do not overwrite unconditionally

ci/semantic-line-breaks/Cargo.toml

@@ -10,3 +10,7 @@ ignore = "0.4"
 [dependencies.regex]
 version = "1"
 features = ["pattern"]
+
+[dependencies.clap]
+version = "4"
+features = ["derive"]

ci/semantic-line-breaks/src/main.rs

@@ -1,17 +1,20 @@
-use std::{env, fs, process};
+use std::{fs, path::PathBuf};
 
 use anyhow::Result;
+use clap::Parser;
 use ignore::Walk;
 use regex::Regex;
 
+#[derive(Parser)]
+struct Cli {
+ root_dir: PathBuf,
+ #[arg(long)]
+ overwrite: bool,
+}
+
 fn main() -> Result<()> {
- let mut args = env::args();
- if args.len() == 1 {
- eprintln!("error: expected root Markdown directory as CLI argument");
- process::exit(1);
- }
- let root_dir = args.nth(1).unwrap();
- for result in Walk::new(root_dir) {
+ let cli = Cli::parse();
+ for result in Walk::new(cli.root_dir) {
  let entry = result?;
  if entry.file_type().expect("no stdin").is_dir() {
  continue;
@@ -27,7 +30,15 @@ fn main() -> Result<()> {
  let old = fs::read_to_string(path)?;
  let new = comply(&old)?;
  if new != old {
- fs::write(path, new)?;
+ if cli.overwrite {
+ fs::write(path, new)?;
+ } else {
+ println!("{}:", path.display());
+ println!("{new}");
+ println!();
+ println!("---");
+ println!();
+ }
  }
  }
  Ok(())