feat: Respect NO_COLOR flag.

fix jwalton/gchalk#2

Author: jwalton

README.md

@@ -67,4 +67,6 @@ By default, supportscolor checks `os.Args` for the `--color` and `--no-color` CL
 
 For situations where using `--color` is not possible, use the environment variable `FORCE_COLOR=1` (level 1 - 16 colors), `FORCE_COLOR=2` (level 2 - 256 colors), or `FORCE_COLOR=3` (level 3 - true color) to forcefully enable color, or `FORCE_COLOR=0` to forcefully disable. The use of `FORCE_COLOR` overrides all other color support checks.
 
+If `NO_COLOR` is specified and `FORCE_COLOR` is not, then colors will be disabled.
+
 Explicit 256/True color mode can be enabled using the `--color=256` and `--color=16m` flags, respectively.

supportscolor.go

@@ -83,7 +83,6 @@ func checkForceColorFlags(env environment) *ColorLevel {
 
 func checkForceColorEnv(env environment) *ColorLevel {
 	forceColor, present := env.LookupEnv("FORCE_COLOR")
-
 	if present {
 		if forceColor == "true" || forceColor == "" {
 			result := Basic
@@ -109,6 +108,11 @@ func checkForceColorEnv(env environment) *ColorLevel {
 		}
 	}
 
+	if _, isNoColor := env.LookupEnv("NO_COLOR"); isNoColor {
+		result := None
+		return &result
+	}
+
 	return nil
 }
 

supportscolor_test.go

@@ -112,6 +112,17 @@ func TestDoNotCacheForceColor(t *testing.T) {
 	}
 }
 
+func TestNoColor(t *testing.T) {
+	result := SupportsColor(0, setEnvironment(&testEnvironment{
+		env:           map[string]string{"NO_COLOR": ""},
+		isNotTerminal: true,
+	}))
+
+	if result.Level != None {
+		t.Errorf("Expected %v, got %v", None, result.Level)
+	}
+}
+
 func TestReturnNoneIfNotTty(t *testing.T) {
 	result := SupportsColor(0, setEnvironment(&testEnvironment{isNotTerminal: true}))
 	if result.Level != None {