add a -version flag to gofumpt

This allows for versioned go get/install commands to bundle the module
version in the binary, then the version flag can print it as-is.

Prebuilt binaries will also include it via ldflags.

Not for gofumports, since its days are counted.

For #99.

gen.go

@@ -248,9 +248,16 @@ const extraSrcLangVersion = `` +
 	}`
 
 func copyGofmt(pkg *Package) {
-	const extraSrc = `
-		// This is the only gofumpt change on gofmt's codebase, besides changing
-		// the name in the usage text.
+	const extraVersion = `
+		// Print the gofumpt version if the user asks for it.
+		if *showVersion {
+			printVersion()
+			return
+		}
+		`
+	const extraFormat = `
+		// Apply gofumpt's changes before we print the code in gofmt's
+		// format.
 		` + extraSrcLangVersion + `
 		gformat.File(fileSet, file, gformat.Options{
 			LangVersion: *langVersion,
@@ -268,8 +275,11 @@ func copyGofmt(pkg *Package) {
 			if i := strings.Index(body, "\t\"mvdan.cc/gofumpt"); i > 0 {
 				body = body[:i] + "\n" + extraImport + "\n" + body[i:]
 			}
+			if i := strings.Index(body, "if *cpuprofile !="); i > 0 {
+				body = body[:i] + "\n" + extraVersion + "\n" + body[i:]
+			}
 			if i := strings.Index(body, "res, err := format("); i > 0 {
-				body = body[:i] + "\n" + extraSrc + "\n" + body[i:]
+				body = body[:i] + "\n" + extraFormat + "\n" + body[i:]
 			}
 		}
 		body = strings.Replace(body, "gofmt", "gofumpt", -1)
@@ -278,7 +288,7 @@ func copyGofmt(pkg *Package) {
 }
 
 func copyGoimports(pkg *Package) {
-	const extraSrc = `
+	const extraFormat = `
 		// This is the only gofumpt change on goimports's codebase, besides changing
 		// the name in the usage text.
 		` + extraSrcLangVersion + `
@@ -299,7 +309,7 @@ func copyGoimports(pkg *Package) {
 				body = body[:i] + "\n" + extraImport + "\n" + body[i:]
 			}
 			if i := strings.Index(body, "if !bytes.Equal"); i > 0 {
-				body = body[:i] + "\n" + extraSrc + "\n" + body[i:]
+				body = body[:i] + "\n" + extraFormat + "\n" + body[i:]
 			}
 		}
 		body = strings.Replace(body, "goimports", "gofumports", -1)

gofmt.go

@@ -122,8 +122,8 @@ func processFile(filename string, in io.Reader, out io.Writer, stdin bool) error
 		simplify(file)
 	}
 
-	// This is the only gofumpt change on gofumpt's codebase, besides changing
-	// the name in the usage text.
+	// Apply gofumpt's changes before we print the code in gofumpt's
+	// format.
 	if *langVersion == "" {
 		out, err := exec.Command("go", "list", "-m", "-f", "{{.GoVersion}}").Output()
 		out = bytes.TrimSpace(out)
@@ -207,6 +207,12 @@ func gofumptMain() {
 	flag.Usage = usage
 	flag.Parse()
 
+	// Print the gofumpt version if the user asks for it.
+	if *showVersion {
+		printVersion()
+		return
+	}
+
 	if *cpuprofile != "" {
 		f, err := os.Create(*cpuprofile)
 		if err != nil {

version.go

@@ -0,0 +1,28 @@
+// Copyright (c) 2020, Daniel Martí <mvdan@mvdan.cc>
+// See LICENSE for licensing information
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"runtime/debug"
+)
+
+var (
+	showVersion = flag.Bool("version", false, "show version and exit")
+
+	version = "(devel)" // to match the default from runtime/debug
+)
+
+func printVersion() {
+	// don't overwrite the version if it was set by -ldflags=-X
+	if info, ok := debug.ReadBuildInfo(); ok && version == "(devel)" {
+		mod := &info.Main
+		if mod.Replace != nil {
+			mod = mod.Replace
+		}
+		version = mod.Version
+	}
+	fmt.Println(version)
+}