Refactor xtasks

xtask/src/pre_commit.rs

@@ -0,0 +1,36 @@
+//! pre-commit hook for code formatting.
+
+use std::{fs, path::PathBuf};
+
+use anyhow::{bail, Result};
+
+use crate::{project_root, run, run_rustfmt, run_with_output, Mode};
+
+// FIXME: if there are changed `.ts` files, also reformat TypeScript (by
+// shelling out to `npm fmt`).
+pub fn run_hook() -> Result<()> {
+    run_rustfmt(Mode::Overwrite)?;
+
+    let diff = run_with_output("git diff --diff-filter=MAR --name-only --cached", ".")?;
+
+    let root = project_root();
+    for line in String::from_utf8(diff.stdout)?.lines() {
+        run(&format!("git update-index --add {}", root.join(line).to_string_lossy()), ".")?;
+    }
+
+    Ok(())
+}
+
+pub fn install_hook() -> Result<()> {
+    let hook_path: PathBuf =
+        format!("./.git/hooks/pre-commit{}", std::env::consts::EXE_SUFFIX).into();
+
+    if hook_path.exists() {
+        bail!("Git hook already created");
+    }
+
+    let me = std::env::current_exe()?;
+    fs::copy(me, hook_path)?;
+
+    Ok(())
+}