Add support for mapping all nullable types as pointers (Khan#198)

This implements the approach suggested in
Khan#178 (comment).
See the added documentation for the full behavior.

docs/CHANGELOG.md

@@ -31,6 +31,7 @@ When releasing a new version:
 - You can now enable `use_extensions` in the configuration file, to receive extensions returned by the GraphQL API server. Generated functions will return extensions as `map[string]interface{}`, if enabled.
 - You can now use `graphql.NewClientUsingGet` to create a client that uses query parameters to pass the query to the GraphQL API server.
 - In config files, `schema`, `operations`, and `generated` can now be absolute paths.
+- You can now configure how nullable types are mapped to Go types in the configuration file. Specifically, you can set `optional: pointer` to have all nullable GraphQL arguments, input fields, and output fields map to pointers.
 
 ### Bug fixes:
 

docs/genqlient.yaml

@@ -98,6 +98,23 @@ use_struct_references: boolean
 use_extensions: boolean
 
 
+# Customize how optional fields are handled.
+optional:
+  # Customize how models are generated for optional fields. This can currently
+  # be set to one of the following values:
+  # - value (default): optional fields are generated as values, the same as
+  #   non-optional fields. E.g. fields with GraphQL types `String` or `String!`
+  #   will both map to the Go type `string`. When values are absent in
+  #   responses the zero value will be used.
+  # - pointer: optional fields are generated as pointers. E.g. fields with
+  #   GraphQL type `String` will map to the Go type `*string`. When values are
+  #   absent in responses `nil` will be used. Optional list fields do not use
+  #   pointers-to-slices, so the GraphQL type `[String]` will map to the Go
+  #   type `[]*string`, not `*[]*string`; GraphQL null and empty list simply
+  #   map to Go nil- and empty-slice.
+  output: value
+
+
 # A map from GraphQL type name to Go fully-qualified type name to override
 # the Go type genqlient will use for this GraphQL type.
 #

generate/config.go

@@ -26,6 +26,7 @@ type Config struct {
 	ContextType      string                  `yaml:"context_type"`
 	ClientGetter     string                  `yaml:"client_getter"`
 	Bindings         map[string]*TypeBinding `yaml:"bindings"`
+	Optional         string                  `yaml:"optional"`
 	StructReferences bool                    `yaml:"use_struct_references"`
 	Extensions       bool                    `yaml:"use_extensions"`
 

generate/convert.go

@@ -256,7 +256,7 @@ func (g *generator) convertType(
 			oe := true
 			options.Omitempty = &oe
 		}
-	} else if options.GetPointer() {
+	} else if options.GetPointer() || (!typ.NonNull && g.Config.Optional == "pointer") {
 		// Whatever we get, wrap it in a pointer.  (Because of the way the
 		// options work, recursing here isn't as connvenient.)
 		// Note this does []*T or [][]*T, not e.g. *[][]T.  See #16.

generate/generate_test.go

@@ -147,55 +147,64 @@ func getDefaultConfig(t *testing.T) *Config {
 // configurations.  It uses snapshots, just like TestGenerate.
 func TestGenerateWithConfig(t *testing.T) {
 	tests := []struct {
-		name    string
-		baseDir string  // relative to dataDir
-		config  *Config // omits Schema and Operations, set below.
+		name       string
+		baseDir    string   // relative to dataDir
+		operations []string // overrides the default set below
+		config     *Config  // omits Schema and Operations, set below.
 	}{
-		{"DefaultConfig", "", getDefaultConfig(t)},
-		{"Subpackage", "", &Config{
+		{"DefaultConfig", "", nil, getDefaultConfig(t)},
+		{"Subpackage", "", nil, &Config{
 			Generated: "mypkg/myfile.go",
 		}},
-		{"SubpackageConfig", "mypkg", &Config{
+		{"SubpackageConfig", "mypkg", nil, &Config{
 			Generated: "myfile.go", // (relative to genqlient.yaml)
 		}},
-		{"PackageName", "", &Config{
+		{"PackageName", "", nil, &Config{
 			Generated: "myfile.go",
 			Package:   "mypkg",
 		}},
-		{"ExportOperations", "", &Config{
+		{"ExportOperations", "", nil, &Config{
 			Generated:        "generated.go",
 			ExportOperations: "operations.json",
 		}},
-		{"CustomContext", "", &Config{
+		{"CustomContext", "", nil, &Config{
 			Generated:   "generated.go",
 			ContextType: "github.com/Khan/genqlient/internal/testutil.MyContext",
 		}},
-		{"StructReferences", "", &Config{
+		{"StructReferences", "", nil, &Config{
 			StructReferences: true,
 			Generated:        "generated-structrefs.go",
 		}},
-		{"NoContext", "", &Config{
+		{"NoContext", "", nil, &Config{
 			Generated:   "generated.go",
 			ContextType: "-",
 		}},
-		{"ClientGetter", "", &Config{
+		{"ClientGetter", "", nil, &Config{
 			Generated:    "generated.go",
 			ClientGetter: "github.com/Khan/genqlient/internal/testutil.GetClientFromContext",
 		}},
-		{"ClientGetterCustomContext", "", &Config{
+		{"ClientGetterCustomContext", "", nil, &Config{
 			Generated:    "generated.go",
 			ClientGetter: "github.com/Khan/genqlient/internal/testutil.GetClientFromMyContext",
 			ContextType:  "github.com/Khan/genqlient/internal/testutil.MyContext",
 		}},
-		{"ClientGetterNoContext", "", &Config{
+		{"ClientGetterNoContext", "", nil, &Config{
 			Generated:    "generated.go",
 			ClientGetter: "github.com/Khan/genqlient/internal/testutil.GetClientFromNowhere",
 			ContextType:  "-",
 		}},
-		{"Extensions", "", &Config{
+		{"Extensions", "", nil, &Config{
 			Generated:  "generated.go",
 			Extensions: true,
 		}},
+		{"OptionalValue", "", []string{"ListInput.graphql", "QueryWithSlices.graphql"}, &Config{
+			Generated: "generated.go",
+			Optional:  "value",
+		}},
+		{"OptionalPointer", "", []string{"ListInput.graphql", "QueryWithSlices.graphql"}, &Config{
+			Generated: "generated.go",
+			Optional:  "pointer",
+		}},
 	}
 
 	sourceFilename := "SimpleQuery.graphql"
@@ -206,7 +215,14 @@ func TestGenerateWithConfig(t *testing.T) {
 		t.Run(test.name, func(t *testing.T) {
 			err := config.ValidateAndFillDefaults(baseDir)
 			config.Schema = []string{filepath.Join(dataDir, "schema.graphql")}
-			config.Operations = []string{filepath.Join(dataDir, sourceFilename)}
+			if test.operations == nil {
+				config.Operations = []string{filepath.Join(dataDir, sourceFilename)}
+			} else {
+				config.Operations = make([]string, len(test.operations))
+				for i := range test.operations {
+					config.Operations[i] = filepath.Join(dataDir, test.operations[i])
+				}
+			}
 			if err != nil {
 				t.Fatal(err)
 			}