fix clippy::map_flatten

crates/hir/src/lib.rs

@@ -231,7 +231,7 @@ impl Crate {
             return None;
         }
 
-        let doc_url = doc_attr_q.tt_values().map(|tt| {
+        let doc_url = doc_attr_q.tt_values().filter_map(|tt| {
             let name = tt.token_trees.iter()
                 .skip_while(|tt| !matches!(tt, TokenTree::Leaf(Leaf::Ident(Ident { text, ..} )) if text == "html_root_url"))
                 .nth(2);
@@ -240,7 +240,7 @@ impl Crate {
                 Some(TokenTree::Leaf(Leaf::Literal(Literal{ref text, ..}))) => Some(text),
                 _ => None
             }
-        }).flatten().next();
+        }).next();
 
         doc_url.map(|s| s.trim_matches('"').trim_end_matches('/').to_owned() + "/")
     }

crates/hir_expand/src/quote.rs

@@ -261,7 +261,7 @@ mod tests {
         // }
         let struct_name = mk_ident("Foo");
         let fields = [mk_ident("name"), mk_ident("id")];
-        let fields = fields.iter().map(|it| quote!(#it: self.#it.clone(), ).token_trees).flatten();
+        let fields = fields.iter().flat_map(|it| quote!(#it: self.#it.clone(), ).token_trees);
 
         let list = tt::Subtree {
             delimiter: Some(tt::Delimiter {

crates/ide/src/annotations.rs

@@ -170,10 +170,9 @@ pub(crate) fn resolve_annotation(db: &RootDatabase, mut annotation: Annotation)
                 result
                     .into_iter()
                     .flat_map(|res| res.references)
-                    .map(|(file_id, access)| {
+                    .flat_map(|(file_id, access)| {
                         access.into_iter().map(move |(range, _)| FileRange { file_id, range })
                     })
-                    .flatten()
                     .collect()
             });
         }

crates/ide_db/src/symbol_index.rs

@@ -120,8 +120,7 @@ fn library_symbols(db: &dyn SymbolsDatabase, source_root_id: SourceRootId) -> Ar
         // we specifically avoid calling SymbolsDatabase::module_symbols here, even they do the same thing,
         // as the index for a library is not going to really ever change, and we do not want to store each
         // module's index in salsa.
-        .map(|module| SymbolCollector::collect(db.upcast(), module))
-        .flatten()
+        .flat_map(|module| SymbolCollector::collect(db.upcast(), module))
         .collect();
 
     Arc::new(SymbolIndex::new(symbols))

crates/rust-analyzer/src/handlers.rs

@@ -532,7 +532,7 @@ pub(crate) fn handle_will_rename_files(
     let mut source_change = source_changes.next().unwrap_or_default();
     source_change.file_system_edits.clear();
     // no collect here because we want to merge text edits on same file ids
-    source_change.extend(source_changes.map(|it| it.source_file_edits).flatten());
+    source_change.extend(source_changes.flat_map(|it| it.source_file_edits));
     if source_change.source_file_edits.is_empty() {
         Ok(None)
     } else {