Cleanup rustfix parse_and_replace test.

This is just some minor code cleanup for the parse_and_replace test,
there should not be any functional differences.

crates/rustfix/tests/parse_and_replace.rs

@@ -1,3 +1,22 @@
+//! Tests that verify rustfix applies the appropriate changes to a file.
+//!
+//! This test works by reading a series of `*.rs` files in the
+//! `tests/everything` directory. For each `.rs` file, it runs `rustc` to
+//! collect JSON diagnostics from the file. It feeds that JSON data into
+//! rustfix and applies the recommended suggestions to the `.rs` file. It then
+//! compares the result with the corresponding `.fixed.rs` file. If they don't
+//! match, then the test fails.
+//!
+//! There are several debugging environment variables for this test that you can set:
+//!
+//! - `RUST_LOG=parse_and_replace=debug`: Print debug information.
+//! - `RUSTFIX_TEST_RECORD_JSON=1`:  Records the JSON output to
+//!   `*.recorded.json` files. You can then move that to `.json` or whatever
+//!   you need.
+//! - `RUSTFIX_TEST_RECORD_FIXED_RUST=1`: Records the fixed result to
+//!   `*.recorded.rs` files. You can then move that to `.rs` or whatever you
+//!   need.
+
 #![allow(clippy::disallowed_methods, clippy::print_stdout, clippy::print_stderr)]
 
 use anyhow::{anyhow, ensure, Context, Error};
@@ -79,15 +98,6 @@ fn compiles_without_errors(file: &Path) -> Result<(), Error> {
     }
 }
 
-fn read_file(path: &Path) -> Result<String, Error> {
-    use std::io::Read;
-
-    let mut buffer = String::new();
-    let mut file = fs::File::open(path)?;
-    file.read_to_string(&mut buffer)?;
-    Ok(buffer)
-}
-
 fn diff(expected: &str, actual: &str) -> String {
     use similar::{ChangeTag, TextDiff};
     use std::fmt::Write;
@@ -104,11 +114,7 @@ fn diff(expected: &str, actual: &str) -> String {
                 ChangeTag::Delete => "-",
             };
             if !different {
-                write!(
+                writeln!(&mut res, "differences found (+ == actual, - == expected):").unwrap();
-                    &mut res,
-                    "differences found (+ == actual, - == expected):\n"
-                )
-                .unwrap();
                 different = true;
             }
             write!(&mut res, "{} {}", prefix, change.value()).unwrap();
@@ -133,7 +139,7 @@ fn test_rustfix_with_file<P: AsRef<Path>>(file: P, mode: &str) -> Result<(), Err
     };
 
     debug!("next up: {:?}", file);
-    let code = read_file(file).context(format!("could not read {}", file.display()))?;
+    let code = fs::read_to_string(file)?;
     let errors =
         compile_and_get_json_errors(file).context(format!("could compile {}", file.display()))?;
     let suggestions =
@@ -141,15 +147,11 @@ fn test_rustfix_with_file<P: AsRef<Path>>(file: P, mode: &str) -> Result<(), Err
             .context("could not load suggestions")?;
 
     if std::env::var(settings::RECORD_JSON).is_ok() {
-        use std::io::Write;
+        fs::write(file.with_extension("recorded.json"), &errors)?;
-        let mut recorded_json = fs::File::create(&file.with_extension("recorded.json")).context(
-            format!("could not create recorded.json for {}", file.display()),
-        )?;
-        recorded_json.write_all(errors.as_bytes())?;
     }
 
     if std::env::var(settings::CHECK_JSON).is_ok() {
-        let expected_json = read_file(&json_file).context(format!(
+        let expected_json = fs::read_to_string(&json_file).context(format!(
             "could not load json fixtures for {}",
             file.display()
         ))?;
@@ -171,13 +173,11 @@ fn test_rustfix_with_file<P: AsRef<Path>>(file: P, mode: &str) -> Result<(), Err
         .context(format!("could not apply suggestions to {}", file.display()))?;
 
     if std::env::var(settings::RECORD_FIXED_RUST).is_ok() {
-        use std::io::Write;
+        fs::write(file.with_extension("recorded.rs"), &fixed)?;
-        let mut recorded_rust = fs::File::create(&file.with_extension("recorded.rs"))?;
-        recorded_rust.write_all(fixed.as_bytes())?;
     }
 
-    let expected_fixed =
+    let expected_fixed = fs::read_to_string(&fixed_file)
-        read_file(&fixed_file).context(format!("could read fixed file for {}", file.display()))?;
+        .context(format!("could read fixed file for {}", file.display()))?;
     ensure!(
         fixed.trim() == expected_fixed.trim(),
         "file {} doesn't look fixed:\n{}",
@@ -191,8 +191,7 @@ fn test_rustfix_with_file<P: AsRef<Path>>(file: P, mode: &str) -> Result<(), Err
 }
 
 fn get_fixture_files(p: &str) -> Result<Vec<PathBuf>, Error> {
-    Ok(fs::read_dir(&p)?
+    Ok(fs::read_dir(p)?
-        .into_iter()
         .map(|e| e.unwrap().path())
         .filter(|p| p.is_file())
         .filter(|p| {
@@ -203,7 +202,7 @@ fn get_fixture_files(p: &str) -> Result<Vec<PathBuf>, Error> {
 }
 
 fn assert_fixtures(dir: &str, mode: &str) {
-    let files = get_fixture_files(&dir)
+    let files = get_fixture_files(dir)
         .context(format!("couldn't load dir `{}`", dir))
         .unwrap();
     let mut failures = 0;