:children_crossing: add GDB pretty printer
diff --git a/README.md b/README.md
index 19d8f72..eb56d6c 100644
--- a/README.md
+++ b/README.md
@@ -1528,6 +1528,7 @@
- [KonanM](https://github.com/KonanM) proposed an implementation for the `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE`/`NLOHMANN_DEFINE_TYPE_INTRUSIVE` macros.
- [Guillaume Racicot](https://github.com/gracicot) implemented `string_view` support and allowed C++20 support.
- [Alex Reinking](https://github.com/alexreinking) improved CMake support for `FetchContent`.
+- [Hannes Domani](https://github.com/ssbssa) provided a GDB pretty printer.
Thanks a lot for helping out! Please [let me know](mailto:mail@nlohmann.me) if I forgot someone.
diff --git a/third_party/gdb_pretty_printer/README.md b/third_party/gdb_pretty_printer/README.md
new file mode 100644
index 0000000..f5f6192
--- /dev/null
+++ b/third_party/gdb_pretty_printer/README.md
@@ -0,0 +1,77 @@
+# GDB Pretty Printer
+
+File [nlohmann-json.py](nlohmann-json.py) contains a pretty printer for GDB for JSON values of this library. It was originally published as [Gist](https://gist.github.com/ssbssa/60da5339c6e6036b2afce17de06050ea#file-nlohmann-json-py) by [Hannes Domani](https://github.com/ssbssa).
+
+## How to use
+
+- Add line
+
+ ```
+ source /path/to/nlohmann-json.py
+ ```
+
+ to `~/.gdbinit`. Note you must replace `/path/to` with whatever path you stored file `nlohmann-json.py`.
+- In GDB, debug as usual. When you want to pretty-print a JSON value `var`, type
+
+ ```
+ p -pretty on -array on -- var
+ ```
+
+ The result should look like
+
+ ```
+ $1 = std::map with 5 elements = {
+ ["Baptiste"] = std::map with 1 element = {
+ ["first"] = "second"
+ },
+ ["Emmanuel"] = std::vector of length 3, capacity 3 = {
+ 3,
+ "25",
+ 0.5
+ },
+ ["Jean"] = 0.7,
+ ["Zorg"] = std::map with 8 elements = {
+ ["array"] = std::vector of length 3, capacity 3 = {
+ 1,
+ 0,
+ 2
+ },
+ ["awesome_str"] = "bleh",
+ ["bool"] = true,
+ ["flex"] = 0.2,
+ ["float"] = 5.22,
+ ["int"] = 5,
+ ["nested"] = std::map with 1 element = {
+ ["bar"] = "barz"
+ },
+ ["trap "] = "you fell"
+ },
+ ["empty"] = nlohmann::detail::value_t::null
+ }
+ ```
+
+Tested with GDB 9.2. See [#1952](https://github.com/nlohmann/json/issues/1952) for more information. Please post questions there.
+
+## Copyright
+
+MIT License
+
+Copyright (C) 2020 [Hannes Domani](https://github.com/ssbssa)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/third_party/gdb_pretty_printer/nlohmann-json.py b/third_party/gdb_pretty_printer/nlohmann-json.py
new file mode 100644
index 0000000..5bac45f
--- /dev/null
+++ b/third_party/gdb_pretty_printer/nlohmann-json.py
@@ -0,0 +1,28 @@
+import gdb
+import re
+
+class JsonValuePrinter:
+ "Print a json-value"
+
+ def __init__(self, val):
+ self.val = val
+
+ def to_string(self):
+ if self.val.type.strip_typedefs().code == gdb.TYPE_CODE_FLT:
+ return ("%.6f" % float(self.val)).rstrip("0")
+ return self.val
+
+def json_lookup_function(val):
+ if re.search("^nlohmann::basic_json<.*>$", val.type.strip_typedefs().name):
+ t = str(val['m_type'])
+ if t.startswith("nlohmann::detail::value_t::"):
+ try:
+ union_val = val['m_value'][t[27:]]
+ if union_val.type.code == gdb.TYPE_CODE_PTR:
+ return gdb.default_visualizer(union_val.dereference())
+ else:
+ return JsonValuePrinter(union_val)
+ except:
+ return JsonValuePrinter(val['m_type'])
+
+gdb.pretty_printers.append(json_lookup_function)
