cmd: silence warnings in kube-controller-manager/kube-apiserver, dedupe/color warnings in kubectl

Kubernetes-commit: 0d674c4edb3af80a5630223819d9203e43679ba5

pkg/util/term/term.go

@@ -19,6 +19,7 @@ package term
 import (
 	"io"
 	"os"
+	"runtime"
 
 	"github.com/moby/term"
 
@@ -70,6 +71,32 @@ func IsTerminal(i interface{}) bool {
 	return terminal
 }
 
+// AllowsColorOutput returns true if the specified writer is a terminal and
+// the process environment indicates color output is supported and desired.
+func AllowsColorOutput(w io.Writer) bool {
+	if !IsTerminal(w) {
+		return false
+	}
+
+	// https://en.wikipedia.org/wiki/Computer_terminal#Dumb_terminals
+	if os.Getenv("TERM") == "dumb" {
+		return false
+	}
+
+	// https://no-color.org/
+	if _, nocolor := os.LookupEnv("NO_COLOR"); nocolor {
+		return false
+	}
+
+	// On Windows WT_SESSION is set by the modern terminal component.
+	// Older terminals have poor support for UTF-8, VT escape codes, etc.
+	if runtime.GOOS == "windows" && os.Getenv("WT_SESSION") == "" {
+		return false
+	}
+
+	return true
+}
+
 // Safe invokes the provided function and will attempt to ensure that when the
 // function returns (or a termination signal is sent) that the terminal state
 // is reset to the condition it was in prior to the function being invoked. If