Implement shell autocompletion for rule codes

For example:

    $ ruff check --select=EM<Tab>
    EM          -- flake8-errmsg
    EM10   EM1  --
    EM101       -- raw-string-in-exception
    EM102       -- f-string-in-exception
    EM103       -- dot-format-in-exception

(You will need to enable autocompletion as described
 in the Autocompletion section in the README.)

Fixes #2808.

(The --help help change in the README is due to a clap bug,
 for which I already submitted a fix:
 https://github.com/clap-rs/clap/pull/4710.)

README.md

@@ -468,7 +468,7 @@ Options:
       --show-settings
           See the settings Ruff will use to lint a given Python file
   -h, --help
-          Print help
+          Print help (see more with '--help')
 
 Rule selection:
       --select <RULE_CODE>

crates/ruff/Cargo.toml

@@ -21,7 +21,7 @@ bisection = { version = "0.1.0" }
 bitflags = { version = "1.3.2" }
 cfg-if = { version = "1.0.0" }
 chrono = { version = "0.4.21", default-features = false, features = ["clock"] }
-clap = { workspace = true, features = ["derive", "env"] }
+clap = { workspace = true, features = ["derive", "env", "string"] }
 colored = { version = "2.0.0" }
 dirs = { version = "4.0.0" }
 fern = { version = "0.6.1" }

crates/ruff/src/rule_selector.rs

@@ -233,3 +233,76 @@ pub(crate) enum Specificity {
     Code4Chars,
     Code5Chars,
 }
+
+mod clap_completion {
+    use clap::builder::{PossibleValue, TypedValueParser, ValueParserFactory};
+    use strum::IntoEnumIterator;
+
+    use crate::{
+        codes::RuleCodePrefix,
+        registry::{Linter, RuleNamespace},
+        RuleSelector,
+    };
+
+    #[derive(Clone)]
+    pub struct RuleSelectorParser;
+
+    impl ValueParserFactory for RuleSelector {
+        type Parser = RuleSelectorParser;
+
+        fn value_parser() -> Self::Parser {
+            RuleSelectorParser
+        }
+    }
+
+    impl TypedValueParser for RuleSelectorParser {
+        type Value = RuleSelector;
+
+        fn parse_ref(
+            &self,
+            _cmd: &clap::Command,
+            _arg: Option<&clap::Arg>,
+            value: &std::ffi::OsStr,
+        ) -> Result<Self::Value, clap::Error> {
+            let value = value
+                .to_str()
+                .ok_or_else(|| clap::Error::new(clap::error::ErrorKind::InvalidUtf8))?;
+
+            value
+                .parse()
+                .map_err(|e| clap::Error::raw(clap::error::ErrorKind::InvalidValue, e))
+        }
+
+        fn possible_values(
+            &self,
+        ) -> Option<Box<dyn Iterator<Item = clap::builder::PossibleValue> + '_>> {
+            Some(Box::new(
+                std::iter::once(PossibleValue::new("ALL").help("all rules")).chain(
+                    Linter::iter()
+                        .filter_map(|l| {
+                            let prefix = l.common_prefix();
+                            (!prefix.is_empty()).then(|| PossibleValue::new(prefix).help(l.name()))
+                        })
+                        .chain(RuleCodePrefix::iter().map(|p| {
+                            let prefix = p.linter().common_prefix();
+                            let code = p.short_code();
+
+                            let mut rules_iter = p.into_iter();
+                            let rule1 = rules_iter.next();
+                            let rule2 = rules_iter.next();
+
+                            let value = PossibleValue::new(format!("{prefix}{code}"));
+
+                            if rule2.is_none() {
+                                let rule1 = rule1.unwrap();
+                                let name: &'static str = rule1.into();
+                                value.help(name)
+                            } else {
+                                value
+                            }
+                        })),
+                ),
+            ))
+        }
+    }
+}

crates/ruff_cli/src/args.rs

@@ -109,7 +109,8 @@ pub struct CheckArgs {
         long,
         value_delimiter = ',',
         value_name = "RULE_CODE",
-        help_heading = "Rule selection"
+        help_heading = "Rule selection",
+        hide_possible_values = true
     )]
     pub select: Option<Vec<RuleSelector>>,
     /// Comma-separated list of rule codes to disable.
@@ -117,7 +118,8 @@ pub struct CheckArgs {
         long,
         value_delimiter = ',',
         value_name = "RULE_CODE",
-        help_heading = "Rule selection"
+        help_heading = "Rule selection",
+        hide_possible_values = true
     )]
     pub ignore: Option<Vec<RuleSelector>>,
     /// Like --select, but adds additional rule codes on top of the selected
@@ -126,7 +128,8 @@ pub struct CheckArgs {
         long,
         value_delimiter = ',',
         value_name = "RULE_CODE",
-        help_heading = "Rule selection"
+        help_heading = "Rule selection",
+        hide_possible_values = true
     )]
     pub extend_select: Option<Vec<RuleSelector>>,
     /// Like --ignore. (Deprecated: You can just use --ignore instead.)
@@ -164,7 +167,8 @@ pub struct CheckArgs {
         long,
         value_delimiter = ',',
         value_name = "RULE_CODE",
-        help_heading = "Rule selection"
+        help_heading = "Rule selection",
+        hide_possible_values = true
     )]
     pub fixable: Option<Vec<RuleSelector>>,
     /// List of rule codes to treat as ineligible for autofix. Only applicable
@@ -173,7 +177,8 @@ pub struct CheckArgs {
         long,
         value_delimiter = ',',
         value_name = "RULE_CODE",
-        help_heading = "Rule selection"
+        help_heading = "Rule selection",
+        hide_possible_values = true
     )]
     pub unfixable: Option<Vec<RuleSelector>>,
     /// Respect file exclusions via `.gitignore` and other standard ignore

crates/ruff_macros/src/register_rules.rs

@@ -57,6 +57,7 @@ pub fn register_rules(input: &Input) -> proc_macro2::TokenStream {
             PartialOrd,
             Ord,
             AsRefStr,
+            ::strum_macros::IntoStaticStr,
         )]
         #[strum(serialize_all = "kebab-case")]
         pub enum Rule { #rule_variants }