New deprecated_suggestion feature, use in tests

Author: jhpratt

compiler/rustc_attr/src/builtin.rs

@@ -741,7 +741,19 @@ where
                                     continue 'outer;
                                 }
                             }
-                            sym::suggestion if attr.has_name(sym::rustc_deprecated) => {
+                            sym::suggestion => {
+                                if !sess.features_untracked().deprecated_suggestion {
+                                    let mut diag = sess.struct_span_err(
+                                        mi.span,
+                                        "suggestions on deprecated items are unstable",
+                                    );
+                                    if sess.is_nightly_build() {
+                                        diag.help("add `#![feature(deprecated_suggestion)]` to the crate root");
+                                    }
+                                    // FIXME(jhpratt) change this to an actual tracking issue
+                                    diag.note("see #XXX for more details").emit();
+                                }
+
                                 if !get(mi, &mut suggestion) {
                                     continue 'outer;
                                 }
@@ -778,10 +790,6 @@ where
             }
         }
 
-        if suggestion.is_some() && attr.has_name(sym::deprecated) {
-            unreachable!("only allowed on rustc_deprecated")
-        }
-
         if attr.has_name(sym::rustc_deprecated) {
             if since.is_none() {
                 handle_errors(&sess.parse_sess, attr.span, AttrError::MissingSince);

compiler/rustc_feature/src/active.rs

@@ -368,6 +368,8 @@ declare_features! (
     (active, default_alloc_error_handler, "1.48.0", Some(66741), None),
     /// Allows default type parameters to influence type inference.
     (active, default_type_parameter_fallback, "1.3.0", Some(27336), None),
+    /// Allows having using `suggestion` in the `#[deprecated]` attribute.
+    (active, deprecated_suggestion, "1.61.0", Some(94785), None),
     /// Allows `#[derive(Default)]` and `#[default]` on enums.
     (active, derive_default_enum, "1.56.0", Some(86985), None),
     /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.

compiler/rustc_span/src/symbol.rs

@@ -562,6 +562,7 @@ symbols! {
         delay_span_bug_from_inside_query,
         deny,
         deprecated,
+        deprecated_suggestion,
         deref,
         deref_method,
         deref_mut,

library/core/src/lib.rs

@@ -166,6 +166,7 @@
 #![feature(const_refs_to_cell)]
 #![feature(decl_macro)]
 #![feature(derive_default_enum)]
+#![cfg_attr(not(bootstrap), feature(deprecated_suggestion))]
 #![feature(doc_cfg)]
 #![feature(doc_notable_trait)]
 #![feature(rustdoc_internals)]

library/std/src/lib.rs

@@ -270,6 +270,7 @@
 #![feature(doc_cfg)]
 #![feature(doc_cfg_hide)]
 #![feature(rustdoc_internals)]
+#![cfg_attr(not(bootstrap), feature(deprecated_suggestion))]
 #![feature(doc_masked)]
 #![feature(doc_notable_trait)]
 #![feature(dropck_eyepatch)]

src/test/ui/deprecation/feature-gate-deprecated_suggestion.rs

@@ -0,0 +1,6 @@
+// compile-flags: --crate-type=lib
+
+#![no_implicit_prelude]
+
+#[deprecated(suggestion = "foo")] //~ ERROR suggestions on deprecated items are unstable
+struct Foo {}

src/test/ui/deprecation/feature-gate-deprecated_suggestion.stderr

@@ -0,0 +1,11 @@
+error: suggestions on deprecated items are unstable
+  --> $DIR/feature-gate-deprecated_suggestion.rs:5:14
+   |
+LL | #[deprecated(suggestion = "foo")]
+   |              ^^^^^^^^^^^^^^^^^^
+   |
+   = help: add `#![feature(deprecated_suggestion)]` to the crate root
+   = note: see #XXX for more details
+
+error: aborting due to previous error
+

src/test/ui/deprecation/suggestion.fixed

@@ -1,6 +1,7 @@
 // run-rustfix
 
 #![feature(staged_api)]
+#![feature(deprecated_suggestion)]
 
 #![stable(since = "1.0.0", feature = "test")]
 

src/test/ui/deprecation/suggestion.rs

@@ -1,6 +1,7 @@
 // run-rustfix
 
 #![feature(staged_api)]
+#![feature(deprecated_suggestion)]
 
 #![stable(since = "1.0.0", feature = "test")]
 

src/test/ui/deprecation/suggestion.stderr

@@ -1,17 +1,17 @@
 error: use of deprecated function `bar::deprecated`: replaced by `replacement`
-  --> $DIR/suggestion.rs:41:10
+  --> $DIR/suggestion.rs:42:10
    |
 LL |     bar::deprecated();
    |          ^^^^^^^^^^ help: replace the use of the deprecated function: `replacement`
    |
 note: the lint level is defined here
-  --> $DIR/suggestion.rs:7:9
+  --> $DIR/suggestion.rs:8:9
    |
 LL | #![deny(deprecated)]
    |         ^^^^^^^^^^
 
 error: use of deprecated associated function `Foo::deprecated`: replaced by `replacement`
-  --> $DIR/suggestion.rs:39:9
+  --> $DIR/suggestion.rs:40:9
    |
 LL |     foo.deprecated();
    |         ^^^^^^^^^^ help: replace the use of the deprecated associated function: `replacement`