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revive/README.md
2018-05-26 15:17:28 -07:00

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# revive
Fast, configurable, extensible, flexible, and beautiful linter for Go.
<p align="center">
<img src="./assets/logo.jpg" alt="" width="300">
</p>
Here's how `revive` is different from `golint`:
* Allows you to enable or disable rules using a configuration file.
* Allows you to configure the linting rules with a TOML file.
* Provides functionality to disable 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 you customize the output.
* Allows you to customize the return code for the entire linter or based on the failure of only some rules.
* Open for addition of new rules or formatters.
* 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.
### 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
| Name | Configuration | Description |
| ------------------- | :---------------------: | ---------------------------------------------------------------: |
| `cyclomatic` | int (for instance, `9`) | Sets restriction ot maximum Cyclomatic complexity. |
| `context-key-type` | Not configurable | Disallows the usage of basic types in `context.WithValue`. |
| `dot-imports` | Not configurable | Forbids `.` imports. |
| `blank-imports` | Not configurable | Disallows blank imports |
| `context-arguments` | Not configurable | `context.Context` should be the first argument of a function. |
| `argument-limit` | int (for instance, `4`) | Specifies the maximum number of arguments a function can receive |
## Available Formatters
This section lists all the available formatters and provides a screenshot for each one.
### Friendly
![Friendly formatter](/assets/friendly-formatter.png)
### Stylish
![Stylish formatter](/assets/stylish-formatter.png)
### Default
![Default formatter](/assets/default-formatter.png)
## 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).
## License
MIT