1 files changed, 61 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/structured_errors/missing_cast_for_variadic_arg.rs b/compiler/rustc_typeck/src/structured_errors/missing_cast_for_variadic_arg.rs
new file mode 100644
index 000000000..324df313e
--- /dev/null
+++ b/compiler/rustc_typeck/src/structured_errors/missing_cast_for_variadic_arg.rs
@@ -0,0 +1,61 @@
+use crate::structured_errors::StructuredDiagnostic;
+use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticId, ErrorGuaranteed};
+use rustc_middle::ty::{Ty, TypeVisitable};
+use rustc_session::Session;
+use rustc_span::Span;
+
+pub struct MissingCastForVariadicArg<'tcx, 's> {
+    pub sess: &'tcx Session,
+    pub span: Span,
+    pub ty: Ty<'tcx>,
+    pub cast_ty: &'s str,
+}
+
+impl<'tcx> StructuredDiagnostic<'tcx> for MissingCastForVariadicArg<'tcx, '_> {
+    fn session(&self) -> &Session {
+        self.sess
+    }
+
+    fn code(&self) -> DiagnosticId {
+        rustc_errors::error_code!(E0617)
+    }
+
+    fn diagnostic_common(&self) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+        let mut err = self.sess.struct_span_err_with_code(
+            self.span,
+            &format!("can't pass `{}` to variadic function", self.ty),
+            self.code(),
+        );
+
+        if self.ty.references_error() {
+            err.downgrade_to_delayed_bug();
+        }
+
+        if let Ok(snippet) = self.sess.source_map().span_to_snippet(self.span) {
+            err.span_suggestion(
+                self.span,
+                &format!("cast the value to `{}`", self.cast_ty),
+                format!("{} as {}", snippet, self.cast_ty),
+                Applicability::MachineApplicable,
+            );
+        } else {
+            err.help(&format!("cast the value to `{}`", self.cast_ty));
+        }
+
+        err
+    }
+
+    fn diagnostic_extended(
+        &self,
+        mut err: DiagnosticBuilder<'tcx, ErrorGuaranteed>,
+    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+        err.note(&format!(
+            "certain types, like `{}`, must be casted before passing them to a \
+                variadic function, because of arcane ABI rules dictated by the C \
+                standard",
+            self.ty
+        ));
+
+        err
+    }
+}