Automatically update README.md from generate_rules_table.rs (#606)

examples/generate_rules_table.rs

@@ -1,28 +1,81 @@
-//! Generate a Markdown-compatible table of supported lint rules.
+use std::fs;
+use std::fs::OpenOptions;
+use std::io::Write;
 
+use anyhow::Result;
+use clap::Parser;
 use ruff::checks::{CheckCategory, CheckCode};
 use strum::IntoEnumIterator;
 
-fn main() {
-    for check_category in CheckCategory::iter() {
-        println!("### {}", check_category.title());
-        println!();
+const FILE: &str = "README.md";
+const BEGIN_PRAGMA: &str = "<!-- Begin auto-generated sections. -->";
+const END_PRAGMA: &str = "<!-- End auto-generated sections. -->";
+
+#[derive(Parser)]
+#[command(author, version, about, long_about = None)]
+/// Generate a Markdown-compatible table of supported lint rules.
+struct Cli {
+    /// Write the generated table to stdout (rather than to `README.md`).
+    #[arg(long)]
+    dry_run: bool,
+}
+
+fn main() -> Result<()> {
+    let cli = Cli::parse();
+
+    // Generate the table string.
+    let mut output = String::new();
+    for check_category in CheckCategory::iter() {
+        output.push_str(&format!("### {}", check_category.title()));
+        output.push('\n');
+        output.push('\n');
+
+        output.push_str("| Coade | Name | Message | Fix |");
+        output.push('\n');
+        output.push_str("| ---- | ---- | ------- | --- |");
+        output.push('\n');
 
-        println!("| Code | Name | Message | Fix |");
-        println!("| ---- | ---- | ------- | --- |");
         for check_code in CheckCode::iter() {
             if check_code.category() == check_category {
                 let check_kind = check_code.kind();
                 let fix_token = if check_kind.fixable() { "🛠" } else { "" };
-                println!(
+                output.push_str(&format!(
                     "| {} | {} | {} | {} |",
                     check_kind.code().as_ref(),
                     check_kind.as_ref(),
                     check_kind.summary().replace("|", r"\|"),
                     fix_token
-                );
+                ));
+                output.push('\n');
             }
         }
-        println!();
+        output.push('\n');
     }
+
+    if cli.dry_run {
+        print!("{}", output);
+    } else {
+        // Read the existing file.
+        let existing = fs::read_to_string(FILE)?;
+
+        // Extract the prefix.
+        let index = existing
+            .find(BEGIN_PRAGMA)
+            .expect("Unable to find begin pragma.");
+        let prefix = &existing[..index + BEGIN_PRAGMA.len()];
+
+        // Extract the suffix.
+        let index = existing
+            .find(END_PRAGMA)
+            .expect("Unable to find end pragma.");
+        let suffix = &existing[index..];
+
+        // Write the prefix, new contents, and suffix.
+        let mut f = OpenOptions::new().write(true).truncate(true).open(FILE)?;
+        write!(f, "{}\n\n", prefix)?;
+        write!(f, "{}", output)?;
+        write!(f, "{}", suffix)?;
+    }
+
+    Ok(())
 }