From f38f80a108071b4e26166d0725812a372a063a04 Mon Sep 17 00:00:00 2001
From: Eric Beard <ericzbeard@gmail.com>
Date: Mon, 4 Mar 2024 15:17:25 -0800
Subject: [PATCH 1/2] empty string and null are the same

---
 cft/diff/compare.go             |  6 +++++
 cft/format/format.go            |  2 --
 cft/format/format_test.go       | 48 +++++++++++++++++++++++++++++++++
 cft/format/transform.go         |  2 ++
 test/templates/getazs-null.yaml | 13 +++++++++
 5 files changed, 69 insertions(+), 2 deletions(-)
 create mode 100644 test/templates/getazs-null.yaml

diff --git a/cft/diff/compare.go b/cft/diff/compare.go
index 9526947f..3e3b16ec 100644
--- a/cft/diff/compare.go
+++ b/cft/diff/compare.go
@@ -14,6 +14,12 @@ func New(a, b cft.Template) Diff {
 
 func compareValues(old, new interface{}) Diff {
 	if reflect.TypeOf(old) != reflect.TypeOf(new) {
+
+		// In YAML there is no difference between "" and null
+		if old == "" && new == nil {
+			return value{new, Unchanged}
+		}
+
 		return value{new, Changed}
 	}
 
diff --git a/cft/format/format.go b/cft/format/format.go
index 213ca644..4b045ef9 100644
--- a/cft/format/format.go
+++ b/cft/format/format.go
@@ -33,8 +33,6 @@ func CheckMultilineBegin(s string) bool {
 func String(t cft.Template, opt Options) string {
 	node := t.Node
 
-	// config.Debugf("%v", rnode.ToSJson(node))
-
 	buf := strings.Builder{}
 	enc := yaml.NewEncoder(&buf)
 	enc.SetIndent(2)
diff --git a/cft/format/format_test.go b/cft/format/format_test.go
index c59d1919..e49065d4 100644
--- a/cft/format/format_test.go
+++ b/cft/format/format_test.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/aws-cloudformation/rain/cft/format"
 	"github.com/aws-cloudformation/rain/cft/parse"
+	"github.com/aws-cloudformation/rain/internal/config"
 	"github.com/google/go-cmp/cmp"
 )
 
@@ -717,3 +718,50 @@ Parameters:
 	}
 
 }
+
+func TestFnGetAZs(t *testing.T) {
+	input := `
+Resources:
+  PrivateSubnet1Subnet:
+    Type: AWS::EC2::Subnet
+    Properties:
+      AvailabilityZone: !Select
+        - 0
+        - !GetAZs ""
+`
+
+	// Parse the template
+	source, err := parse.String(string(input))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	config.Debug = true
+
+	output := format.String(source, format.Options{
+		JSON:     false,
+		Unsorted: true,
+	})
+
+	config.Debugf("TestFnGetAZs output: %s", output)
+
+	// Verify the output is valid
+	if err = parse.Verify(source, output); err != nil {
+		t.Fatal(err)
+	}
+
+	expected := `
+Resources:
+  PrivateSubnet1Subnet:
+    Type: AWS::EC2::Subnet
+    Properties:
+      AvailabilityZone: !Select
+        - 0
+        - !GetAZs 
+`
+
+	if strings.TrimSpace(output) != strings.TrimSpace(expected) {
+		t.Fatalf("Got:\n%s\n\nExpected:\n%s", output, expected)
+	}
+
+}
diff --git a/cft/format/transform.go b/cft/format/transform.go
index 433b32f1..9bc5cb15 100644
--- a/cft/format/transform.go
+++ b/cft/format/transform.go
@@ -28,6 +28,7 @@ func formatNode(n *yaml.Node) *yaml.Node {
 	if n.Kind == yaml.MappingNode {
 		// Does it have just one key/value pair?
 		if len(n.Content) == 2 {
+
 			// Is the key relevant?
 			for tag, funcName := range cft.Tags {
 				if n.Content[0].Value == funcName {
@@ -85,6 +86,7 @@ func formatNode(n *yaml.Node) *yaml.Node {
 					n.Style = newNode.Content[0].Style
 				}
 			}
+
 		}
 	}
 
diff --git a/test/templates/getazs-null.yaml b/test/templates/getazs-null.yaml
new file mode 100644
index 00000000..76f7c781
--- /dev/null
+++ b/test/templates/getazs-null.yaml
@@ -0,0 +1,13 @@
+Parameters:
+  VpcId:
+    Type: String
+
+Resources:
+
+  PrivateSubnet1Subnet:
+    Type: AWS::EC2::Subnet
+    Properties:
+      AvailabilityZone: !Select
+        - 0
+        - !GetAZs ""
+      VpcId: !Ref VpcId

From 3ffd1ab6b7361925696e51b556281106c7d38eed Mon Sep 17 00:00:00 2001
From: Eric Beard <ericzbeard@gmail.com>
Date: Mon, 4 Mar 2024 15:20:17 -0800
Subject: [PATCH 2/2] Remove debugs

---
 cft/format/format_test.go | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/cft/format/format_test.go b/cft/format/format_test.go
index e49065d4..ef15537a 100644
--- a/cft/format/format_test.go
+++ b/cft/format/format_test.go
@@ -7,7 +7,6 @@ import (
 
 	"github.com/aws-cloudformation/rain/cft/format"
 	"github.com/aws-cloudformation/rain/cft/parse"
-	"github.com/aws-cloudformation/rain/internal/config"
 	"github.com/google/go-cmp/cmp"
 )
 
@@ -736,15 +735,11 @@ Resources:
 		t.Fatal(err)
 	}
 
-	config.Debug = true
-
 	output := format.String(source, format.Options{
 		JSON:     false,
 		Unsorted: true,
 	})
 
-	config.Debugf("TestFnGetAZs output: %s", output)
-
 	// Verify the output is valid
 	if err = parse.Verify(source, output); err != nil {
 		t.Fatal(err)