Add a feature gate for the #[diagnostic] tool namespace

Author: weiznich

compiler/rustc_feature/src/active.rs

@@ -379,6 +379,8 @@ declare_features! (
     (active, deprecated_safe, "1.61.0", Some(94978), None),
     /// Allows having using `suggestion` in the `#[deprecated]` attribute.
     (active, deprecated_suggestion, "1.61.0", Some(94785), None),
+    /// Allows using the `#[diagnostic]` attribute tool namespace
+    (active, diagnostic_namespace, "CURRENT_RUSTC_VERSION", Some(94785), None),
     /// Controls errors in trait implementations.
     (active, do_not_recommend, "1.67.0", Some(51992), None),
     /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.

compiler/rustc_lint_defs/src/builtin.rs

@@ -4259,6 +4259,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
+    /// #![feature(diagnostic_namespace)]
     /// #[diagnostic::does_not_exist]
     /// struct Foo;
     /// ```

compiler/rustc_resolve/src/macros.rs

@@ -143,7 +143,9 @@ pub(crate) fn registered_tools(tcx: TyCtxt<'_>, (): ()) -> RegisteredTools {
     // but it's not an error to register them explicitly.
     let predefined_tools = [sym::clippy, sym::rustfmt];
     registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
-    registered_tools.insert(Ident::with_dummy_span(sym::diagnostic));
+    if tcx.features().diagnostic_namespace {
+        registered_tools.insert(Ident::with_dummy_span(sym::diagnostic));
+    }
     registered_tools
 }
 
@@ -496,7 +498,8 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             Err(Determinacy::Undetermined) => return Err(Indeterminate),
         };
 
-        if kind == MacroKind::Attr
+        if self.tcx.features().diagnostic_namespace
+            && kind == MacroKind::Attr
             && !path.segments.is_empty()
             && path.segments[0].ident.as_str() == "diagnostic"
         {

compiler/rustc_span/src/symbol.rs

@@ -620,6 +620,7 @@ symbols! {
         destruct,
         destructuring_assignment,
         diagnostic,
+        diagnostic_namespace,
         direct,
         discriminant_kind,
         discriminant_type,

tests/ui/diagnostic_namespace/feature-gate-diagnostic_namespace.rs

@@ -0,0 +1,12 @@
+// check-fail
+#[diagnostic::non_existing_attribute]
+//~^ERROR use of undeclared crate or module `diagnostic
+pub trait Bar {
+}
+
+#[diagnostic::non_existing_attribute(with_option = "foo")]
+//~^ERROR use of undeclared crate or module `diagnostic
+struct Foo;
+
+fn main() {
+}

tests/ui/diagnostic_namespace/feature-gate-diagnostic_namespace.stderr

@@ -0,0 +1,15 @@
+error[E0433]: failed to resolve: use of undeclared crate or module `diagnostic`
+  --> $DIR/feature-gate-diagnostic_namespace.rs:7:3
+   |
+LL | #[diagnostic::non_existing_attribute(with_option = "foo")]
+   |   ^^^^^^^^^^ use of undeclared crate or module `diagnostic`
+
+error[E0433]: failed to resolve: use of undeclared crate or module `diagnostic`
+  --> $DIR/feature-gate-diagnostic_namespace.rs:2:3
+   |
+LL | #[diagnostic::non_existing_attribute]
+   |   ^^^^^^^^^^ use of undeclared crate or module `diagnostic`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0433`.

tests/ui/diagnostic_namespace/non_existing_attributes_accepted.rs

@@ -1,3 +1,4 @@
+#![feature(diagnostic_namespace)]
 // check-pass
 #[diagnostic::non_existing_attribute]
 //~^WARN Unknown diagnostic attribute

tests/ui/diagnostic_namespace/non_existing_attributes_accepted.stderr

@@ -1,13 +1,13 @@
 warning: Unknown diagnostic attribute
-  --> $DIR/non_existing_attributes_accepted.rs:2:15
+  --> $DIR/non_existing_attributes_accepted.rs:3:15
    |
 LL | #[diagnostic::non_existing_attribute]
    |               ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(unknown_diagnostic_attribute)]` on by default
 
 warning: Unknown diagnostic attribute
-  --> $DIR/non_existing_attributes_accepted.rs:7:15
+  --> $DIR/non_existing_attributes_accepted.rs:8:15
    |
 LL | #[diagnostic::non_existing_attribute(with_option = "foo")]
    |               ^^^^^^^^^^^^^^^^^^^^^^

tests/ui/diagnostic_namespace/requires_path.rs

@@ -1,3 +1,4 @@
+#![feature(diagnostic_namespace)]
 // check-fail
 
 #[diagnostic]

tests/ui/diagnostic_namespace/requires_path.stderr

@@ -1,17 +1,17 @@
 error: Diagnostic attributes requires a path with 2 segments
-  --> $DIR/requires_path.rs:3:3
+  --> $DIR/requires_path.rs:4:3
    |
 LL | #[diagnostic]
    |   ^^^^^^^^^^
 
 error: Diagnostic attributes requires a path with 2 segments
-  --> $DIR/requires_path.rs:3:3
+  --> $DIR/requires_path.rs:4:3
    |
 LL | #[diagnostic]
    |   ^^^^^^^^^^
 
 error: cannot find attribute `diagnostic` in this scope
-  --> $DIR/requires_path.rs:3:3
+  --> $DIR/requires_path.rs:4:3
    |
 LL | #[diagnostic]
    |   ^^^^^^^^^^