Implement scalar leafs validator

ast.go

@@ -172,12 +172,17 @@ type Directive struct {
 
 type Type interface {
 	Name() string
+	String() string
 }
 
 func (t NamedType) Name() string   { return string(t) }
 func (t ListType) Name() string    { return t.Type.Name() }
 func (t NonNullType) Name() string { return t.Type.Name() }
 
+func (t NamedType) String() string   { return string(t) }
+func (t ListType) String() string    { return "[" + t.Type.Name() + "]" }
+func (t NonNullType) String() string { return t.Type.Name() + "!" }
+
 type NamedType string
 
 type ListType struct {
@@ -238,6 +243,10 @@ func (d *Definition) Field(name string) *FieldDefinition {
 	return nil
 }
 
+func (d *Definition) IsLeafType() bool {
+	return d.Kind == Enum || d.Kind == Scalar
+}
+
 func (d *Definition) IsAbstractType() bool {
 	return d.Kind == Interface || d.Kind == Union
 }

validator/error.go

@@ -30,11 +30,17 @@ func Message(msg string, args ...interface{}) Option {
 	}
 }
 
-func Suggest(typed string, suggestions []string) Option {
+func SuggestList(typed string, suggestions []string) Option {
 	suggested := suggestionList(typed, suggestions)
 	return func(err *errors.Validation) {
 		if len(suggested) > 0 {
 			err.Message += " Did you mean " + quotedOrList(suggested...) + "?"
 		}
 	}
 }
+
+func Suggestf(suggestion string, args ...interface{}) Option {
+	return func(err *errors.Validation) {
+		err.Message += " Did you mean " + fmt.Sprintf(suggestion, args...) + "?"
+	}
+}

validator/known_argument_names.go

@@ -28,7 +28,7 @@ func knownFieldArgumentNames(ctx *vctx, parentDef *gqlparser.Definition, fieldDe
 		ctx.errors = append(ctx.errors, Error(
 			Rule("KnownArgumentNames"),
 			Message(`Unknown argument "%s" on field "%s" of type "%s".`, arg.Name, field.Name, parentDef.Name),
-			Suggest(arg.Name, suggestions),
+			SuggestList(arg.Name, suggestions),
 		))
 	}
 }
@@ -51,7 +51,7 @@ func knowDirectiveArgumentNames(ctx *vctx, parentDef *gqlparser.Definition, dire
 		ctx.errors = append(ctx.errors, Error(
 			Rule("KnownArgumentNames"),
 			Message(`Unknown argument "%s" on directive "@%s".`, arg.Name, directive.Name),
-			Suggest(arg.Name, suggestions),
+			SuggestList(arg.Name, suggestions),
 		))
 	}
 }

validator/scalar_leafs.go

@@ -0,0 +1,33 @@
+package validator
+
+import "github.com/vektah/gqlparser"
+
+func init() {
+	fieldVisitors = append(fieldVisitors, scalarLeafs)
+}
+
+func scalarLeafs(ctx *vctx, parentDef *gqlparser.Definition, fieldDef *gqlparser.FieldDefinition, field *gqlparser.Field) {
+	if fieldDef == nil {
+		return
+	}
+
+	fieldType := ctx.schema.Types[fieldDef.Type.Name()]
+	if fieldType == nil {
+		return
+	}
+
+	if fieldType.IsLeafType() && len(field.SelectionSet) > 0 {
+		ctx.errors = append(ctx.errors, Error(
+			Rule("ScalarLeafs"),
+			Message(`Field "%s" must not have a selection since type "%s" has no subfields.`, field.Name, fieldType.Name),
+		))
+	}
+
+	if !fieldType.IsLeafType() && len(field.SelectionSet) == 0 {
+		ctx.errors = append(ctx.errors, Error(
+			Rule("ScalarLeafs"),
+			Message(`Field "%s" of type "%s" must have a selection of subfields.`, field.Name, fieldDef.Type.String()),
+			Suggestf(`"%s { ... }"`, field.Name),
+		))
+	}
+}

validator/validate_test.go

@@ -40,6 +40,8 @@ func TestSpec(t *testing.T) {
 	t.Run("FragmentsOnCompositeTypes", runSpec(schemas, deviations, "../spec/validation/FragmentsOnCompositeTypes.yml"))
 	t.Run("KnownArgumentNames", runSpec(schemas, deviations, "../spec/validation/KnownArgumentNames.yml"))
 	t.Run("KnownDirectives", runSpec(schemas, deviations, "../spec/validation/KnownDirectives.yml"))
+
+	t.Run("ScalarLeafs", runSpec(schemas, deviations, "../spec/validation/ScalarLeafs.yml"))
 }
 
 func runSpec(schemas []*gqlparser.Schema, deviations map[string]*Spec, filename string) func(t *testing.T) {