gron: Implement a simplified variant of @tomnomnom's "gron"

This program takes JSON input and turns it into JavaScript statements
that construct the same data step by step. This format is much more
greppable than what "jp" gives us. :^)

Userland/gron.cpp

@@ -0,0 +1,93 @@
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <AK/JsonValue.h>
+#include <AK/StringBuilder.h>
+#include <LibCore/CFile.h>
+#include <stdio.h>
+
+static bool use_color = false;
+static void print(const String& name, const JsonValue&, Vector<String>& trail);
+
+static const char* color_name = "";
+static const char* color_index = "";
+static const char* color_brace = "";
+static const char* color_bool = "";
+static const char* color_null = "";
+static const char* color_string = "";
+static const char* color_off = "";
+
+int main(int argc, char** argv)
+{
+    if (argc != 2) {
+        fprintf(stderr, "usage: gron <file>\n");
+        return 0;
+    }
+    auto file = CFile::construct(argv[1]);
+    if (!file->open(CIODevice::ReadOnly)) {
+        fprintf(stderr, "Couldn't open %s for reading: %s\n", argv[1], file->error_string());
+        return 1;
+    }
+
+    auto file_contents = file->read_all();
+    auto json = JsonValue::from_string(file_contents);
+
+    if (isatty(STDOUT_FILENO))
+        use_color = true;
+
+    if (use_color) {
+        color_name = "\033[33;1m";
+        color_index = "\033[35;1m";
+        color_brace = "\033[36m";
+        color_bool = "\033[32;1m";
+        color_string = "\033[31;1m";
+        color_null = "\033[34;1m";
+        color_off = "\033[0m";
+    }
+
+    Vector<String> trail;
+    print("json", json, trail);
+    return 0;
+}
+
+static void print(const String& name, const JsonValue& value, Vector<String>& trail)
+{
+    for (int i = 0; i < trail.size(); ++i)
+        printf("%s", trail[i].characters());
+
+    printf("%s%s%s = ", color_name, name.characters(), color_off);
+
+    if (value.is_object()) {
+        printf("%s{}%s;\n", color_brace, color_off);
+        trail.append(String::format("%s%s%s.", color_name, name.characters(), color_off));
+        value.as_object().for_each_member([&](auto& on, auto& ov) { print(on, ov, trail); });
+        trail.take_last();
+        return;
+    }
+    if (value.is_array()) {
+        printf("%s[]%s;\n", color_brace, color_off);
+        trail.append(String::format("%s%s%s", color_name, name.characters(), color_off));
+        for (int i = 0; i < value.as_array().size(); ++i) {
+            auto element_name = String::format("%s%s[%s%s%d%s%s]%s", color_off, color_brace, color_off, color_index, i, color_off, color_brace, color_off);
+            print(element_name, value.as_array()[i], trail);
+        }
+        trail.take_last();
+        return;
+    }
+    switch (value.type()) {
+    case JsonValue::Type::Null:
+    case JsonValue::Type::Undefined:
+        printf("%s", color_null);
+        break;
+    case JsonValue::Type::Bool:
+        printf("%s", color_bool);
+        break;
+    case JsonValue::Type::String:
+        printf("%s", color_string);
+        break;
+    default:
+        printf("%s", color_index);
+        break;
+    }
+
+    printf("%s%s;\n", value.serialized<StringBuilder>().characters(), color_off);
+}