internal/tagresource: Initial generator for individual tag resources,…

… switch aws_ec2_tag implementation

Reference: #9061

Output from acceptance testing:

```
--- PASS: TestAccAWSEc2Tag_disappears (429.66s)
--- PASS: TestAccAWSEc2Tag_Value (530.85s)
--- PASS: TestAccAWSEc2Tag_basic (537.38s)
```

GNUmakefile

@@ -12,6 +12,7 @@ build: fmtcheck
 	go install
 
 gen:
+	rm -f aws/*_gen.go aws/*_gen_test.go
 	rm -f aws/internal/keyvaluetags/*_gen.go
 	go generate ./...
 

aws/internal/tagresource/README.md

@@ -0,0 +1,13 @@
+# tagresource
+
+The `tagresource` package is designed to provide a generator and consistent interface for Terraform AWS Provider resources that handle individual resource tags. Most of the heavy lifting is done by the `keyvaluetags` package to smooth over inconsistencies across AWS service APIs, but this generator does implement some final user experience improvements.
+
+## Code Structure
+
+```text
+aws/internal/tagresource
+├── generator/main.go (generates tag resource)
+├── tag_resources_test.go (unit tests for shared tag resource logic)
+├── tag_resources.go (shared tag resource logic)
+└── service_generation_customizations.go (AWS Go SDK service customizations for generator)
+```

aws/internal/tagresource/generator/main.go

@@ -0,0 +1,288 @@
+// +build ignore
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/format"
+	"log"
+	"os"
+	"strings"
+	"text/template"
+
+	"github.com/terraform-providers/terraform-provider-aws/aws/internal/tagresource"
+)
+
+var (
+	serviceName = flag.String("servicename", "", "lowercase service name")
+)
+
+type TemplateData struct {
+	ServiceName string
+}
+
+func main() {
+	flag.Parse()
+
+	if len(*serviceName) == 0 {
+		flag.Usage()
+		os.Exit(2)
+	}
+
+	resourceName := fmt.Sprintf("aws_%s_tag", *serviceName)
+	resourceFilename := fmt.Sprintf("resource_%s_gen.go", resourceName)
+	resourceTestFilename := fmt.Sprintf("resource_%s_gen_test.go", resourceName)
+
+	templateData := TemplateData{
+		ServiceName: *serviceName,
+	}
+	templateFuncMap := template.FuncMap{
+		"IdentifierAttributeName": tagresource.ServiceIdentifierAttributeName,
+		"Title":                   strings.Title,
+	}
+
+	if err := generateTemplateFile(resourceFilename, resourceTemplateBody, templateFuncMap, templateData); err != nil {
+		log.Fatal(err)
+	}
+
+	if err := generateTemplateFile(resourceTestFilename, resourceTestTemplateBody, templateFuncMap, templateData); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func generateTemplateFile(filename string, templateBody string, templateFuncs template.FuncMap, templateData interface{}) error {
+	tmpl, err := template.New(filename).Funcs(templateFuncs).Parse(templateBody)
+
+	if err != nil {
+		return fmt.Errorf("error parsing template: %w", err)
+	}
+
+	var buffer bytes.Buffer
+	err = tmpl.Execute(&buffer, templateData)
+
+	if err != nil {
+		return fmt.Errorf("error executing template: %w", err)
+	}
+
+	generatedFileContents, err := format.Source(buffer.Bytes())
+
+	if err != nil {
+		return fmt.Errorf("error formatting generated file: %w", err)
+	}
+
+	f, err := os.Create(filename)
+
+	if err != nil {
+		return fmt.Errorf("error creating file (%s): %w", filename, err)
+	}
+
+	defer f.Close()
+
+	_, err = f.Write(generatedFileContents)
+
+	if err != nil {
+		return fmt.Errorf("error writing to file (%s): %w", filename, err)
+	}
+
+	return nil
+}
+
+const (
+	resourceTemplateBody = `
+// Code generated by internal/tagresource/generator/main.go; DO NOT EDIT.
+
+package aws
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/hashicorp/terraform-plugin-sdk/helper/schema"
+	"github.com/terraform-providers/terraform-provider-aws/aws/internal/keyvaluetags"
+	"github.com/terraform-providers/terraform-provider-aws/aws/internal/tagresource"
+)
+
+func resourceAws{{ .ServiceName | Title }}Tag() *schema.Resource {
+	return &schema.Resource{
+		Create: resourceAws{{ .ServiceName | Title }}TagCreate,
+		Read:   resourceAws{{ .ServiceName | Title }}TagRead,
+		Update: resourceAws{{ .ServiceName | Title }}TagUpdate,
+		Delete: resourceAws{{ .ServiceName | Title }}TagDelete,
+		Importer: &schema.ResourceImporter{
+			State: schema.ImportStatePassthrough,
+		},
+
+		Schema: map[string]*schema.Schema{
+			"{{ .ServiceName | IdentifierAttributeName }}": {
+				Type:     schema.TypeString,
+				Required: true,
+				ForceNew: true,
+			},
+			"key": {
+				Type:     schema.TypeString,
+				Required: true,
+				ForceNew: true,
+			},
+			"value": {
+				Type:     schema.TypeString,
+				Required: true,
+			},
+		},
+	}
+}
+
+func resourceAws{{ .ServiceName | Title }}TagCreate(d *schema.ResourceData, meta interface{}) error {
+	conn := meta.(*AWSClient).{{ .ServiceName }}conn
+
+	identifier := d.Get("{{ .ServiceName | IdentifierAttributeName }}").(string)
+	key := d.Get("key").(string)
+	value := d.Get("value").(string)
+
+	{{ if eq .ServiceName "ec2" }}
+	if err := keyvaluetags.{{ .ServiceName | Title }}CreateTags(conn, identifier, map[string]string{key: value}); err != nil {
+	{{- else }}
+	if err := keyvaluetags.{{ .ServiceName | Title }}UpdateTags(conn, identifier, nil, map[string]string{key: value}); err != nil {
+	{{- end }}
+		fmt.Errorf("error creating {{ .ServiceName }} resource (%s) tag (%s): %w", identifier, key, err)
+	}
+
+	d.SetId(tagresource.SetResourceId(identifier, key))
+
+	return resourceAws{{ .ServiceName | Title }}TagRead(d, meta)
+}
+
+func resourceAws{{ .ServiceName | Title }}TagRead(d *schema.ResourceData, meta interface{}) error {
+	conn := meta.(*AWSClient).{{ .ServiceName }}conn
+	identifier, key, err := tagresource.GetResourceId(d.Id())
+
+	if err != nil {
+		return err
+	}
+
+	exists, value, err := keyvaluetags.{{ .ServiceName | Title }}GetTag(conn, identifier, key)
+
+	if err != nil {
+		fmt.Errorf("error reading {{ .ServiceName }} resource (%s) tag (%s): %w", identifier, key, err)
+	}
+
+	if !exists {
+		log.Printf("[WARN] {{ .ServiceName }} resource (%s) tag (%s) not found, removing from state", identifier, key)
+		d.SetId("")
+		return nil
+	}
+
+	d.Set("{{ .ServiceName | IdentifierAttributeName }}", identifier)
+	d.Set("key", key)
+	d.Set("value", value)
+
+	return nil
+}
+
+func resourceAws{{ .ServiceName | Title }}TagUpdate(d *schema.ResourceData, meta interface{}) error {
+	conn := meta.(*AWSClient).{{ .ServiceName }}conn
+	identifier, key, err := tagresource.GetResourceId(d.Id())
+
+	if err != nil {
+		return err
+	}
+
+	if err := keyvaluetags.{{ .ServiceName | Title }}UpdateTags(conn, identifier, nil, map[string]string{key: d.Get("value").(string)}); err != nil {
+		return fmt.Errorf("error updating {{ .ServiceName }} resource (%s) tag (%s): %w", identifier, key, err)
+	}
+
+	return resourceAws{{ .ServiceName | Title }}TagRead(d, meta)
+}
+
+func resourceAws{{ .ServiceName | Title }}TagDelete(d *schema.ResourceData, meta interface{}) error {
+	conn := meta.(*AWSClient).{{ .ServiceName }}conn
+	identifier, key, err := tagresource.GetResourceId(d.Id())
+
+	if err != nil {
+		return err
+	}
+
+	if err := keyvaluetags.{{ .ServiceName | Title }}UpdateTags(conn, identifier, map[string]string{key: d.Get("value").(string)}, nil); err != nil {
+		return fmt.Errorf("error deleting {{ .ServiceName }} resource (%s) tag (%s): %w", identifier, key, err)
+	}
+
+	return nil
+}
+`
+	resourceTestTemplateBody = `
+// Code generated by internal/tagresource/generator/main.go; DO NOT EDIT.
+
+package aws
+
+import (
+	"fmt"
+
+	"github.com/hashicorp/terraform-plugin-sdk/helper/resource"
+	"github.com/hashicorp/terraform-plugin-sdk/terraform"
+	"github.com/terraform-providers/terraform-provider-aws/aws/internal/keyvaluetags"
+	"github.com/terraform-providers/terraform-provider-aws/aws/internal/tagresource"
+)
+
+func testAccCheck{{ .ServiceName | Title }}TagDestroy(s *terraform.State) error {
+	conn := testAccProvider.Meta().(*AWSClient).{{ .ServiceName }}conn
+
+	for _, rs := range s.RootModule().Resources {
+		if rs.Type != "aws_{{ .ServiceName }}_tag" {
+			continue
+		}
+
+		identifier, key, err := tagresource.GetResourceId(rs.Primary.ID)
+
+		if err != nil {
+			return err
+		}
+
+		exists, _, err := keyvaluetags.{{ .ServiceName | Title }}GetTag(conn, identifier, key)
+
+		if err != nil {
+			return err
+		}
+
+		if exists {
+			return fmt.Errorf("resource (%s) tag (%s) still exists", identifier, key)
+		}
+	}
+
+	return nil
+}
+
+func testAccCheck{{ .ServiceName | Title }}TagExists(resourceName string) resource.TestCheckFunc {
+	return func(s *terraform.State) error {
+		rs, ok := s.RootModule().Resources[resourceName]
+		if !ok {
+			return fmt.Errorf("not found: %s", resourceName)
+		}
+
+		if rs.Primary.ID == "" {
+			return fmt.Errorf("%s: missing resource ID", resourceName)
+		}
+
+		identifier, key, err := tagresource.GetResourceId(rs.Primary.ID)
+
+		if err != nil {
+			return err
+		}
+
+		conn := testAccProvider.Meta().(*AWSClient).{{ .ServiceName }}conn
+
+		exists, _, err := keyvaluetags.{{ .ServiceName | Title }}GetTag(conn, identifier, key)
+
+		if err != nil {
+			return err
+		}
+
+		if !exists {
+			return fmt.Errorf("resource (%s) tag (%s) not found", identifier, key)
+		}
+
+		return nil
+	}
+}
+`
+)

aws/internal/tagresource/service_generation_customizations.go

@@ -0,0 +1,15 @@
+package tagresource
+
+import (
+	"github.com/terraform-providers/terraform-provider-aws/aws/internal/keyvaluetags"
+)
+
+// ServiceIdentifierAttributeName determines the schema identifier attribute name.
+func ServiceIdentifierAttributeName(serviceName string) string {
+	switch serviceName {
+	case "ec2":
+		return "resource_id"
+	default:
+		return toSnakeCase(keyvaluetags.ServiceTagInputIdentifierField(serviceName))
+	}
+}

aws/internal/tagresource/tag_resources.go

@@ -0,0 +1,38 @@
+package tagresource
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+const (
+	// Separator used in resource identifiers
+	ResourceIdSeparator = `,`
+)
+
+// GetResourceId parses a given resource identifier for tag identifier and tag key.
+func GetResourceId(resourceId string) (string, string, error) {
+	parts := strings.SplitN(resourceId, ",", 2)
+
+	if len(parts) != 2 || parts[0] == "" || parts[1] == "" {
+		return "", "", fmt.Errorf("invalid resource identifier (%s), expected ID,KEY", resourceId)
+	}
+
+	return parts[0], parts[1], nil
+}
+
+// SetResourceId creates a resource identifier given a tag identifier and a tag key.
+func SetResourceId(identifier string, key string) string {
+	return identifier + ResourceIdSeparator + key
+}
+
+// toSnakeCase converts a string to snake case.
+//
+// For example, AWS Go SDK field names are in PascalCase,
+// while Terraform schema attribute names are in snake_case.
+func toSnakeCase(str string) string {
+	result := regexp.MustCompile("(.)([A-Z][a-z]+)").ReplaceAllString(str, "${1}_${2}")
+	result = regexp.MustCompile("([a-z0-9])([A-Z])").ReplaceAllString(result, "${1}_${2}")
+	return strings.ToLower(result)
+}