ckpt

go.mod

@@ -54,6 +54,7 @@ require (
 	github.com/mattn/goveralls v0.0.2 // indirect
 	github.com/opencensus-integrations/ocsql v0.1.1
 	github.com/pkg/errors v0.8.0 // indirect
+	github.com/pmezard/go-difflib v1.0.0
 	github.com/prometheus/client_golang v0.9.0 // indirect
 	github.com/prometheus/common v0.0.0-20181015124227-bcb74de08d37 // indirect
 	github.com/prometheus/procfs v0.0.0-20181005140218-185b4288413d // indirect

wire/cmd/wire/main.go

@@ -33,7 +33,7 @@ import (
 	"golang.org/x/tools/go/types/typeutil"
 )
 
-const usage = "usage: wire [gen] [PKG] | wire show [...] | wire check [...]"
+const usage = "usage: wire [gen] [PKG] | wire show [...] | wire check [...] | wire diff [...]"
 
 func main() {
 	var err error
@@ -51,6 +51,10 @@ func main() {
 		err = check(".")
 	case len(os.Args) > 2 && os.Args[1] == "check":
 		err = check(os.Args[2:]...)
+	case len(os.Args) == 2 && os.Args[1] == "diff":
+		err = diff(".")
+	case len(os.Args) > 2 && os.Args[1] == "diff":
+		err = diff(os.Args[2:]...)
 	case len(os.Args) == 2:
 		err = generate(os.Args[1])
 	case len(os.Args) == 3 && os.Args[1] == "gen":
@@ -85,6 +89,33 @@ func generate(pkg string) error {
 	return out.Commit()
 }
 
+// diff runs the diff subcommand. Given a package, diff will generate
+// the content for the wire_gen.go file, and output the diff against the
+// existing file.
+func diff(pkgs ...string) error {
+	wd, err := os.Getwd()
+	if err != nil {
+		return err
+	}
+	for _, pkg := range pkgs {
+		fmt.Println(pkg)
+		out, errs := wire.Generate(context.Background(), wd, os.Environ(), pkg)
+		if len(errs) > 0 {
+			logErrors(errs)
+			return errors.New("generate failed")
+		}
+		if len(out.Content) == 0 {
+			// No Wire directives, don't write anything.
+			fmt.Fprintln(os.Stderr, "wire: no injector found for", pkg)
+			continue
+		}
+		if err := out.Diff(os.Stderr); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // show runs the show subcommand.
 //
 // Given one or more packages, show will find all the provider sets

wire/internal/wire/wire.go

@@ -26,6 +26,7 @@ import (
 	"go/printer"
 	"go/token"
 	"go/types"
+	"io"
 	"io/ioutil"
 	"path/filepath"
 	"sort"
@@ -34,6 +35,7 @@ import (
 	"unicode"
 	"unicode/utf8"
 
+	"github.com/pmezard/go-difflib/difflib"
 	"golang.org/x/tools/go/ast/astutil"
 	"golang.org/x/tools/go/packages"
 )
@@ -53,6 +55,16 @@ func (gen GeneratedFile) Commit() error {
 	return ioutil.WriteFile(gen.Path, gen.Content, 0666)
 }
 
+// Diff writes a diff of the current file on disk vs the generated file to out.
+func (gen GeneratedFile) Diff(out io.Writer) error {
+	// Assume the current file is empty if we can't read it.
+	cur, _ := ioutil.ReadFile(gen.Path)
+	return difflib.WriteUnifiedDiff(out, difflib.UnifiedDiff{
+		A: difflib.SplitLines(string(cur)),
+		B: difflib.SplitLines(string(gen.Content)),
+	})
+}
+
 // Generate performs dependency injection for a single package,
 // returning the gofmt'd Go source code. The package pattern is defined
 // by the underlying build system. For the go tool, this is described at