3 files changed, 26 insertions, 2 deletions
diff --git a/src/libexpr/print.cc b/src/libexpr/print.cc
index 87db004b2..6eb321c43 100644
--- a/src/libexpr/print.cc
+++ b/src/libexpr/print.cc
@@ -264,10 +264,15 @@ private:
             return true;
         }
 
+        if (options.force) {
+            // The item is going to be forced during printing anyway, but we need its type now.
+            state.forceValue(*item, item->determinePos(noPos));
+        }
+
         // Pretty-print single-item attrsets only if they contain nested
         // structures.
         auto itemType = item->type();
-        return itemType == nList || itemType == nAttrs || itemType == nThunk;
+        return itemType == nList || itemType == nAttrs;
     }
 
     void printAttrs(Value & v, size_t depth)
@@ -335,10 +340,15 @@ private:
             return true;
         }
 
+        if (options.force) {
+            // The item is going to be forced during printing anyway, but we need its type now.
+            state.forceValue(*item, item->determinePos(noPos));
+        }
+
         // Pretty-print single-item lists only if they contain nested
         // structures.
         auto itemType = item->type();
-        return itemType == nList || itemType == nAttrs || itemType == nThunk;
+        return itemType == nList || itemType == nAttrs;
     }
 
     void printList(Value & v, size_t depth)
diff --git a/tests/functional/repl_characterization/data/idempotent.test b/tests/functional/repl_characterization/data/idempotent.test
new file mode 100644
index 000000000..4ab087d45
--- /dev/null
+++ b/tests/functional/repl_characterization/data/idempotent.test
@@ -0,0 +1,13 @@
+A previously unforced thunk in an attribute set does not lead to indentation when it won't evaluate to a nested structure:
+  nix-repl> :p let x = 1 + 2; in [ { inherit x; } { inherit x; } ]
+  [
+    { x = 3; }
+    { x = 3; }
+  ]
+
+Same for a list:
+  nix-repl> :p let x = 1 + 2; in [ [ x ] [ x ] ]
+  [
+    [ 3 ]
+    [ 3 ]
+  ]
diff --git a/tests/functional/repl_characterization/repl_characterization.cc b/tests/functional/repl_characterization/repl_characterization.cc
index c91d6c1e3..f2cf0ca3d 100644
--- a/tests/functional/repl_characterization/repl_characterization.cc
+++ b/tests/functional/repl_characterization/repl_characterization.cc
@@ -185,5 +185,6 @@ REPL_TEST(repl_overlays_error);
 REPL_TEST(repl_printing);
 REPL_TEST(stack_vars);
 REPL_TEST(errors);
+REPL_TEST(idempotent);
 
 }; // namespace nix