Implement config subcommand

The synopsis is as follows.

List all top-level config keys:

    $ ruff config
    allowed-confusables
    builtins
    cache-dir
    ... etc.

List all config keys in a specific section:

    $ ruff config mccabe
    max-complexity

Describe a specific config option:

    $ ruff config mccabe.max-complexity
    The maximum McCabe complexity to allow before triggering `C901` errors.

    Default value: 10
    Type: int
    Example usage:
    ```toml
    # Flag errors (`C901`) whenever the complexity level exceeds 5.
    max-complexity = 5
    ```

README.md

@@ -393,6 +393,7 @@ Usage: ruff [OPTIONS] <COMMAND>
 Commands:
   check   Run Ruff on the given files or directories (default)
   rule    Explain a rule
+  config  List or describe the available configuration options
   linter  List all supported upstream linters
   clean   Clear any caches in the current directory and any subdirectories
   help    Print this message or the help of the given subcommand(s)

crates/ruff_cli/src/args.rs

@@ -44,6 +44,8 @@ pub enum Command {
         #[arg(long, value_enum, default_value = "pretty")]
         format: HelpFormat,
     },
+    /// List or describe the available configuration options
+    Config { option: Option<String> },
     /// List all supported upstream linters
     Linter {
         /// Output format

crates/ruff_cli/src/commands/config.rs

@@ -0,0 +1,48 @@
+use ruff::settings::{
+    options::Options,
+    options_base::{ConfigurationOptions, OptionEntry, OptionField},
+};
+
+use crate::ExitStatus;
+
+#[allow(clippy::print_stdout)]
+pub(crate) fn config(option: Option<&str>) -> ExitStatus {
+    let entries = Options::get_available_options();
+    let mut entries = &entries;
+
+    let mut parts_iter = option.iter().flat_map(|s| s.split('.'));
+
+    while let Some(part) = parts_iter.next() {
+        let Some((_, field)) = entries.iter().find(|(name, _)| *name == part) else {
+            println!("Unknown option");
+            return ExitStatus::Error;
+        };
+        match field {
+            OptionEntry::Field(OptionField {
+                doc,
+                default,
+                value_type,
+                example,
+            }) => {
+                if parts_iter.next().is_some() {
+                    println!("Unknown option");
+                    return ExitStatus::Error;
+                }
+
+                println!("{doc}");
+                println!();
+                println!("Default value: {default}");
+                println!("Type: {value_type}");
+                println!("Example usage:\n```toml\n{example}\n```");
+                return ExitStatus::Success;
+            }
+            OptionEntry::Group(fields) => {
+                entries = fields;
+            }
+        }
+    }
+    for (name, _) in entries {
+        println!("{name}");
+    }
+    ExitStatus::Success
+}

crates/ruff_cli/src/commands/mod.rs

@@ -9,6 +9,7 @@ pub use show_settings::show_settings;
 
 mod add_noqa;
 mod clean;
+pub mod config;
 mod linter;
 mod rule;
 mod run;

crates/ruff_cli/src/main.rs

@@ -101,6 +101,7 @@ quoting the executed command, along with the relevant file contents and `pyproje
 
     match command {
         Command::Rule { rule, format } => commands::rule(&rule, format)?,
+        Command::Config { option } => return Ok(commands::config::config(option.as_deref())),
         Command::Linter { format } => commands::linter(format)?,
         Command::Clean => commands::clean(log_level)?,
         Command::GenerateShellCompletion { shell } => {