Test and document NO_COLOR support.

0.20.0-release-notes.md

@@ -25,6 +25,10 @@ Draft release notes for Elvish 0.20.0.
 -   The language server now supports showing the documentation of builtin
     functions and variables on hover ([#1684](https://b.elv.sh/1684)).
 
+-   Elvish now respects the [`NO_COLOR`](https://no-color.org) environment
+    variable. Builtin UI elements as well as styled texts will no have colors if
+    it is set and non-empty.
+
 # Notable bugfixes
 
 -   `has-value $li $v` now works correctly when `$li` is a list and `$v` is a

pkg/env/env.go

@@ -6,6 +6,7 @@ package env
 const (
 	HOME      = "HOME"
 	LS_COLORS = "LS_COLORS"
+	NO_COLOR  = "NO_COLOR"
 	PATH      = "PATH"
 	PWD       = "PWD"
 	SHLVL     = "SHLVL"

pkg/eval/builtin_fn_styled.d.elv

@@ -77,6 +77,11 @@ fn styled-segment {|object &fg-color=default &bg-color=default &bold=$false &dim
 # [ANSI SGR code](https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_.28Select_Graphic_Rendition.29_parameters)
 # is built to render the style.
 #
+# If the [`NO_COLOR`](https://no-color.org) environment variable is set and
+# non-empty when Elvish starts, color output is suppressed. Modifications to
+# `NO_COLOR` within Elvish (including from `rc.elv`) do not affect the current
+# process, but will affect child Elvish processes.
+#
 # Examples:
 #
 # ```elvish

pkg/shell/shell.go

@@ -62,7 +62,8 @@ func (p *Program) Run(fds [3]*os.File, args []string) error {
 	cleanup2 := initSignal(fds)
 	defer cleanup2()
 
-	ui.NoColor = os.Getenv("NO_COLOR") != ""
+	// https://no-color.org
+	ui.NoColor = os.Getenv(env.NO_COLOR) != ""
 	interactive := len(args) == 0
 	ev := p.makeEvaler(fds[2], interactive)
 	defer ev.PreExit()

pkg/shell/shell_test.go

@@ -79,6 +79,28 @@ func TestShell_LibPath_Legacy(t *testing.T) {
 // Most high-level tests against Program are specific to either script mode or
 // interactive mode, and are found in script_test.go and interact_test.go.
 
+var noColorTests = []struct {
+	name       string
+	value      string
+	unset      bool
+	wantRedFoo string
+}{
+	{name: "unset", unset: true, wantRedFoo: "\033[;31mfoo\033[m"},
+	{name: "empty", value: "", wantRedFoo: "\033[;31mfoo\033[m"},
+	{name: "non-empty", value: "yes", wantRedFoo: "\033[mfoo"},
+}
+
+func TestShell_NO_COLOR(t *testing.T) {
+	for _, test := range noColorTests {
+		t.Run(test.name, func(t *testing.T) {
+			setOrUnsetenv(t, env.NO_COLOR, test.unset, test.value)
+			Test(t, &Program{},
+				ThatElvish("-c", "print (styled foo red)").
+					WritesStdout(test.wantRedFoo))
+		})
+	}
+}
+
 var incSHLVLTests = []struct {
 	name    string
 	old     string
@@ -104,12 +126,7 @@ var incSHLVLTests = []struct {
 func TestShell_SHLVL(t *testing.T) {
 	for _, test := range incSHLVLTests {
 		t.Run(test.name, func(t *testing.T) {
-			if test.unset {
-				testutil.Unsetenv(t, env.SHLVL)
-			} else {
-				testutil.Setenv(t, env.SHLVL, test.old)
-			}
-
+			setOrUnsetenv(t, env.SHLVL, test.unset, test.old)
 			Test(t, &Program{},
 				ThatElvish("-c", "print $E:SHLVL").WritesStdout(test.wantNew))
 
@@ -128,6 +145,14 @@ func TestShell_SHLVL(t *testing.T) {
 	}
 }
 
+func setOrUnsetenv(t *testing.T, name string, unset bool, set string) {
+	if unset {
+		testutil.Unsetenv(t, name)
+	} else {
+		testutil.Setenv(t, name, set)
+	}
+}
+
 // Common test utilities.
 
 func setupCleanHomePaths(t testutil.Cleanuper) string {

pkg/ui/style.go

@@ -5,6 +5,8 @@ import (
 	"strings"
 )
 
+// NoColor can be set to true to suppress foreground and background colors when
+// writing text to the terminal.
 var NoColor bool = false
 
 // Style specifies how something (mostly a string) shall be displayed.

pkg/ui/style_test.go

@@ -2,6 +2,8 @@ package ui
 
 import (
 	"testing"
+
+	"src.elv.sh/pkg/testutil"
 )
 
 func TestStyleSGR(t *testing.T) {
@@ -20,6 +22,15 @@ func TestStyleSGR(t *testing.T) {
 	})
 }
 
+func TestStyleSGR_NoColor(t *testing.T) {
+	testutil.Set(t, &NoColor, true)
+	testTextVTString(t, []textVTStringTest{
+		{T("foo", FgRed), "\033[mfoo"},
+		{T("foo", BgRed), "\033[mfoo"},
+		{T("foo", FgRed, BgBlue), "\033[mfoo"},
+	})
+}
+
 type mergeFromOptionsTest struct {
 	style     Style
 	options   map[string]any