envconfig: fix bug where slice data is deleted

envconfig.go

@@ -184,7 +184,12 @@ func gatherInfo(prefix string, spec interface{}, env map[string]string, isInside
 				}
 			}
 
-			f.Set(reflect.MakeSlice(f.Type(), l, l))
+			if l != 0 {
+				f.Set(reflect.MakeSlice(f.Type(), l, l))
+			} else {
+				l = f.Len()
+			}
+
 			for i := 0; i < l; i++ {
 				var structPtrValue reflect.Value
 

envconfig_test.go

@@ -14,8 +14,66 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+type (
+	Config struct {
+		Generators []struct {
+			Input Input
+		}
+	}
+
+	Input struct {
+		Type string `envconfig:"TEST"`
+	}
 )
 
+func TestStilLoadsSecrets(t *testing.T) {
+	os.Clearenv()
+	os.Setenv("WORKER_GENERATORS_0_INPUT_TEST", "test")
+
+	config := Config{
+		Generators: []struct {
+			Input Input
+		}{
+			{
+				Input: Input{
+					Type: "foo",
+				},
+			},
+			{
+				Input: Input{
+					Type: "haha",
+				},
+			},
+		},
+	}
+
+	require.NoError(t, Process("WORKER", &config))
+	require.Len(t, config.Generators, 1)
+	require.Equal(t, "test", config.Generators[0].Input.Type)
+}
+
+func TestNotNukesStructs(t *testing.T) {
+	config := Config{
+		Generators: []struct {
+			Input Input
+		}{
+			{
+				Input: Input{
+					Type: "foo",
+				},
+			},
+		},
+	}
+
+	require.NoError(t, Process("WORKER", &config))
+	require.Len(t, config.Generators, 1)
+	require.Equal(t, "foo", config.Generators[0].Input.Type)
+}
+
 type HonorDecodeInStruct struct {
 	Value string
 }

go.mod

@@ -1,3 +1,5 @@
 module github.com/colega/envconfig
 
 go 1.14
+
+require github.com/stretchr/testify v1.8.1 // indirect

go.sum

@@ -0,0 +1,16 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
+github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
+github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=