diff --git a/compiler/rustc_ast_lowering/src/errors.rs b/compiler/rustc_ast_lowering/src/errors.rs
index 3644e664cebf..2da42c96ec0c 100644
--- a/compiler/rustc_ast_lowering/src/errors.rs
+++ b/compiler/rustc_ast_lowering/src/errors.rs
@@ -306,3 +306,24 @@ pub struct MisplacedDoubleDot {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(SessionDiagnostic, Clone, Copy)]
+#[error(ast_lowering::misplaced_relax_trait_bound)]
+pub struct MisplacedRelaxTraitBound {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(SessionDiagnostic, Clone, Copy)]
+#[error(ast_lowering::not_supported_for_lifetime_binder_async_closure)]
+pub struct NotSupportedForLifetimeBinderAsyncClosure {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(SessionDiagnostic, Clone, Copy)]
+#[error(ast_lowering::arbitrary_expression_in_pattern)]
+pub struct ArbitraryExpressionInPattern {
+    #[primary_span]
+    pub span: Span,
+}
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index e470df122b6d..61f8c0216f1c 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -1,7 +1,8 @@
 use super::errors::{
     AsyncGeneratorsNotSupported, AsyncNonMoveClosureNotSupported, AwaitOnlyInAsyncFnAndBlocks,
     BaseExpressionDoubleDot, ClosureCannotBeStatic, FunctionalRecordUpdateDestructuringAssignemnt,
-    GeneratorTooManyParameters, RustcBoxAttributeError, UnderscoreExprLhsAssign,
+    GeneratorTooManyParameters, NotSupportedForLifetimeBinderAsyncClosure, RustcBoxAttributeError,
+    UnderscoreExprLhsAssign,
 };
 use super::ResolverAstLoweringExt;
 use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
@@ -915,10 +916,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         fn_decl_span: Span,
     ) -> hir::ExprKind<'hir> {
         if let &ClosureBinder::For { span, .. } = binder {
-            self.tcx.sess.span_err(
-                span,
-                "`for<...>` binders on `async` closures are not currently supported",
-            );
+            self.tcx.sess.emit_err(NotSupportedForLifetimeBinderAsyncClosure { span });
         }
 
         let (binder_clause, generic_params) = self.lower_closure_binder(binder);
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index a789268dfdaf..fd338ffc0c5e 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -1,4 +1,4 @@
-use super::errors::InvalidAbi;
+use super::errors::{InvalidAbi, MisplacedRelaxTraitBound};
 use super::ResolverAstLoweringExt;
 use super::{AstOwner, ImplTraitContext, ImplTraitPosition};
 use super::{FnDeclKind, LoweringContext, ParamMode};
@@ -1339,11 +1339,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 }
                 let is_param = *is_param.get_or_insert_with(compute_is_param);
                 if !is_param {
-                    self.diagnostic().span_err(
-                        bound.span(),
-                        "`?Trait` bounds are only permitted at the \
-                        point where a type parameter is declared",
-                    );
+                    self.tcx.sess.emit_err(MisplacedRelaxTraitBound { span: bound.span() });
                 }
             }
         }
diff --git a/compiler/rustc_ast_lowering/src/pat.rs b/compiler/rustc_ast_lowering/src/pat.rs
index abe9b354252a..1efa19a3a828 100644
--- a/compiler/rustc_ast_lowering/src/pat.rs
+++ b/compiler/rustc_ast_lowering/src/pat.rs
@@ -1,4 +1,6 @@
-use super::errors::{ExtraDoubleDot, MisplacedDoubleDot, SubTupleBinding};
+use super::errors::{
+    ArbitraryExpressionInPattern, ExtraDoubleDot, MisplacedDoubleDot, SubTupleBinding,
+};
 use super::ResolverAstLoweringExt;
 use super::{ImplTraitContext, LoweringContext, ParamMode};
 use crate::ImplTraitPosition;
@@ -330,8 +332,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             ExprKind::Path(..) if allow_paths => {}
             ExprKind::Unary(UnOp::Neg, ref inner) if matches!(inner.kind, ExprKind::Lit(_)) => {}
             _ => {
-                self.diagnostic()
-                    .span_err(expr.span, "arbitrary expressions aren't allowed in patterns");
+                self.tcx.sess.emit_err(ArbitraryExpressionInPattern { span: expr.span });
                 return self.arena.alloc(self.expr_err(expr.span));
             }
         }
diff --git a/compiler/rustc_error_messages/locales/en-US/ast_lowering.ftl b/compiler/rustc_error_messages/locales/en-US/ast_lowering.ftl
index 438fbd8e57ba..8effd9ca7501 100644
--- a/compiler/rustc_error_messages/locales/en-US/ast_lowering.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/ast_lowering.ftl
@@ -120,3 +120,12 @@ ast_lowering_previously_used_here = previously used here
 ast_lowering_misplaced_double_dot =
     `..` patterns are not allowed here
     .note = only allowed in tuple, tuple struct, and slice patterns
+
+ast_lowering_misplaced_relax_trait_bound =
+    `?Trait` bounds are only permitted at the point where a type parameter is declared
+
+ast_lowering_not_supported_for_lifetime_binder_async_closure =
+    `for<...>` binders on `async` closures are not currently supported
+
+ast_lowering_arbitrary_expression_in_pattern =
+    arbitrary expressions aren't allowed in patterns