C++ Style Guide

The style guide can be summed up as 'clang-format with the Google style set'. In addition, the Google Style Guide is followed and cpplint is the source of truth. When in doubt, defer to what code in the project already does.

Base rules:

80 column line length max
LF (Unix-style) line endings
2-space soft tabs, no TABs!
Google Style Guide for naming/casing/etc
Sort includes according to the style guide rules
Comments are properly punctuated (that means capitalization and periods, etc)
TODO's must be attributed like // TODO(yourgithubname): foo.

Code that really breaks from the formatting rules will not be accepted, as then no one else can use clang-format on the code without also touching all your lines.

Why?

To quote the Google Style Guide:

One way in which we keep the code base manageable is by enforcing consistency.
It is very important that any programmer be able to look at another's code and
quickly understand it. Maintaining a uniform style and following conventions
means that we can more easily use "pattern-matching" to infer what various
symbols are and what invariants are true about them. Creating common, required
idioms and patterns makes code much easier to understand. In some cases there
might be good arguments for changing certain style rules, but we nonetheless
keep things as they are in order to preserve consistency.

Buildbot Verification

The buildbot runs xb lint --all on the master branch, and will run xb lint --origin on pull requests. Run xb format before you commit each local change so that you are consistently clean, otherwise you may have to rebase. If you forget, run xb format --origin and rebase your changes (so you don't end up with 5 changes and then a 6th 'whoops' one — that's nasty).

The buildbot is running LLVM 3.8.0. If you are noticing style differences between your local lint/format and the buildbot, ensure you are running that version.

Tools

clang-format

clang-format with the Google style is used to format all files. I recommend installing/wiring it up to your editor of choice so that you don't even have to think about tabs and wrapping and such.

Command Line

To use the xb format auto-formatter, you need to have a clang-format on your PATH. If you're on Windows you can do this by installing an LLVM binary package from the LLVM downloads page. If you install it to the default location the xb format command will find it automatically even if you don't choose to put all of LLVM onto your PATH.

Visual Studio

Grab the official experimental Visual Studio plugin. To switch to the Google style go Tools -> Options -> LLVM/Clang -> ClangFormat and set Style to Google. Then use ctrl-r/ctrl-f to trigger the formatting. Unfortunately it only does the cursor by default, so you'll have to select the whole doc and invoke it to get it all done.

If you have a better option, let me know!

Xcode

Install Alcatraz to get the ClangFormat package. Set it to use the Google style and format on save. Never think about tabs or linefeeds or whatever again.

cpplint

TODO(benvanik): write a cool script to do this/editor plugins. In the future, the linter will run as a git commit hook and on travis.

Android Style Guide

Android Java and Groovy code and XML files currently don't have automatic format verification during builds, however, stick to the AOSP Java Code Style Rules, which contain guidelines not only for code formatting, but for the usage of language features as well.

The formatting rules used in Xenia match the default Android Studio settings. They diverge from the C++ code style rules of Xenia in many areas, such as indentation width and the maximum line length, however, the goal for Android formatting in Xenia is to ensure quick development environment setup.

In Java code, limit the length of each line to 100 characters. If an assignment doesn't fit in the limit, move the right-hand side of it to a separate line with 8-space indentation. Similarly, if the argument list of a method declaration or a call is too long, start the entire argument list on a new line, also indented with 8 spaces — this is one of the differences from the C++ code style in Xenia, where arguments may be aligned with the opening bracket. In general, follow the rectangle rule so expressions in the code constitute a hierarchy of their bounding rectangles, ensuring that with 4-space indentation for block contents and 8-space indentation for subexpressions.

In XML files, if the width of the line with an element exceeds 100 characters, or in most cases when there are multiple attributes, each attribute should be placed on a separate line with 4-space indentation, with the exception of the first xmlns, which should stay on the same line as the element name.

In Groovy, use 4-space indentation for blocks and 8-space indentation for splitting arguments into multiple lines. String literals should be written in single quotes unless string interpolation is used.

You can use the Code -> Reformat Code and Code -> Reformat File options in Android Studio to apply coarse formatting rules for different kinds of files supported by Android Studio, such as Java, XML and Groovy. While clang-format is very strict and generates code with the single allowed way of formatting, Android Studio, however, preserves many style choices in the original code, so it's recommended to approximate the final style manually instead of relying entirely on automatic formatting. Also use Code -> Rearrange Code to maintain a consistent structure of Java class declarations.

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