Add FORCE_COLOR environment variable support

README.md

@@ -148,6 +148,12 @@ There might be a case where you want to explicitly disable/enable color output.
 The `color` package also disables color output if the [`NO_COLOR`](https://no-color.org) environment
 variable is set to a non-empty string.
 
+It also supports the [`FORCE_COLOR`](https://force-color.org) environment variable. When
+`FORCE_COLOR` is set (to any value other than `"0"`), colors will be enabled regardless of
+terminal detection. This is useful in CI environments like GitHub Actions and GitLab CI that
+support ANSI colors but are not detected as TTYs. `NO_COLOR` takes precedence over
+`FORCE_COLOR`.
+
 `Color` has support to disable/enable colors programmatically both globally and
 for single color definitions. For example suppose you have a CLI app and a
 `-no-color` bool flag. You can easily disable the color output with:
@@ -176,7 +182,9 @@ c.Println("This prints again cyan...")
 
 ## GitHub Actions
 
-To output color in GitHub Actions (or other CI systems that support ANSI colors), make sure to set `color.NoColor = false` so that it bypasses the check for non-tty output streams. 
+To output color in GitHub Actions (or other CI systems that support ANSI colors), you can
+set the `FORCE_COLOR=1` environment variable. Alternatively, set `color.NoColor = false`
+programmatically to bypass the check for non-tty output streams.
 
 
 ## Credits

color.go

@@ -19,7 +19,11 @@ var (
 	// set (regardless of its value). This is a global option and affects all
 	// colors. For more control over each color block use the methods
 	// DisableColor() individually.
-	NoColor = noColorIsSet() || os.Getenv("TERM") == "dumb" || !stdoutIsTerminal()
+	//
+	// If the FORCE_COLOR environment variable is set (to any value other than
+	// "0"), colors will be enabled regardless of terminal detection. NO_COLOR
+	// takes precedence over FORCE_COLOR.
+	NoColor = noColorIsSet() || (!forceColorIsSet() && (os.Getenv("TERM") == "dumb" || !stdoutIsTerminal()))
 
 	// Output defines the standard output of the print functions. By default,
 	// stdOut() is used.
@@ -67,6 +71,13 @@ func stdErr() io.Writer {
 	return colorable.NewColorableStderr()
 }
 
+// forceColorIsSet returns true if the environment variable FORCE_COLOR is set
+// to a value other than "0". See https://force-color.org for more details.
+func forceColorIsSet() bool {
+	val, ok := os.LookupEnv("FORCE_COLOR")
+	return ok && val != "0"
+}
+
 // Color defines a custom color object which is defined by SGR parameters.
 type Color struct {
 	params  []Attribute
@@ -178,6 +189,9 @@ func New(value ...Attribute) *Color {
 	if noColorIsSet() {
 		c.noColor = boolPtr(true)
 	}
+	if forceColorIsSet() && !noColorIsSet() {
+		c.noColor = boolPtr(false)
+	}
 
 	c.Add(value...)
 	return c

color_test.go

@@ -662,3 +662,94 @@ func TestRGB(t *testing.T) {
 		})
 	}
 }
+
+func Test_forceColorIsSet(t *testing.T) {
+	t.Run("default", func(t *testing.T) {
+		if forceColorIsSet() {
+			t.Errorf("forceColorIsSet() = true, want false")
+		}
+	})
+
+	tests := []struct {
+		name  string
+		value string
+		want  bool
+	}{
+		{
+			name:  "FORCE_COLOR=1",
+			value: "1",
+			want:  true,
+		},
+		{
+			name:  "FORCE_COLOR=0",
+			value: "0",
+			want:  false,
+		},
+		{
+			name:  "FORCE_COLOR=true",
+			value: "true",
+			want:  true,
+		},
+		{
+			name:  "FORCE_COLOR=",
+			value: "",
+			want:  true,
+		},
+		{
+			name:  "FORCE_COLOR=whatever",
+			value: "whatever",
+			want:  true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv("FORCE_COLOR", tt.value)
+			if got := forceColorIsSet(); got != tt.want {
+				t.Errorf("forceColorIsSet() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestForceColor(t *testing.T) {
+	rb := new(bytes.Buffer)
+	Output = rb
+
+	t.Setenv("FORCE_COLOR", "1")
+
+	NoColor = false
+
+	testColors := []struct {
+		text string
+		code Attribute
+	}{
+		{text: "black", code: FgBlack},
+		{text: "red", code: FgRed},
+		{text: "green", code: FgGreen},
+	}
+
+	for _, c := range testColors {
+		p := New(c.code)
+		p.Print(c.text)
+
+		line, _ := rb.ReadString('\n')
+		scannedLine := fmt.Sprintf("%q", line)
+		colored := fmt.Sprintf("\x1b[%dm%s\x1b[0m", c.code, c.text)
+		escapedForm := fmt.Sprintf("%q", colored)
+
+		if scannedLine != escapedForm {
+			t.Errorf("Expecting %s, got '%s'\n", escapedForm, scannedLine)
+		}
+	}
+}
+
+func TestForceColorOverriddenByNoColor(t *testing.T) {
+	// NO_COLOR should take precedence over FORCE_COLOR
+	t.Setenv("FORCE_COLOR", "1")
+	t.Setenv("NO_COLOR", "1")
+
+	c := New(FgRed)
+	if !c.isNoColorSet() {
+		t.Error("Expected NO_COLOR to take precedence over FORCE_COLOR")
+	}
+}