From 2899bb19b8ff274f1056f19efe2bb3cfe59d0709 Mon Sep 17 00:00:00 2001
From: Martin Helmich <m.helmich@mittwald.de>
Date: Fri, 5 Jan 2024 11:37:10 +0100
Subject: [PATCH] Fix panic when a nil *uuid.UUID is provided

---
 go.mod                            |  1 +
 go.sum                            |  2 ++
 internal/valueutil/string.go      | 19 ++++++++++++++++++-
 internal/valueutil/string_test.go | 31 +++++++++++++++++++++++++++++++
 4 files changed, 52 insertions(+), 1 deletion(-)
 create mode 100644 internal/valueutil/string_test.go

diff --git a/go.mod b/go.mod
index 30daa14..4f2a151 100644
--- a/go.mod
+++ b/go.mod
@@ -65,6 +65,7 @@ require (
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/mohae/deepcopy v0.0.0-20170929034955-c48cc78d4826 // indirect
 	github.com/oklog/run v1.0.0 // indirect
+	github.com/onsi/gomega v1.30.0 // indirect
 	github.com/perimeterx/marshmallow v1.1.5 // indirect
 	github.com/posener/complete v1.2.3 // indirect
 	github.com/russross/blackfriday v1.6.0 // indirect
diff --git a/go.sum b/go.sum
index b1a37fb..7af9296 100644
--- a/go.sum
+++ b/go.sum
@@ -192,6 +192,8 @@ github.com/oapi-codegen/runtime v1.1.0 h1:rJpoNUawn5XTvekgfkvSZr0RqEnoYpFkyvrzfW
 github.com/oapi-codegen/runtime v1.1.0/go.mod h1:BeSfBkWWWnAnGdyS+S/GnlbmHKzf8/hwkvelJZDeKA8=
 github.com/oklog/run v1.0.0 h1:Ru7dDtJNOyC66gQ5dQmaCa0qIsAUFY3sFpK1Xk8igrw=
 github.com/oklog/run v1.0.0/go.mod h1:dlhp/R75TPv97u0XWUtDeV/lRKWPKSdTuV0TZvrmrQA=
+github.com/onsi/gomega v1.30.0 h1:hvMK7xYz4D3HapigLTeGdId/NcfQx1VHMJc60ew99+8=
+github.com/onsi/gomega v1.30.0/go.mod h1:9sxs+SwGrKI0+PWe4Fxa9tFQQBG5xSsSbMXOI8PPpoQ=
 github.com/perimeterx/marshmallow v1.1.5 h1:a2LALqQ1BlHM8PZblsDdidgv1mWi1DgC2UmX50IvK2s=
 github.com/perimeterx/marshmallow v1.1.5/go.mod h1:dsXbUu8CRzfYP5a87xpp0xq9S3u0Vchtcl8we9tYaXw=
 github.com/pjbgf/sha1cd v0.3.0 h1:4D5XXmUUBUl/xQ6IjCkEAbqXskkq/4O7LmGn0AqMDs4=
diff --git a/internal/valueutil/string.go b/internal/valueutil/string.go
index 324a485..e14a850 100644
--- a/internal/valueutil/string.go
+++ b/internal/valueutil/string.go
@@ -3,6 +3,7 @@ package valueutil
 import (
 	"fmt"
 	"github.com/hashicorp/terraform-plugin-framework/types"
+	"reflect"
 )
 
 func StringOrNull[T string](s T) types.String {
@@ -20,8 +21,24 @@ func StringPtrOrNull[T ~string](s *T) types.String {
 }
 
 func StringerOrNull(s fmt.Stringer) types.String {
-	if s == nil {
+	if isReallyNil(s) {
 		return types.StringNull()
 	}
 	return types.StringValue(s.String())
 }
+
+func isReallyNil(v any) bool {
+	if v == nil {
+		return true
+	}
+
+	rv := reflect.ValueOf(v)
+	switch rv.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
+		return rv.IsNil()
+	case reflect.Array:
+		return rv.Len() == 0
+	default:
+		return false
+	}
+}
diff --git a/internal/valueutil/string_test.go b/internal/valueutil/string_test.go
new file mode 100644
index 0000000..03d9399
--- /dev/null
+++ b/internal/valueutil/string_test.go
@@ -0,0 +1,31 @@
+package valueutil
+
+import (
+	"github.com/google/uuid"
+	. "github.com/onsi/gomega"
+	"testing"
+)
+
+func TestStringerOrNullAcceptsStringer(t *testing.T) {
+	g := NewWithT(t)
+	u := uuid.New()
+	s := StringerOrNull(u)
+
+	g.Expect(s.IsNull()).To(BeFalse())
+	g.Expect(s.ValueString()).To(Equal(u.String()))
+}
+
+func TestStringerOrNullAcceptsNil(t *testing.T) {
+	g := NewWithT(t)
+	s := StringerOrNull(nil)
+
+	g.Expect(s.IsNull()).To(BeTrue())
+}
+
+func TestStringerOrNullAcceptsNilInterface(t *testing.T) {
+	g := NewWithT(t)
+	u := (*uuid.UUID)(nil)
+	s := StringerOrNull(u)
+
+	g.Expect(s.IsNull()).To(BeTrue())
+}