Sema: Better -debug-constraints output when we failed because of free type variables

Author: slavapestov

lib/Sema/CSStep.cpp

@@ -438,6 +438,20 @@ StepResult ComponentStep::take(bool prevFailed) {
     // If there are no disjunctions or type variables to bind
     // we can't solve this system unless we have free type variables
     // allowed in the solution.
+    if (CS.isDebugMode()) {
+      PrintOptions PO;
+      PO.PrintTypesForDebugging = true;
+
+      auto &log = getDebugLogger();
+      log << "(failed due to free variables:";
+      for (auto *typeVar : CS.getTypeVariables()) {
+        if (!typeVar->getImpl().hasRepresentativeOrFixed()) {
+          log << " " << typeVar->getString(PO);
+        }
+      }
+      log << ")\n";
+    }
+
     return finalize(/*isSuccess=*/false);
   }