PropelLint

The goal of this tool is to detect bad patterns which are not detectable via only dynamic profiling, or only static analysis. To achieve this, the tool uses a profile as input, and then inspects the source code to determine if a warning should be issued.

The current focus is to detect unintentional map inserts with operator[]. In C++, map[key] always inserts a default value. Sometimes, these are not intended and can cause bugs and/or performance regressions.

Warning This project is a work in progress.

How it works

Profile

The profile must be a JSON file with the following format.

[
    {
        "stack_combined": [
            "someFunction@some_source_file.cpp:13",
            "someOtherFunction@some_other_source_file.cpp:31",
            <...>
        ],
        "total_weight": 458188117
    },
    <...>
]

Internally, we use a profiler called Strobelight, and pre-filter the data to only contain stacks with operator[].

Analysis

The profile is parsed, and only operator[] locations that insert are kept. We can find those by looking for specific sub-functions that we know are signs of insertion.
For each file, we need to file the necessary compile commands. The tool is currently based on Buck, which it queries to find the compilation database of each file.
The AST is generated using Clang, and inspected to filter out cases with a high-likelihood of intentional.

Getting started

[~] git clone https://github.com/facebookexperimental/propellint.git
[~] cd propellint
[~/propellint] mkdir build
[~/propellint] cd build
[~/propellint/build] cmake ..
[~/propellint/build] make

License

This work is licensed under the Apache License 2.0.

facebookexperimental / propellint