Enable color output on windows (#928)

Color output on PowerShell needs to be explicitly enabled. Usually logrus does that, but only when printing a log message. To be on the safe side, do this explicitly during the CLI initialization. The implementation is based on how logrus does it.

Gopkg.lock

@@ -614,6 +614,14 @@
   revision = "f7279a603edee96fe7764d3de9c6ff8cf9970994"
   version = "1.0.4"
 
+[[projects]]
+  digest = "1:0f51cee70b0d254dbc93c22666ea2abf211af81c1701a96d04e2284b408621db"
+  name = "github.com/konsorten/go-windows-terminal-sequences"
+  packages = ["."]
+  pruneopts = ""
+  revision = "f55edac94c9bbba5d6182a4be46d86a2c9b5b50e"
+  version = "v1.0.2"
+
 [[projects]]
   branch = "master"
   digest = "1:ccc20cacf54eb16464dad02efa1c14fa7c0b9e124639b0d2a51dcc87b0154e4c"
@@ -1608,12 +1616,14 @@
     "github.com/gosuri/uitable",
     "github.com/hpcloud/tail",
     "github.com/jbrukh/bayesian",
+    "github.com/konsorten/go-windows-terminal-sequences",
     "github.com/oklog/ulid",
     "github.com/rjeczalik/notify",
     "github.com/sirupsen/logrus",
     "github.com/spf13/cobra",
     "github.com/spf13/pflag",
     "github.com/technosophos/moniker",
+    "golang.org/x/crypto/ssh/terminal",
     "golang.org/x/net/context",
     "google.golang.org/grpc",
     "k8s.io/api/core/v1",

pkg/cmdline/cmdline.go

@@ -2,7 +2,6 @@ package cmdline
 
 import (
 	"fmt"
-	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -37,7 +36,9 @@ func (cli *cmdline) Init(rootctx context.Context, opts ...Option) {
 	for _, opt := range opts {
 		opt(&cli.opts)
 	}
-	if !consoleSupportsColor() {
+	if out := cli.opts.stdout; isTerminal(out) {
+		initTerminal(out)
+	} else {
 		NoColor()(&cli.opts)
 	}
 
@@ -184,10 +185,3 @@ func concatStrAndEmoji(text string, emoji string, displayEmoji bool) string {
 	}
 	return concatStr.String()
 }
-
-func consoleSupportsColor() bool {
-	// We could try to detect the shell in use (and the mode for the Windows
-	// console), and see if it accepts VT100 escape sequences, but this is
-	// a good enough heuristic to start with!
-	return runtime.GOOS != "windows"
-}

pkg/cmdline/terminal_notwindows.go

@@ -0,0 +1,26 @@
+// +build !windows
+
+// NOTICE: This implementation comes from logrus, unfortunately they
+// do not expose a public interface to call it.
+//   https://github.com/sirupsen/logrus/blob/master/terminal_check_notappengine.go
+//   https://github.com/sirupsen/logrus/blob/master/terminal_windows.go
+
+package cmdline
+
+import (
+	"io"
+	"os"
+
+	"golang.org/x/crypto/ssh/terminal"
+)
+
+// initTerminal enables ANSI color escape sequences. On UNIX, they are always enabled.
+func initTerminal(_ io.Writer) {
+}
+
+func isTerminal(w io.Writer) bool {
+	if f, ok := w.(*os.File); ok {
+		return terminal.IsTerminal(int(f.Fd()))
+	}
+	return false
+}

pkg/cmdline/terminal_windows.go

@@ -0,0 +1,33 @@
+// +build windows
+
+// NOTICE: This implementation comes from logrus, unfortunately they
+// do not expose a public interface to call it.
+//   https://github.com/sirupsen/logrus/blob/master/terminal_check_notappengine.go
+//   https://github.com/sirupsen/logrus/blob/master/terminal_windows.go
+
+package cmdline
+
+import (
+	"io"
+	"os"
+	"syscall"
+
+	sequences "github.com/konsorten/go-windows-terminal-sequences"
+)
+
+// initTerminal enables ANSI color escape on windows. Usually, this is done by logrus,
+// but only after the first log message. So instead we take care of this ourselves.
+func initTerminal(w io.Writer) {
+	if f, ok := w.(*os.File); ok {
+		sequences.EnableVirtualTerminalProcessing(syscall.Handle(f.Fd()), true)
+	}
+}
+
+func isTerminal(w io.Writer) bool {
+	if f, ok := w.(*os.File); ok {
+		var mode uint32
+		err := syscall.GetConsoleMode(syscall.Handle(f.Fd()), &mode)
+		return err == nil
+	}
+	return false
+}