Allow required options to be satisfied by env var (#43)

* Allow required options to be satisfied by env var

If an option is required, but omitted from the argument list,
allow it to fallback to a configured environment variable instead.

Continue to disallow falling back to a default value - ie. the end user
must either supply the option on the command line, or set the
environment variable.

matchers.go

@@ -53,7 +53,7 @@ type optMatcher struct {
 
 func (o *optMatcher) match(args []string, c *parseContext) (bool, []string) {
 	if len(args) == 0 || c.rejectOptions {
-		return false, args
+		return o.theOne.valueSetFromEnv, args
 	}
 
 	idx := 0
@@ -63,15 +63,15 @@ func (o *optMatcher) match(args []string, c *parseContext) (bool, []string) {
 		case arg == "-":
 			idx++
 		case arg == "--":
-			return false, nil
+			return o.theOne.valueSetFromEnv, nil
 		case strings.HasPrefix(arg, "--"):
 			matched, consumed, nargs := o.matchLongOpt(args, idx, c)
 
 			if matched {
 				return true, nargs
 			}
 			if consumed == 0 {
-				return false, args
+				return o.theOne.valueSetFromEnv, args
 			}
 			idx += consumed
 
@@ -81,15 +81,15 @@ func (o *optMatcher) match(args []string, c *parseContext) (bool, []string) {
 				return true, nargs
 			}
 			if consumed == 0 {
-				return false, args
+				return o.theOne.valueSetFromEnv, args
 			}
 			idx += consumed
 
 		default:
-			return false, args
+			return o.theOne.valueSetFromEnv, args
 		}
 	}
-	return false, args
+	return o.theOne.valueSetFromEnv, args
 }
 
 func (o *optMatcher) matchLongOpt(args []string, idx int, c *parseContext) (bool, int, []string) {

spec_n_parse_test.go

@@ -2,7 +2,10 @@ package cli
 
 import (
 	"flag"
+	"os"
+	"strings"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"testing"
@@ -1194,3 +1197,92 @@ func TestWardDoesntRunTooSlowly(t *testing.T) {
 	okCmd(t, spec, init, []string{"--min-length", "10", "--no-symbol", "--no-lower", "--length", "42", "--gen"})
 
 }
+
+func TestEnvOverrideOk(t *testing.T) {
+	defer os.Unsetenv("envopt")
+
+	cases := []struct {
+		setenv bool
+		spec   string
+		args   []string
+		envval string
+	}{
+		// pickup the value from the environment variable
+		{true, "--envopt --other", []string{"--other", "otheropt"}, "fromenv"},
+		{true, "[--envopt] --other", []string{"--other", "otheropt"}, "fromenv"},
+		{true, "--envopt", []string{}, "fromenv"},
+		{true, "--envopt", []string{"--"}, "fromenv"},
+
+		// override on command line
+		{true, "--envopt", []string{"-e", "fromopt"}, "fromopt"},
+		{true, "--envopt", []string{"--envopt", "fromopt"}, "fromopt"},
+
+		// no env set
+		{false, "--envopt", []string{"--envopt", "fromopt"}, "fromopt"},
+		{false, "--envopt", []string{"-e", "fromopt"}, "fromopt"},
+
+		// no env var, fallback to default
+		{false, "[--envopt]", []string{}, "envdefault"},
+		{false, "[--envopt] --other", []string{"--other", "otheropt"}, "envdefault"},
+	}
+
+	for _, cas := range cases {
+		var envopt *string
+		var otheropt *string
+
+		init := func(c *Cmd) {
+			os.Unsetenv("envopt")
+			if cas.setenv {
+				os.Setenv("envopt", "fromenv")
+			}
+			envopt = c.String(StringOpt{
+				Name:   "e envopt",
+				Value:  "envdefault",
+				EnvVar: "envopt",
+			})
+			if strings.Contains(cas.spec, "other") {
+				otheropt = c.StringOpt("o other", "", "")
+			}
+		}
+		okCmd(t, cas.spec, init, cas.args)
+		if strings.Contains(cas.spec, "other") {
+			// if the test spec defined --other, make sure it was actually set
+			assert.Equal(t, "otheropt", *otheropt)
+		}
+		// ensure --envopt was actually set to the test's expectations
+		assert.Equal(t, cas.envval, *envopt)
+	}
+}
+
+// Test that not setting an environment variable correctly causes
+// required options to fail if no value is supplied in args.
+func TestEnvOverrideFail(t *testing.T) {
+	os.Unsetenv("envopt")
+
+	cases := []struct {
+		spec   string
+		args   []string
+		envval string
+	}{
+		// no env var, not optional; should fail
+		{"--envopt", []string{}, ""},
+		{"--envopt --other", []string{"--other", "otheropt"}, ""},
+	}
+
+	for _, cas := range cases {
+		var envopt *string
+		var otheropt *string
+
+		init := func(c *Cmd) {
+			envopt = c.String(StringOpt{
+				Name:   "e envopt",
+				Value:  "envdefault",
+				EnvVar: "envopt",
+			})
+			if strings.Contains(cas.spec, "other") {
+				otheropt = c.StringOpt("o other", "", "")
+			}
+		}
+		failCmd(t, cas.spec, init, cas.args)
+	}
+}