cleanup: remove extern crate declarations

`extern crate` is no longer needed since edition 2018.

lib/build.rs

@@ -12,9 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-extern crate protobuf_codegen;
-extern crate version_check;
-
 use std::path::Path;
 
 fn main() {

lib/src/dag_walk.rs

@@ -239,6 +239,8 @@ where
 
 #[cfg(test)]
 mod tests {
+    use maplit::{hashmap, hashset};
+
     use super::*;
 
     #[test]

lib/src/index.rs

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-extern crate byteorder;
-
 use std::cmp::{max, min, Ordering};
 use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashSet};
 use std::fmt::{Debug, Formatter};

lib/src/lib.rs

@@ -15,13 +15,6 @@
 #![deny(unused_must_use)]
 #![cfg_attr(feature = "map_first_last", feature(map_first_last))]
 
-#[macro_use]
-extern crate pest_derive;
-
-#[cfg(test)]
-#[macro_use]
-extern crate maplit;
-
 pub mod backend;
 pub mod commit;
 pub mod commit_builder;

lib/src/matchers.rs

@@ -322,6 +322,8 @@ impl Dirs {
 
 #[cfg(test)]
 mod tests {
+    use maplit::hashset;
+
     use super::*;
     use crate::repo_path::{RepoPath, RepoPathComponent};
 

lib/src/revset.rs

@@ -22,6 +22,7 @@ use std::sync::Arc;
 use itertools::Itertools;
 use pest::iterators::Pairs;
 use pest::Parser;
+use pest_derive::Parser;
 use thiserror::Error;
 
 use crate::backend::{BackendError, BackendResult, CommitId};

lib/src/simple_op_store.rs

@@ -365,6 +365,8 @@ fn ref_target_from_proto(proto: &crate::protos::op_store::RefTarget) -> RefTarge
 
 #[cfg(test)]
 mod tests {
+    use maplit::{btreemap, hashmap, hashset};
+
     use super::*;
     use crate::testutils;
 

lib/src/stacked_table.rs

@@ -18,8 +18,6 @@
 //! a parent file, and the parent may have its own parent, and so on. The child
 //! file then represents the union of the entries.
 
-extern crate byteorder;
-
 use std::cmp::Ordering;
 use std::collections::{BTreeMap, HashMap};
 use std::fs::File;

src/commands.rs

@@ -12,11 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-extern crate chrono;
-extern crate clap;
-extern crate clap_mangen;
-extern crate config;
-
 use std::collections::{HashSet, VecDeque};
 use std::ffi::OsString;
 use std::fmt::Debug;
@@ -28,6 +23,7 @@ use std::sync::Arc;
 use std::time::Instant;
 use std::{fs, io};
 
+use chrono::{FixedOffset, TimeZone, Utc};
 use clap::{ArgGroup, CommandFactory, Subcommand};
 use config::Value;
 use criterion::Criterion;
@@ -65,7 +61,6 @@ use jujutsu_lib::{conflicts, dag_walk, diff, files, git, revset, tree};
 use maplit::{hashmap, hashset};
 use pest::Parser;
 
-use self::chrono::{FixedOffset, TimeZone, Utc};
 use crate::commands::CommandError::UserError;
 use crate::diff_edit::DiffEditError;
 use crate::formatter::Formatter;

src/lib.rs

@@ -14,9 +14,6 @@
 
 #![deny(unused_must_use)]
 
-#[macro_use]
-extern crate pest_derive;
-
 pub mod commands;
 pub mod config;
 pub mod diff_edit;

src/template_parser.rs

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-extern crate pest;
-
 use chrono::{FixedOffset, TimeZone, Utc};
 use jujutsu_lib::backend::{CommitId, Signature};
 use jujutsu_lib::commit::Commit;
@@ -21,6 +19,7 @@ use jujutsu_lib::op_store::WorkspaceId;
 use jujutsu_lib::repo::RepoRef;
 use pest::iterators::{Pair, Pairs};
 use pest::Parser;
+use pest_derive::Parser;
 
 use crate::formatter::PlainTextFormatter;
 use crate::templater::{