cleanup: use fs:read() instead of File::open().read_to_end()

lib/src/default_index_store.rs

@@ -24,7 +24,7 @@ use std::io::{Read, Write};
 use std::ops::Range;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
-use std::{io, iter};
+use std::{fs, io, iter};
 
 use blake2::Blake2b512;
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
@@ -86,11 +86,7 @@ impl DefaultIndexStore {
         op_id: &OperationId,
     ) -> Result<Arc<ReadonlyIndexImpl>, IndexLoadError> {
         let op_id_file = self.dir.join("operations").join(op_id.hex());
-        let mut buf = vec![];
-        File::open(op_id_file)
-            .unwrap()
-            .read_to_end(&mut buf)
-            .unwrap();
+        let buf = fs::read(op_id_file).unwrap();
         let index_file_id_hex = String::from_utf8(buf).unwrap();
         let index_file_path = self.dir.join(&index_file_id_hex);
         let mut index_file = File::open(index_file_path).unwrap();

lib/src/gitignore.rs

@@ -14,8 +14,7 @@
 
 #![allow(missing_docs)]
 
-use std::fs::File;
-use std::io::Read;
+use std::fs;
 use std::path::PathBuf;
 use std::sync::Arc;
 
@@ -184,9 +183,7 @@ impl GitIgnoreFile {
         file: PathBuf,
     ) -> Arc<GitIgnoreFile> {
         if file.is_file() {
-            let mut file = File::open(file).unwrap();
-            let mut buf = Vec::new();
-            file.read_to_end(&mut buf).unwrap();
+            let buf = fs::read(file).unwrap();
             self.chain(prefix, &buf)
         } else {
             self.clone()

lib/src/local_backend.rs

@@ -161,9 +161,7 @@ impl Backend for LocalBackend {
 
     fn read_symlink(&self, _path: &RepoPath, id: &SymlinkId) -> Result<String, BackendError> {
         let path = self.symlink_path(id);
-        let mut file = File::open(path).map_err(|err| map_not_found_err(err, id))?;
-        let mut target = String::new();
-        file.read_to_string(&mut target).unwrap();
+        let target = fs::read_to_string(path).map_err(|err| map_not_found_err(err, id))?;
         Ok(target)
     }
 

lib/src/working_copy.rs

@@ -975,16 +975,10 @@ impl TreeState {
         if let Some(TreeValue::Conflict(conflict_id)) = &current_tree_value {
             let conflict = self.store.read_conflict(repo_path, conflict_id)?;
             if let Some(old_file_ids) = conflict.to_file_merge() {
-                let mut file = File::open(disk_path).map_err(|err| SnapshotError::IoError {
+                let content = fs::read(disk_path).map_err(|err| SnapshotError::IoError {
                     message: format!("Failed to open file {}", disk_path.display()),
                     err,
                 })?;
-                let mut content = vec![];
-                file.read_to_end(&mut content)
-                    .map_err(|err| SnapshotError::IoError {
-                        message: format!("Failed to read file {}", disk_path.display()),
-                        err,
-                    })?;
                 let new_file_ids = conflicts::update_from_content(
                     &old_file_ids,
                     self.store.as_ref(),

lib/src/workspace.rs

@@ -14,8 +14,9 @@
 
 #![allow(missing_docs)]
 
+use std::fs;
 use std::fs::File;
-use std::io::{self, Read, Write};
+use std::io::{self, Write};
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
@@ -304,9 +305,7 @@ impl WorkspaceLoader {
         // If .jj/repo is a file, then we interpret its contents as a relative path to
         // the actual repo directory (typically in another workspace).
         if repo_dir.is_file() {
-            let mut repo_file = File::open(&repo_dir).context(&repo_dir)?;
-            let mut buf = Vec::new();
-            repo_file.read_to_end(&mut buf).context(&repo_dir)?;
+            let buf = fs::read(&repo_dir).context(&repo_dir)?;
             let repo_path_str =
                 String::from_utf8(buf).map_err(|_| WorkspaceLoadError::NonUnicodePath)?;
             repo_dir = jj_dir