Include both ruff help and ruff help check in README (#2325)

ruff_cli/src/lib.rs

@@ -1,5 +1,5 @@
 //! This library only exists to enable the Ruff internal tooling (`ruff_dev`)
-//! to automatically update the `ruff --help` output in the `README.md`.
+//! to automatically update the `ruff help` output in the `README.md`.
 //!
 //! For the actual Ruff library, see [`ruff`].
 #![forbid(unsafe_code)]
@@ -10,7 +10,26 @@ mod args;
 
 use clap::CommandFactory;
 
-/// Returns the output of `ruff --help`.
-pub fn help() -> String {
+/// Returns the output of `ruff help`.
+pub fn command_help() -> String {
     args::Args::command().render_help().to_string()
 }
+
+/// Returns the output of `ruff help check`.
+pub fn subcommand_help() -> String {
+    let output = args::Args::command()
+        .find_subcommand_mut("check")
+        .expect("`check` subcommand not found")
+        .render_help()
+        .to_string();
+
+    // Replace the header, to fix Clap's omission of "ruff" on the "Usage: check" line.
+    let header =
+        "Run Ruff on the given files or directories (default)\n\nUsage: check [OPTIONS] [FILES]...";
+    let replacement =
+        "Run Ruff on the given files or directories\n\nUsage: ruff check [OPTIONS] [FILES]...";
+    let output = output
+        .strip_prefix(header)
+        .expect("`output` does not start expected header");
+    format!("{replacement}{output}")
+}