cli: respect the "NO_COLOR" convention

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+* Add support for the `NO_COLOR` environment variable
+
+    The CLI will now omit color if the `NO_COLOR` environment variable is present, which is an existing convention that is followed by some other software. See https://no-color.org/ for more information.
+
 ## 0.11.23
 
 * Add a shim function for unbundled uses of `require` ([#1202](https://github.com/evanw/esbuild/issues/1202))

cmd/esbuild/main.go

@@ -13,6 +13,15 @@ import (
 )
 
 var helpText = func(colors logger.Colors) string {
+	// Read "NO_COLOR" from the environment. This is a convention that some
+	// software follows. See https://no-color.org/ for more information.
+	for _, key := range os.Environ() {
+		if strings.HasPrefix(key, "NO_COLOR=") {
+			colors = logger.Colors{}
+			break
+		}
+	}
+
 	return `
 ` + colors.Bold + `Usage:` + colors.Reset + `
   esbuild [options] [entry points]

pkg/cli/cli_impl.go

@@ -626,10 +626,10 @@ func runImpl(osArgs []string) int {
 
 	switch {
 	case buildOptions != nil:
-		// Read the "NODE_PATH" from the environment. This is part of node's
-		// module resolution algorithm. Documentation for this can be found here:
-		// https://nodejs.org/api/modules.html#modules_loading_from_the_global_folders
 		for _, key := range os.Environ() {
+			// Read the "NODE_PATH" from the environment. This is part of node's
+			// module resolution algorithm. Documentation for this can be found here:
+			// https://nodejs.org/api/modules.html#modules_loading_from_the_global_folders
 			if strings.HasPrefix(key, "NODE_PATH=") {
 				value := key[len("NODE_PATH="):]
 				separator := ":"
@@ -640,6 +640,12 @@ func runImpl(osArgs []string) int {
 				buildOptions.NodePaths = strings.Split(value, separator)
 				break
 			}
+
+			// Read "NO_COLOR" from the environment. This is a convention that some
+			// software follows. See https://no-color.org/ for more information.
+			if buildOptions.Color == api.ColorIfTerminal && strings.HasPrefix(key, "NO_COLOR=") {
+				buildOptions.Color = api.ColorNever
+			}
 		}
 
 		// Read from stdin when there are no entry points