Merge pull request #8 from SimonRichardson/no_color

#8

The following supports the NO_COLOR standard. The idea is that we don't
write color to the term if the env var of NO_COLOR is set to anything
that can be truthy.

This brings juju inline with more new CLI.

See: https://no-color.org/

go.mod

@@ -0,0 +1,10 @@
+module github.com/juju/ansiterm
+
+go 1.14
+
+require (
+	github.com/lunixbochs/vtclean v1.0.0
+	github.com/mattn/go-colorable v0.1.10
+	github.com/mattn/go-isatty v0.0.14
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c
+)

go.sum

@@ -0,0 +1,18 @@
+github.com/kr/pretty v0.2.1 h1:Fmg33tUaq4/8ym9TJN1x7sLJnHVwhP33CNkpYV/7rwI=
+github.com/kr/pretty v0.2.1/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
+github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
+github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/lunixbochs/vtclean v1.0.0 h1:xu2sLAri4lGiovBDQKxl5mrXyESr3gUr5m5SM5+LVb8=
+github.com/lunixbochs/vtclean v1.0.0/go.mod h1:pHhQNgMf3btfWnGBVipUOjRYhoOsdGqdm/+2c2E2WMI=
+github.com/mattn/go-colorable v0.1.10 h1:KWqbp83oZ6YOEgIbNW3BM1Jbe2tz4jgmWA9FOuAF8bw=
+github.com/mattn/go-colorable v0.1.10/go.mod h1:u6P/XSegPjTcexA+o6vUJrdnUu04hMope9wVRipJSqc=
+github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
+github.com/mattn/go-isatty v0.0.14 h1:yVuAays6BHfxijgZPzw+3Zlu5yQgKGP2/hcQbHb7S9Y=
+github.com/mattn/go-isatty v0.0.14/go.mod h1:7GGIvUiUoEMVVmxf/4nioHXj79iQHKdU27kJ6hsGG94=
+golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c h1:F1jZWGFhYfh0Ci55sIpILtKKK8p3i2/krTr0H1rg74I=
+golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=

terminal.go

@@ -20,6 +20,18 @@ func colorEnabledWriter(w io.Writer) (io.Writer, bool) {
 	if !ok {
 		return w, false
 	}
+
+	// NO_COLOR is a relatively new standard for preventing color enabled
+	// writers rather than using the TERM env.
+	//
+	// "...should check for the presence of a NO_COLOR environment variable
+	//  that, when present (regardless of its value), prevents the addition of
+	//  ANSI color."
+	// See: https://no-color.org/
+	if _, ok := os.LookupEnv("NO_COLOR"); ok {
+		return w, false
+	}
+
 	// Check the TERM environment variable specifically
 	// to check for "dumb" terminals.
 	if os.Getenv("TERM") == "dumb" {

terminal_test.go

@@ -0,0 +1,40 @@
+// Copyright 2021 Canonical Ltd.
+// Licensed under the LGPLv3, see LICENCE file for details.
+
+package ansiterm
+
+import (
+	"io/ioutil"
+	"os"
+
+	gc "gopkg.in/check.v1"
+)
+
+type colorWriterSuite struct{}
+
+var _ = gc.Suite(&colorWriterSuite{})
+
+func (s *colorWriterSuite) TestNoColor(c *gc.C) {
+	file, err := ioutil.TempFile("", "")
+	c.Assert(err, gc.IsNil)
+
+	os.Setenv("NO_COLOR", "")
+	defer os.Unsetenv("NO_COLOR")
+
+	writer, ok := colorEnabledWriter(file)
+	c.Assert(ok, gc.Equals, false)
+	c.Assert(writer, gc.Equals, file)
+
+}
+
+func (s *colorWriterSuite) TestNoColorEvenIfFalse(c *gc.C) {
+	file, err := ioutil.TempFile("", "")
+	c.Assert(err, gc.IsNil)
+
+	os.Setenv("NO_COLOR", "false")
+	defer os.Unsetenv("NO_COLOR")
+
+	writer, ok := colorEnabledWriter(file)
+	c.Assert(ok, gc.Equals, false)
+	c.Assert(writer, gc.Equals, file)
+}