[](https://travis-ci.org/mgechev/revive)
# 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](https://github.com/Microsoft/vscode-go/pull/1699).
### Installation
```bash
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
```shell
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:
```toml
# 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`).
```shell
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
```shell
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)](https://golang.org/pkg/plugin/).
### Custom Rule
Each rule needs to implement the `lint.Rule` interface:
```go
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:
```toml
[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](/rule/argument-limit.go).
### Custom Formatter
Each formatter needs to implement the following interface:
```go
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](/formatter/json.go).
## 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
```shell
time golint kubernetes/... > /dev/null
real 0m54.837s
user 0m57.844s
sys 0m9.146s
```
### revive
```shell
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`:
```shell
time revive kubernetes/... > /dev/null
real 0m26.211s
user 2m6.708s
sys 0m17.192s
```
Currently, type checking is enabled by default.
## License
MIT