Reimplement format-hook using a rust binary

crates/tools/src/bin/pre-commit.rs

@@ -0,0 +1,37 @@
+use std::{
+    process::{Command},
+};
+
+use tools::{Result, run_rustfmt, run, project_root};
+use failure::bail;
+
+fn main() -> tools::Result<()> {
+    run_rustfmt(tools::Overwrite)?;
+    update_staged()
+}
+
+fn update_staged() -> Result<()> {
+    let root = project_root();
+    let output = Command::new("git")
+        .arg("diff")
+        .arg("--name-only")
+        .arg("--cached")
+        .current_dir(&root)
+        .output()?;
+    if !output.status.success() {
+        bail!(
+            "`git diff --name-only --cached` exited with {}",
+            output.status
+        );
+    }
+    for line in String::from_utf8(output.stdout)?.lines() {
+        run(
+            &format!(
+                "git update-index --add {}",
+                root.join(line).to_string_lossy()
+            ),
+            ".",
+        )?;
+    }
+    Ok(())
+}