text: support NO_COLOR/FORCE_COLOR env directives; fixes #352 (#360)

text/color.go

@@ -2,13 +2,14 @@ package text
 
 import (
 	"fmt"
+	"os"
 	"sort"
 	"strconv"
 	"strings"
 	"sync"
 )
 
-var colorsEnabled = areANSICodesSupported()
+var colorsEnabled = areColorsOnInTheEnv() && areANSICodesSupported()
 
 // DisableColors (forcefully) disables color coding globally.
 func DisableColors() {
@@ -20,6 +21,15 @@ func EnableColors() {
 	colorsEnabled = true
 }
 
+// areColorsOnInTheEnv returns true is colors are not disable using
+// well known environment variables.
+func areColorsOnInTheEnv() bool {
+	if os.Getenv("FORCE_COLOR") == "1" {
+		return true
+	}
+	return os.Getenv("NO_COLOR") == "" || os.Getenv("NO_COLOR") == "0"
+}
+
 // The logic here is inspired from github.com/fatih/color; the following is
 // the bare minimum logic required to print Colored to the console.
 // The differences:

text/color_test.go

@@ -2,6 +2,7 @@ package text
 
 import (
 	"fmt"
+	"os"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -24,6 +25,24 @@ func TestColor_EnableAndDisable(t *testing.T) {
 	assert.Equal(t, "\x1b[31mtest\x1b[0m", FgRed.Sprint("test"))
 }
 
+func TestColor_areColorsOnInTheEnv(t *testing.T) {
+	_ = os.Setenv("FORCE_COLOR", "0")
+	_ = os.Setenv("NO_COLOR", "0")
+	assert.True(t, areColorsOnInTheEnv())
+
+	_ = os.Setenv("FORCE_COLOR", "0")
+	_ = os.Setenv("NO_COLOR", "1")
+	assert.False(t, areColorsOnInTheEnv())
+
+	_ = os.Setenv("FORCE_COLOR", "1")
+	_ = os.Setenv("NO_COLOR", "0")
+	assert.True(t, areColorsOnInTheEnv())
+
+	_ = os.Setenv("FORCE_COLOR", "1")
+	_ = os.Setenv("NO_COLOR", "1")
+	assert.True(t, areColorsOnInTheEnv())
+}
+
 func ExampleColor_EscapeSeq() {
 	fmt.Printf("Black Background: %#v\n", BgBlack.EscapeSeq())
 	fmt.Printf("Black Foreground: %#v\n", FgBlack.EscapeSeq())