Remove support for compiler plugins.

They've been deprecated for four years.

This commit includes the following changes.
- It eliminates the `rustc_plugin_impl` crate.
- It changes the language used for lints in
  `compiler/rustc_driver_impl/src/lib.rs` and
  `compiler/rustc_lint/src/context.rs`. External lints are now called
  "loaded" lints, rather than "plugins" to avoid confusion with the old
  plugins. This only has a tiny effect on the output of `-W help`.
- E0457 and E0498 are no longer used.
- E0463 is narrowed, now only relating to unfound crates, not plugins.
- The `plugin` feature was moved from "active" to "removed".
- It removes the entire plugins chapter from the unstable book.
- It removes quite a few tests, mostly all of those in
  `tests/ui-fulldeps/plugin/`.

Closes #29597.

28 files changed, 52 insertions, 322 deletions

diff --git a/compiler/rustc_codegen_cranelift/scripts/test_rustc_tests.sh b/compiler/rustc_codegen_cranelift/scripts/test_rustc_tests.sh
index b485f2571cc..a299b6de6b1 100755
--- a/compiler/rustc_codegen_cranelift/scripts/test_rustc_tests.sh
+++ b/compiler/rustc_codegen_cranelift/scripts/test_rustc_tests.sh
@@ -68,7 +68,6 @@ rm -r tests/run-make/split-debuginfo # same
 rm -r tests/run-make/symbols-include-type-name # --emit=asm not supported
 rm -r tests/run-make/target-specs # i686 not supported by Cranelift
 rm -r tests/run-make/mismatching-target-triples # same
-rm -r tests/run-make/use-extern-for-plugins # same
 rm tests/ui/asm/x86_64/issue-82869.rs # vector regs in inline asm not yet supported
 rm tests/ui/asm/x86_64/issue-96797.rs # const and sym inline asm operands don't work entirely correctly
 
diff --git a/compiler/rustc_driver_impl/Cargo.toml b/compiler/rustc_driver_impl/Cargo.toml
index 252803e3cba..da7c2440faa 100644
--- a/compiler/rustc_driver_impl/Cargo.toml
+++ b/compiler/rustc_driver_impl/Cargo.toml
@@ -39,7 +39,6 @@ rustc_mir_transform = { path = "../rustc_mir_transform" }
 rustc_monomorphize = { path = "../rustc_monomorphize" }
 rustc_parse = { path = "../rustc_parse" }
 rustc_passes = { path = "../rustc_passes" }
-rustc_plugin_impl = { path = "../rustc_plugin_impl" }
 rustc_privacy = { path = "../rustc_privacy" }
 rustc_query_system = { path = "../rustc_query_system" }
 rustc_resolve = { path = "../rustc_resolve" }
diff --git a/compiler/rustc_driver_impl/src/lib.rs b/compiler/rustc_driver_impl/src/lib.rs
index 2c7cc707e29..ee4337754a9 100644
--- a/compiler/rustc_driver_impl/src/lib.rs
+++ b/compiler/rustc_driver_impl/src/lib.rs
@@ -20,8 +20,6 @@
 #[macro_use]
 extern crate tracing;
 
-pub extern crate rustc_plugin_impl as plugin;
-
 use rustc_ast as ast;
 use rustc_codegen_ssa::{traits::CodegenBackend, CodegenErrors, CodegenResults};
 use rustc_data_structures::profiling::{
@@ -132,7 +130,6 @@ pub static DEFAULT_LOCALE_RESOURCES: &[&str] = &[
     rustc_monomorphize::DEFAULT_LOCALE_RESOURCE,
     rustc_parse::DEFAULT_LOCALE_RESOURCE,
     rustc_passes::DEFAULT_LOCALE_RESOURCE,
-    rustc_plugin_impl::DEFAULT_LOCALE_RESOURCE,
     rustc_privacy::DEFAULT_LOCALE_RESOURCE,
     rustc_query_system::DEFAULT_LOCALE_RESOURCE,
     rustc_resolve::DEFAULT_LOCALE_RESOURCE,
@@ -994,16 +991,14 @@ the command line flag directly.
 }
 
 /// Write to stdout lint command options, together with a list of all available lints
-pub fn describe_lints(sess: &Session, lint_store: &LintStore, loaded_plugins: bool) {
+pub fn describe_lints(sess: &Session, lint_store: &LintStore, loaded_lints: bool) {
     safe_println!(
         "
 Available lint options:
     -W <foo>           Warn about <foo>
-    -A <foo>           \
-              Allow <foo>
+    -A <foo>           Allow <foo>
     -D <foo>           Deny <foo>
-    -F <foo>           Forbid <foo> \
-              (deny <foo> and all attempts to override)
+    -F <foo>           Forbid <foo> (deny <foo> and all attempts to override)
 
 "
     );
@@ -1022,18 +1017,18 @@ Available lint options:
         lints
     }
 
-    let (plugin, builtin): (Vec<_>, _) =
-        lint_store.get_lints().iter().cloned().partition(|&lint| lint.is_plugin);
-    let plugin = sort_lints(sess, plugin);
+    let (loaded, builtin): (Vec<_>, _) =
+        lint_store.get_lints().iter().cloned().partition(|&lint| lint.is_loaded);
+    let loaded = sort_lints(sess, loaded);
     let builtin = sort_lints(sess, builtin);
 
-    let (plugin_groups, builtin_groups): (Vec<_>, _) =
+    let (loaded_groups, builtin_groups): (Vec<_>, _) =
         lint_store.get_lint_groups().partition(|&(.., p)| p);
-    let plugin_groups = sort_lint_groups(plugin_groups);
+    let loaded_groups = sort_lint_groups(loaded_groups);
     let builtin_groups = sort_lint_groups(builtin_groups);
 
     let max_name_len =
-        plugin.iter().chain(&builtin).map(|&s| s.name.chars().count()).max().unwrap_or(0);
+        loaded.iter().chain(&builtin).map(|&s| s.name.chars().count()).max().unwrap_or(0);
     let padded = |x: &str| {
         let mut s = " ".repeat(max_name_len - x.chars().count());
         s.push_str(x);
@@ -1061,7 +1056,7 @@ Available lint options:
 
     let max_name_len = max(
         "warnings".len(),
-        plugin_groups
+        loaded_groups
             .iter()
             .chain(&builtin_groups)
             .map(|&(s, _)| s.chars().count())
@@ -1099,20 +1094,22 @@ Available lint options:
 
     print_lint_groups(builtin_groups, true);
 
-    match (loaded_plugins, plugin.len(), plugin_groups.len()) {
+    match (loaded_lints, loaded.len(), loaded_groups.len()) {
         (false, 0, _) | (false, _, 0) => {
-            safe_println!("Lint tools like Clippy can provide additional lints and lint groups.");
+            safe_println!("Lint tools like Clippy can load additional lints and lint groups.");
+        }
+        (false, ..) => panic!("didn't load additional lints but got them anyway!"),
+        (true, 0, 0) => {
+            safe_println!("This crate does not load any additional lints or lint groups.")
         }
-        (false, ..) => panic!("didn't load lint plugins but got them anyway!"),
-        (true, 0, 0) => safe_println!("This crate does not load any lint plugins or lint groups."),
         (true, l, g) => {
             if l > 0 {
-                safe_println!("Lint checks provided by plugins loaded by this crate:\n");
-                print_lints(plugin);
+                safe_println!("Lint checks loaded by this crate:\n");
+                print_lints(loaded);
             }
             if g > 0 {
-                safe_println!("Lint groups provided by plugins loaded by this crate:\n");
-                print_lint_groups(plugin_groups, false);
+                safe_println!("Lint groups loaded by this crate:\n");
+                print_lint_groups(loaded_groups, false);
             }
         }
     }
@@ -1129,7 +1126,7 @@ pub fn describe_flag_categories(handler: &EarlyErrorHandler, matches: &Matches)
         rustc_errors::FatalError.raise();
     }
 
-    // Don't handle -W help here, because we might first load plugins.
+    // Don't handle -W help here, because we might first load additional lints.
     let debug_flags = matches.opt_strs("Z");
     if debug_flags.iter().any(|x| *x == "help") {
         describe_debug_flags();
diff --git a/compiler/rustc_error_codes/src/error_codes/E0457.md b/compiler/rustc_error_codes/src/error_codes/E0457.md
index 2c33d1e6a24..e2dbf53a0f8 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0457.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0457.md
@@ -1,3 +1,5 @@
+#### Note: this error code is no longer emitted by the compiler`
+
 Plugin `..` only found in rlib format, but must be available in dylib format.
 
 Erroneous code example:
diff --git a/compiler/rustc_error_codes/src/error_codes/E0463.md b/compiler/rustc_error_codes/src/error_codes/E0463.md
index d0cd1b1dcb7..9bd8d0e834b 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0463.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0463.md
@@ -1,16 +1,13 @@
-A plugin/crate was declared but cannot be found.
+A crate was declared but cannot be found.
 
 Erroneous code example:
 
 ```compile_fail,E0463
-#![feature(plugin)]
-#![plugin(cookie_monster)] // error: can't find crate for `cookie_monster`
-extern crate cake_is_a_lie; // error: can't find crate for `cake_is_a_lie`
+extern crate foo; // error: can't find crate
 ```
 
 You need to link your code to the relevant crate in order to be able to use it
-(through Cargo or the `-L` option of rustc example). Plugins are crates as
-well, and you link to them the same way.
+(through Cargo or the `-L` option of rustc, for example).
 
 ## Common causes
 
diff --git a/compiler/rustc_error_codes/src/error_codes/E0498.md b/compiler/rustc_error_codes/src/error_codes/E0498.md
index c9ea4a7947f..a67a9317db4 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0498.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0498.md
@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 The `plugin` attribute was malformed.
 
 Erroneous code example:
 
-```compile_fail,E0498
+```ignore (E0498 is no longer emitted)
 #![feature(plugin)]
 #![plugin(foo(args))] // error: invalid argument
 #![plugin(bar="test")] // error: invalid argument
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index e808e4815fe..214de3ca402 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -417,24 +417,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         naked_functions, experimental!(naked)
     ),
 
-    // Plugins:
-    BuiltinAttribute {
-        name: sym::plugin,
-        only_local: false,
-        type_: CrateLevel,
-        template: template!(List: "name"),
-        duplicates: DuplicatesOk,
-        gate: Gated(
-            Stability::Deprecated(
-                "https://github.com/rust-lang/rust/pull/64675",
-                Some("may be removed in a future compiler version"),
-            ),
-            sym::plugin,
-            "compiler plugins are deprecated",
-            cfg_fn!(plugin)
-        ),
-    },
-
     // Testing:
     gated!(
         test_runner, CrateLevel, template!(List: "path"), ErrorFollowing, custom_test_frameworks,
diff --git a/compiler/rustc_feature/src/removed.rs b/compiler/rustc_feature/src/removed.rs
index ed19274a7cc..03f92f69b41 100644
--- a/compiler/rustc_feature/src/removed.rs
+++ b/compiler/rustc_feature/src/removed.rs
@@ -152,9 +152,12 @@ declare_features! (
      Some("removed in favor of `#![feature(marker_trait_attr)]`")),
     (removed, panic_implementation, "1.28.0", Some(44489), None,
      Some("subsumed by `#[panic_handler]`")),
+    /// Allows using `#![plugin(myplugin)]`.
+    (removed, plugin, "CURRENT_RUSTC_VERSION", Some(29597), None,
+     Some("plugins are no longer supported")),
     /// Allows using `#[plugin_registrar]` on functions.
     (removed, plugin_registrar, "1.54.0", Some(29597), None,
-     Some("a __rustc_plugin_registrar symbol must now be defined instead")),
+     Some("plugins are no longer supported")),
     (removed, proc_macro_expr, "1.27.0", Some(54727), None,
      Some("subsumed by `#![feature(proc_macro_hygiene)]`")),
     (removed, proc_macro_gen, "1.27.0", Some(54727), None,
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 72100863bb5..11782e33d84 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -528,8 +528,6 @@ declare_features! (
     (unstable, object_safe_for_dispatch, "1.40.0", Some(43561), None),
     /// Allows using `#[optimize(X)]`.
     (unstable, optimize_attribute, "1.34.0", Some(54882), None),
-    /// Allows using `#![plugin(myplugin)]`.
-    (unstable, plugin, "1.0.0", Some(29597), None),
     /// Allows exhaustive integer pattern matching on `usize` and `isize`.
     (unstable, precise_pointer_size_matching, "1.32.0", Some(56354), None),
     /// Allows macro attributes on expressions, statements and non-inline modules.
diff --git a/compiler/rustc_interface/Cargo.toml b/compiler/rustc_interface/Cargo.toml
index a73152601b3..fd587e53f91 100644
--- a/compiler/rustc_interface/Cargo.toml
+++ b/compiler/rustc_interface/Cargo.toml
@@ -36,7 +36,6 @@ rustc_mir_transform = { path = "../rustc_mir_transform" }
 rustc_monomorphize = { path = "../rustc_monomorphize" }
 rustc_parse = { path = "../rustc_parse" }
 rustc_passes = { path = "../rustc_passes" }
-rustc_plugin_impl = { path = "../rustc_plugin_impl" }
 rustc_privacy = { path = "../rustc_privacy" }
 rustc_query_impl = { path = "../rustc_query_impl" }
 rustc_query_system = { path = "../rustc_query_system" }
diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 8fb6216f381..c4962707f69 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -354,7 +354,7 @@ pub struct Config {
     pub hash_untracked_state: Option<Box<dyn FnOnce(&Session, &mut StableHasher) + Send>>,
 
     /// This is a callback from the driver that is called when we're registering lints;
-    /// it is called during plugin registration when we have the LintStore in a non-shared state.
+    /// it is called during lint loading when we have the LintStore in a non-shared state.
     ///
     /// Note that if you find a Some here you probably want to call that function in the new
     /// function being registered.
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index 2099a6d59cb..7d14d088e59 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -23,11 +23,10 @@ use rustc_middle::util::Providers;
 use rustc_mir_build as mir_build;
 use rustc_parse::{parse_crate_from_file, parse_crate_from_source_str, validate_attr};
 use rustc_passes::{self, abi_test, hir_stats, layout_test};
-use rustc_plugin_impl as plugin;
 use rustc_resolve::Resolver;
 use rustc_session::code_stats::VTableSizeInfo;
 use rustc_session::config::{CrateType, Input, OutFileName, OutputFilenames, OutputType};
-use rustc_session::cstore::{MetadataLoader, Untracked};
+use rustc_session::cstore::Untracked;
 use rustc_session::output::filename_for_input;
 use rustc_session::search_paths::PathKind;
 use rustc_session::{Limit, Session};
@@ -75,25 +74,12 @@ fn count_nodes(krate: &ast::Crate) -> usize {
 
 pub(crate) fn create_lint_store(
     sess: &Session,
-    metadata_loader: &dyn MetadataLoader,
     register_lints: Option<impl Fn(&Session, &mut LintStore)>,
-    pre_configured_attrs: &[ast::Attribute],
 ) -> LintStore {
     let mut lint_store = rustc_lint::new_lint_store(sess.enable_internal_lints());
     if let Some(register_lints) = register_lints {
         register_lints(sess, &mut lint_store);
     }
-
-    let registrars = sess.time("plugin_loading", || {
-        plugin::load::load_plugins(sess, metadata_loader, pre_configured_attrs)
-    });
-    sess.time("plugin_registration", || {
-        let mut registry = plugin::Registry { lint_store: &mut lint_store };
-        for registrar in registrars {
-            registrar(&mut registry);
-        }
-    });
-
     lint_store
 }
 
diff --git a/compiler/rustc_interface/src/queries.rs b/compiler/rustc_interface/src/queries.rs
index 4fb295da640..3a5f788e8dd 100644
--- a/compiler/rustc_interface/src/queries.rs
+++ b/compiler/rustc_interface/src/queries.rs
@@ -148,12 +148,8 @@ impl<'tcx> Queries<'tcx> {
             );
             let dep_graph = setup_dep_graph(sess, crate_name, stable_crate_id)?;
 
-            let lint_store = Lrc::new(passes::create_lint_store(
-                sess,
-                &*self.codegen_backend().metadata_loader(),
-                self.compiler.register_lints.as_deref(),
-                &pre_configured_attrs,
-            ));
+            let lint_store =
+                Lrc::new(passes::create_lint_store(sess, self.compiler.register_lints.as_deref()));
             let cstore = FreezeLock::new(Box::new(CStore::new(
                 self.codegen_backend().metadata_loader(),
                 stable_crate_id,
diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index 5b7ba03d9ad..a5f4c5ff045 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -109,7 +109,7 @@ struct LintAlias {
 
 struct LintGroup {
     lint_ids: Vec<LintId>,
-    from_plugin: bool,
+    is_loaded: bool,
     depr: Option<LintAlias>,
 }
 
@@ -160,9 +160,7 @@ impl LintStore {
                 // Don't display deprecated lint groups.
                 depr.is_none()
             })
-            .map(|(k, LintGroup { lint_ids, from_plugin, .. })| {
-                (*k, lint_ids.clone(), *from_plugin)
-            })
+            .map(|(k, LintGroup { lint_ids, is_loaded, .. })| (*k, lint_ids.clone(), *is_loaded))
     }
 
     pub fn register_early_pass(
@@ -221,7 +219,7 @@ impl LintStore {
                         .entry(edition.lint_name())
                         .or_insert(LintGroup {
                             lint_ids: vec![],
-                            from_plugin: lint.is_plugin,
+                            is_loaded: lint.is_loaded,
                             depr: None,
                         })
                         .lint_ids
@@ -234,7 +232,7 @@ impl LintStore {
                         .entry("future_incompatible")
                         .or_insert(LintGroup {
                             lint_ids: vec![],
-                            from_plugin: lint.is_plugin,
+                            is_loaded: lint.is_loaded,
                             depr: None,
                         })
                         .lint_ids
@@ -249,7 +247,7 @@ impl LintStore {
             alias,
             LintGroup {
                 lint_ids: vec![],
-                from_plugin: false,
+                is_loaded: false,
                 depr: Some(LintAlias { name: lint_name, silent: true }),
             },
         );
@@ -257,21 +255,21 @@ impl LintStore {
 
     pub fn register_group(
         &mut self,
-        from_plugin: bool,
+        is_loaded: bool,
         name: &'static str,
         deprecated_name: Option<&'static str>,
         to: Vec<LintId>,
     ) {
         let new = self
             .lint_groups
-            .insert(name, LintGroup { lint_ids: to, from_plugin, depr: None })
+            .insert(name, LintGroup { lint_ids: to, is_loaded, depr: None })
             .is_none();
         if let Some(deprecated) = deprecated_name {
             self.lint_groups.insert(
                 deprecated,
                 LintGroup {
                     lint_ids: vec![],
-                    from_plugin,
+                    is_loaded,
                     depr: Some(LintAlias { name, silent: false }),
                 },
             );
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index d61c59af1e0..54adedd3c09 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -10,7 +10,7 @@
 //! all other analyses. The `LintPass`es built into rustc are defined
 //! within [rustc_session::lint::builtin],
 //! which has further comments on how to add such a lint.
-//! rustc can also load user-defined lint plugins via the plugin mechanism.
+//! rustc can also load external lint plugins, as is done for Clippy.
 //!
 //! Some of rustc's lints are defined elsewhere in the compiler and work by
 //! calling `add_lint()` on the overall `Session` object. This works when
diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index 7ba589c3b5a..878c1a65dbf 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/compiler/rustc_lint_defs/src/lib.rs
@@ -321,7 +321,7 @@ pub struct Lint {
 
     pub future_incompatible: Option<FutureIncompatibleInfo>,
 
-    pub is_plugin: bool,
+    pub is_loaded: bool,
 
     /// `Some` if this lint is feature gated, otherwise `None`.
     pub feature_gate: Option<Symbol>,
@@ -399,7 +399,7 @@ impl Lint {
             default_level: Level::Forbid,
             desc: "",
             edition_lint_opts: None,
-            is_plugin: false,
+            is_loaded: false,
             report_in_external_macro: false,
             future_incompatible: None,
             feature_gate: None,
@@ -735,7 +735,7 @@ macro_rules! declare_lint {
             name: stringify!($NAME),
             default_level: $crate::$Level,
             desc: $desc,
-            is_plugin: false,
+            is_loaded: false,
             $($v: true,)*
             $(feature_gate: Some($gate),)?
             $(future_incompatible: Some($crate::FutureIncompatibleInfo {
@@ -777,7 +777,7 @@ macro_rules! declare_tool_lint {
             edition_lint_opts: None,
             report_in_external_macro: $external,
             future_incompatible: None,
-            is_plugin: true,
+            is_loaded: true,
             $(feature_gate: Some($gate),)?
             crate_level_only: false,
             ..$crate::Lint::default_fields_for_macro()
diff --git a/compiler/rustc_metadata/messages.ftl b/compiler/rustc_metadata/messages.ftl
index 633004fdddf..d1815717e22 100644
--- a/compiler/rustc_metadata/messages.ftl
+++ b/compiler/rustc_metadata/messages.ftl
@@ -196,9 +196,6 @@ metadata_newer_crate_version =
 metadata_no_crate_with_triple =
     couldn't find crate `{$crate_name}` with expected target triple {$locator_triple}{$add_info}
 
-metadata_no_dylib_plugin =
-    plugin `{$crate_name}` only found in rlib format, but must be available in dylib format
-
 metadata_no_link_mod_override =
     overriding linking modifiers from command line is not supported
 
diff --git a/compiler/rustc_metadata/src/errors.rs b/compiler/rustc_metadata/src/errors.rs
index 59b35a6406d..70daee291e7 100644
--- a/compiler/rustc_metadata/src/errors.rs
+++ b/compiler/rustc_metadata/src/errors.rs
@@ -683,14 +683,6 @@ impl IntoDiagnostic<'_> for CannotFindCrate {
 }
 
 #[derive(Diagnostic)]
-#[diag(metadata_no_dylib_plugin, code = "E0457")]
-pub struct NoDylibPlugin {
-    #[primary_span]
-    pub span: Span,
-    pub crate_name: Symbol,
-}
-
-#[derive(Diagnostic)]
 #[diag(metadata_crate_location_unknown_type)]
 pub struct CrateLocationUnknownType<'a> {
     #[primary_span]
diff --git a/compiler/rustc_metadata/src/locator.rs b/compiler/rustc_metadata/src/locator.rs
index 3062939d8da..3a99ddc1b7a 100644
--- a/compiler/rustc_metadata/src/locator.rs
+++ b/compiler/rustc_metadata/src/locator.rs
@@ -220,7 +220,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::memmap::Mmap;
 use rustc_data_structures::owned_slice::slice_owned;
 use rustc_data_structures::svh::Svh;
-use rustc_errors::{DiagnosticArgValue, FatalError, IntoDiagnosticArg};
+use rustc_errors::{DiagnosticArgValue, IntoDiagnosticArg};
 use rustc_fs_util::try_canonicalize;
 use rustc_session::config;
 use rustc_session::cstore::{CrateSource, MetadataLoader};
@@ -857,46 +857,6 @@ fn get_metadata_section<'p>(
     }
 }
 
-/// Look for a plugin registrar. Returns its library path and crate disambiguator.
-pub fn find_plugin_registrar(
-    sess: &Session,
-    metadata_loader: &dyn MetadataLoader,
-    span: Span,
-    name: Symbol,
-) -> PathBuf {
-    find_plugin_registrar_impl(sess, metadata_loader, name).unwrap_or_else(|err| {
-        // `core` is always available if we got as far as loading plugins.
-        err.report(sess, span, false);
-        FatalError.raise()
-    })
-}
-
-fn find_plugin_registrar_impl<'a>(
-    sess: &'a Session,
-    metadata_loader: &dyn MetadataLoader,
-    name: Symbol,
-) -> Result<PathBuf, CrateError> {
-    info!("find plugin registrar `{}`", name);
-    let mut locator = CrateLocator::new(
-        sess,
-        metadata_loader,
-        name,
-        false, // is_rlib
-        None,  // hash
-        None,  // extra_filename
-        true,  // is_host
-        PathKind::Crate,
-    );
-
-    match locator.maybe_load_library_crate()? {
-        Some(library) => match library.source.dylib {
-            Some(dylib) => Ok(dylib.0),
-            None => Err(CrateError::NonDylibPlugin(name)),
-        },
-        None => Err(locator.into_error(None)),
-    }
-}
-
 /// A diagnostic function for dumping crate metadata to an output stream.
 pub fn list_file_metadata(
     target: &Target,
@@ -964,7 +924,6 @@ pub(crate) enum CrateError {
     DlOpen(String),
     DlSym(String),
     LocatorCombined(Box<CombinedLocatorError>),
-    NonDylibPlugin(Symbol),
     NotFound(Symbol),
 }
 
@@ -1134,9 +1093,6 @@ impl CrateError {
                     });
                 }
             }
-            CrateError::NonDylibPlugin(crate_name) => {
-                sess.emit_err(errors::NoDylibPlugin { span, crate_name });
-            }
             CrateError::NotFound(crate_name) => {
                 sess.emit_err(errors::CannotFindCrate {
                     span,
diff --git a/compiler/rustc_middle/src/lint.rs b/compiler/rustc_middle/src/lint.rs
index 07142293f38..eada116f896 100644
--- a/compiler/rustc_middle/src/lint.rs
+++ b/compiler/rustc_middle/src/lint.rs
@@ -17,8 +17,7 @@ use crate::ty::TyCtxt;
 /// How a lint level was set.
 #[derive(Clone, Copy, PartialEq, Eq, HashStable, Debug)]
 pub enum LintLevelSource {
-    /// Lint is at the default level as declared
-    /// in rustc or a plugin.
+    /// Lint is at the default level as declared in rustc.
     Default,
 
     /// Lint level was set by an attribute.
diff --git a/compiler/rustc_passes/messages.ftl b/compiler/rustc_passes/messages.ftl
index 38e1a7f372b..be50aad1303 100644
--- a/compiler/rustc_passes/messages.ftl
+++ b/compiler/rustc_passes/messages.ftl
@@ -589,9 +589,6 @@ passes_pass_by_value =
     `pass_by_value` attribute should be applied to a struct, enum or type alias
     .label = is not a struct, enum or type alias
 
-passes_plugin_registrar =
-    `#[plugin_registrar]` only has an effect on functions
-
 passes_proc_macro_bad_sig = {$kind} has incorrect signature
 
 passes_repr_conflicting =
diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index a8a27e761cb..c5767fd902f 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -211,7 +211,6 @@ impl CheckAttrVisitor<'_> {
                 sym::deprecated => self.check_deprecated(hir_id, attr, span, target),
                 sym::macro_use | sym::macro_escape => self.check_macro_use(hir_id, attr, target),
                 sym::path => self.check_generic_attr(hir_id, attr, target, Target::Mod),
-                sym::plugin_registrar => self.check_plugin_registrar(hir_id, attr, target),
                 sym::macro_export => self.check_macro_export(hir_id, attr, target),
                 sym::ignore | sym::should_panic => {
                     self.check_generic_attr(hir_id, attr, target, Target::Fn)
@@ -2237,17 +2236,6 @@ impl CheckAttrVisitor<'_> {
         }
     }
 
-    fn check_plugin_registrar(&self, hir_id: HirId, attr: &Attribute, target: Target) {
-        if target != Target::Fn {
-            self.tcx.emit_spanned_lint(
-                UNUSED_ATTRIBUTES,
-                hir_id,
-                attr.span,
-                errors::PluginRegistrar,
-            );
-        }
-    }
-
     fn check_unused_attribute(&self, hir_id: HirId, attr: &Attribute) {
         // Warn on useless empty attributes.
         let note = if matches!(
diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index b0862704003..411c9410195 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -717,10 +717,6 @@ pub enum MacroExport {
     TooManyItems,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(passes_plugin_registrar)]
-pub struct PluginRegistrar;
-
 #[derive(Subdiagnostic)]
 pub enum UnusedNote {
     #[note(passes_unused_empty_lints_note)]
diff --git a/compiler/rustc_plugin_impl/Cargo.toml b/compiler/rustc_plugin_impl/Cargo.toml
deleted file mode 100644
index a0762e815e3..00000000000
--- a/compiler/rustc_plugin_impl/Cargo.toml
+++ /dev/null
@@ -1,18 +0,0 @@
-[package]
-name = "rustc_plugin_impl"
-version = "0.0.0"
-build = false
-edition = "2021"
-
-[dependencies]
-# tidy-alphabetical-start
-libloading = "0.7.1"
-rustc_ast = { path = "../rustc_ast" }
-rustc_errors = { path = "../rustc_errors" }
-rustc_fluent_macro = { path = "../rustc_fluent_macro" }
-rustc_lint = { path = "../rustc_lint" }
-rustc_macros = { path = "../rustc_macros" }
-rustc_metadata = { path = "../rustc_metadata" }
-rustc_session = { path = "../rustc_session" }
-rustc_span = { path = "../rustc_span" }
-# tidy-alphabetical-end
diff --git a/compiler/rustc_plugin_impl/messages.ftl b/compiler/rustc_plugin_impl/messages.ftl
deleted file mode 100644
index 8db32a42c1d..00000000000
--- a/compiler/rustc_plugin_impl/messages.ftl
+++ /dev/null
@@ -1,4 +0,0 @@
-plugin_impl_load_plugin_error = {$msg}
-
-plugin_impl_malformed_plugin_attribute = malformed `plugin` attribute
-    .label = malformed attribute
diff --git a/compiler/rustc_plugin_impl/src/errors.rs b/compiler/rustc_plugin_impl/src/errors.rs
deleted file mode 100644
index e6a7fc86bee..00000000000
--- a/compiler/rustc_plugin_impl/src/errors.rs
+++ /dev/null
@@ -1,20 +0,0 @@
-//! Errors emitted by plugin_impl
-
-use rustc_macros::Diagnostic;
-use rustc_span::Span;
-
-#[derive(Diagnostic)]
-#[diag(plugin_impl_load_plugin_error)]
-pub struct LoadPluginError {
-    #[primary_span]
-    pub span: Span,
-    pub msg: String,
-}
-
-#[derive(Diagnostic)]
-#[diag(plugin_impl_malformed_plugin_attribute, code = "E0498")]
-pub struct MalformedPluginAttribute {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-}
diff --git a/compiler/rustc_plugin_impl/src/lib.rs b/compiler/rustc_plugin_impl/src/lib.rs
deleted file mode 100644
index 0e1c80a1f64..00000000000
--- a/compiler/rustc_plugin_impl/src/lib.rs
+++ /dev/null
@@ -1,33 +0,0 @@
-//! Infrastructure for compiler plugins.
-//!
-//! Plugins are a deprecated way to extend the behavior of `rustc` in various ways.
-//!
-//! See the [`plugin`
-//! feature](https://doc.rust-lang.org/nightly/unstable-book/language-features/plugin.html)
-//! of the Unstable Book for some examples.
-
-#![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
-#![cfg_attr(not(bootstrap), doc(rust_logo))]
-#![cfg_attr(not(bootstrap), feature(rustdoc_internals))]
-#![cfg_attr(not(bootstrap), allow(internal_features))]
-#![recursion_limit = "256"]
-#![deny(rustc::untranslatable_diagnostic)]
-#![deny(rustc::diagnostic_outside_of_impl)]
-
-use rustc_errors::{DiagnosticMessage, SubdiagnosticMessage};
-use rustc_fluent_macro::fluent_messages;
-use rustc_lint::LintStore;
-
-mod errors;
-pub mod load;
-
-fluent_messages! { "../messages.ftl" }
-
-/// Structure used to register plugins.
-///
-/// A plugin registrar function takes an `&mut Registry` and should call
-/// methods to register its plugins.
-pub struct Registry<'a> {
-    /// The `LintStore` allows plugins to register new lints.
-    pub lint_store: &'a mut LintStore,
-}
diff --git a/compiler/rustc_plugin_impl/src/load.rs b/compiler/rustc_plugin_impl/src/load.rs
deleted file mode 100644
index 27e5cb9f0d0..00000000000
--- a/compiler/rustc_plugin_impl/src/load.rs
+++ /dev/null
@@ -1,78 +0,0 @@
-//! Used by `rustc` when loading a plugin.
-
-use crate::errors::{LoadPluginError, MalformedPluginAttribute};
-use crate::Registry;
-use libloading::Library;
-use rustc_ast::Attribute;
-use rustc_metadata::locator;
-use rustc_session::cstore::MetadataLoader;
-use rustc_session::Session;
-use rustc_span::symbol::{sym, Ident};
-
-use std::env;
-use std::mem;
-use std::path::PathBuf;
-
-/// Pointer to a registrar function.
-type PluginRegistrarFn = fn(&mut Registry<'_>);
-
-/// Read plugin metadata and dynamically load registrar functions.
-pub fn load_plugins(
-    sess: &Session,
-    metadata_loader: &dyn MetadataLoader,
-    attrs: &[Attribute],
-) -> Vec<PluginRegistrarFn> {
-    let mut plugins = Vec::new();
-
-    for attr in attrs {
-        if !attr.has_name(sym::plugin) {
-            continue;
-        }
-
-        for plugin in attr.meta_item_list().unwrap_or_default() {
-            match plugin.ident() {
-                Some(ident) if plugin.is_word() => {
-                    load_plugin(&mut plugins, sess, metadata_loader, ident)
-                }
-                _ => {
-                    sess.emit_err(MalformedPluginAttribute { span: plugin.span() });
-                }
-            }
-        }
-    }
-
-    plugins
-}
-
-fn load_plugin(
-    plugins: &mut Vec<PluginRegistrarFn>,
-    sess: &Session,
-    metadata_loader: &dyn MetadataLoader,
-    ident: Ident,
-) {
-    let lib = locator::find_plugin_registrar(sess, metadata_loader, ident.span, ident.name);
-    let fun = dylink_registrar(lib).unwrap_or_else(|err| {
-        // This is fatal: there are almost certainly macros we need inside this crate, so
-        // continuing would spew "macro undefined" errors.
-        sess.emit_fatal(LoadPluginError { span: ident.span, msg: err.to_string() });
-    });
-    plugins.push(fun);
-}
-
-/// Dynamically link a registrar function into the compiler process.
-fn dylink_registrar(lib_path: PathBuf) -> Result<PluginRegistrarFn, libloading::Error> {
-    // Make sure the path contains a / or the linker will search for it.
-    let lib_path = env::current_dir().unwrap().join(&lib_path);
-
-    let lib = unsafe { Library::new(&lib_path) }?;
-
-    let registrar_sym = unsafe { lib.get::<PluginRegistrarFn>(b"__rustc_plugin_registrar") }?;
-
-    // Intentionally leak the dynamic library. We can't ever unload it
-    // since the library can make things that will live arbitrarily long
-    // (e.g., an Rc cycle or a thread).
-    let registrar_sym = unsafe { registrar_sym.into_raw() };
-    mem::forget(lib);
-
-    Ok(*registrar_sym)
-}