Plugins deprecation: don’t suggest simply removing the attribute

Building Servo with a recent Nightly produces:

```rust
warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See rust-lang#29597
  --> components/script/lib.rs:14:1
   |
14 | #![plugin(script_plugins)]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
   |
   = note: `#[warn(deprecated)]` on by default
```

First, linking to rust-lang#29597 is not ideal
since there is pretty much no discussion there of the deprecation
and what can be used instead.
This PR changes the link to the deprecation PR which does have more discussion.

Second, the “remove this attribute” suggestion is rather unhelpful.
Just because a feature is deprecated doesn’t mean that simply removing its use
without a replacement is acceptable.

In the case of custom lint, there is no replacement available.
Prefixing a message with “help:” when telling users that they’re screwed
honestly feels disrespectful.

This PR also changes the message to be more factual.

src/libsyntax/feature_gate/builtin_attrs.rs

@@ -286,7 +286,10 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     (
         sym::plugin_registrar, Normal, template!(Word),
         Gated(
-            Stability::Deprecated("https://github.com/rust-lang/rust/issues/29597", None),
+            Stability::Deprecated(
+                "https://github.com/rust-lang/rust/pull/64675",
+                Some("may be removed in a future compiler version"),
+            ),
             sym::plugin_registrar,
             "compiler plugins are deprecated",
             cfg_fn!(plugin_registrar)
@@ -295,7 +298,10 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     (
         sym::plugin, CrateLevel, template!(List: "name|name(args)"),
         Gated(
-            Stability::Deprecated("https://github.com/rust-lang/rust/issues/29597", None),
+            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)

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

@@ -7,11 +7,11 @@ 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
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/gated-plugin.rs:3:1
    |
 LL | #![plugin(attr_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

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

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-15778-fail.rs:6:1
    |
 LL | #![plugin(lint_for_crate)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

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

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-15778-pass.rs:8:1
    |
 LL | #![plugin(lint_for_crate_rpass)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

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

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-40001.rs:6:1
    |
 LL | #![plugin(issue_40001_plugin)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

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

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-group-plugin-deny-cmdline.rs:7:1
    |
 LL | #![plugin(lint_group_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

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

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-group-plugin.rs:6:1
    |
 LL | #![plugin(lint_group_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/lint-plugin-cmdline-allow.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-plugin-cmdline-allow.rs:8:1
    |
 LL | #![plugin(lint_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/lint-plugin-deny-attr.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-plugin-deny-attr.rs:5:1
    |
 LL | #![plugin(lint_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

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

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-plugin-deny-cmdline.rs:6:1
    |
 LL | #![plugin(lint_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/lint-plugin-forbid-attrs.stderr

@@ -7,11 +7,11 @@ LL | #![forbid(test_lint)]
 LL | #[allow(test_lint)]
    |         ^^^^^^^^^ overruled by previous forbid
 
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-plugin-forbid-attrs.rs:5:1
    |
 LL | #![plugin(lint_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/lint-plugin-forbid-cmdline.stderr

@@ -6,11 +6,11 @@ LL | #[allow(test_lint)]
    |
    = note: `forbid` lint level was set on command line
 
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-plugin-forbid-cmdline.rs:6:1
    |
 LL | #![plugin(lint_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

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

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-plugin.rs:5:1
    |
 LL | #![plugin(lint_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/lint-tool-cmdline-allow.stderr

@@ -2,11 +2,11 @@ warning: lint name `test_lint` is deprecated and does not have an effect anymore
    |
    = note: requested on the command line with `-A test_lint`
 
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-tool-cmdline-allow.rs:8:1
    |
 LL | #![plugin(lint_tool_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/lint-tool-test.stderr

@@ -32,11 +32,11 @@ warning: lint name `test_lint` is deprecated and may not have an effect in the f
 LL | #![cfg_attr(foo, warn(test_lint))]
    |                       ^^^^^^^^^ help: change it to: `clippy::test_lint`
 
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lint-tool-test.rs:6:1
    |
 LL | #![plugin(lint_tool_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/llvm-pass-plugin.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/llvm-pass-plugin.rs:6:1
    |
 LL | #![plugin(llvm_pass_plugin)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/lto-syntax-extension.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/lto-syntax-extension.rs:9:1
    |
 LL | #![plugin(lto_syntax_extension_plugin)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/macro-crate-rlib.stderr

@@ -4,11 +4,11 @@ error[E0457]: plugin `rlib_crate_test` only found in rlib format, but must be av
 LL | #![plugin(rlib_crate_test)]
    |           ^^^^^^^^^^^^^^^
 
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/macro-crate-rlib.rs:6:1
    |
 LL | #![plugin(rlib_crate_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/outlive-expansion-phase.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/outlive-expansion-phase.rs:6:1
    |
 LL | #![plugin(outlive_expansion_phase)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/plugin-args-1.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/plugin-args-1.rs:6:1
    |
 LL | #![plugin(plugin_args)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/plugin-args-2.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/plugin-args-2.rs:6:1
    |
 LL | #![plugin(plugin_args())]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/plugin-args-3.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/plugin-args-3.rs:6:1
    |
 LL | #![plugin(plugin_args(hello(there), how(are="you")))]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/plugin-attr-register-deny.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/plugin-attr-register-deny.rs:5:1
    |
 LL | #![plugin(attr_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

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

@@ -10,11 +10,11 @@ note: consider marking `mac` as `pub` in the imported module
 LL | pub use mac as reexport;
    |         ^^^^^^^^^^^^^^^
 
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/plugin-reexport.rs:6:1
    |
 LL | #![plugin(attr_plugin_test)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui-fulldeps/roman-numerals-macro.stderr

@@ -1,8 +1,8 @@
-warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/roman-numerals-macro.rs:6:1
    |
 LL | #![plugin(roman_numerals)]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 

src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs.stderr

@@ -186,43 +186,43 @@ LL |     mod inner { #![macro_escape] }
    |
    = help: consider an outer attribute, `#[macro_use]` mod ...
 
-warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:219:17
    |
 LL |     mod inner { #![plugin_registrar] }
-   |                 ^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |                 ^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default
 
-warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:224:5
    |
 LL |     #[plugin_registrar] struct S;
-   |     ^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |     ^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
 
-warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:227:5
    |
 LL |     #[plugin_registrar] type T = S;
-   |     ^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |     ^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
 
-warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:230:5
    |
 LL |     #[plugin_registrar] impl S { }
-   |     ^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |     ^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
 
-warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:216:1
    |
 LL | #[plugin_registrar]
-   | ^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
 
-warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/issues/29597
+warning: use of deprecated attribute `plugin_registrar`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:40:1
    |
 LL | #![plugin_registrar]
-   | ^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
 
 warning: use of deprecated attribute `crate_id`: no longer used.
   --> $DIR/issue-43106-gating-of-builtin-attrs.rs:90:1

src/test/ui/feature-gates/feature-gate-plugin.stderr

@@ -7,11 +7,11 @@ LL | #![plugin(foo)]
    = 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
+warning: use of deprecated attribute `plugin`: compiler plugins are deprecated. See https://github.com/rust-lang/rust/pull/64675
   --> $DIR/feature-gate-plugin.rs:3:1
    |
 LL | #![plugin(foo)]
-   | ^^^^^^^^^^^^^^^ help: remove this attribute
+   | ^^^^^^^^^^^^^^^ help: may be removed in a future compiler version
    |
    = note: `#[warn(deprecated)]` on by default