From 0e4d5eeea738f77051390d67edb1093f39156edc Mon Sep 17 00:00:00 2001
From: Martin Fischer <martin@push-f.com>
Date: Sat, 11 Feb 2023 18:37:11 +0100
Subject: [PATCH] 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                              |  1 +
 crates/ruff_cli/src/args.rs            |  2 ++
 crates/ruff_cli/src/commands/config.rs | 48 ++++++++++++++++++++++++++
 crates/ruff_cli/src/commands/mod.rs    |  1 +
 crates/ruff_cli/src/main.rs            |  1 +
 5 files changed, 53 insertions(+)
 create mode 100644 crates/ruff_cli/src/commands/config.rs

diff --git a/README.md b/README.md
index c34bc17320..9f598d63b9 100644
--- a/README.md
+++ b/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)
diff --git a/crates/ruff_cli/src/args.rs b/crates/ruff_cli/src/args.rs
index 784f0a9236..70110d8ba1 100644
--- a/crates/ruff_cli/src/args.rs
+++ b/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
diff --git a/crates/ruff_cli/src/commands/config.rs b/crates/ruff_cli/src/commands/config.rs
new file mode 100644
index 0000000000..88d58ab8ec
--- /dev/null
+++ b/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
+}
diff --git a/crates/ruff_cli/src/commands/mod.rs b/crates/ruff_cli/src/commands/mod.rs
index a4deee4a14..bc08aa1cd8 100644
--- a/crates/ruff_cli/src/commands/mod.rs
+++ b/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;
diff --git a/crates/ruff_cli/src/main.rs b/crates/ruff_cli/src/main.rs
index 26d6731549..d8ed2bc85e 100644
--- a/crates/ruff_cli/src/main.rs
+++ b/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 } => {