1 files changed, 19 insertions, 0 deletions

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 584bbc879..7f2065656 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -173,7 +173,17 @@ void Value::print(const SymbolTable & symbols, std::ostream & str,
     case tFloat:
         str << fpoint;
         break;
+    case tBlackhole:
+        // Although we know for sure that it's going to be an infinite recursion
+        // when this value is accessed _in the current context_, it's likely
+        // that the user will misinterpret a simpler «infinite recursion» output
+        // as a definitive statement about the value, while in fact it may be
+        // a valid value after `builtins.trace` and perhaps some other steps
+        // have completed.
+        str << "«potential infinite recursion»";
+        break;
     default:
+        printError("Nix evaluator internal error: Value::print(): invalid value type %1%", internalType);
         abort();
     }
 }
@@ -229,6 +239,9 @@ std::string_view showType(ValueType type)
 
 std::string showType(const Value & v)
 {
+    // Allow selecting a subset of enum values
+    #pragma GCC diagnostic push
+    #pragma GCC diagnostic ignored "-Wswitch-enum"
     switch (v.internalType) {
         case tString: return v.string.context ? "a string with context" : "a string";
         case tPrimOp:
@@ -242,16 +255,21 @@ std::string showType(const Value & v)
     default:
         return std::string(showType(v.type()));
     }
+    #pragma GCC diagnostic pop
 }
 
 PosIdx Value::determinePos(const PosIdx pos) const
 {
+    // Allow selecting a subset of enum values
+    #pragma GCC diagnostic push
+    #pragma GCC diagnostic ignored "-Wswitch-enum"
     switch (internalType) {
         case tAttrs: return attrs->pos;
         case tLambda: return lambda.fun->pos;
         case tApp: return app.left->determinePos(pos);
         default: return pos;
     }
+    #pragma GCC diagnostic pop
 }
 
 bool Value::isTrivial() const
@@ -2327,6 +2345,7 @@ bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_v
         case nFloat:
             return v1.fpoint == v2.fpoint;
 
+        case nThunk: // Must not be left by forceValue
         default:
             error("cannot compare %1% with %2%", showType(v1), showType(v2)).withTrace(pos, errorCtx).debugThrow<EvalError>();
     }