libexpr: extend Value::print to allow limited depth

src/libexpr/eval.cc

@@ -96,10 +96,15 @@ RootValue allocRootValue(Value * v)
 }
 
 void Value::print(const SymbolTable &symbols, std::ostream &str,
-    std::set<const void *> * seen) const
+                  std::set<const void *> *seen, int depth) const
+
 {
     checkInterrupt();
 
+    if (depth <= 0) {
+        str << "«too deep»";
+        return;
+    }
     switch (internalType) {
     case tInt:
         str << integer;
@@ -123,7 +128,7 @@ void Value::print(const SymbolTable & symbols, std::ostream & str,
             str << "{ ";
             for (auto & i : attrs->lexicographicOrder(symbols)) {
                 str << symbols[i->name] << " = ";
-                i->value->print(symbols, str, seen);
+                i->value->print(symbols, str, seen, depth - 1);
                 str << "; ";
             }
             str << "}";
@@ -139,7 +144,7 @@ void Value::print(const SymbolTable & symbols, std::ostream & str,
             str << "[ ";
             for (auto v2 : listItems()) {
                 if (v2)
-                    v2->print(symbols, str, seen);
+                    v2->print(symbols, str, seen, depth - 1);
                 else
                     str << "(nullptr)";
                 str << " ";
@@ -181,11 +186,10 @@ void Value::print(const SymbolTable & symbols, std::ostream & str,
     }
 }
 
-
+void Value::print(const SymbolTable &symbols, std::ostream &str,
-void Value::print(const SymbolTable & symbols, std::ostream & str, bool showRepeated) const
+                  bool showRepeated, int depth) const {
-{
     std::set<const void *> seen;
-    print(symbols, str, showRepeated ? nullptr : &seen);
+    print(symbols, str, showRepeated ? nullptr : &seen, depth);
 }
 
 // Pretty print types for assertion errors

src/libexpr/tests/value/print.cc

@@ -167,4 +167,70 @@ TEST_F(ValuePrintingTests, vBlackhole)
     test(vBlackhole, "«potential infinite recursion»");
 }
 
+TEST_F(ValuePrintingTests, depthAttrs)
+{
+    Value vOne;
+    vOne.mkInt(1);
+
+    Value vTwo;
+    vTwo.mkInt(2);
+
+    BindingsBuilder builder(state, state.allocBindings(10));
+    builder.insert(state.symbols.create("one"), &vOne);
+    builder.insert(state.symbols.create("two"), &vTwo);
+
+    Value vAttrs;
+    vAttrs.mkAttrs(builder.finish());
+
+    BindingsBuilder builder2(state, state.allocBindings(10));
+    builder2.insert(state.symbols.create("one"), &vOne);
+    builder2.insert(state.symbols.create("two"), &vTwo);
+    builder2.insert(state.symbols.create("nested"), &vAttrs);
+
+    Value vNested;
+    vNested.mkAttrs(builder2.finish());
+
+    test(vNested, "{ nested = «too deep»; one = «too deep»; two = «too deep»; }", false, 1);
+    test(vNested, "{ nested = { one = «too deep»; two = «too deep»; }; one = 1; two = 2; }", false, 2);
+    test(vNested, "{ nested = { one = 1; two = 2; }; one = 1; two = 2; }", false, 3);
+    test(vNested, "{ nested = { one = 1; two = 2; }; one = 1; two = 2; }", false, 4);
+}
+
+TEST_F(ValuePrintingTests, depthList)
+{
+    Value vOne;
+    vOne.mkInt(1);
+
+    Value vTwo;
+    vTwo.mkInt(2);
+
+    BindingsBuilder builder(state, state.allocBindings(10));
+    builder.insert(state.symbols.create("one"), &vOne);
+    builder.insert(state.symbols.create("two"), &vTwo);
+
+    Value vAttrs;
+    vAttrs.mkAttrs(builder.finish());
+
+    BindingsBuilder builder2(state, state.allocBindings(10));
+    builder2.insert(state.symbols.create("one"), &vOne);
+    builder2.insert(state.symbols.create("two"), &vTwo);
+    builder2.insert(state.symbols.create("nested"), &vAttrs);
+
+    Value vNested;
+    vNested.mkAttrs(builder2.finish());
+
+    Value vList;
+    state.mkList(vList, 5);
+    vList.bigList.elems[0] = &vOne;
+    vList.bigList.elems[1] = &vTwo;
+    vList.bigList.elems[2] = &vNested;
+    vList.bigList.size = 3;
+
+    test(vList, "[ «too deep» «too deep» «too deep» ]", false, 1);
+    test(vList, "[ 1 2 { nested = «too deep»; one = «too deep»; two = «too deep»; } ]", false, 2);
+    test(vList, "[ 1 2 { nested = { one = «too deep»; two = «too deep»; }; one = 1; two = 2; } ]", false, 3);
+    test(vList, "[ 1 2 { nested = { one = 1; two = 2; }; one = 1; two = 2; } ]", false, 4);
+    test(vList, "[ 1 2 { nested = { one = 1; two = 2; }; one = 1; two = 2; } ]", false, 5);
+}
+
 } // namespace nix

src/libexpr/value.hh

@@ -2,6 +2,7 @@
 ///@file
 
 #include <cassert>
+#include <climits>
 
 #include "symbol-table.hh"
 #include "value/context.hh"
@@ -137,11 +138,11 @@ private:
 
     friend std::string showType(const Value & v);
 
-    void print(const SymbolTable & symbols, std::ostream & str, std::set<const void *> * seen) const;
+    void print(const SymbolTable &symbols, std::ostream &str, std::set<const void *> *seen, int depth) const;
 
 public:
 
-    void print(const SymbolTable & symbols, std::ostream & str, bool showRepeated = false) const;
+    void print(const SymbolTable &symbols, std::ostream &str, bool showRepeated = false, int depth = INT_MAX) const;
 
     // Functions needed to distinguish the type
     // These should be removed eventually, by putting the functionality that's