Merge pull request #6201 from edolstra/print-value

printValue(): Don't show repeated values

src/libexpr/eval.cc

@@ -86,15 +86,10 @@ RootValue allocRootValue(Value * v)
 }
 
 
-void printValue(std::ostream & str, std::set<const Value *> & active, const Value & v)
+void printValue(std::ostream & str, std::set<const void *> & seen, const Value & v)
 {
     checkInterrupt();
 
-    if (!active.insert(&v).second) {
-        str << "<CYCLE>";
-        return;
-    }
-
     switch (v.internalType) {
     case tInt:
         str << v.integer;
@@ -120,24 +115,32 @@ void printValue(std::ostream & str, std::set<const Value *> & active, const Valu
         str << "null";
         break;
     case tAttrs: {
-        str << "{ ";
+        if (!v.attrs->empty() && !seen.insert(v.attrs).second)
-        for (auto & i : v.attrs->lexicographicOrder()) {
+            str << "<REPEAT>";
-            str << i->name << " = ";
+        else {
-            printValue(str, active, *i->value);
+            str << "{ ";
-            str << "; ";
+            for (auto & i : v.attrs->lexicographicOrder()) {
+                str << i->name << " = ";
+                printValue(str, seen, *i->value);
+                str << "; ";
+            }
+            str << "}";
         }
-        str << "}";
         break;
     }
     case tList1:
     case tList2:
     case tListN:
-        str << "[ ";
+        if (v.listSize() && !seen.insert(v.listElems()).second)
-        for (auto v2 : v.listItems()) {
+            str << "<REPEAT>";
-            printValue(str, active, *v2);
+        else {
-            str << " ";
+            str << "[ ";
+            for (auto v2 : v.listItems()) {
+                printValue(str, seen, *v2);
+                str << " ";
+            }
+            str << "]";
         }
-        str << "]";
         break;
     case tThunk:
     case tApp:
@@ -161,15 +164,13 @@ void printValue(std::ostream & str, std::set<const Value *> & active, const Valu
     default:
         abort();
     }
-
-    active.erase(&v);
 }
 
 
 std::ostream & operator << (std::ostream & str, const Value & v)
 {
-    std::set<const Value *> active;
+    std::set<const void *> seen;
-    printValue(str, active, v);
+    printValue(str, seen, v);
     return str;
 }
 

src/libexpr/value.hh

@@ -114,8 +114,8 @@ struct Value
 private:
     InternalType internalType;
 
-friend std::string showType(const Value & v);
+    friend std::string showType(const Value & v);
-friend void printValue(std::ostream & str, std::set<const Value *> & active, const Value & v);
+    friend void printValue(std::ostream & str, std::set<const void *> & seen, const Value & v);
 
 public:
 

src/nix/repl.cc

@@ -800,7 +800,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
                 else
                     printStringValue(str, i.first.c_str());
                 str << " = ";
-                if (seen.find(i.second) != seen.end())
+                if (seen.count(i.second))
                     str << "«repeated»";
                 else
                     try {