Add a cli.NoColour option for disabling all colour/style (#122)

* Check `$FORCE_COLOR` and `$NO_COLOR` only once

* Add a `cli.NoColour` option

* Tweak the help layout

codecov.yml

@@ -1,2 +1,3 @@
 ignore:
   - examples # Demo programs to showcase the library, coverage tracking not needed
+  - internal/colour # Done this a bunch of times, annoying to test because of $FORCE_COLOR and $NO_COLOR and sync.OnceValues

command.go

@@ -600,7 +600,7 @@ func writeArgumentsSection(cmd *Command, s *strings.Builder) error {
 		case requiredArgMarker:
 			tab.Row("  %s\t%s [required]\n", colour.Bold(arg.name), arg.description)
 		case "":
-			tab.Row("  %s\t%s\n", colour.Bold(arg.name), arg.description)
+			tab.Row("  %s\t%s [default %q]\n", colour.Bold(arg.name), arg.description, arg.defaultValue)
 		default:
 			tab.Row("  %s\t%s [default %s]\n", colour.Bold(arg.name), arg.description, arg.defaultValue)
 		}

command_test.go

@@ -464,6 +464,7 @@ func TestHelp(t *testing.T) {
 				cli.OverrideArgs([]string{"--help"}),
 				cli.RequiredArg("src", "The file to copy"),                  // This one is required
 				cli.OptionalArg("dest", "Destination to copy to", "./dest"), // This one is optional
+				cli.OptionalArg("other", "Something else", ""),              // This is optional but default is empty
 				cli.Run(func(cmd *cli.Command, args []string) error { return nil }),
 			},
 			wantErr: false,
@@ -543,16 +544,17 @@ func TestHelp(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			// Force no colour in tests
-			t.Setenv("NO_COLOR", "true")
-
 			snap := snapshot.New(t, snapshot.Update(*update))
 
 			stderr := &bytes.Buffer{}
 			stdout := &bytes.Buffer{}
 
 			// Test specific overrides to the options in the table
-			options := []cli.Option{cli.Stdout(stdout), cli.Stderr(stderr)}
+			options := []cli.Option{
+				cli.Stdout(stdout),
+				cli.Stderr(stderr),
+				cli.NoColour(true),
+			}
 
 			cmd, err := cli.New("test", slices.Concat(options, tt.options)...)
 
@@ -681,14 +683,15 @@ func TestVersion(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			// Force no colour in tests
-			t.Setenv("NO_COLOR", "true")
-
 			stderr := &bytes.Buffer{}
 			stdout := &bytes.Buffer{}
 
 			// Test specific overrides to the options in the table
-			options := []cli.Option{cli.Stdout(stdout), cli.Stderr(stderr)}
+			options := []cli.Option{
+				cli.Stdout(stdout),
+				cli.Stderr(stderr),
+				cli.NoColour(true),
+			}
 
 			cmd, err := cli.New("version-test", slices.Concat(tt.options, options)...)
 			test.Ok(t, err)

internal/colour/colour.go

@@ -4,7 +4,10 @@
 // the same length, which means [text/tabwriter] will correctly calculate alignment as long as styles are not mixed within a table.
 package colour
 
-import "os"
+import (
+	"os"
+	"sync"
+)
 
 // ANSI codes for coloured output, they are all the same length so as not to throw off
 // alignment of [text/tabwriter].
@@ -14,6 +17,24 @@ const (
 	CodeBold  = "\x1b[1;0039m" // Bold & white
 )
 
+// Disable is a flag that disables all colour text, it overrides both
+// $FORCE_COLOR and $NO_COLOR, setting it to true will always make this
+// package return plain text and not check any other config.
+var Disable bool = false
+
+// getColourOnce is a [sync.OnceValues] function that returns the state of
+// $NO_COLOR and $FORCE_COLOR, once and only once to avoid us calling
+// os.Getenv on every call to a colour function.
+var getColourOnce = sync.OnceValues(getColour)
+
+// getColour returns whether $NO_COLOR and $FORCE_COLOR were set.
+func getColour() (noColour bool, forceColour bool) {
+	no := os.Getenv("NO_COLOR") != ""
+	force := os.Getenv("FORCE_COLOR") != ""
+
+	return no, force
+}
+
 // Title returns the given text in a title style, bold white and underlined.
 //
 // If $NO_COLOR is set, text will be returned unmodified.
@@ -30,13 +51,15 @@ func Bold(text string) string {
 
 // sprint returns a string with a given colour and the reset code.
 //
-// It handles checking for NO_COLOR and FORCE_COLOR.
+// It handles checking for NO_COLOR and FORCE_COLOR. If the global var
+// [Disable] is true then nothing else is checked and plain text is returned.
 func sprint(code, text string) string {
-	// TODO(@FollowTheProcess): I don't like checking *every* time but doing it
-	// via e.g. sync.Once means that tests are annoying unless we ensure env vars are
-	// set at the process level
-	noColor := os.Getenv("NO_COLOR") != ""
-	forceColor := os.Getenv("FORCE_COLOR") != ""
+	// Our global variable is above all else
+	if Disable {
+		return text
+	}
+
+	noColor, forceColor := getColourOnce()
 
 	// $FORCE_COLOR overrides $NO_COLOR
 	if forceColor {

option.go

@@ -7,6 +7,7 @@ import (
 	"slices"
 	"strings"
 
+	"github.com/FollowTheProcess/cli/internal/colour"
 	"github.com/FollowTheProcess/cli/internal/flag"
 )
 
@@ -164,6 +165,21 @@ func Stderr(stderr io.Writer) Option {
 	return option(f)
 }
 
+// NoColour is an [Option] that disables all colour output from the [Command].
+//
+// CLI respects the values of $NO_COLOR and $FORCE_COLOR automatically so this need
+// not be set for most applications.
+//
+// Setting this option takes precedence over all other colour configuration.
+func NoColour(noColour bool) Option {
+	f := func(cfg *config) error {
+		// Just disable the internal colour package entirely
+		colour.Disable = noColour
+		return nil
+	}
+	return option(f)
+}
+
 // Short is an [Option] that sets the one line usage summary for a [Command].
 //
 // The one line usage will appear in the help text as well as alongside

testdata/snapshots/TestHelp/with_named_arguments.snap.txt

@@ -1,10 +1,11 @@
 A placeholder for something cool
 
-Usage: test [OPTIONS] SRC [DEST] 
+Usage: test [OPTIONS] SRC [DEST] [OTHER] 
 
 Arguments:
-  src   The file to copy [required]
-  dest  Destination to copy to [default ./dest]
+  src    The file to copy [required]
+  dest   Destination to copy to [default ./dest]
+  other  Something else [default ""]
 
 Options:
   -h  --help     bool  Show help for test