builtins.toJSON: fix __toString usage

(cherry picked from commit e583df52800b4baa1564b027fe3b83a21756c2cc)

1 files changed, 6 insertions, 1 deletions

diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index 72e413e4491e..5fe8570adeb4 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -40,7 +40,12 @@ void printValueAsJSON(EvalState & state, bool strict,
             break;
 
         case tAttrs: {
-            Bindings::iterator i = v.attrs->find(state.sOutPath);
+            auto maybeString = state.tryAttrsToString(noPos, v, context, false, false);
+            if (maybeString) {
+                out.write(*maybeString);
+                break;
+            }
+            auto i = v.attrs->find(state.sOutPath);
             if (i == v.attrs->end()) {
                 auto obj(out.object());
                 StringSet names;