Fancy serializer can limit recursion depth

Elides objects with ... if that limit is exceeded

include/nlohmann/detail/output/fancy_serializer.hpp

@@ -29,6 +29,8 @@ struct fancy_serializer_style
     unsigned int indent_step = 0;
     char indent_char = ' ';
 
+    unsigned int depth_limit = std::numeric_limits<unsigned>::max();
+
     unsigned int strings_maximum_length = 0;
 };
 
@@ -156,6 +158,11 @@ class fancy_serializer
             o->write_characters("{}", 2);
             return;
         }
+        else if (depth >= style.depth_limit)
+        {
+            o->write_characters("{...}", 5);
+            return;
+        }
 
         // variable to hold indentation for recursive calls
         const auto old_indent = depth * style.indent_step;
@@ -201,6 +208,11 @@ class fancy_serializer
             o->write_characters("[]", 2);
             return;
         }
+        else if (depth >= style.depth_limit)
+        {
+            o->write_characters("[...]", 5);
+            return;
+        }
 
         // variable to hold indentation for recursive calls
         const auto old_indent = depth * style.indent_step;

single_include/nlohmann/json.hpp

@@ -10099,6 +10099,8 @@ struct fancy_serializer_style
     unsigned int indent_step = 0;
     char indent_char = ' ';
 
+    unsigned int depth_limit = std::numeric_limits<unsigned>::max();
+
     unsigned int strings_maximum_length = 0;
 };
 
@@ -10226,6 +10228,11 @@ class fancy_serializer
             o->write_characters("{}", 2);
             return;
         }
+        else if (depth >= style.depth_limit)
+        {
+            o->write_characters("{...}", 5);
+            return;
+        }
 
         // variable to hold indentation for recursive calls
         const auto old_indent = depth * style.indent_step;
@@ -10271,6 +10278,11 @@ class fancy_serializer
             o->write_characters("[]", 2);
             return;
         }
+        else if (depth >= style.depth_limit)
+        {
+            o->write_characters("[...]", 5);
+            return;
+        }
 
         // variable to hold indentation for recursive calls
         const auto old_indent = depth * style.indent_step;

test/src/unit-fancy-serialization.cpp

@@ -183,23 +183,59 @@ TEST_CASE("serialization")
         // behavior to be, first. :-)
     }
 
+    SECTION("maximum depth")
+    {
+        SECTION("recursing past the maximum depth with a list elides the subobjects")
+        {
+            fancy_serializer_style style;
+            style.depth_limit = 1;
+
+            auto str_flat = fancy_to_string({1, {1}}, style);
+            CHECK(str_flat == "[1,[...]]");
+
+            style.indent_step = 4;
+            auto str_lines = fancy_to_string({1, {1}}, style);
+            CHECK(str_lines == dedent(R"(
+                  [
+                      1,
+                      [...]
+                  ])"));
+        }
+
+        SECTION("recursing past the maximum depth with an object elides the subobjects")
+        {
+            fancy_serializer_style style;
+            style.depth_limit = 1;
+
+            auto str_flat = fancy_to_string({1, {{"one", 1}}}, style);
+            CHECK(str_flat == "[1,{...}]");
+
+            style.indent_step = 4;
+            auto str_lines = fancy_to_string({1, {{"one", 1}}}, style);
+            CHECK(str_lines == dedent(R"(
+                  [
+                      1,
+                      {...}
+                  ])"));
+        }
+    }
+
     SECTION("given width")
     {
         fancy_serializer_style style;
         style.indent_step = 4;
         auto str = fancy_to_string({"foo", 1, 2, 3, false, {{"one", 1}}}, style);
-        CHECK(str ==
+        CHECK(str == dedent(R"(
-              dedent(R"(
+              [
-                  [
+                  "foo",
-                      "foo",
+                  1,
-                      1,
+                  2,
-                      2,
+                  3,
-                      3,
+                  false,
-                      false,
+                  {
-                      {
+                      "one": 1
-                          "one": 1
+                  }
-                      }
+              ])"));
-                  ])"));
     }
 
     SECTION("given fill")