Fix:(issue_1842) Make value source chain more user friendly

flag_bool_with_inverse.go

@@ -90,7 +90,7 @@ func (parent *BoolWithInverseFlag) initialize() {
 	parent.negativeFlag = &BoolFlag{
 		Category:    child.Category,
 		DefaultText: child.DefaultText,
-		Sources:     ValueSourceChain{Chain: append([]ValueSource{}, child.Sources.Chain...)},
+		Sources:     NewValueSourceChain(child.Sources.Chain...),
 		Usage:       child.Usage,
 		Required:    child.Required,
 		Hidden:      child.Hidden,
@@ -109,12 +109,13 @@ func (parent *BoolWithInverseFlag) initialize() {
 	parent.negativeFlag.Name = parent.inverseName()
 	parent.negativeFlag.Aliases = parent.inverseAliases()
 
-	if len(child.Sources.Chain) > 0 {
-		parent.negativeFlag.Sources = ValueSourceChain{Chain: make([]ValueSource, len(child.Sources.Chain))}
+	if len(child.Sources.EnvKeys()) > 0 {
+		sources := []ValueSource{}
 
-		for idx, envVar := range child.GetEnvVars() {
-			parent.negativeFlag.Sources.Chain[idx] = &envVarValueSource{Key: strings.ToUpper(parent.InversePrefix) + envVar}
+		for _, envVar := range child.GetEnvVars() {
+			sources = append(sources, &envVarValueSource{Key: strings.ToUpper(parent.InversePrefix) + envVar})
 		}
+		parent.negativeFlag.Sources = NewValueSourceChain(sources...)
 	}
 }
 

flag_impl.go

@@ -238,15 +238,7 @@ func (f *FlagBase[T, C, V]) GetUsage() string {
 
 // GetEnvVars returns the env vars for this flag
 func (f *FlagBase[T, C, V]) GetEnvVars() []string {
-	vals := []string{}
-
-	for _, src := range f.Sources.Chain {
-		if v, ok := src.(*envVarValueSource); ok {
-			vals = append(vals, v.Key)
-		}
-	}
-
-	return vals
+	return f.Sources.EnvKeys()
 }
 
 // TakesValue returns true if the flag takes a value, otherwise false

godoc-current.txt

@@ -967,6 +967,8 @@ type ValueSource interface {
     ValueSource is a source which can be used to look up a value, typically for
     use with a cli.Flag
 
+func EnvVar(key string) ValueSource
+
 type ValueSourceChain struct {
 	Chain []ValueSource
 }
@@ -981,6 +983,12 @@ func Files(paths ...string) ValueSourceChain
     Files is a helper function to encapsulate a number of fileValueSource
     together as a ValueSourceChain
 
+func NewValueSourceChain(src ...ValueSource) ValueSourceChain
+
+func (vsc *ValueSourceChain) Append(other ValueSourceChain)
+
+func (vsc *ValueSourceChain) EnvKeys() []string
+
 func (vsc *ValueSourceChain) GoString() string
 
 func (vsc *ValueSourceChain) Lookup() (string, bool)

testdata/godoc-v3.x.txt

@@ -967,6 +967,8 @@ type ValueSource interface {
     ValueSource is a source which can be used to look up a value, typically for
     use with a cli.Flag
 
+func EnvVar(key string) ValueSource
+
 type ValueSourceChain struct {
 	Chain []ValueSource
 }
@@ -981,6 +983,12 @@ func Files(paths ...string) ValueSourceChain
     Files is a helper function to encapsulate a number of fileValueSource
     together as a ValueSourceChain
 
+func NewValueSourceChain(src ...ValueSource) ValueSourceChain
+
+func (vsc *ValueSourceChain) Append(other ValueSourceChain)
+
+func (vsc *ValueSourceChain) EnvKeys() []string
+
 func (vsc *ValueSourceChain) GoString() string
 
 func (vsc *ValueSourceChain) Lookup() (string, bool)

value_source.go

@@ -24,6 +24,28 @@ type ValueSourceChain struct {
 	Chain []ValueSource
 }
 
+func NewValueSourceChain(src ...ValueSource) ValueSourceChain {
+	return ValueSourceChain{
+		Chain: src,
+	}
+}
+
+func (vsc *ValueSourceChain) Append(other ValueSourceChain) {
+	vsc.Chain = append(vsc.Chain, other.Chain...)
+}
+
+func (vsc *ValueSourceChain) EnvKeys() []string {
+	vals := []string{}
+
+	for _, src := range vsc.Chain {
+		if v, ok := src.(*envVarValueSource); ok {
+			vals = append(vals, v.Key)
+		}
+	}
+
+	return vals
+}
+
 func (vsc *ValueSourceChain) String() string {
 	s := []string{}
 
@@ -73,6 +95,12 @@ func (e *envVarValueSource) GoString() string {
 	return fmt.Sprintf("&envVarValueSource{Key:%[1]q}", e.Key)
 }
 
+func EnvVar(key string) ValueSource {
+	return &envVarValueSource{
+		Key: key,
+	}
+}
+
 // EnvVars is a helper function to encapsulate a number of
 // envVarValueSource together as a ValueSourceChain
 func EnvVars(keys ...string) ValueSourceChain {

value_source_test.go

@@ -12,13 +12,13 @@ import (
 
 func TestEnvVarValueSource(t *testing.T) {
 	t.Run("implements ValueSource", func(t *testing.T) {
-		src := &envVarValueSource{Key: "foo"}
+		src := EnvVar("foo")
 		require.Implements(t, (*ValueSource)(nil), src)
 
 		t.Run("not found", func(t *testing.T) {
 			t.Setenv("foo", "bar")
 
-			src := &envVarValueSource{Key: "foo_1"}
+			src := EnvVar("foo_1")
 			_, ok := src.Lookup()
 			require.False(t, ok)
 		})
@@ -27,7 +27,7 @@ func TestEnvVarValueSource(t *testing.T) {
 			t.Setenv("foo", "bar")
 
 			r := require.New(t)
-			src := &envVarValueSource{Key: "foo"}
+			src := EnvVar("foo")
 
 			str, ok := src.Lookup()
 			r.True(ok)
@@ -37,15 +37,15 @@ func TestEnvVarValueSource(t *testing.T) {
 	})
 
 	t.Run("implements fmt.Stringer", func(t *testing.T) {
-		src := &envVarValueSource{Key: "foo"}
+		src := EnvVar("foo")
 		r := require.New(t)
 
 		r.Implements((*fmt.Stringer)(nil), src)
 		r.Equal("environment variable \"foo\"", src.String())
 	})
 
 	t.Run("implements fmt.GoStringer", func(t *testing.T) {
-		src := &envVarValueSource{Key: "foo"}
+		src := EnvVar("foo")
 		r := require.New(t)
 
 		r.Implements((*fmt.GoStringer)(nil), src)
@@ -122,6 +122,16 @@ func TestFilePaths(t *testing.T) {
 	r.Contains(src.String(), fmt.Sprintf("%[1]q", fileName))
 }
 
+func TestValueSourceChainEnvKeys(t *testing.T) {
+	chain := NewValueSourceChain(
+		&staticValueSource{"hello"},
+	)
+	chain.Append(EnvVars("foo", "bar"))
+
+	r := require.New(t)
+	r.Equal([]string{"foo", "bar"}, chain.EnvKeys())
+}
+
 func TestValueSourceChain(t *testing.T) {
 	t.Run("implements ValueSource", func(t *testing.T) {
 		vsc := &ValueSourceChain{}
@@ -140,11 +150,10 @@ func TestValueSourceChain(t *testing.T) {
 		r.Implements((*fmt.GoStringer)(nil), vsc)
 		r.Equal("&ValueSourceChain{Chain:{}}", vsc.GoString())
 
-		vsc.Chain = []ValueSource{
-			&staticValueSource{v: "yahtzee"},
+		vsc1 := NewValueSourceChain(&staticValueSource{v: "yahtzee"},
 			&staticValueSource{v: "matzoh"},
-		}
-		r.Equal("&ValueSourceChain{Chain:{&staticValueSource{v:\"yahtzee\"},&staticValueSource{v:\"matzoh\"}}}", vsc.GoString())
+		)
+		r.Equal("&ValueSourceChain{Chain:{&staticValueSource{v:\"yahtzee\"},&staticValueSource{v:\"matzoh\"}}}", vsc1.GoString())
 	})
 
 	t.Run("implements fmt.Stringer", func(t *testing.T) {
@@ -154,12 +163,12 @@ func TestValueSourceChain(t *testing.T) {
 		r.Implements((*fmt.Stringer)(nil), vsc)
 		r.Equal("", vsc.String())
 
-		vsc.Chain = []ValueSource{
+		vsc1 := NewValueSourceChain(
 			&staticValueSource{v: "soup"},
 			&staticValueSource{v: "salad"},
 			&staticValueSource{v: "pumpkins"},
-		}
-		r.Equal("soup,salad,pumpkins", vsc.String())
+		)
+		r.Equal("soup,salad,pumpkins", vsc1.String())
 	})
 }