@ -164,24 +164,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 {
                     for param in
                         [param_to_point_at, fallback_param_to_point_at, self_param_to_point_at]
+                            .into_iter()
+                            .flatten()
                     {
-                        if let Some(param) = param {
-                            let refined_expr = self.point_at_field_if_possible(
-                                def_id,
-                                param,
-                                variant_def_id,
-                                fields,
-                            );
-
-                            match refined_expr {
-                                None => {}
-                                Some((refined_expr, _)) => {
-                                    error.obligation.cause.span = refined_expr
-                                        .span
-                                        .find_ancestor_in_same_ctxt(error.obligation.cause.span)
-                                        .unwrap_or(refined_expr.span);
-                                    return true;
-                                }
+                        let refined_expr =
+                            self.point_at_field_if_possible(def_id, param, variant_def_id, fields);
+
+                        match refined_expr {
+                            None => {}
+                            Some((refined_expr, _)) => {
+                                error.obligation.cause.span = refined_expr
+                                    .span
+                                    .find_ancestor_in_same_ctxt(error.obligation.cause.span)
+                                    .unwrap_or(refined_expr.span);
+                                return true;
                             }
                         }
                     }

Diff for: compiler/rustc_monomorphize/src/partitioning/default.rs

@@ -89,7 +89,7 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
         }
 
         PreInliningPartitioning {
-            codegen_units: codegen_units.into_values().map(|codegen_unit| codegen_unit).collect(),
+            codegen_units: codegen_units.into_values().collect(),
             roots,
             internalization_candidates,
         }

Diff for: src/librustdoc/passes/collect_intra_doc_links.rs

@@ -1349,7 +1349,7 @@ impl LinkCollector<'_, '_> {
                         if has_derive_trait_collision {
                             candidates.macro_ns = None;
                         }
-                        candidates.into_iter().filter_map(|res| res).flatten().collect::<Vec<_>>()
+                        candidates.into_iter().flatten().flatten().collect::<Vec<_>>()
                     }
                 }
             }