THIS IS A TEST INSTANCE ONLY! REPOSITORIES CAN BE DELETED AT ANY TIME!

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Style guide

This document aims to be a reference for the desired style for patches to mgmt, and the associated mcl language. In particular it describes conventions which are not officially enforced by tools and in test cases, or that aren't clearly defined elsewhere. We try to turn as many of these into automated tests as we can. If something here is not defined in a test, or you think it should be, please write one! Even better, you can write a tool to automatically fix it, since this is more useful and can easily be turned into a test!

Overview for golang code

Most style issues are enforced by the gofmt tool. Other style aspects are often common sense to seasoned programmers, and we hope this will be a useful reference for new programmers.

There are a lot of useful code review comments described here. We don't necessarily follow everything strictly, but it is in general a very good guide.

Basics

  • All of our golang code is formatted with gofmt.

Comments

All of our code is commented with the minimums required for godoc to function, and so that our comments pass golint. Code comments should either be full sentences (which end with a period, use proper punctuation, and capitalize the first word when it is not a lower cased identifier), or are short one-line comments in the source which are not full sentences and don't end with a period.

They should explain algorithms, describe non-obvious behaviour, or situations which would otherwise need explanation or additional research during a code review. Notes about use of unfamiliar API's is a good idea for a code comment.

Example

Here you can see a function with the correct godoc string. The first word must match the name of the function. It is not capitalized because the function is private.

// square multiplies the input integer by itself and returns this product.
func square(x int) int {
	return x * x // we don't care about overflow errors
}

Line length

In general we try to stick to 80 character lines when it is appropriate. It is almost always appropriate for function godoc comments and most longer paragraphs. Exceptions are always allowed based on the will of the maintainer.

It is usually better to exceed 80 characters than to break code unnecessarily. If your code often exceeds 80 characters, it might be an indication that it needs refactoring.

Occasionally inline, two line source code comments are used within a function. These should usually be balanced so that you don't have one line with 78 characters and the second with only four. Split the comment between the two.

Default values

Whenever a constant or function parameter is defined, try and have the safer or default value be the zero value. For example, instead of const NoDanger, use const AllowDanger so that the false value is the safe scenario.

Method receiver naming

Contrary to the specialized naming of the method receiver variable, we usually name all of these obj for ease of code copying throughout the project, and for faster identification when reviewing code. Some anecdotal studies have shown that it makes the code easier to read since you don't need to remember the name of the method receiver variable in each different method. This is very similar to what is done in python.

Example

// Bar does a thing, and returns the number of baz results found in our
database.
func (obj *Foo) Bar(baz string) int {
	if len(obj.s) > 0 {
		return strings.Count(obj.s, baz)
	}
	return -1
}

Variable naming

We prefer shorter, scoped variables rather than unnecessarilyLongIdentifiers. Remember the scoping rules and feel free to use new variables where appropriate. For example, in a short string snippet you can use s instead of myString, as well as other common choices. i is a common int counter, f for files, fn for functions, x for something else and so on.

Variable re-use

Feel free to create and use new variables instead of attempting to re-use the same string. For example, if a function input arg is named s, you can use a new variable to receive the first computation result on s instead of storing it back into the original s. This avoids confusion if a different part of the code wants to read the original input, and it avoids any chance of edit by reference of the original callers copy of the variable.

Example

MyNotIdealFunc(s string, b bool) string {
	if !b {
		return s + "hey"
	}
	s = strings.Replace(s, "blah", "", -1) // not ideal (re-use of `s` var)
	return s
}

MyOkayFunc(s string, b bool) string {
	if !b {
		return s + "hey"
	}
	s2 := strings.Replace(s, "blah", "", -1) // doesn't re-use `s` variable
	return s2
}

MyGreatFunc(s string, b bool) string {
	if !b {
		return s + "hey"
	}
	return strings.Replace(s, "blah", "", -1) // even cleaner
}

Constants in code

If a function takes a specifier (often a bool) it's sometimes better to name that variable (often with a const) rather than leaving a naked bool in the code. For example, x := MyFoo("blah", false) is less clear than const useMagic = false; x := MyFoo("blah", useMagic).

Consistent ordering

In general we try to preserve a logical ordering in source files which usually matches the common order of execution that a lazy evaluator would follow.

This is also the order which is recommended when creating interface types. When implementing an interface, arrange your methods in the same order that they are declared in the interface.

When implementing code for the various types in the language, please follow this order: bool, str, int, float, list, map, struct, func.

For other aspects where you have a set of items, try to be internally consistent as well. For example, if you have two switch statements with A, B, and C, please use the same ordering for these elements elsewhere that they appear in the code and in the commentary if it is not illogical to do so.

Product identifiers

Try to avoid references in the code to mgmt or a specific program name string if possible. This makes it easier to rename code if we ever pick a better name or support libmgmt better if we embed it. You can use the Program variable which is available in numerous places if you want a string to put in the logs.

It is also recommended to avoid the go (programming language name) string if possible. Try to use golang if required, since the word go is already overloaded, and in particular it was even already used by the go!.

Overview for mcl code

The mcl language is quite new, so this guide will probably change over time as we find what's best, and hopefully we'll be able to add an mclfmt tool in the future so that less of this needs to be documented. (Patches welcome!)

Indentation

Code indentation is done with tabs. The tab-width is a private preference, which is the beauty of using tabs: you can have your own personal preference. The inventor of mgmt uses and recommends a width of eight, and that is what should be used if your tool requires a modeline to be publicly committed.

Line length

We recommend you stick to 80 char line width. If you find yourself with deeper nesting, it might be a hint that your code could be refactored in a more pleasant way.

Capitalization

At the moment, variables, function names, and classes are all lowercase and do not contain underscores. We will probably figure out what style to recommend when the language is a bit further along. For example, we haven't decided if we should have a notion of public and private variables, and if we'd like to reserve capitalization for this situation.

Module naming

We recommend you name your modules with an mgmt- prefix. For example, a module about bananas might be named mgmt-banana. This is helpful for the useful magic built-in to the module import code, which will by default take a remote import like: import "https://github.com/purpleidea/mgmt-banana/" and namespace it as banana. Of course you can always pick the namespace yourself on import with: import "https://github.com/purpleidea/mgmt-banana/" as tomato or something similar.

Licensing

We believe that sharing code helps reduce unnecessary re-invention, so that we can stand on the shoulders of giants and hopefully make faster progress in science, medicine, exploration, etc... As a result, we recommend releasing your modules under the LGPLv3+ license for the maximum balance of freedom and re-usability. We strongly oppose any CLA requirements and believe that the "inbound==outbound" rule applies. Lastly, we do not support software patents and we hope you don't either!

Suggestions

If you have any ideas for suggestions or other improvements to this guide, please let us know!