code_formatting_rules.md

Code formatting rules

Why this emphasis on formatting?

Code in general (and Open Source code specifically) is read by developers many more times during its lifecycle than it is modified. With this fact in mind, the Golang language was designed for readability (among other goals). While the enforced formatting of go fmt and some best practices already eliminate many discussions, the resulting code can still look and feel very differently among different developers.

We aim to enforce a few additional rules to unify the look and feel of all code in lnd to help improve the overall readability.

Spacing

Blocks of code within lnd should be segmented into logical stanzas of operation. Such spacing makes the code easier to follow at a skim, and reduces unnecessary line noise. Coupled with the commenting scheme specified in the contribution guide, proper spacing allows readers to quickly scan code, extracting semantics quickly. Functions should not just be laid out as a bare contiguous block of code.

WRONG

	witness := make([][]byte, 4)
	witness[0] = nil
	if bytes.Compare(pubA, pubB) == -1 {
		witness[1] = sigB
		witness[2] = sigA
	} else {
		witness[1] = sigA
		witness[2] = sigB
	}
	witness[3] = witnessScript
	return witness

RIGHT

	witness := make([][]byte, 4)

	// When spending a p2wsh multi-sig script, rather than an OP_0, we add
	// a nil stack element to eat the extra pop.
	witness[0] = nil

	// When initially generating the witnessScript, we sorted the serialized
	// public keys in descending order. So we do a quick comparison in order
	// to ensure the signatures appear on the Script Virtual Machine stack in
	// the correct order.
	if bytes.Compare(pubA, pubB) == -1 {
		witness[1] = sigB
		witness[2] = sigA
	} else {
		witness[1] = sigA
		witness[2] = sigB
	}

	// Finally, add the preimage as the last witness element.
	witness[3] = witnessScript

	return witness

Additionally, we favor spacing between stanzas within syntax like: switch case statements and select statements.

WRONG

	switch {
		case a:
			<code block>
		case b:
			<code block>
		case c:
			<code block>
		case d:
			<code block>
		default:
			<code block>
	}

RIGHT

	switch {
		// Brief comment detailing instances of this case (repeat below).
		case a:
			<code block>

		case b:
			<code block>

		case c:
			<code block>

		case d:
			<code block>

		default:
			<code block>
	}

Additional Style Constraints

Before a PR is submitted, the proposer should ensure that the file passes the set of linting scripts run by make lint. These include gofmt. In addition to gofmt we've opted to enforce the following style guidelines.

80 character line length

ALL columns (on a best effort basis) should be wrapped to 80 line columns. Editors should be set to treat a tab as 8 spaces.

WRONG

myKey := "0214cd678a565041d00e6cf8d62ef8add33b4af4786fb2beb87b366a2e151fcee7"

RIGHT

myKey := "0214cd678a565041d00e6cf8d62ef8add33b4af4786fb2beb87b366a2e1" +
	"51fcee7"

Wrapping long function calls

When wrapping a line that contains a function call as the unwrapped line exceeds the column limit, the close parenthesis should be placed on its own line. Additionally, all arguments should begin in a new line after the open parenthesis.

WRONG

value, err := bar(a,
	a, b, c)

RIGHT

value, err := bar(
	a, a, b, c,
)

Exception for log and error message formatting

Note that the above guidelines don't apply to log or error messages. For log and error messages, committers should attempt to minimize the number of lines utilized, while still adhering to the 80-character column limit. For example:

WRONG

return fmt.Errorf(
	"this is a long error message with a couple (%d) place holders",
	len(things),
)

log.Debugf(
	"Something happened here that we need to log: %v",
	longVariableNameHere,
)

RIGHT

return fmt.Errorf("this is a long error message with a couple (%d) place "+
	"holders", len(things))

log.Debugf("Something happened here that we need to log: %v",
	longVariableNameHere)

This helps to visually distinguish those formatting statements (where nothing of consequence happens except for formatting an error message or writing to a log) from actual method or function calls. This compact formatting should be used for calls to formatting functions like fmt.Errorf, log.(Trace|Debug|Info|Warn|Error)f and fmt.Printf. But not for statements that are important for the flow or logic of the code, like require.NoErrorf().

Exceptions and additional styling for structured logging

When making use of structured logging calls (there are any btclog.Logger methods ending in S), a few different rules and exceptions apply.

1. Static messages: Structured log calls take a context.Context as a first parameter and a static string as the second parameter (the msg parameter). Formatted strings should ideally not be used for the construction of the msg parameter. Instead, key-value pairs (or slog attributes) should be used to provide additional variables to the log line.

WRONG

log.DebugS(ctx, fmt.Sprintf("User %d just spent %.8f to open a channel", userID, 0.0154))

RIGHT

log.InfoS(ctx, "Channel open performed",
        slog.Int("user_id", userID),
        btclog.Fmt("amount", "%.8f", 0.00154))

2. Key-value attributes: The third parameter in any structured log method is a variadic list of the any type but it is required that these are provided in key-value pairs such that an associated slog.Attr variable can be created for each key-value pair. The simplest way to specify this is to directly pass in the key-value pairs as raw literals as follows:

log.InfoS(ctx, "Channel open performed", "user_id", userID, "amount", 0.00154)

This does work, but it becomes easy to make a mistake and accidentally leave out a value for each key provided leading to a nonsensical log line. To avoid this, it is suggested to make use of the various slog.Attr helper functions as follows:

log.InfoS(ctx, "Channel open performed",
        slog.Int("user_id", userID),
        btclog.Fmt("amount", "%.8f", 0.00154))

3. Line wrapping: Structured log lines are an exception to the 80-character line wrapping rule. This is so that the key-value pairs can be easily read and reasoned about. If it is the case that there is only a single key-value pair and the entire log line is still less than 80 characters, it is acceptable to have the key-value pair on the same line as the log message. However, if there are multiple key-value pairs, it is suggested to use the one line per key-value pair format. Due to this suggestion, it is acceptable for any single key-value pair line to exceed 80 characters for the sake of readability.

WRONG

// Example 1.
log.InfoS(ctx, "User connected", 
        "user_id", userID)

// Example 2.
log.InfoS(ctx, "Channel open performed", "user_id", userID,
        btclog.Fmt("amount", "%.8f", 0.00154), "channel_id", channelID)

// Example 3.
log.InfoS(ctx, "Bytes received", 
        "user_id", userID, 
        btclog.Hex("peer_id", peerID.SerializeCompressed()),
        btclog.Hex("message", []bytes{
                0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
        })))

RIGHT

// Example 1.
log.InfoS(ctx, "User connected", "user_id", userID)

// Example 2.
log.InfoS(ctx, "Channel open performed",
        slog.Int("user_id", userID),
        btclog.Fmt("amount", "%.8f", 0.00154),
        slog.String("channel_id", channelID))

// Example 3.
log.InfoS(ctx, "Bytes received", 
        "user_id", userID,
        btclog.Hex("peer_id", peerID.SerializeCompressed()),
        btclog.Hex("message", []bytes{0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08})))

Wrapping long function definitions

If one is forced to wrap lines of function arguments that exceed the 80-character limit, then indentation must be kept on the following lines. Also, lines should not end with an open parenthesis if the function definition isn't finished yet.

WRONG

func foo(a, b, c,
) (d, error) {

func bar(a, b, c) (
	d, error,
) {

func baz(a, b, c) (
	d, error) {

RIGHT

func foo(a, b,
	c) (d, error) {

func baz(a, b, c) (d,
	error) {

func longFunctionName(
	a, b, c) (d, error) {

If a function declaration spans multiple lines the body should start with an empty line to help visually distinguishing the two elements.

WRONG

func foo(a, b, c,
	d, e) error {
	var a int
}

RIGHT

func foo(a, b, c,
	d, e) error {

	var a int
}

Recommended settings for your editor

To make it easier to follow the rules outlined above, we recommend setting up your editor with at least the following two settings:

1. Set your tabulator width (also called "tab size") to 8 spaces.
2. Set a ruler or visual guide at 80 character.

Note that the two above settings are automatically applied in editors that support the EditorConfig scheme (for example GoLand, GitHub, GitLab, VisualStudio). In addition, specific settings for Visual Studio Code are checked into the code base as well.

Other editors (for example Atom, Notepad++, Vim, Emacs and so on) might install a plugin to understand the rules in the .editorconfig file.

In Vim, you might want to use set colorcolumn=80.