gofactor

gofactor

Advanced utility for golang refactor based on DSL transformations provided by bblfsh/sdk

Usage example

Imagine you have a piece of code

package main

import "fmt"

func main() {
	var (
		i int
		X int
		j int
	)

	if i%2 == 0 {
		i = 5
	}

	if X%2 == 0 {
		X = 5
	}

	fmt.Println(i)

	if i%2 == 0 {
		i = 5
	}

	if j%2 == 0 {
		j = 5
	}
}

func a(i, X int) {
	if i%2 == 0 {
		i = 5
	}

	if X%2 == 0 {
		X = 5
	}

	fmt.Println(i)

	if i%2 == 0 {
		i = 5
	}

	if X%2 == 0 {
		X = 5
	}
}

And you want to replace all code patterns like

if i%2 == 0 {
    i = 5
}

if X%2 == 0 {
    X = 5
}

to

if i%2 == 1 {
    i = 1
} else {
    X = 1
}

Here's where refactor library comes for help.

1. Init refactor object

refactor, err := gofactor.NewRefactor(beforeSnippet, afterSnippet)
if err != nil {
    log.Error(err)
    os.Exit(1)
}

1. call Prepare function to generate transformations mappings

if err := refactor.Prepare(); err != nil {
    log.Error(err)
    os.Exit(1)
}

1. Apply generated transformations to the desired code

code, err := refactor.Apply(desiredCode)
if err != nil {
    log.Error(err)
    os.Exit(1)
}

Result

package main

import "fmt"

func main() {
	var (
		i int
		X int
		j int
	)
	if i%2 == 1 {
		i = 1
	} else {
		X = 1
	}
	fmt.Println(i)
	if i%2 == 1 {
		i = 1
	} else {
		j = 1
	}
}
func a(i, X int) {
	if i%2 == 1 {
		i = 1
	} else {
		X = 1
	}
	fmt.Println(i)
	if i%2 == 1 {
		i = 1
	} else {
		X = 1
	}
}

Supported cases

See fixtures

Under the hood

1. both input and output patterns are converted to go AST nodes
2. both input and output nodes converted to bblfsh uast.Nodes
3. define mapping of transformation operations from input to output node
4. apply transformation mapping to the desired code: traverse over the uast.Nodes tree and transform matching nodes
5. convert transformed tree back to golang AST
6. convert golang AST to string

Roadmap

• currently library cannot be build because of bblfsh/go-driver dependency issue, fix this part
• support functions refactor
• handle cases with cascade ifs, switches and tail recursions
• during the transformations we are forced to drop nodes positions, need to investigate the possibilities of preserving/reconstructing them(probably using DST nodes could help, related issue https://github.com/dave/dst/issues/38)