add fallbacks

fallback_test.go

@@ -0,0 +1,144 @@
+package flags
+
+import (
+	"os"
+	"reflect"
+	"testing"
+	"time"
+)
+
+// Test that when `long` is absent, it attempts to fall back to `json`, and
+// when `env` is absent, it attempts to fall back to `long` (and to `json`)
+func TestFallback(t *testing.T) {
+	type Options struct {
+		Int   int            `long:"int" json:"json-int" default:"1"`
+		Time  time.Duration  `json:"time" default:"1m"`
+		Map   map[string]int `json:"map,omitempty" default:"a:1" env-delim:";"`
+		Slice []int          `long:"slice" default:"1" default:"2" env:"OVERRIDE_SLICE" env-delim:","`
+	}
+
+	var tests = []struct {
+		msg      string
+		args     []string
+		expected Options
+		env      map[string]string
+	}{
+		{
+			msg:  "JSON override",
+			args: []string{},
+			expected: Options{
+				Int: 23,
+				Time: time.Minute * 3,
+				Map: map[string]int{"key1": 1},
+				Slice: []int{3,4,5},
+			},
+			env: map[string]string{
+				// since both `json` and `long` are present, `long` ("int") wins
+				"json-int": "4",
+				"int": "23",
+				"time": "3m",
+				"map": "key1:1",
+				// since both `env` and `long` are present, `env` ("OVERRIDE_SLICE") wins
+				"slice": "3,2,1",
+				"OVERRIDE_SLICE": "3,4,5",
+			},
+		},
+		{
+			msg:  "no arguments, no env, expecting default values",
+			args: []string{},
+			expected: Options{
+				Int:   1,
+				Time:  time.Minute,
+				Map:   map[string]int{"a": 1},
+				Slice: []int{1, 2},
+			},
+		},
+		{
+			msg:  "no arguments, env defaults, expecting env default values",
+			args: []string{},
+			expected: Options{
+				Int:   2,
+				Time:  2 * time.Minute,
+				Map:   map[string]int{"a": 2, "b": 3},
+				Slice: []int{4, 5, 6},
+			},
+			env: map[string]string{
+				"Int": "2",
+				"Time": "2m",
+				"Map": "a:2;b:3",
+				"OVERRIDE_SLICE": "4,5,6",
+			},
+		},
+		{
+			msg:  "non-zero value arguments, expecting overwritten arguments",
+			args: []string{"--int=3", "--time=3ms", "--map=c:3", "--slice=3", "--map=d:4", "--slice=1"},
+			expected: Options{
+				Int:   3,
+				Time:  3 * time.Millisecond,
+				Map:   map[string]int{"c": 3,"d":4},
+				Slice: []int{3,1},
+			},
+			env: map[string]string{
+				"Int": "2",
+				"Time": "2m",
+				"Map": "a:2;b:3",
+				"OVERRIDE_SLICE": "4,5,6",
+			},
+		},
+		{
+			msg:  "zero value arguments, expecting overwritten arguments",
+			args: []string{"--int=0", "--time=0ms", "--map=:0", "--slice=0"},
+			expected: Options{
+				Int:   0,
+				Time:  0,
+				Map:   map[string]int{"": 0},
+				Slice: []int{0},
+			},
+			env: map[string]string{
+				"Int": "2",
+				"Time": "2m",
+				"Map": "a:2;b:3",
+				"OVERRIDE_SLICE": "4,5,6",
+			},
+		},
+		{
+			msg:  "`long` used for env name even though `env` was present",
+			args: []string{"--int=0", "--time=0ms", "--map=:0", "--slice=0"},
+			expected: Options{
+				Int:   0,
+				Time:  0,
+				Map:   map[string]int{"": 0},
+				Slice: []int{0},
+			},
+			env: map[string]string{
+				"Int": "2",
+				"Time": "2m",
+				"Map": "a:2;b:3",
+				"Slice": "4,5,6",
+			},
+		},
+	}
+
+	oldEnv := EnvSnapshot()
+	defer oldEnv.Restore()
+
+	for _, test := range tests {
+		var opts Options
+		oldEnv.Restore()
+		for envKey, envValue := range test.env {
+			os.Setenv(envKey, envValue)
+		}
+		_, _, _, err := ParseArgs(&opts, test.args)
+		if err != nil {
+			t.Fatalf("%s:\nUnexpected error: %v", test.msg, err)
+		}
+
+		if opts.Slice == nil {
+			opts.Slice = []int{}
+		}
+
+		if !reflect.DeepEqual(opts, test.expected) {
+			t.Errorf("%s:\nUnexpected options with arguments %+v\nexpected\n%+v\nbut got\n%+v\n", test.msg, test.args, test.expected, opts)
+		}
+	}
+}

group.go

@@ -234,6 +234,13 @@ func (g *Group) scanStruct(realval reflect.Value, sfield *reflect.StructField, h
 		longname := mtag.Get("long")
 		shortname := mtag.Get("short")
 
+		// If `long` is not specified, try the JSON key
+		if longname == "" {
+			if j := mtag.Get("json"); j != "" {
+				// key = anything before a comma, if one is present
+				longname = strings.SplitN(j, ",", 2)[0]
+			}
+		}
 		// Need at least either a short or long name
 		if longname == "" && shortname == "" && mtag.Get("ini-name") == "" {
 			continue
@@ -268,7 +275,7 @@ func (g *Group) scanStruct(realval reflect.Value, sfield *reflect.StructField, h
 			ShortName:        short,
 			LongName:         longname,
 			Default:          def,
-			EnvDefaultKey:    mtag.Get("env"),
+			EnvDefaultKey:    mtag.OptGet("env", longname),
 			EnvDefaultDelim:  mtag.Get("env-delim"),
 			OptionalArgument: optional,
 			OptionalValue:    optionalValue,

multitag.go

@@ -124,6 +124,14 @@ func (x *multiTag) Get(key string) string {
 	return ""
 }
 
+// OptGet returns Get(key), unless it is empty, when it returns def
+func (x *multiTag) OptGet(key string, def string) string {
+	if ret := x.Get(key); ret != "" {
+		return ret
+	}
+	return def
+}
+
 func (x *multiTag) GetMany(key string) []string {
 	c := x.cached()
 	return c[key]