Treat @skip/@include fields as nullable (#424)

docs/CHANGELOG.md

@@ -14,6 +14,7 @@ When releasing a new version:
 
 ### Bug fixes:
 
+- fields with `@skip` or `@include` are now treated as nullable: under `optional: pointer` or `optional: generic` they generate as a pointer or `Option` and can represent an absent value, instead of silently decoding an absent field to the zero value (#424). This is technically a breaking change for non-null fields with `@skip`/`@include` under those configs.
 -->
 
 ## next

generate/convert.go

@@ -950,8 +950,18 @@ func (g *generator) convertField(
 
 	namePrefix = nextPrefix(namePrefix, field, g.Config.GetDefaultCasingAlgorithm())
 
+	// A field with @skip or @include may be absent from the response even when
+	// its schema type is non-null, so treat it as nullable (like `id: ID` rather
+	// than `id: ID!`) and let the usual optional-handling decide.
+	fieldType := field.Definition.Type
+	if field.Directives.ForName("skip") != nil || field.Directives.ForName("include") != nil {
+		nullableType := *fieldType
+		nullableType.NonNull = false
+		fieldType = &nullableType
+	}
+
 	fieldGoType, err := g.convertType(
-		namePrefix, field.Definition.Type, field.SelectionSet,
+		namePrefix, fieldType, field.SelectionSet,
 		fieldOptions, queryOptions)
 	if err != nil {
 		return nil, err

generate/generate_test.go

@@ -226,6 +226,7 @@ func TestGenerateWithConfig(t *testing.T) {
 			"QueryWithSlices.graphql",
 			"SimpleQueryWithPointerFalseOverride.graphql",
 			"SimpleQueryNoOverride.graphql",
+			"SkipInclude.graphql",
 		}, &Config{
 			Optional: "pointer",
 		}},

generate/testdata/queries/SkipInclude.graphql

@@ -0,0 +1,7 @@
+query SkipInclude($skipId: Boolean!, $includeEmails: Boolean!) {
+  user {
+    id @skip(if: $skipId)
+    name
+    emails @include(if: $includeEmails)
+  }
+}

generate/testdata/snapshots/TestGenerate-SkipInclude.graphql-SkipInclude.graphql.json

@@ -0,0 +1,9 @@
+{
+  "operations": [
+    {
+      "operationName": "SkipInclude",
+      "query": "\nquery SkipInclude ($skipId: Boolean!, $includeEmails: Boolean!) {\n\tuser {\n\t\tid @skip(if: $skipId)\n\t\tname\n\t\temails @include(if: $includeEmails)\n\t}\n}\n",
+      "sourceLocation": "testdata/queries/SkipInclude.graphql"
+    }
+  ]
+}