revive/README.md

revive

Fast, configurable, extensible, flexible, and beautiful linter for Go. Drop-in replacement of golint. Most importantly revive allows you to develop your own rules and build a strict preset for enhancing your development & code review processes.

Logo by Georgi Serev

Here's how revive is different from golint:

• Allow us to enable or disable rules using a configuration file.
• Allows us to configure the linting rules with a TOML file.
• Provides functionality for disabling a specific rule or the entire linter for a file or a range of lines.
  • golint allows this only for generated files.
• Provides multiple formatters which let us customize the output.
• Allows us to customize the return code for the entire linter or based on the failure of only some rules.
• Everyone can extend it easily with custom rules or formatters.
• Revive provides more rules compared to golint.
• Faster. It runs the rules over each file in a separate goroutine.

Usage

Since the default behavior of revive is compatible with golint, without providing any additional flags, the only difference you'd notice is faster execution.

Text Editors

• Support for VSCode in vscode-go.

Installation

go get -u github.com/mgechev/revive

Command Line Flags

revive accepts three command line parameters:

• -config [PATH] - path to config file in TOML format.
• -exclude [PATTERN] - pattern for files/directories/packages to be excluded for linting. You can specify the files you want to exclude for linting either as package name (i.e. github.com/mgechev/revive), list them as individual files (i.e. file.go), directories (i.e. ./foo/...), or any combination of the three.
• -formatter [NAME] - formatter to be used for the output. The currently available formatters are:
  • default - will output the failures the same way that golint does.
  • json - outputs the failures in JSON format.
  • friendly - outputs the failures when found. Shows summary of all the failures.
  • stylish - formats the failures in a table. Keep in mind that it doesn't stream the output so it might be perceived as slower compared to others.

Sample Invocations

revive -config revive.toml -exclude file1.go -exclude file2.go -formatter friendly github.com/mgechev/revive package/...

• The command above will use the configuration from revive.toml
• revive will ignore file1.go and file2.go
• The output will be formatted with the friendly formatter
• The linter will analyze github.com/mgechev/revive and the files in package

Configuration

revive can be configured with a TOML file. Here's a sample configuration with explanation for the individual properties:

# Ignores files with "GENERATED" header, similar to golint
ignoreGeneratedHeader = true

# Sets the default severity to "warning"
severity = "warning"

# Sets the default failure confidence. This means that linting errors
# with less than 0.8 confidence will be ignored.
confidence = 0.8

# Sets the error code for failures with severity "error"
errorCode = 0

# Sets the error code for failures with severity "warning"
warningCode = 0

# Configuration of the `cyclomatic` rule. Here we specify that
# the rule should fail if it detects code with higher complexity than 10.
[rule.cyclomatic]
  arguments = [10]

# Sets the severity of the `package-comments` rule to "error".
[rule.package-comments]
  severity = "error"

Default Configuration

The default configuration of revive can be found at defaults.toml. This will enable all rules available in golint and use their default configuration (i.e. the way they are hardcoded in golint).

revive -config defaults.toml github.com/mgechev/revive

This will use the configuration file defaults.toml, the default formatter, and will run linting over the github.com/mgechev/revive package.

Recommended Configuration

revive -config config.toml -formatter friendly github.com/mgechev/revive

This will use config.toml, the friendly formatter, and will run linting over the github.com/mgechev/revive package.

Available Rules

List of all available rules. The rules ported from golint are left unchanged and indicated in the golit column.

Name	Config	Description	golint
blank-imports	n/a	Disallows blank imports	yes
context-as-argument	n/a	context.Context should be the first argument of a function.	yes
context-keys-type	n/a	Disallows the usage of basic types in context.WithValue.	yes
dot-imports	n/a	Forbids . imports.	yes
error-return	n/a	The error return parameter should be last.	yes
error-strings	n/a	Conventions around error strings.	yes
error-naming	n/a	Naming of error variables.	yes
exported	n/a	Naming and commenting conventions on exported symbols.	yes
if-return	n/a	Redundant if when returning an error.	yes
increment-decrement	n/a	Use i++ and i-- instead of i += 1 and i -= 1.	yes
var-naming	n/a	Naming rules.	yes
var-declaration	n/a	Reduces redundancies around variable declaration.	yes
package-comments	n/a	Package commenting conventions.	yes
range	n/a	Prevents redundant variables when iterating over a collection.	yes
receiver-naming	n/a	Conventions around the naming of receivers.	yes
time-naming	n/a	Conventions around the naming of time variables.	yes
unexported-return	n/a	Warns when a public return is from unexported type.	yes
indent-error-flow	n/a	Prevents redundant else statements.	yes
errorf	n/a	Should replace error.New(fmt.Sprintf()) with error.Errorf()	yes
argument-limit	int	Specifies the maximum number of arguments a function can receive	no
cyclomatic	int	Sets restriction for maximum Cyclomatic complexity.	no
max-public-structs	int	The maximum number of public structs in a file.	no
file-header	string	Header which each file should have.	no

Available Formatters

This section lists all the available formatters and provides a screenshot for each one.

Friendly

Stylish

Default

Extensibility

The tool can be extended with custom rules or formatters. This section contains additional information on how to implement such.

To extend the linter with a custom rule or a formatter you'll have to push it to this repository or fork it. This is due to the limited -buildmode=plugin support which works only on Linux (with known issues).

Custom Rule

Each rule needs to implement the lint.Rule interface:

type Rule interface {
	Name() string
	Apply(*File, Arguments) []Failure
}

The Arguments type is an alias of the type []interface{}. The arguments of the rule are passed from the configuration file.

Example

Let's suppose we have developed a rule called BanStructNameRule which disallow us to name a structure with given identifier. We can set the banned identifier by using the TOML configuration file:

[rule.ban-struct-name]
  arguments = ["Foo"]

With the snippet above we:

• Enable the rule with name ban-struct-name. The Name() method of our rule should return a string which matches ban-struct-name.
• Configure the rule with the argument Foo. The list of arguments will be passed to Apply(*File, Arguments) together with the target file we're linting currently.

A sample rule implementation can be found here.

Custom Formatter

Each formatter needs to implement the following interface:

type Formatter interface {
	Format(<-chan Failure, RulesConfig) (string, error)
	Name() string
}

The Format method accepts a channel of Failure instances and the configuration of the enabled rules. The Name() method should return a string different from the names of the already existing rules. This string is used when specifying the formatter when invoking the revive CLI tool.

For a sample formatter, take a look at this file.

Speed Comparison

Compared to golint, revive performs better because it lints the files for each individual rule into a separate goroutine. Here's a basic performance benchmark on MacBook Pro Early 2013 run on kubernetes:

golint

time golint kubernetes/... > /dev/null

real    0m54.837s
user    0m57.844s
sys     0m9.146s

revive

time revive kubernetes/... > /dev/null

real    0m13.515s
user    0m53.472s
sys     0m3.199s

Keep in mind that with type checking enabled, the performance may drop to twice faster than golint:

time revive kubernetes/... > /dev/null

real    0m26.211s
user    2m6.708s
sys     0m17.192s

Currently, type checking is enabled by default.

License

MIT