Specifying {} to remove nested fields should yield {}, not nil

typed/remove.go

@@ -19,6 +19,8 @@ import (
 	"sigs.k8s.io/structured-merge-diff/v4/value"
 )
 
+var REMOVEKEEPEMPTYCOLLECTIONS = false
+
 type removingWalker struct {
 	value         value.Value
 	out           interface{}
@@ -58,6 +60,9 @@ func (w *removingWalker) doList(t *schema.List) (errs ValidationErrors) {
 	defer w.allocator.Free(l)
 	// If list is null or empty just return
 	if l == nil || l.Length() == 0 {
+		if REMOVEKEEPEMPTYCOLLECTIONS {
+			w.out = w.value.Unstructured()
+		}
 		return nil
 	}
 
@@ -66,6 +71,10 @@ func (w *removingWalker) doList(t *schema.List) (errs ValidationErrors) {
 	if t.ElementRelationship == schema.Atomic {
 		if w.shouldExtract {
 			w.out = w.value.Unstructured()
+		} else if !w.toRemove.Has(fieldpath.Path{}) && REMOVEKEEPEMPTYCOLLECTIONS {
+			// If the atomic list itself wasn't being removed, then it
+			// is being set to empty list (we only get here if a prefix of this fieldPath is in toRemove)
+			w.out = []interface{}{}
 		}
 		return nil
 	}
@@ -97,7 +106,7 @@ func (w *removingWalker) doList(t *schema.List) (errs ValidationErrors) {
 		}
 		newItems = append(newItems, item.Unstructured())
 	}
-	if len(newItems) > 0 {
+	if len(newItems) > 0 || REMOVEKEEPEMPTYCOLLECTIONS {
 		w.out = newItems
 	}
 	return nil
@@ -113,6 +122,9 @@ func (w *removingWalker) doMap(t *schema.Map) ValidationErrors {
 	}
 	// If map is null or empty just return
 	if m == nil || m.Empty() {
+		if REMOVEKEEPEMPTYCOLLECTIONS {
+			w.out = w.value
+		}
 		return nil
 	}
 
@@ -121,6 +133,10 @@ func (w *removingWalker) doMap(t *schema.Map) ValidationErrors {
 	if t.ElementRelationship == schema.Atomic {
 		if w.shouldExtract {
 			w.out = w.value.Unstructured()
+		} else if !w.toRemove.Has(fieldpath.Path{}) && REMOVEKEEPEMPTYCOLLECTIONS {
+			// If the atomic map itself wasn't being removed, then it
+			// is being set to empty map (we only get here if a prefix of this fieldPath is in toRemove)
+			w.out = map[string]interface{}{}
 		}
 		return nil
 	}
@@ -158,7 +174,7 @@ func (w *removingWalker) doMap(t *schema.Map) ValidationErrors {
 		newMap[k] = val.Unstructured()
 		return true
 	})
-	if len(newMap) > 0 {
+	if len(newMap) > 0 || REMOVEKEEPEMPTYCOLLECTIONS {
 		w.out = newMap
 	}
 	return nil

typed/update_test.go

@@ -0,0 +1,141 @@
+package typed_test
+
+import (
+	"testing"
+
+	"sigs.k8s.io/structured-merge-diff/v4/internal/fixture"
+	"sigs.k8s.io/structured-merge-diff/v4/typed"
+)
+
+var updateParser = func() fixture.Parser {
+	parser, err := typed.NewParser(`
+types:
+- name: nestedOptionalFields
+  map:
+    fields:
+    - name: nestedList
+      type:
+        list:
+          elementRelationship: associative
+          keys:
+          - name
+          elementType:
+            map:
+                fields:
+                - name: name
+                  type:
+                    scalar: string
+                - name: value
+                  type:
+                    scalar: numeric                            
+    - name: nestedMap
+      type:
+        map:
+          elementType:
+            scalar: numeric
+    - name: nested
+      type:
+        map:
+          fields:
+            - name: numeric
+              type:
+                scalar: numeric
+            - name: string
+              type:
+                scalar: string
+`)
+	if err != nil {
+		panic(err)
+	}
+	return fixture.SameVersionParser{T: parser.Type("nestedOptionalFields")}
+}()
+
+func TestUpdate(t *testing.T) {
+	tests := map[string]fixture.TestCase{
+		"delete_nested_fields_struct": {
+			Ops: []fixture.Operation{
+				fixture.Apply{
+					Manager:    "default",
+					APIVersion: "v1",
+					Object: `
+                        nested:
+                            numeric: 1
+                            string: my string
+                    `,
+				},
+				fixture.Apply{
+					Manager:    "default",
+					APIVersion: "v1",
+					Object: `
+                        nested: {}
+                    `,
+				},
+			},
+			APIVersion: `v1`,
+			Object:     `{nested: {}}`,
+		},
+		"delete_nested_fields_list": {
+			Ops: []fixture.Operation{
+				fixture.Apply{
+					Manager:    "default",
+					APIVersion: "v1",
+					Object: `
+                        nestedList:
+                            - name: first
+                            - name: second
+                    `,
+				},
+				fixture.Apply{
+					Manager:    "default",
+					APIVersion: "v1",
+					Object: `
+                        nestedList: []
+                    `,
+				},
+			},
+			APIVersion: `v1`,
+			Object:     `{nestedList: []}`,
+		},
+		"delete_nested_fields_map": {
+			Ops: []fixture.Operation{
+				fixture.Apply{
+					Manager:    "default",
+					APIVersion: "v1",
+					Object: `
+                        nestedMap:
+                            first: 1
+                            second: 2
+
+                    `,
+				},
+				fixture.Apply{
+					Manager:    "default",
+					APIVersion: "v1",
+					Object: `
+                        nestedMap: {}
+                    `,
+				},
+			},
+			APIVersion: `v1`,
+			Object:     `{nestedMap: {}}`,
+		},
+	}
+
+	for name, tc := range tests {
+		tc2 := tc
+		t.Run(name, func(t *testing.T) {
+			typed.REMOVEKEEPEMPTYCOLLECTIONS = true
+			if err := tc.Test(updateParser); err != nil {
+				t.Fatal(err)
+			}
+		})
+
+		t.Run(name+"Nil", func(t *testing.T) {
+			typed.REMOVEKEEPEMPTYCOLLECTIONS = false
+			if err := tc2.Test(updateParser); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+
+}