gofix: don't rewrite O_APPEND opens

R=r, rog
CC=golang-dev
https://golang.org/cl/4364041

misc/dashboard/builder/exec.go

@@ -49,7 +49,7 @@ func runLog(envv []string, logfile, dir string, argv ...string) (output string,
 	b := new(bytes.Buffer)
 	var w io.Writer = b
 	if logfile != "" {
-		f, err := os.Create(logfile)
+		f, err := os.OpenFile(logfile, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
 		if err != nil {
 			return
 		}

src/cmd/gofix/osopen.go

@@ -70,6 +70,7 @@ func osopen(f *ast.File) bool {
 func isCreateFlag(flag ast.Expr) bool {
 	foundCreate := false
 	foundTrunc := false
+	foundAppend := false
 	// OR'ing of flags: is O_CREATE on?  + or | would be fine; we just look for os.O_CREATE
 	// and don't worry about the actual opeator.
 	p := flag.Pos()
@@ -85,12 +86,21 @@ func isCreateFlag(flag ast.Expr) bool {
 		if isPkgDot(lhs, "os", "O_TRUNC") {
 			foundTrunc = true
 		}
+		if isPkgDot(lhs, "os", "O_APPEND") {
+			foundAppend = true
+		}
 		if !isBinary {
 			break
 		}
 		flag = expr.X
 	}
-	if foundCreate && !foundTrunc {
+	if !foundCreate {
+		return false
+	}
+	if foundAppend {
+		return false
+	}
+	if !foundTrunc {
 		warn(p, "rewrote os.Open with O_CREATE but not O_TRUNC to os.Create")
 	}
 	return foundCreate

src/cmd/gofix/osopen_test.go

@@ -27,6 +27,7 @@ func f() {
 	os.Open(a, os.O_CREATE, 0666)
 	os.Open(a, os.O_CREATE|os.O_TRUNC, 0664)
 	os.Open(a, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+	os.Open(a, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
 	_ = os.O_CREAT
 }
 `,
@@ -46,6 +47,7 @@ func f() {
 	os.Create(a)
 	os.Create(a)
 	os.Create(a)
+	os.OpenFile(a, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
 	_ = os.O_CREATE
 }
 `,

src/cmd/goinstall/main.go

@@ -120,7 +120,7 @@ func logPackage(pkg string) {
 	if installedPkgs[pkg] {
 		return
 	}
-	fout, err := os.Create(logfile)
+	fout, err := os.OpenFile(logfile, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "%s: %s\n", argv0, err)
 		return

src/pkg/crypto/tls/generate_cert.go

@@ -59,7 +59,7 @@ func main() {
 	certOut.Close()
 	log.Print("written cert.pem\n")
 
-	keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREAT, 0600)
+	keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREAT|os.O_TRUNC, 0600)
 	if err != nil {
 		log.Print("failed to open key.pem for writing:", err)
 		return