`#[diagnostic::on_unimplemented]` without filters

This commit adds support for a `#[diagnostic::on_unimplemented]`
attribute with the following options:

* `message` to customize the primary error message
* `note` to add a customized note message to an error message
* `label` to customize the label part of the error message

Co-authored-by: León Orell Valerian Liehr <me@fmease.dev>
Co-authored-by: Michael Goulet <michael@errs.io>

1 files changed, 21 insertions, 1 deletions

diff --git a/compiler/rustc_passes/src/check_attr.rs b/compiler/rustc_passes/src/check_attr.rs
index 50a087c7847..ba9e7ddaf51 100644
--- a/compiler/rustc_passes/src/check_attr.rs
+++ b/compiler/rustc_passes/src/check_attr.rs
@@ -16,6 +16,7 @@ use rustc_hir::{
     self, FnSig, ForeignItem, HirId, Item, ItemKind, TraitItem, CRATE_HIR_ID, CRATE_OWNER_ID,
 };
 use rustc_hir::{MethodKind, Target, Unsafety};
+use rustc_macros::LintDiagnostic;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault;
 use rustc_middle::query::Providers;
@@ -24,7 +25,7 @@ use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::lint::builtin::{
     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, INVALID_MACRO_EXPORT_ARGUMENTS,
-    UNUSED_ATTRIBUTES,
+    UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES, UNUSED_ATTRIBUTES,
 };
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::{kw, sym, Symbol};
@@ -36,6 +37,10 @@ use rustc_trait_selection::traits::ObligationCtxt;
 use std::cell::Cell;
 use std::collections::hash_map::Entry;
 
+#[derive(LintDiagnostic)]
+#[diag(passes_diagnostic_diagnostic_on_unimplemented_only_for_traits)]
+pub struct DiagnosticOnUnimplementedOnlyForTraits;
+
 pub(crate) fn target_from_impl_item<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_item: &hir::ImplItem<'_>,
@@ -104,6 +109,9 @@ impl CheckAttrVisitor<'_> {
         let mut seen = FxHashMap::default();
         let attrs = self.tcx.hir().attrs(hir_id);
         for attr in attrs {
+            if attr.path_matches(&[sym::diagnostic, sym::on_unimplemented]) {
+                self.check_diagnostic_on_unimplemented(attr.span, hir_id, target);
+            }
             match attr.name_or_empty() {
                 sym::do_not_recommend => self.check_do_not_recommend(attr.span, target),
                 sym::inline => self.check_inline(hir_id, attr, span, target),
@@ -284,6 +292,18 @@ impl CheckAttrVisitor<'_> {
         }
     }
 
+    /// Checks if `#[diagnostic::on_unimplemented]` is applied to a trait definition
+    fn check_diagnostic_on_unimplemented(&self, attr_span: Span, hir_id: HirId, target: Target) {
+        if !matches!(target, Target::Trait) {
+            self.tcx.emit_spanned_lint(
+                UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES,
+                hir_id,
+                attr_span,
+                DiagnosticOnUnimplementedOnlyForTraits,
+            );
+        }
+    }
+
     /// Checks if an `#[inline]` is applied to a function or a closure. Returns `true` if valid.
     fn check_inline(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) -> bool {
         match target {