Auto merge of #77671 - flip1995:lint_list_always_plugins, r=oli-obk,Manishearth

Always print lints from plugins, if they're available

Currently you can get a list of lints and lint groups by running `rustc
-Whelp`. This prints an additional line at the end:
```
Compiler plugins can provide additional lints and lint groups. To see a listing of these, re-run `rustc -W help` with a crate filename.
```

Clippy is such a "compiler plugin", that provides additional lints.
Running `clippy-driver -Whelp` (`rustc` wrapper) still only prints the
rustc lints with the above message at the end. But when running
`clippy-driver -Whelp main.rs`, where `main.rs` is any rust file, it
also prints Clippy lints. I don't think this is a good approach from a
UX perspective: Why is a random file necessary to print a help message?

This PR changes this behavior: Whenever a compiler callback
registers lints, it is assumed that these lints come from a plugin and
are printed without having to specify a Rust source file.

Fixes rust-lang/rust-clippy#6122

cc `@Manishearth` `@ebroto` for the Clippy changes.

2 files changed, 13 insertions, 6 deletions

diff --git a/compiler/rustc_driver/src/lib.rs b/compiler/rustc_driver/src/lib.rs
index e87d8b7ab45..c1741bfaaba 100644
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@@ -248,11 +248,18 @@ fn run_compiler(
                 interface::run_compiler(config, |compiler| {
                     let sopts = &compiler.session().opts;
                     if sopts.describe_lints {
-                        let lint_store = rustc_lint::new_lint_store(
+                        let mut lint_store = rustc_lint::new_lint_store(
                             sopts.debugging_opts.no_interleave_lints,
                             compiler.session().unstable_options(),
                         );
-                        describe_lints(compiler.session(), &lint_store, false);
+                        let registered_lints =
+                            if let Some(register_lints) = compiler.register_lints() {
+                                register_lints(compiler.session(), &mut lint_store);
+                                true
+                            } else {
+                                false
+                            };
+                        describe_lints(compiler.session(), &lint_store, registered_lints);
                         return;
                     }
                     let should_stop = RustcDefaultCalls::print_crate_info(
@@ -954,10 +961,7 @@ Available lint options:
 
     match (loaded_plugins, plugin.len(), plugin_groups.len()) {
         (false, 0, _) | (false, _, 0) => {
-            println!(
-                "Compiler plugins can provide additional lints and lint groups. To see a \
-                      listing of these, re-run `rustc -W help` with a crate filename."
-            );
+            println!("Lint tools like Clippy can provide additional lints and lint groups.");
         }
         (false, ..) => panic!("didn't load lint plugins but got them anyway!"),
         (true, 0, 0) => println!("This crate does not load any lint plugins or lint groups."),
diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 73a51ad477b..11dd6ec32c0 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -56,6 +56,9 @@ impl Compiler {
     pub fn output_file(&self) -> &Option<PathBuf> {
         &self.output_file
     }
+    pub fn register_lints(&self) -> &Option<Box<dyn Fn(&Session, &mut LintStore) + Send + Sync>> {
+        &self.register_lints
+    }
     pub fn build_output_filenames(
         &self,
         sess: &Session,