From f6c35be2128d8d0ec6c0c0d63bc0f135292ab5fe Mon Sep 17 00:00:00 2001
From: Thomas Prebble <6523587+tprebs@users.noreply.github.com>
Date: Wed, 13 Oct 2021 14:12:52 +0100
Subject: [PATCH] Add ReplacePlugin option to replace a specific plugin (#1657)

* Add Helper Option for replacing plugins

* Update recipe to use ReplacePlugin instead of NoPlugin and AddPlugin

* fix linting issue on comment
---
 api/option.go                         | 20 +++++++++
 api/option_test.go                    | 58 +++++++++++++++++++++++++++
 docs/content/recipes/modelgen-hook.md | 18 ++++-----
 3 files changed, 85 insertions(+), 11 deletions(-)
 create mode 100644 api/option_test.go

diff --git a/api/option.go b/api/option.go
index f7ba6774bd..ab41dfa205 100644
--- a/api/option.go
+++ b/api/option.go
@@ -18,3 +18,23 @@ func AddPlugin(p plugin.Plugin) Option {
 		*plugins = append(*plugins, p)
 	}
 }
+
+// ReplacePlugin replaces any existing plugin with a matching plugin name
+func ReplacePlugin(p plugin.Plugin) Option {
+	return func(cfg *config.Config, plugins *[]plugin.Plugin) {
+		if plugins != nil {
+			found := false
+			ps := *plugins
+			for i, o := range ps {
+				if p.Name() == o.Name() {
+					ps[i] = p
+					found = true
+				}
+			}
+			if !found {
+				ps = append(ps, p)
+			}
+			*plugins = ps
+		}
+	}
+}
diff --git a/api/option_test.go b/api/option_test.go
new file mode 100644
index 0000000000..749e29dd40
--- /dev/null
+++ b/api/option_test.go
@@ -0,0 +1,58 @@
+package api
+
+import (
+	"testing"
+
+	"github.com/99designs/gqlgen/codegen/config"
+	"github.com/99designs/gqlgen/plugin"
+	"github.com/99designs/gqlgen/plugin/federation"
+	"github.com/99designs/gqlgen/plugin/modelgen"
+	"github.com/99designs/gqlgen/plugin/resolvergen"
+	"github.com/stretchr/testify/require"
+)
+
+type testPlugin struct {
+}
+
+// Name returns the plugin name
+func (t *testPlugin) Name() string {
+	return "modelgen"
+}
+
+// MutateConfig mutates the configuration
+func (t *testPlugin) MutateConfig(_ *config.Config) error {
+	return nil
+}
+
+func TestReplacePlugin(t *testing.T) {
+
+	t.Run("replace plugin if exists", func(t *testing.T) {
+		pg := []plugin.Plugin{
+			federation.New(),
+			modelgen.New(),
+			resolvergen.New(),
+		}
+
+		expectedPlugin := &testPlugin{}
+		ReplacePlugin(expectedPlugin)(config.DefaultConfig(), &pg)
+
+		require.EqualValues(t, federation.New(), pg[0])
+		require.EqualValues(t, expectedPlugin, pg[1])
+		require.EqualValues(t, resolvergen.New(), pg[2])
+	})
+
+	t.Run("add plugin if doesn't exist", func(t *testing.T) {
+		pg := []plugin.Plugin{
+			federation.New(),
+			resolvergen.New(),
+		}
+
+		expectedPlugin := &testPlugin{}
+		ReplacePlugin(expectedPlugin)(config.DefaultConfig(), &pg)
+
+		require.EqualValues(t, federation.New(), pg[0])
+		require.EqualValues(t, resolvergen.New(), pg[1])
+		require.EqualValues(t, expectedPlugin, pg[2])
+	})
+
+}
diff --git a/docs/content/recipes/modelgen-hook.md b/docs/content/recipes/modelgen-hook.md
index eb65d625c2..695ca74cb9 100644
--- a/docs/content/recipes/modelgen-hook.md
+++ b/docs/content/recipes/modelgen-hook.md
@@ -49,10 +49,8 @@ func main() {
 		MutateHook: mutateHook,
 	}
 
-	err = api.Generate(cfg,
-		api.NoPlugins(),
-		api.AddPlugin(&p),
-	)
+	err = api.Generate(cfg, api.ReplacePlugin(&p))
+
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err.Error())
 		os.Exit(3)
@@ -82,7 +80,7 @@ type Object struct {
 
 ## FieldMutateHook
 
-For more fine grained control over model generation, a graphql schema aware a FieldHook can be provided. This hook has access to type and field graphql definitions enabling the hook to modify the `modelgen.Field` using directives defined within the schema. 
+For more fine grained control over model generation, a graphql schema aware a FieldHook can be provided. This hook has access to type and field graphql definitions enabling the hook to modify the `modelgen.Field` using directives defined within the schema.
 
 The below recipe uses this feature to add validate tags to the generated model for use with `go-playground/validator` where the validate tags are defined in a constraint directive in the schema.
 
@@ -103,11 +101,11 @@ func constraintFieldHook(td *ast.Definition, fd *ast.FieldDefinition, f *modelge
 	c := fd.Directives.ForName("constraint")
 	if c != nil {
 		formatConstraint := c.Arguments.ForName("format")
-		
+
 		if formatConstraint != nil{
 			f.Tag += " validate:"+formatConstraint.Value.String()
 		}
-		
+
 	}
 
 	return f, nil
@@ -125,10 +123,8 @@ func main() {
 		FieldHook: constraintFieldHook,
 	}
 
-	err = api.Generate(cfg,
-		api.NoPlugins(),
-		api.AddPlugin(&p),
-	)
+	err = api.Generate(cfg, api.ReplacePlugin(&p))
+
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err.Error())
 		os.Exit(3)