From 58d6a2c2c8ec5f48e5b6df603ba22c070403c41c Mon Sep 17 00:00:00 2001
From: Robert van Gent <rvangent@google.com>
Date: Tue, 27 Nov 2018 14:57:54 -0800
Subject: [PATCH] wire: add a diff command (google/go-cloud#745)

---
 cmd/wire/main.go | 56 +++++++++++++++++++++++++++++++++++++++++++++++-
 go.mod           |  1 +
 go.sum           |  2 ++
 3 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/cmd/wire/main.go b/cmd/wire/main.go
index 0494c07..6060982 100644
--- a/cmd/wire/main.go
+++ b/cmd/wire/main.go
@@ -23,6 +23,7 @@ import (
 	"fmt"
 	"go/token"
 	"go/types"
+	"io/ioutil"
 	"os"
 	"reflect"
 	"sort"
@@ -30,10 +31,11 @@ import (
 	"strings"
 
 	"github.com/google/wire/internal/wire"
+	"github.com/pmezard/go-difflib/difflib"
 	"golang.org/x/tools/go/types/typeutil"
 )
 
-const usage = "usage: wire [gen] [PKG] | wire show [...] | wire check [...]"
+const usage = "usage: wire [gen|diff|show|check] [...]"
 
 func main() {
 	var err error
@@ -49,6 +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 && os.Args[1] == "gen":
 		err = generate(".")
 	case len(os.Args) > 2 && os.Args[1] == "gen":
@@ -108,6 +114,54 @@ func generate(pkgs ...string) error {
 	return nil
 }
 
+// diff runs the diff subcommand.
+//
+// Given one or more packages, 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
+	}
+	outs, errs := wire.Generate(context.Background(), wd, os.Environ(), pkgs)
+	if len(errs) > 0 {
+		logErrors(errs)
+		return errors.New("generate failed")
+	}
+	if len(outs) == 0 {
+		return nil
+	}
+	success := true
+	for _, out := range outs {
+		if len(out.Errs) > 0 {
+			fmt.Fprintf(os.Stderr, "%s: generate failed\n", out.PkgPath)
+			logErrors(out.Errs)
+			success = false
+		}
+		if len(out.Content) == 0 {
+			// No Wire output. Maybe errors, maybe no Wire directives.
+			continue
+		}
+		// Assumes the current file is empty if we can't read it.
+		cur, _ := ioutil.ReadFile(out.OutputPath)
+		if diff, err := difflib.GetUnifiedDiffString(difflib.UnifiedDiff{
+			A: difflib.SplitLines(string(cur)),
+			B: difflib.SplitLines(string(out.Content)),
+		}); err == nil {
+			if diff != "" {
+				fmt.Fprintf(os.Stderr, "%s: diff from %s:\n%s", out.PkgPath, out.OutputPath, diff)
+			}
+		} else {
+			fmt.Fprintf(os.Stderr, "%s: failed to diff %s: %v\n", out.PkgPath, out.OutputPath, err)
+			success = false
+		}
+	}
+	if !success {
+		return errors.New("at least one generate failure")
+	}
+	return nil
+}
+
 // show runs the show subcommand.
 //
 // Given one or more packages, show will find all the provider sets
diff --git a/go.mod b/go.mod
index bbf04d7..363b5ed 100644
--- a/go.mod
+++ b/go.mod
@@ -2,5 +2,6 @@ module github.com/google/wire
 
 require (
 	github.com/google/go-cmp v0.2.0
+	github.com/pmezard/go-difflib v1.0.0
 	golang.org/x/tools v0.0.0-20181017214349-06f26fdaaa28
 )
diff --git a/go.sum b/go.sum
index e21816b..ca6a0e4 100644
--- a/go.sum
+++ b/go.sum
@@ -1,4 +1,6 @@
 github.com/google/go-cmp v0.2.0 h1:+dTQ8DZQJz0Mb/HjFlkptS1FeQ4cWSnN941F8aEG4SQ=
 github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 golang.org/x/tools v0.0.0-20181017214349-06f26fdaaa28 h1:vnbqcYKfOxPnXXUlBo7t+R4pVIh0wInyOSNxih1S9Dc=
 golang.org/x/tools v0.0.0-20181017214349-06f26fdaaa28/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=