Rollup merge of rust-lang#64675 - Centril:deprecate-plugin, r=oli-obk

Deprecate `#![plugin]` & `#[plugin_registrar]`

This PR deprecates `#![plugin]` and `#[plugin_registrar]`.

~A removal deadline is set: 1.44.0. This will be in 9 months from now and should give everyone who is still relying on the feature ample time to rid themselves of this dependency.~

cc rust-lang#29597

r? @Mark-Simulacrum

Author: tmandry

src/libsyntax/feature_gate/builtin_attrs.rs

@@ -278,10 +278,23 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ),
 
     // Plugins:
-    ungated!(plugin_registrar, Normal, template!(Word)),
-    gated!(
-        plugin, CrateLevel, template!(List: "name|name(args)"),
-        "compiler plugins are experimental and possibly buggy",
+    (
+        sym::plugin_registrar, Normal, template!(Word),
+        Gated(
+            Stability::Deprecated("https://github.com/rust-lang/rust/issues/29597", None),
+            sym::plugin_registrar,
+            "compiler plugins are deprecated",
+            cfg_fn!(plugin_registrar)
+        )
+    ),
+    (
+        sym::plugin, CrateLevel, template!(List: "name|name(args)"),
+        Gated(
+            Stability::Deprecated("https://github.com/rust-lang/rust/issues/29597", None),
+            sym::plugin,
+            "compiler plugins are deprecated",
+            cfg_fn!(plugin)
+        )
     ),
 
     // Testing:

src/test/run-make-fulldeps/hotplug_codegen_backend/the_backend.rs

@@ -41,7 +41,7 @@ impl MetadataLoader for NoLlvmMetadataLoader {
 struct TheBackend;
 
 impl CodegenBackend for TheBackend {
-    fn metadata_loader(&self) -> Box<MetadataLoader + Sync> {
+    fn metadata_loader(&self) -> Box<dyn MetadataLoader + Sync> {
         Box::new(NoLlvmMetadataLoader)
     }
 
@@ -64,15 +64,15 @@ impl CodegenBackend for TheBackend {
         tcx: TyCtxt<'tcx>,
         _metadata: EncodedMetadata,
         _need_metadata_module: bool,
-    ) -> Box<Any> {
+    ) -> Box<dyn Any> {
         use rustc::hir::def_id::LOCAL_CRATE;
 
         Box::new(tcx.crate_name(LOCAL_CRATE) as Symbol)
     }
 
     fn join_codegen_and_link(
         &self,
-        ongoing_codegen: Box<Any>,
+        ongoing_codegen: Box<dyn Any>,
         sess: &Session,
         _dep_graph: &DepGraph,
         outputs: &OutputFilenames,
@@ -97,6 +97,6 @@ impl CodegenBackend for TheBackend {
 
 /// This is the entrypoint for a hot plugged rustc_codegen_llvm
 #[no_mangle]
-pub fn __rustc_codegen_backend() -> Box<CodegenBackend> {
+pub fn __rustc_codegen_backend() -> Box<dyn CodegenBackend> {
     Box::new(TheBackend)
 }

src/test/ui-fulldeps/gated-plugin.rs

@@ -1,6 +1,7 @@
 // aux-build:attr-plugin-test.rs
 
 #![plugin(attr_plugin_test)]
-//~^ ERROR compiler plugins are experimental and possibly buggy
+//~^ ERROR compiler plugins are deprecated
+//~| WARN use of deprecated attribute `plugin`: compiler plugins are deprecated
 
 fn main() {}

src/test/ui-fulldeps/gated-plugin.stderr

@@ -1,4 +1,4 @@
-error[E0658]: compiler plugins are experimental and possibly buggy
+error[E0658]: compiler plugins are deprecated
   --> $DIR/gated-plugin.rs:3:1
    |
 LL | #![plugin(attr_plugin_test)]
@@ -7,6 +7,14 @@ LL | #![plugin(attr_plugin_test)]
    = note: for more information, see https://github.com/rust-lang/rust/issues/29597
    = help: add `#![feature(plugin)]` to the crate attributes to enable
 
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+  --> $DIR/gated-plugin.rs:3:1
+   |
+LL | #![plugin(attr_plugin_test)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: `#[warn(deprecated)]` on by default
+
 error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0658`.

src/test/ui-fulldeps/issue-15778-fail.rs

@@ -4,5 +4,6 @@
 
 #![feature(plugin)] //~ ERROR crate is not marked with #![crate_okay]
 #![plugin(lint_for_crate)]
+//~^ WARN use of deprecated attribute `plugin`
 
 pub fn main() { }

src/test/ui-fulldeps/issue-15778-fail.stderr

@@ -1,9 +1,18 @@
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+  --> $DIR/issue-15778-fail.rs:6:1
+   |
+LL | #![plugin(lint_for_crate)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: `#[warn(deprecated)]` on by default
+
 error: crate is not marked with #![crate_okay]
   --> $DIR/issue-15778-fail.rs:5:1
    |
 LL | / #![feature(plugin)]
 LL | | #![plugin(lint_for_crate)]
 LL | |
+LL | |
 LL | | pub fn main() { }
    | |_________________^
    |

src/test/ui-fulldeps/issue-15778-pass.stderr

@@ -0,0 +1,8 @@
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+  --> $DIR/issue-15778-pass.rs:8:1
+   |
+LL | #![plugin(lint_for_crate_rpass)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: `#[warn(deprecated)]` on by default
+

src/test/ui-fulldeps/issue-40001.stderr

@@ -0,0 +1,8 @@
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+  --> $DIR/issue-40001.rs:6:1
+   |
+LL | #![plugin(issue_40001_plugin)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: `#[warn(deprecated)]` on by default
+

src/test/ui-fulldeps/lint-group-plugin-deny-cmdline.rs

@@ -3,7 +3,9 @@
 // compile-flags: -D lint-me
 
 #![feature(plugin)]
+
 #![plugin(lint_group_plugin_test)]
+//~^ WARN use of deprecated attribute `plugin`
 
 fn lintme() { } //~ ERROR item is named 'lintme'
 

src/test/ui-fulldeps/lint-group-plugin-deny-cmdline.stderr

@@ -1,13 +1,21 @@
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+  --> $DIR/lint-group-plugin-deny-cmdline.rs:7:1
+   |
+LL | #![plugin(lint_group_plugin_test)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+   = note: `#[warn(deprecated)]` on by default
+
 error: item is named 'lintme'
-  --> $DIR/lint-group-plugin-deny-cmdline.rs:8:1
+  --> $DIR/lint-group-plugin-deny-cmdline.rs:10:1
    |
 LL | fn lintme() { }
    | ^^^^^^^^^^^^^^^
    |
    = note: `-D test-lint` implied by `-D lint-me`
 
 error: item is named 'pleaselintme'
-  --> $DIR/lint-group-plugin-deny-cmdline.rs:10:1
+  --> $DIR/lint-group-plugin-deny-cmdline.rs:12:1
    |
 LL | fn pleaselintme() { }
    | ^^^^^^^^^^^^^^^^^^^^^