Auto merge of #4175 - yaahallo:master, r=oli-obk

Implement better help for clippy-driver

https://github.com/rust-lang/rust-clippy/issues/4173

clippy_dev/src/main.rs

@@ -87,9 +87,31 @@ fn print_lints() {
 
 fn update_lints(update_mode: &UpdateMode) {
     let lint_list: Vec<Lint> = gather_all().collect();
+
     let usable_lints: Vec<Lint> = Lint::usable_lints(lint_list.clone().into_iter()).collect();
     let lint_count = usable_lints.len();
 
+    let mut sorted_usable_lints = usable_lints.clone();
+    sorted_usable_lints.sort_by_key(|lint| lint.name.clone());
+
+    std::fs::write(
+        "../src/lintlist/mod.rs",
+        &format!(
+            "\
+//! This file is managed by `util/dev update_lints`. Do not edit.
+
+pub mod lint;
+pub use lint::Level;
+pub use lint::Lint;
+pub use lint::LINT_LEVELS;
+
+pub const ALL_LINTS: [Lint; {}] = {:#?};\n",
+            sorted_usable_lints.len(),
+            sorted_usable_lints
+        ),
+    )
+    .expect("can write to file");
+
     let mut file_change = replace_region_in_file(
         "../README.md",
         r#"\[There are \d+ lints included in this crate!\]\(https://rust-lang.github.io/rust-clippy/master/index.html\)"#,

src/driver.rs

@@ -15,6 +15,8 @@ use rustc_tools_util::*;
 use std::path::Path;
 use std::process::{exit, Command};
 
+mod lintlist;
+
 /// If a command-line option matches `find_arg`, then apply the predicate `pred` on its value. If
 /// true, then return it. The parameter is assumed to be either `--arg=value` or `--arg value`.
 fn arg_value<'a>(
@@ -108,6 +110,142 @@ impl rustc_driver::Callbacks for ClippyCallbacks {
     }
 }
 
+#[allow(clippy::find_map, clippy::filter_map)]
+fn describe_lints() {
+    use lintlist::*;
+    use std::collections::HashSet;
+
+    println!(
+        "
+Available lint options:
+    -W <foo>           Warn about <foo>
+    -A <foo>           Allow <foo>
+    -D <foo>           Deny <foo>
+    -F <foo>           Forbid <foo> (deny <foo> and all attempts to override)
+
+"
+    );
+
+    let lint_level = |lint: &Lint| {
+        LINT_LEVELS
+            .iter()
+            .find(|level_mapping| level_mapping.0 == lint.group)
+            .map(|(_, level)| match level {
+                Level::Allow => "allow",
+                Level::Warn => "warn",
+                Level::Deny => "deny",
+            })
+            .unwrap()
+    };
+
+    let mut lints: Vec<_> = ALL_LINTS.iter().collect();
+    // The sort doesn't case-fold but it's doubtful we care.
+    lints.sort_by_cached_key(|x: &&Lint| (lint_level(x), x.name));
+
+    let max_lint_name_len = lints
+        .iter()
+        .map(|lint| lint.name.len())
+        .map(|len| len + "clippy::".len())
+        .max()
+        .unwrap_or(0);
+
+    let padded = |x: &str| {
+        let mut s = " ".repeat(max_lint_name_len - x.chars().count());
+        s.push_str(x);
+        s
+    };
+
+    let scoped = |x: &str| format!("clippy::{}", x);
+
+    let lint_groups: HashSet<_> = lints.iter().map(|lint| lint.group).collect();
+
+    println!("Lint checks provided by clippy:\n");
+    println!("    {}  {:7.7}  meaning", padded("name"), "default");
+    println!("    {}  {:7.7}  -------", padded("----"), "-------");
+
+    let print_lints = |lints: &[&Lint]| {
+        for lint in lints {
+            let name = lint.name.replace("_", "-");
+            println!(
+                "    {}  {:7.7}  {}",
+                padded(&scoped(&name)),
+                lint_level(lint),
+                lint.desc
+            );
+        }
+        println!("\n");
+    };
+
+    print_lints(&lints);
+
+    let max_group_name_len = std::cmp::max(
+        "clippy::all".len(),
+        lint_groups
+            .iter()
+            .map(|group| group.len())
+            .map(|len| len + "clippy::".len())
+            .max()
+            .unwrap_or(0),
+    );
+
+    let padded_group = |x: &str| {
+        let mut s = " ".repeat(max_group_name_len - x.chars().count());
+        s.push_str(x);
+        s
+    };
+
+    println!("Lint groups provided by clippy:\n");
+    println!("    {}  sub-lints", padded_group("name"));
+    println!("    {}  ---------", padded_group("----"));
+    println!("    {}  the set of all clippy lints", padded_group("clippy::all"));
+
+    let print_lint_groups = || {
+        for group in lint_groups {
+            let name = group.to_lowercase().replace("_", "-");
+            let desc = lints
+                .iter()
+                .filter(|&lint| lint.group == group)
+                .map(|lint| lint.name)
+                .map(|name| name.replace("_", "-"))
+                .collect::<Vec<String>>()
+                .join(", ");
+            println!("    {}  {}", padded_group(&scoped(&name)), desc);
+        }
+        println!("\n");
+    };
+
+    print_lint_groups();
+}
+
+fn display_help() {
+    println!(
+        "\
+Checks a package to catch common mistakes and improve your Rust code.
+
+Usage:
+    cargo clippy [options] [--] [<opts>...]
+
+Common options:
+    -h, --help               Print this message
+    -V, --version            Print version info and exit
+
+Other options are the same as `cargo check`.
+
+To allow or deny a lint from the command line you can use `cargo clippy --`
+with:
+
+    -W --warn OPT       Set lint warnings
+    -A --allow OPT      Set lint allowed
+    -D --deny OPT       Set lint denied
+    -F --forbid OPT     Set lint forbidden
+
+You can use tool lints to allow or deny lints from your code, eg.:
+
+    #[allow(clippy::needless_lifetimes)]
+"
+    );
+}
+
 pub fn main() {
     rustc_driver::init_rustc_env_logger();
     exit(
@@ -153,13 +291,34 @@ pub fn main() {
 
             // Setting RUSTC_WRAPPER causes Cargo to pass 'rustc' as the first argument.
             // We're invoking the compiler programmatically, so we ignore this/
-            if orig_args.len() <= 1 {
-                std::process::exit(1);
-            }
-            if Path::new(&orig_args[1]).file_stem() == Some("rustc".as_ref()) {
+            let wrapper_mode = Path::new(&orig_args[1]).file_stem() == Some("rustc".as_ref());
+
+            if wrapper_mode {
                 // we still want to be able to invoke it normally though
                 orig_args.remove(1);
             }
+
+            if !wrapper_mode && std::env::args().any(|a| a == "--help" || a == "-h") {
+                display_help();
+                exit(0);
+            }
+
+            let should_describe_lints = || {
+                let args: Vec<_> = std::env::args().collect();
+                args.windows(2).any(|args| {
+                    args[1] == "help"
+                        && match args[0].as_str() {
+                            "-W" | "-A" | "-D" | "-F" => true,
+                            _ => false,
+                        }
+                })
+            };
+
+            if !wrapper_mode && should_describe_lints() {
+                describe_lints();
+                exit(0);
+            }
+
             // this conditional check for the --sysroot flag is there so users can call
             // `clippy_driver` directly
             // without having to pass --sysroot or anything

src/lintlist/lint.rs

@@ -0,0 +1,27 @@
+/// Lint data parsed from the Clippy source code.
+#[derive(Clone, PartialEq, Debug)]
+pub struct Lint {
+    pub name: &'static str,
+    pub group: &'static str,
+    pub desc: &'static str,
+    pub deprecation: Option<&'static str>,
+    pub module: &'static str,
+}
+
+#[derive(PartialOrd, PartialEq, Ord, Eq)]
+pub enum Level {
+    Allow,
+    Warn,
+    Deny,
+}
+
+pub const LINT_LEVELS: [(&str, Level); 8] = [
+    ("correctness", Level::Deny),
+    ("style", Level::Warn),
+    ("complexity", Level::Warn),
+    ("perf", Level::Warn),
+    ("restriction", Level::Allow),
+    ("pedantic", Level::Allow),
+    ("nursery", Level::Allow),
+    ("cargo", Level::Allow),
+];