Only skip fallback when errors have been reported in the same function

rust-lang · Aaron1011 · Jan 12, 2020 · Jan 12, 2020 · Jan 12, 2020 · Jan 12, 2020
commit 409e8d71a9a12225f8fee6a80b0d795c34e3d2e3
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
@@ -1164,11 +1164,12 @@ fn typeck_tables_of_with_fallback<'tcx>(
            fcx.require_type_is_sized(ty, span, code);
        }

-        fcx.select_all_obligations_or_error();
-
-        // Report other errors in preference to never-type
-        // fallback errors.
-        never_compat.post_fallback(&fcx);
+        if !fcx.select_all_obligations_or_error() {
+            // If we just reported some errors, don't run
+            // never-type fallbakc - inference variables may
+            // be in a weird state, leading to spurious errors
+            never_compat.post_fallback(&fcx);
+        }

        if fn_decl.is_some() {
            fcx.regionck_fn(id, body);
@@ -3473,10 +3474,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
        true
    }

-    fn select_all_obligations_or_error(&self) {
+    /// Returns whether or not errors were reported
+    fn select_all_obligations_or_error(&self) -> bool {
        debug!("select_all_obligations_or_error");
        if let Err(errors) = self.fulfillment_cx.borrow_mut().select_all_or_error(&self) {
            self.report_fulfillment_errors(&errors, self.inh.body_id, false);
+            true
+        } else {
+            false
        }
    }


diff --git a/src/librustc_typeck/check/never_compat.rs b/src/librustc_typeck/check/never_compat.rs
@@ -404,11 +404,6 @@ impl<'tcx> NeverCompatHandler<'tcx> {
    /// We look for any "questionable" calls, generating diagnostic
    /// message for them.
    pub fn post_fallback(self, fcx: &FnCtxt<'a, 'tcx>) {
-        if fcx.tcx.sess.has_errors() {
-            debug!("post_fallback: sess has errors, bailing out");
-            return;
-        }
-
        let tcx = fcx.tcx;
        for (call_id, path) in &self.unresolved_paths {
            debug!(