The lint name must be plural according to RFC-344

Author: weiznich

compiler/rustc_lint_defs/src/builtin.rs

@@ -3398,7 +3398,7 @@ declare_lint_pass! {
         UNFULFILLED_LINT_EXPECTATIONS,
         UNINHABITED_STATIC,
         UNKNOWN_CRATE_TYPES,
-    UNKNOWN_DIAGNOSTIC_ATTRIBUTE,
+        UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
         UNKNOWN_LINTS,
         UNREACHABLE_CODE,
         UNREACHABLE_PATTERNS,
@@ -4272,7 +4272,7 @@ declare_lint! {
     /// the spelling, and check the diagnostic attribute listing for the correct name. Also
     /// consider if you are using an old version of the compiler, and the attribute
     /// is only available in a newer version.
-    pub UNKNOWN_DIAGNOSTIC_ATTRIBUTE,
+    pub UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
     Warn,
     "unrecognized diagnostic attribute"
 }

compiler/rustc_resolve/src/macros.rs

@@ -22,7 +22,7 @@ use rustc_middle::middle::stability;
 use rustc_middle::ty::RegisteredTools;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::lint::builtin::{
-    LEGACY_DERIVE_HELPERS, SOFT_UNSTABLE, UNKNOWN_DIAGNOSTIC_ATTRIBUTE,
+    LEGACY_DERIVE_HELPERS, SOFT_UNSTABLE, UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
 };
 use rustc_session::lint::builtin::{UNUSED_MACROS, UNUSED_MACRO_RULES};
 use rustc_session::lint::BuiltinLintDiagnostics;
@@ -512,7 +512,7 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                     .span_err(path.span, "Diagnostic attributes requires a path with 2 segments");
             } else {
                 self.tcx.sess.parse_sess.buffer_lint(
-                    UNKNOWN_DIAGNOSTIC_ATTRIBUTE,
+                    UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
                     path.segments[1].span(),
                     node_id,
                     "Unknown diagnostic attribute",

tests/ui/diagnostic_namespace/non_existing_attributes_accepted.stderr

@@ -4,7 +4,7 @@ warning: Unknown diagnostic attribute
 LL | #[diagnostic::non_existing_attribute]
    |               ^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `#[warn(unknown_diagnostic_attribute)]` on by default
+   = note: `#[warn(unknown_diagnostic_attributes)]` on by default
 
 warning: Unknown diagnostic attribute
   --> $DIR/non_existing_attributes_accepted.rs:8:15