Address review comments.

- Add newline at end of file.
- Remove unnecessary rustfmt changes.
- Move file writing code to `write_if_changed`.

src/cargo/core/compiler/custom_build.rs

@@ -560,17 +560,10 @@ fn prepare_metabuild<'a, 'cfg>(
     for dep in &meta_deps {
         output.push(format!("    {}::metabuild();\n", dep));
     }
-    output.push("}".to_string());
+    output.push("}\n".to_string());
     let output = output.join("");
     let path = cx.files().metabuild_path(unit);
-    let changed = if let Ok(orig) = fs::read_to_string(&path) {
-        orig != output
-    } else {
-        true
-    };
-    if changed {
-        fs::write(&path, output)?;
-    }
+    paths::write_if_changed(path, &output)?;
     Ok(())
 }
 
@@ -622,8 +615,7 @@ pub fn build_map<'b, 'cfg>(cx: &mut Context<'b, 'cfg>, units: &[Unit<'b>]) -> Ca
         }
 
         {
-            let key = unit
-                .pkg
+            let key = unit.pkg
                 .manifest()
                 .links()
                 .map(|l| (l.to_string(), unit.kind));

src/cargo/util/paths.rs

@@ -142,6 +142,26 @@ pub fn write(path: &Path, contents: &[u8]) -> CargoResult<()> {
     Ok(())
 }
 
+pub fn write_if_changed<P: AsRef<Path>, C: AsRef<[u8]>>(path: P, contents: C) -> CargoResult<()> {
+    (|| -> CargoResult<()> {
+        let contents = contents.as_ref();
+        let mut f = OpenOptions::new()
+            .read(true)
+            .write(true)
+            .create(true)
+            .open(&path)?;
+        let mut orig = Vec::new();
+        f.read_to_end(&mut orig)?;
+        if orig != contents {
+            f.set_len(0)?;
+            f.write_all(contents)?;
+        }
+        Ok(())
+    })()
+        .chain_err(|| format!("failed to write `{}`", path.as_ref().display()))?;
+    Ok(())
+}
+
 pub fn append(path: &Path, contents: &[u8]) -> CargoResult<()> {
     (|| -> CargoResult<()> {
         let mut f = OpenOptions::new()

src/cargo/util/toml/targets.rs

@@ -528,14 +528,7 @@ fn clean_targets_with_legacy_path(
     validate_unique_names(&toml_targets, target_kind)?;
     let mut result = Vec::new();
     for target in toml_targets {
-        let path = target_path(
-            &target,
-            inferred,
-            target_kind,
-            package_root,
-            edition,
-            legacy_path,
-        );
+        let path = target_path(&target, inferred, target_kind, package_root, edition, legacy_path);
         let path = match path {
             Ok(path) => path,
             Err(e) => {