Add tool to find directly recursive calls in toxcore.

[iphydf]

We should avoid recursion, as it makes reasoning about stack growth
harder. This tool shows (currently) 2 (non-tail) recursive functions. We exempt only these. New recursive functions are not allowed.

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This change is 

[nurupo]

Does it still fail? You removed its use on Travis.

[nurupo]

Reviewable status: 0 of 1 approvals obtained (waiting on @iphydf)

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other/analysis/check-recursion, line 19 at r1 (raw file):

            "opt -analyze -print-callgraph "
            "2>&1".format(inputs=INPUTS, cflags=CFLAGS),
            shell=True).split("\n")

Make that line

 shell=True).decode('utf8').split("\n")

That works for both Python 2 and Python 3.

Otherwise it fails in Python 3 with:

c-toxcore$ python3 t.py
[+0000=0000] Generating callgraph
Traceback (most recent call last):
  File "t.py", line 71, in <module>
    find_recursion()
  File "t.py", line 52, in find_recursion
    cg = load_callgraph()
  File "t.py", line 19, in load_callgraph
    shell=True).split("\n")
TypeError: a bytes-like object is required, not 'str'

[nurupo]

Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @iphydf)

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other/analysis/check-recursion, line 19 at r1 (raw file):
From Python3 Docs:

By default, this function will return the data as encoded bytes. The actual encoding of the output data may depend on the command being invoked, so the decoding to text will often need to be handled at the application level.

[codecov]

Codecov Report

Merging #1138 into master will increase coverage by <.1%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1138     +/-   ##
========================================
+ Coverage    82.7%   82.8%   +<.1%     
========================================
  Files          82      82             
  Lines       14667   14667             
========================================
+ Hits        12140   12147      +7     
+ Misses       2527    2520      -7

Impacted Files	Coverage Δ
toxcore/group.c	76% <0%> (-0.4%)	⬇️
toxcore/friend_connection.c	94.5% <0%> (-0.3%)	⬇️
toxcore/DHT.c	76.6% <0%> (-0.1%)	⬇️
toxcore/Messenger.c	86.5% <0%> (-0.1%)	⬇️
toxav/toxav.c	68% <0%> (+0.3%)	⬆️
toxav/msi.c	65.3% <0%> (+0.8%)	⬆️
toxcore/LAN_discovery.c	85.8% <0%> (+2.8%)	⬆️
auto_tests/toxav_many_test.c	96.6% <0%> (+4%)	⬆️

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[iphydf]

Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @nurupo)

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other/analysis/check-recursion, line 19 at r1 (raw file):

Previously, nurupo wrote…

From Python3 Docs:

By default, this function will return the data as encoded bytes. The actual encoding of the output data may depend on the command being invoked, so the decoding to text will often need to be handled at the application level.

Done.

[nurupo]

Reviewed 5 of 5 files at r2, 2 of 2 files at r3.
Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @iphydf)

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other/analysis/check_recursion, line 81 at r3 (raw file):

            "-Itoxencryptsave",
            "$CPPFLAGS",
        )),

Seems like you forgot to remove inputs and cflags as they are not being used anywhere.

[iphydf]

Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @nurupo)

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other/analysis/check_recursion, line 81 at r3 (raw file):

Previously, nurupo wrote…

Seems like you forgot to remove inputs and cflags as they are not being used anywhere.

Done.

[nurupo]

Reviewed 1 of 1 files at r4.
Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @iphydf)

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other/analysis/check_recursion, line 104 at r4 (raw file):

    "add_to_closest -> add_to_closest",
    "add_to_list -> add_to_list",
})

Funny how you went out of your way to make the script generic, to remove all of the hardcoded toxcore and clang commands, yet kept this expected in it. I'd expect the expected check to be done in another python file that imports this one just to call find_recursion(expected={...}). Well, fair enough, I assume you wanted to make the scrips as generic as possible, yet didn't want to make this a multi-file ordeal, so you have settled on having this non-generic part which can be easily removed if needed be.