Add indent size for json pretty printing

Summary: Adds `pretty_formating_indent_size` option which is used to change the indentation size when used with `pretty_formatting`

Reviewed By: yfeldblum

Differential Revision: D26793086

fbshipit-source-id: 53efea33d7daa5c8f8840fc7f087d2d976ed3eda

folly/json.cpp

@@ -189,7 +189,8 @@ struct Printer {
 
   void newline() const {
     if (indentLevel_) {
-      out_ += to<std::string>('\n', std::string(*indentLevel_ * 2, ' '));
+      auto indent = *indentLevel_ * opts_.pretty_formatting_indent_width;
+      out_ += to<std::string>('\n', std::string(indent, ' '));
     }
   }
 

folly/json.h

@@ -58,6 +58,7 @@ struct serialization_opts {
       : allow_non_string_keys(false),
         javascript_safe(false),
         pretty_formatting(false),
+        pretty_formatting_indent_width(2),
         encode_non_ascii(false),
         validate_utf8(false),
         allow_trailing_comma(false),
@@ -87,6 +88,9 @@ struct serialization_opts {
   // try to be minimally "pretty".
   bool pretty_formatting;
 
+  // The number of spaces to indent by when pretty_formatting is enabled.
+  unsigned int pretty_formatting_indent_width;
+
   // If true, non-ASCII utf8 characters would be encoded as \uXXXX:
   // - if the code point is in [U+0000..U+FFFF] => encode as a single \uXXXX
   // - if the code point is > U+FFFF => encode as 2 UTF-16 surrogate pairs.

folly/test/JsonTest.cpp

@@ -797,6 +797,41 @@ TEST(Json, SortKeys) {
       inverse_sorted_keys, folly::json::serialize(value, opts_custom_sort));
 }
 
+TEST(Json, PrettyPrintIndent) {
+  folly::json::serialization_opts opts;
+  opts.sort_keys = true;
+  opts.pretty_formatting = true;
+  opts.pretty_formatting_indent_width = 4;
+
+  // clang-format off
+  dynamic value = dynamic::object
+    ("foo", "bar")
+    ("nested",
+      dynamic::object
+        ("abc", "def")
+        ("qrs", dynamic::array("tuv", 789))
+        ("xyz", 123)
+    )
+    ("zzz", 456)
+    ;
+  // clang-format on
+
+  std::string expected = R"({
+    "foo": "bar",
+    "nested": {
+        "abc": "def",
+        "qrs": [
+            "tuv",
+            789
+        ],
+        "xyz": 123
+    },
+    "zzz": 456
+})";
+
+  EXPECT_EQ(expected, folly::json::serialize(value, opts));
+}
+
 TEST(Json, PrintTo) {
   std::ostringstream oss;