From d96f4fa77b124dc663ab4bf2ed8f50243c0bcbe5 Mon Sep 17 00:00:00 2001
From: Radek Simko <radek.simko@gmail.com>
Date: Sun, 13 Jan 2019 22:51:05 +0000
Subject: [PATCH] command/format: Ignore removal of empty strings

---
 command/format/diff.go      | 26 +++++++++++++++++++++++---
 command/format/diff_test.go | 21 +++++++++++++++++++++
 2 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/command/format/diff.go b/command/format/diff.go
index a7635e862..b697b1726 100644
--- a/command/format/diff.go
+++ b/command/format/diff.go
@@ -855,13 +855,33 @@ func (p *blockBodyDiffPrinter) pathForcesNewResource(path cty.Path) bool {
 	return p.requiredReplace.Has(path)
 }
 
+func ctyEmptyString(value cty.Value) bool {
+	if !value.IsNull() && value.IsKnown() {
+		valueType := value.Type()
+		if valueType == cty.String && value.AsString() == "" {
+			return true
+		}
+	}
+	return false
+}
+
 func ctyGetAttrMaybeNull(val cty.Value, name string) cty.Value {
+	attrType := val.Type().AttributeType(name)
+
 	if val.IsNull() {
-		ty := val.Type().AttributeType(name)
-		return cty.NullVal(ty)
+		return cty.NullVal(attrType)
 	}
 
-	return val.GetAttr(name)
+	// We treat "" as null here
+	// as existing SDK doesn't support null yet.
+	// This allows us to avoid spurious diffs
+	// until we introduce null to the SDK.
+	attrValue := val.GetAttr(name)
+	if ctyEmptyString(attrValue) {
+		return cty.NullVal(attrType)
+	}
+
+	return attrValue
 }
 
 func ctyCollectionValues(val cty.Value) []cty.Value {
diff --git a/command/format/diff_test.go b/command/format/diff_test.go
index c5c666048..314173fb8 100644
--- a/command/format/diff_test.go
+++ b/command/format/diff_test.go
@@ -48,6 +48,27 @@ func TestResourceChange_primitiveTypes(t *testing.T) {
   - resource "test_instance" "example" {
       - id = "i-02ae66f368e8518a9" -> null
     }
+`,
+		},
+		"deletion (empty string)": {
+			Action: plans.Delete,
+			Mode:   addrs.ManagedResourceMode,
+			Before: cty.ObjectVal(map[string]cty.Value{
+				"id":                 cty.StringVal("i-02ae66f368e8518a9"),
+				"intentionally_long": cty.StringVal(""),
+			}),
+			After: cty.NullVal(cty.EmptyObject),
+			Schema: &configschema.Block{
+				Attributes: map[string]*configschema.Attribute{
+					"id":                 {Type: cty.String, Computed: true},
+					"intentionally_long": {Type: cty.String, Optional: true},
+				},
+			},
+			RequiredReplace: cty.NewPathSet(),
+			ExpectedOutput: `  # test_instance.example will be destroyed
+  - resource "test_instance" "example" {
+      - id = "i-02ae66f368e8518a9" -> null
+    }
 `,
 		},
 		"string in-place update": {