Add a GDB pretty printer to aid in debugging

[Mitten-O]

The GDB debugger supports pretty-printing of a project's custom types using a python script.
This PR adds a GDB pretty-printer script that can pretty-print Godot's String, StringName and Vector.
This significantly increses the readability, especially of the two latter objects, as the payload is deep in them.

Before:

gdb bin/godot.linuxbsd.editor.dev.x86_64
(gdb) break gdscript.cpp:1079
(gdb) set args --test --test-suite="*GDScript*"
(gdb) run
...
(gdb) print sourcef
$1 = {write = {<No data fields>}, _cowdata = {static MAX_INT = <optimized out>, static REF_COUNT_OFFSET = <optimized out>, static SIZE_OFFSET = <optimized out>, 
    static DATA_OFFSET = <optimized out>, _ptr = 0x5555624edd40 "const dictionary := {0: [0]}\n\nfunc test():\n\tvar array := dictionary[0]\n\tvar key: int = 0\n\tarray[key] = 0\n"}}
(gdb) print p_path
$2 = (const String &) @0x7fffffffcf60: {_cowdata = {static MAX_INT = <optimized out>, static REF_COUNT_OFFSET = <optimized out>, static SIZE_OFFSET = <optimized out>, 
    static DATA_OFFSET = <optimized out>, _ptr = 0x555562365f50 U"/mnt/SSD-General2/projects/godot/godot/modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_is_deep.gd"}, 
  static _null = 0 U'\000', static _replacement_char = 65533 U'�'}

After:

(gdb) source misc/scripts/godot_gdb_pretty_print.py
(gdb) print sourcef
$3 = Vector<unsigned char> [106] = {99 'c', 111 'o', 110 'n', 115 's', 116 't', 32 ' ', 100 'd', 105 'i', 99 'c', 116 't', 105 'i', 111 'o', 110 'n', 97 'a', 114 'r', 121 'y', 32 ' ', 58 ':', 
  61 '=', 32 ' ', 123 '{', 48 '0', 58 ':', 32 ' ', 91 '[', 48 '0', 93 ']', 125 '}', 10 '\n', 10 '\n', 102 'f', 117 'u', 110 'n', 99 'c', 32 ' ', 116 't', 101 'e', 115 's', 116 't', 40 '(', 
  41 ')', 58 ':', 10 '\n', 9 '\t', 118 'v', 97 'a', 114 'r', 32 ' ', 97 'a', 114 'r', 114 'r', 97 'a', 121 'y', 32 ' ', 58 ':', 61 '=', 32 ' ', 100 'd', 105 'i', 99 'c', 116 't', 105 'i', 
  111 'o', 110 'n', 97 'a', 114 'r', 121 'y', 91 '[', 48 '0', 93 ']', 10 '\n', 9 '\t', 118 'v', 97 'a', 114 'r', 32 ' ', 107 'k', 101 'e', 121 'y', 58 ':', 32 ' ', 105 'i', 110 'n', 116 't', 
  32 ' ', 61 '=', 32 ' ', 48 '0', 10 '\n', 9 '\t', 97 'a', 114 'r', 114 'r', 97 'a', 121 'y', 91 '[', 107 'k', 101 'e', 121 'y', 93 ']', 32 ' ', 61 '=', 32 ' ', 48 '0', 10 '\n', 0 '\000'}
(gdb) print p_path
$4 = (const String &) @0x7fffffffcf60: U"/mnt/SSD-General2/projects/godot/godot/modules/gdscript/tests/scripts/runtime/errors/constant_dictionary_is_deep.gd"

You can enable the pretty printer by default in VS code by adding this to your configuration in launch.json:

"setupCommands": [
                {
                    "description": "Enable pretty-printing for gdb",
                    "text": "-enable-pretty-printing",
                    "ignoreFailures": true
                },
                {
                    "description": "Load custom pretty-printers for Godot types.",
                    "text": "source ${workspaceRoot}/misc/scripts/godot_gdb_pretty_print.py"
                }
]

Vector<StringName> in VS code without this:

Vector<StringName> in VS code with this:

GDB supports some ways of loading the pretty printer automatically, but all of the would require adding the source of
the script to the safe autoload path. If the user needs to do configuration anyway, best to let them specify the loading of pretty printing explicitly, instead of making them enable magic that does the loading implicitly.

[Calinou]

Add shebang (and make file executable with chmod +x):

Suggested change

	# Load this file to your GDB session to enable pretty-printing
	#!/usr/bin/env python3
	#
	# Load this file to your GDB session to enable pretty-printing

Also, remember to format the file with black -l120 path/to/file.py (it's what we use for other scripts in the repository). I also suggest running isort path/to/file.py.

[Mitten-O]

Fixed.

[AThousandShips]

Your commit seems not to be linked to your GitHub account. See: Why are my commits linked to the wrong user? for more info.

[Mitten-O]

Your commit seems not to be linked to your GitHub account. See: Why are my commits linked to the wrong user? for more info.

The email in the commits had different capitalization than in my profile. They still appeared as linked to me, but regardless, I updated the capitalizations to match. Thanks for the heads up!

[AThousandShips]

Still not linked, are you sure that email address is used for this account? As you can see the commits don't have your profile picture

My bad the icon was just scaled and invisible

[akien-mga]

Thanks for the contribution, this is really great! I've spent countless time trying to print Strings and StringNames in gdb and figuring out where's a hint of what the actual human-readable string is.

For your Vector printing example, it does make sense to me, but I notice that we're losing some convenience where gdb used to actually print the _ptr as a readable string:

_ptr = 0x5555624edd40 "const dictionary := {0: [0]}\n\nfunc test():\n\tvar array := dictionary[0]\n\tvar key: int = 0\n\tarray[key] = 0\n"

Not sure why, and that's probably only applicable for Vector<unsigned char>, so I don't know if we can (or should) preserve some of that behavior?

---

Could you also squash the commits? See PR workflow for instructions.

[akien-mga]

Tested with command line gdb, works great!

[Calinou]

Remember to open a PR to document this on https://github.com/godotengine/godot-docs/blob/master/contributing/development/configuring_an_ide/visual_studio_code.rst 🙂

[Mitten-O]

Remember to open a PR to document this on https://github.com/godotengine/godot-docs/blob/master/contributing/development/configuring_an_ide/visual_studio_code.rst 🙂

Good point. Here: godotengine/godot-docs#9348

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉