Add 'json4cpp/' from commit '9a737481aed085fd289f82dff1fa8c3c66627a7e'

git-subtree-dir: json4cpp
git-subtree-mainline: 292baed7ac0cf84263263966ed32ed113cae857f
git-subtree-split: 9a737481aed085fd289f82dff1fa8c3c66627a7e

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diff --git a/json4cpp/tools/gdb_pretty_printer/README.md b/json4cpp/tools/gdb_pretty_printer/README.md
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index 0000000000..4a95776df4
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+++ b/json4cpp/tools/gdb_pretty_printer/README.md
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+# 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
+    }
+    ```
+
+Requires Python 3.9+. Last tested with GDB 12.1.
+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/json4cpp/tools/gdb_pretty_printer/nlohmann-json.py b/json4cpp/tools/gdb_pretty_printer/nlohmann-json.py
new file mode 100644
index 0000000000..2c120befd9
--- /dev/null
+++ b/json4cpp/tools/gdb_pretty_printer/nlohmann-json.py
@@ -0,0 +1,35 @@
+import gdb
+import re
+
+ns_pattern = re.compile(r'nlohmann(::json_abi(?P<tags>\w*)(_v(?P<v_major>\d+)_(?P<v_minor>\d+)_(?P<v_patch>\d+))?)?::(?P<name>.+)')
+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 m := ns_pattern.fullmatch(str(val.type.strip_typedefs().name)):
+        name = m.group('name')
+        if name and name.startswith('basic_json<') and name.endswith('>'):
+            m_data = val['m_data']
+            m_type = m_data['m_type']
+            m = ns_pattern.fullmatch(str(m_type))
+            t = m.group('name')
+            prefix = 'detail::value_t::'
+            if t and t.startswith(prefix):
+                try:
+                    union_val = m_data['m_value'][t.replace(prefix, '', 1)]
+                    if union_val.type.code == gdb.TYPE_CODE_PTR:
+                        return gdb.default_visualizer(union_val.dereference())
+                    else:
+                        return JsonValuePrinter(union_val)
+                except Exception:
+                    return JsonValuePrinter(m_type)
+
+gdb.pretty_printers.append(json_lookup_function)