[Fix] StructToData: allow empty values through for Optional+Computed fields

NEXT_CHANGELOG.md

@@ -8,7 +8,9 @@
 
 ### Bug Fixes
 
+* Fixed `lifecycle { ignore_changes }` not working for `Optional+Computed` fields whose API returns empty values. The shared `StructToData` gate in `common/reflect_resource.go` was silently dropping empty/nil values for all `Optional` fields, including `Computed` ones, causing perpetual `(known after apply)` diffs and preventing `ignore_changes` from preserving externally-set values.
 * Fix `databricks_metastore` so that updating `external_access_enabled` from `true` to `false` is sent in the PATCH request. Previously the field was silently dropped from the request body, so the change never reached the API.
+||||||| parent of 7a333420 ([Fix] StructToData gate: allow empty values through for Optional+Computed fields)
 
 ### Documentation
 

common/reflect_resource_test.go

@@ -973,3 +973,45 @@ func TestStructToData_IndirectString(t *testing.T) {
 	}, scm, d)
 	assert.NoError(t, err)
 }
+
+func TestStructToData_OptionalComputedEmptyMapWrittenToState(t *testing.T) {
+	type Resource struct {
+		Name string            `json:"name"`
+		Tags map[string]string `json:"tags,omitempty"`
+	}
+	s := StructToSchema(Resource{}, func(s map[string]*schema.Schema) map[string]*schema.Schema {
+		s["tags"].Optional = true
+		s["tags"].Computed = true
+		return s
+	})
+	d := schema.TestResourceDataRaw(t, s, map[string]any{"name": "test"})
+	d.SetId("existing-resource")
+	err := StructToData(Resource{Name: "test", Tags: map[string]string{}}, s, d)
+	assert.NoError(t, err)
+	// Optional+Computed empty maps must reach state so ignore_changes and drift
+	// detection work correctly; without the !fieldSchema.Computed guard they
+	// were silently dropped, causing a perpetual "(known after apply)" diff.
+	tags := d.Get("tags")
+	assert.NotNil(t, tags)
+	tagsMap, ok := tags.(map[string]interface{})
+	assert.True(t, ok)
+	assert.Empty(t, tagsMap)
+}
+
+func TestStructToData_OptionalOnlyEmptyMapNotWrittenToState(t *testing.T) {
+	type Resource struct {
+		Name string            `json:"name"`
+		Tags map[string]string `json:"tags,omitempty"`
+	}
+	s := StructToSchema(Resource{}, nil)
+	d := schema.TestResourceDataRaw(t, s, map[string]any{"name": "test"})
+	d.SetId("existing-resource")
+	err := StructToData(Resource{Name: "test", Tags: map[string]string{}}, s, d)
+	assert.NoError(t, err)
+	// Optional-only (non-Computed) empty maps are still filtered to avoid
+	// writing server defaults into state for unconfigured fields.
+	tags := d.Get("tags")
+	tagsMap, ok := tags.(map[string]interface{})
+	assert.True(t, ok)
+	assert.Empty(t, tagsMap)
+}