================================================================================ Cleanup C++/C headers

This simple script helps in removing unnecessary includes from C/C++ files.

A huge code base or legacy code usually means that implementation files are full of includes pilled up over years. Likewise, creating a new project by forking an old one ends up with tons of leftovers.

How it works?

The only thing you need is the full command that creates an object file.

The script systematically comments out one include file at once and recompiles source. When program/object file still compiles, then the commented out include is considered unneeded.

Caveat 1 (noticed by my colleague Leszek): such a mechanical way of removing includes may lead to creating indirect dependencies. Some symbols required by implementation might be provided (accidentally) by includes present in headers files. When one remove include from the implementation file, then later changes to the header file might break the compilation.

Caveat 2: the script doesn't interpret any other preprocessor directive than #include. Conditional includes enabled by ifdefs will be removed unconditionally.

How to use it?

Here's an example from my toy project https://github.com/WojciechMula/avx512popcnt-superoptimizer

The head of the main program::

$ head -n 15 avx512popcnt.cpp
#include <cstdint>
#include <cstdlib>
#include <cstdio>
#include <cassert>
#include <vector>
#include <memory>
#include <random>
#include <algorithm>
#include <bitset>

#include <sys/types.h>
#include <unistd.h>

#include "binary.cpp"

When run make, we capture the command which builds the program::

$ make avx512popcnt
g++ -Wall -Wextra -pedantic -std=c++14 -O3 avx512popcnt.cpp -o lineavx512popcnt

Now the script comes::

$ python cleanup.py g++ -Wall -Wextra -pedantic -std=c++14 -O3 avx512popcnt.cpp -o avx512popcnt
Checking compilation of avx512popcnt.cpp... OK
Removing cstdint (1/12)... OK
Removing cstdlib (2/12)... OK
Removing cstdio (3/12)... OK
Removing cassert (4/12)... not possible
Removing vector (5/12)... OK
Removing memory (6/12)... not possible
Removing random (7/12)... not possible
Removing algorithm (8/12)... OK
Removing bitset (9/12)... OK
Removing sys/types.h (10/12)... OK
Removing unistd.h (11/12)... not possible
Removing binary.cpp (12/12)... not possible
avx512popcnt.cpp: not required cstdint, cstdlib, cstdio, vector, algorithm, bitset, sys/types.h
avx512popcnt.cpp was updated

It turned out that eight includes weren't needed at all.

Configuration

You can control behaviour of the script via a config file. The config file must be located either in ~/.config/cleanup-headers/config.ini or its path must be provided by the environment variable CLEANUP_HEADERS_CONFIG. Please refer to the sample config.ini for more details.