1 files changed, 18 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
index 088fa668914..cb074261cde 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
@@ -1796,6 +1796,24 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                 StringPart::highlighted("cargo tree".to_string()),
                 StringPart::normal("` to explore your dependency tree".to_string()),
             ]);
+
+            // FIXME: this is a giant hack for the benefit of this specific diagnostic. Because
+            // we're so nested in method calls before the error gets emitted, bubbling a single bit
+            // flag informing the top level caller to stop adding extra detail to the diagnostic,
+            // would actually be harder to follow. So we do something naughty here: we consume the
+            // diagnostic, emit it and leave in its place a "delayed bug" that will continue being
+            // modified but won't actually be printed to end users. This *is not ideal*, but allows
+            // us to reduce the verbosity of an error that is already quite verbose and increase its
+            // specificity. Below we modify the main message as well, in a way that *could* break if
+            // the implementation of Diagnostics change significantly, but that would be caught with
+            // a make test failure when this diagnostic is tested.
+            err.primary_message(format!(
+                "{} because the trait comes from a different crate version",
+                err.messages[0].0.as_str().unwrap(),
+            ));
+            let diag = err.clone();
+            err.downgrade_to_delayed_bug();
+            self.tcx.dcx().emit_diagnostic(diag);
             return true;
         }