Developing a 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.

Example

Let us implement a sample formatter which outputs the rule failures to plain text.

First, you need to clone the repository and create a file under revive/formatter called sample.go. After that, add the following imports and struct declaration:

package formatter

import (
    "fmt"

    "github.com/mgechev/revive/lint"
)

type Sample struct {
    Metadata lint.FormatterMetadata
}

Now, Sample has to implement the Formatter interface, which means that we need to define two methods: Name which returns the name of the formatter, and the method Format. As a first argument Format receives a channel where we'll receive the failures, and as second argument the method accepts the user's configuration.

func (f *Sample) Name() string {
    return "sample"
}

// Format formats the failures gotten from the lint.
func (f *Sample) Format(failures <-chan lint.Failure, _ lint.RulesConfig) (string, error) {
    for failure := range failures {
        fmt.Printf("%v: %s\n", failure.Position.Start, failure.Failure)
    }
    return "", nil
}

In the implementations above, Name returns the string "sample" and Format prints the failures one by one, first displaying the failure's position and after that its description.