Create diff suppresser for maps that have a value that doesn't always come back.

.changelog/4158.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+pubsub: Fixed permadiff on push_config.attributes.
+```

google/common_diff_suppress.go

@@ -5,7 +5,9 @@ package google
 import (
 	"crypto/sha256"
 	"encoding/hex"
+	"log"
 	"reflect"
+	"strconv"
 	"strings"
 
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
@@ -17,6 +19,28 @@ func optionalPrefixSuppress(prefix string) schema.SchemaDiffSuppressFunc {
 	}
 }
 
+func ignoreMissingKeyInMap(key string) schema.SchemaDiffSuppressFunc {
+	return func(k, old, new string, d *schema.ResourceData) bool {
+		log.Printf("suppressing diff %q with old %q, new %q", k, old, new)
+		if strings.HasSuffix(k, ".%") {
+			oldNum, err := strconv.Atoi(old)
+			if err != nil {
+				log.Printf("[ERROR] could not parse %q as number, no longer attempting diff suppress", old)
+				return false
+			}
+			newNum, err := strconv.Atoi(new)
+			if err != nil {
+				log.Printf("[ERROR] could not parse %q as number, no longer attempting diff suppress", new)
+				return false
+			}
+			return oldNum+1 == newNum
+		} else if strings.HasSuffix(k, "."+key) {
+			return old == ""
+		}
+		return false
+	}
+}
+
 func optionalSurroundingSpacesSuppress(k, old, new string, d *schema.ResourceData) bool {
 	return strings.TrimSpace(old) == strings.TrimSpace(new)
 }

google/resource_pubsub_subscription.go

@@ -222,8 +222,9 @@ For example, a Webhook endpoint might use
 "https://example.com/push".`,
 						},
 						"attributes": {
-							Type:     schema.TypeMap,
-							Optional: true,
+							Type:             schema.TypeMap,
+							Optional:         true,
+							DiffSuppressFunc: ignoreMissingKeyInMap("x-goog-version"),
 							Description: `Endpoint configuration attributes.
 
 Every endpoint has a set of API supported attributes that can

google/resource_pubsub_subscription_generated_test.go

@@ -23,6 +23,61 @@ import (
 	"github.com/hashicorp/terraform-plugin-sdk/v2/terraform"
 )
 
+func TestAccPubsubSubscription_pubsubSubscriptionPushExample(t *testing.T) {
+	t.Parallel()
+
+	context := map[string]interface{}{
+		"random_suffix": randString(t, 10),
+	}
+
+	vcrTest(t, resource.TestCase{
+		PreCheck:  func() { testAccPreCheck(t) },
+		Providers: testAccProviders,
+		ExternalProviders: map[string]resource.ExternalProvider{
+			"random": {},
+		},
+		CheckDestroy: testAccCheckPubsubSubscriptionDestroyProducer(t),
+		Steps: []resource.TestStep{
+			{
+				Config: testAccPubsubSubscription_pubsubSubscriptionPushExample(context),
+			},
+			{
+				ResourceName:            "google_pubsub_subscription.example",
+				ImportState:             true,
+				ImportStateVerify:       true,
+				ImportStateVerifyIgnore: []string{"topic"},
+			},
+		},
+	})
+}
+
+func testAccPubsubSubscription_pubsubSubscriptionPushExample(context map[string]interface{}) string {
+	return Nprintf(`
+resource "google_pubsub_topic" "example" {
+  name = "tf-test-example-topic%{random_suffix}"
+}
+
+resource "google_pubsub_subscription" "example" {
+  name  = "tf-test-example-subscription%{random_suffix}"
+  topic = google_pubsub_topic.example.name
+
+  ack_deadline_seconds = 20
+
+  labels = {
+    foo = "bar"
+  }
+
+  push_config {
+    push_endpoint = "https://example.com/push"
+
+    attributes = {
+      x-goog-version = "v1"
+    }
+  }
+}
+`, context)
+}
+
 func TestAccPubsubSubscription_pubsubSubscriptionPullExample(t *testing.T) {
 	t.Parallel()
 

website/docs/r/pubsub_subscription.html.markdown

@@ -33,6 +33,11 @@ To get more information about Subscription, see:
 * How-to Guides
     * [Managing Subscriptions](https://cloud.google.com/pubsub/docs/admin#managing_subscriptions)
 
+<div class = "oics-button" style="float: right; margin: 0 0 -15px">
+  <a href="https://console.cloud.google.com/cloudshell/open?cloudshell_git_repo=https%3A%2F%2Fgithub.com%2Fterraform-google-modules%2Fdocs-examples.git&cloudshell_working_dir=pubsub_subscription_push&cloudshell_image=gcr.io%2Fgraphite-cloud-shell-images%2Fterraform%3Alatest&open_in_editor=main.tf&cloudshell_print=.%2Fmotd&cloudshell_tutorial=.%2Ftutorial.md" target="_blank">
+    <img alt="Open in Cloud Shell" src="//gstatic.com/cloudssh/images/open-btn.svg" style="max-height: 44px; margin: 32px auto; max-width: 100%;">
+  </a>
+</div>
 ## Example Usage - Pubsub Subscription Push