feat: print diff

go.mod

@@ -4,6 +4,7 @@ go 1.19
 
 require (
 	github.com/make-go-great/color-go v0.4.1
+	github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e
 	github.com/urfave/cli/v2 v2.23.5
 	golang.org/x/mod v0.7.0
 	golang.org/x/tools v0.3.0

go.sum

@@ -9,6 +9,8 @@ github.com/mattn/go-colorable v0.1.9/go.mod h1:u6P/XSegPjTcexA+o6vUJrdnUu04hMope
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 github.com/mattn/go-isatty v0.0.14 h1:yVuAays6BHfxijgZPzw+3Zlu5yQgKGP2/hcQbHb7S9Y=
 github.com/mattn/go-isatty v0.0.14/go.mod h1:7GGIvUiUoEMVVmxf/4nioHXj79iQHKdU27kJ6hsGG94=
+github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e h1:aoZm08cpOy4WuID//EZDgcC4zIxODThtZNPirFr42+A=
+github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/russross/blackfriday/v2 v2.1.0 h1:JIOH55/0cWyOuilr9/qlrm0BSXldqnqwMsf35Ld67mk=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
 github.com/urfave/cli/v2 v2.23.5 h1:xbrU7tAYviSpqeR3X4nEFWUdB/uDZ6DE+HxmRU7Xtyw=

internal/imports/formatter.go

@@ -13,6 +13,7 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/pkg/diff"
 	"golang.org/x/mod/modfile"
 	"golang.org/x/tools/go/packages"
 )
@@ -133,10 +134,25 @@ func (ft *Formatter) formatFile(path string) error {
 	}
 	ft.log("formatFile: moduleName: %+v\n", moduleName)
 
-	if err := ft.formatImports(path, pathBytes, moduleName); err != nil {
+	formattedBytes, err := ft.formatImports(path, pathBytes, moduleName)
+	if err != nil {
 		return err
 	}
 
+	if ft.isList {
+		fmt.Println(path)
+	}
+
+	if ft.isWrite {
+		ft.log("TODO: write to file\n")
+	}
+
+	if ft.isDiff {
+		if err := diff.Text("before", "after", pathBytes, formattedBytes, os.Stdout); err != nil {
+			return fmt.Errorf("diff: failed to slices: %w", err)
+		}
+	}
+
 	ft.muFormattedPaths.Lock()
 	ft.formattedPaths[path] = struct{}{}
 	ft.muFormattedPaths.Unlock()
@@ -149,7 +165,7 @@ func (ft *Formatter) formatImports(
 	path string,
 	pathBytes []byte,
 	moduleName string,
-) error {
+) ([]byte, error) {
 	// Parse ast
 	fset := token.NewFileSet()
 
@@ -158,12 +174,12 @@ func (ft *Formatter) formatImports(
 
 	astFile, err := parser.ParseFile(fset, path, pathBytes, parserMode)
 	if err != nil {
-		return fmt.Errorf("parser: failed to parse file [%s]: %w", path, err)
+		return nil, fmt.Errorf("parser: failed to parse file [%s]: %w", path, err)
 	}
 
 	// Ignore generated file
 	if isGoGenerated(astFile) {
-		return ErrGoGeneratedFile
+		return nil, ErrGoGeneratedFile
 	}
 
 	// Extract imports
@@ -175,7 +191,7 @@ func (ft *Formatter) formatImports(
 
 	groupedImportSpecs, err := ft.groupImportSpecs(importSpecs, moduleName)
 	if err != nil {
-		return err
+		return nil, err
 	}
 
 	formattedImportSpecs, err := ft.formatImportSpecs(
@@ -183,7 +199,7 @@ func (ft *Formatter) formatImports(
 		groupedImportSpecs,
 	)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	ft.mustLogImportSpecs("formatImports: formattedImportSpecs: ", formattedImportSpecs)
 
@@ -220,12 +236,10 @@ func (ft *Formatter) formatImports(
 	var formattedBytes []byte
 	formattedBuffer := bytes.NewBuffer(formattedBytes)
 	if err := printer.Fprint(formattedBuffer, fset, astFile); err != nil {
-		return err
+		return nil, err
 	}
 
-	fmt.Println(formattedBuffer.String())
-
-	return nil
+	return formattedBuffer.Bytes(), nil
 }
 
 // Copy from goimports-reviser