Auto merge of #30728 - athaeryn:mention-warning-lint-group, r=Manishearth

Fixes #30203.

This is my first time writing Rust, and I think this code could be a bit better. Any suggestions?

Author: bors

src/librustc_driver/lib.rs

@@ -70,6 +70,7 @@ use rustc_metadata::loader;
 use rustc_metadata::cstore::CStore;
 use rustc::util::common::time;
 
+use std::cmp::max;
 use std::cmp::Ordering::Equal;
 use std::env;
 use std::io::{self, Read, Write};
@@ -627,11 +628,13 @@ Available lint options:
 
 
 
-    let max_name_len = plugin_groups.iter()
-                                    .chain(&builtin_groups)
-                                    .map(|&(s, _)| s.chars().count())
-                                    .max()
-                                    .unwrap_or(0);
+    let max_name_len = max("warnings".len(),
+                           plugin_groups.iter()
+                                        .chain(&builtin_groups)
+                                        .map(|&(s, _)| s.chars().count())
+                                        .max()
+                                        .unwrap_or(0));
+
     let padded = |x: &str| {
         let mut s = repeat(" ")
                         .take(max_name_len - x.chars().count())
@@ -643,6 +646,7 @@ Available lint options:
     println!("Lint groups provided by rustc:\n");
     println!("    {}  {}", padded("name"), "sub-lints");
     println!("    {}  {}", padded("----"), "---------");
+    println!("    {}  {}", padded("warnings"), "all built-in lints");
 
     let print_lint_groups = |lints: Vec<(&'static str, Vec<lint::LintId>)>| {
         for (name, to) in lints {