Merge pull request #11100 from NixOS/pretty-print-idempotent

Pretty print idempotently

src/libexpr/print.cc

@@ -299,6 +299,9 @@ private:
             output << ANSI_NORMAL;
     }
 
+    /**
+     * @note This may force items.
+     */
     bool shouldPrettyPrintAttrs(AttrVec & v)
     {
         if (!options.shouldPrettyPrint() || v.empty()) {
@@ -315,6 +318,9 @@ private:
             return true;
         }
 
+        // It is ok to force the item(s) here, because they will be printed anyway.
+        state.forceValue(*item, item->determinePos(noPos));
+
         // Pretty-print single-item attrsets only if they contain nested
         // structures.
         auto itemType = item->type();
@@ -371,6 +377,9 @@ private:
         }
     }
 
+    /**
+     * @note This may force items.
+     */
     bool shouldPrettyPrintList(std::span<Value * const> list)
     {
         if (!options.shouldPrettyPrint() || list.empty()) {
@@ -387,6 +396,9 @@ private:
             return true;
         }
 
+        // It is ok to force the item(s) here, because they will be printed anyway.
+        state.forceValue(*item, item->determinePos(noPos));
+
         // Pretty-print single-item lists only if they contain nested
         // structures.
         auto itemType = item->type();

tests/functional/repl/pretty-print-idempotent.expected

@@ -0,0 +1,29 @@
+Nix <nix version>
+Type :? for help.
+Added <number omitted> variables.
+
+{ homepage = "https://example.com"; }
+
+{ homepage = "https://example.com"; }
+
+{
+  layerOne = { ... };
+}
+
+{
+  layerOne = { ... };
+}
+
+[ "https://example.com" ]
+
+[ "https://example.com" ]
+
+[
+  [ ... ]
+]
+
+[
+  [ ... ]
+]
+
+

tests/functional/repl/pretty-print-idempotent.in

@@ -0,0 +1,9 @@
+:l pretty-print-idempotent.nix
+oneDeep
+oneDeep
+twoDeep
+twoDeep
+oneDeepList
+oneDeepList
+twoDeepList
+twoDeepList

tests/functional/repl/pretty-print-idempotent.nix

@@ -0,0 +1,19 @@
+{
+  oneDeep = {
+    homepage = "https://" + "example.com";
+  };
+  twoDeep = {
+    layerOne = {
+      homepage = "https://" + "example.com";
+    };
+  };
+
+  oneDeepList = [
+    ("https://" + "example.com")
+  ];
+  twoDeepList = [
+    [
+      ("https://" + "example.com")
+    ]
+  ];
+}