Only Inject Builtin Scalars if Defined in Schema

codegen/config/config.go

@@ -342,8 +342,6 @@ func (c *Config) InjectBuiltins(s *ast.Schema) {
 		"Float":               {Model: StringList{"github.com/99designs/gqlgen/graphql.Float"}},
 		"String":              {Model: StringList{"github.com/99designs/gqlgen/graphql.String"}},
 		"Boolean":             {Model: StringList{"github.com/99designs/gqlgen/graphql.Boolean"}},
-		"Time":                {Model: StringList{"github.com/99designs/gqlgen/graphql.Time"}},
-		"Map":                 {Model: StringList{"github.com/99designs/gqlgen/graphql.Map"}},
 		"Int": {Model: StringList{
 			"github.com/99designs/gqlgen/graphql.Int",
 			"github.com/99designs/gqlgen/graphql.Int32",
@@ -362,6 +360,18 @@ func (c *Config) InjectBuiltins(s *ast.Schema) {
 			c.Models[typeName] = entry
 		}
 	}
+
+	// These are additional types that are injected if defined in the schema as scalars.
+	extraBuiltins := TypeMap{
+		"Time": {Model: StringList{"github.com/99designs/gqlgen/graphql.Time"}},
+		"Map":  {Model: StringList{"github.com/99designs/gqlgen/graphql.Map"}},
+	}
+
+	for typeName, entry := range extraBuiltins {
+		if t, ok := s.Types[typeName]; ok && t.Kind == ast.Scalar {
+			c.Models[typeName] = entry
+		}
+	}
 }
 
 func (c *Config) LoadSchema() (*ast.Schema, map[string]string, error) {

codegen/testserver/builtinscalar.graphql

@@ -0,0 +1,8 @@
+
+"""
+Since gqlgen defines default implementation for a Map scalar, this tests that the builtin is _not_
+added to the TypeMap
+"""
+type Map {
+    id: ID!
+}

docs/content/reference/scalars.md

@@ -1,14 +1,32 @@
 ---
-linkTitle: Custom Scalars
-title: Using custom graphql types in golang
-description: Defining custom GraphQL scalar types using gqlgen
+linkTitle: Scalars
+title: Mapping GraphQL scalar types to Go types
+description: Mapping GraphQL scalar types to Go types
 menu: { main: { parent: 'reference' } }
 ---
 
-There are two different ways to implement scalars in gqlgen, depending on your need.
+## Built-in helpers
 
+gqlgen ships with two built-in helpers for common custom scalar use-cases, `Time` and `Map`.  Adding either of these to a schema will automatically add the marshalling behaviour to Go types.
+
+### Time
+
+```graphql
+scalar Time
+```
+
+Maps a `Time` GraphQL scalar to a Go `time.Time` struct.
+
+### Map
+
+```graphql
+scalar Map
+```
+
+Maps an arbitrary GraphQL value to a `map[string]{interface}` Go type.
+
+##  Custom scalars with user defined types
 
-## With user defined types
 For user defined types you can implement the graphql.Marshal and graphql.Unmarshal interfaces and they will be called.
 
 ```go
@@ -55,7 +73,7 @@ models:
 ```
 
 
-## Custom scalars for types you don't control
+## Custom scalars with third party types
 
 Sometimes you cant add methods to a type because its in another repo, part of the standard 
 library (eg string or time.Time). To do this we can build an external marshaler: