Enable environment variable hints for --token flag (#945)

Moved envVars to env.Vars
Add test case for env.Vars
Add slices package for slices.Contains
Actually test something sensible
Check error value from Setenv since windows does not set values
Test with common variables instead
Mark tests on other platforms as skip
Document Vars method

Author: andersjanmyr

go.mod

@@ -56,6 +56,7 @@ require (
 	github.com/rogpeppe/go-internal v1.8.0 // indirect
 	github.com/ulikunitz/xz v0.5.10 // indirect
 	github.com/xi2/xz v0.0.0-20171230120015-48954b6210f8 // indirect
+	golang.org/x/exp v0.0.0-20230522175609-2e198f4a06a1 // indirect
 	golang.org/x/net v0.10.0 // indirect
 	golang.org/x/text v0.9.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect

go.sum

@@ -125,6 +125,8 @@ github.com/xi2/xz v0.0.0-20171230120015-48954b6210f8 h1:nIPpBwaJSVYIxUFsDv3M8ofm
 github.com/xi2/xz v0.0.0-20171230120015-48954b6210f8/go.mod h1:HUYIGzjTL3rfEspMxjDjgmT5uz5wzYJKVo23qUhYTos=
 golang.org/x/crypto v0.9.0 h1:LF6fAI+IutBocDJ2OT0Q1g8plpYljMZ4+lty+dsqw3g=
 golang.org/x/crypto v0.9.0/go.mod h1:yrmDGqONDYtNj3tH8X9dzUun2m2lzPa9ngI6/RUPGR0=
+golang.org/x/exp v0.0.0-20230522175609-2e198f4a06a1 h1:k/i9J1pBpvlfR+9QsetwPyERsqu1GIbi967PQMq3Ivc=
+golang.org/x/exp v0.0.0-20230522175609-2e198f4a06a1/go.mod h1:V1LtkGg67GoY2N1AnLN78QLrzxkLyJw7RJb1gzOOz9w=
 golang.org/x/net v0.10.0 h1:X2//UzNDwYmtCLn7To6G58Wr6f5ahEAQgKNzv9Y951M=
 golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
 golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

pkg/app/run.go

@@ -91,7 +91,7 @@ func Run(opts RunOpts) error {
 	app.Flag("non-interactive", "Do not prompt for user input - suitable for CI processes. Equivalent to --accept-defaults and --auto-yes").Short('i').BoolVar(&g.Flags.NonInteractive)
 	app.Flag("profile", "Switch account profile for single command execution (see also: 'fastly profile switch')").Short('o').StringVar(&g.Flags.Profile)
 	app.Flag("quiet", "Silence all output except direct command output. This won't prevent interactive prompts (see: --accept-defaults, --auto-yes, --non-interactive)").Short('q').BoolVar(&g.Flags.Quiet)
-	app.Flag("token", tokenHelp).Short('t').StringVar(&g.Flags.Token)
+	app.Flag("token", tokenHelp).HintAction(env.Vars).Short('t').StringVar(&g.Flags.Token)
 	app.Flag("verbose", "Verbose logging").Short('v').BoolVar(&g.Flags.Verbose)
 
 	commands := defineCommands(app, &g, md, opts)

pkg/env/env.go

@@ -1,5 +1,13 @@
 package env
 
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/fastly/cli/pkg/runtime"
+)
+
 const (
 	// Token is the env var we look in for the Fastly API token.
 	// gosec flagged this:
@@ -17,3 +25,30 @@ const (
 	// CustomerID is the env var we look in for a Customer ID.
 	CustomerID = "FASTLY_CUSTOMER_ID"
 )
+
+// Vars returns a slice of environment variables appropriate to platform.
+// *nix: $HOME, $USER, ...
+// Windows: %HOME%, %USER%, ...
+func Vars() []string {
+	vars := []string{}
+	for _, e := range os.Environ() {
+		pair := strings.SplitN(e, "=", 2)
+		vars = append(vars, toVar(pair[0]))
+	}
+	return vars
+}
+
+func toVar(v string) string {
+	if runtime.Windows {
+		return toWin(v)
+	}
+	return toNix(v)
+}
+
+func toNix(v string) string {
+	return fmt.Sprintf("\\$%s", v)
+}
+
+func toWin(v string) string {
+	return fmt.Sprintf("%%%s%%", v)
+}

pkg/env/env_test.go

@@ -0,0 +1,43 @@
+package env
+
+import (
+	"runtime"
+	"testing"
+
+	"golang.org/x/exp/slices"
+)
+
+func TestVars(t *testing.T) {
+	tcs := []struct {
+		os       string
+		vars     map[string]string
+		expected []string
+	}{
+		{
+			os:       "windows",
+			expected: []string{"%HOME%", "%PATH%"},
+		},
+		{
+			os:       "darwin",
+			expected: []string{"\\$HOME", "\\$PATH"},
+		},
+		{
+			os:       "linux",
+			expected: []string{"\\$HOME", "\\$PATH"},
+		},
+	}
+	for _, tc := range tcs {
+		t.Run(tc.os, func(t *testing.T) {
+			vars := Vars()
+			if runtime.GOOS == tc.os {
+				for _, v := range tc.expected {
+					if !slices.Contains(vars, v) {
+						t.Errorf("expected %s in %v", v, vars)
+					}
+				}
+			} else {
+				t.Skip()
+			}
+		})
+	}
+}