Supress diffs for differences in resource_group_name capitalisation.

builtin/providers/azurerm/provider.go

@@ -236,3 +236,9 @@ func azureStateRefreshFunc(resourceURI string, client *ArmClient, command rivier
 		panic(fmt.Errorf("azureStateRefreshFunc called on structure %T with no mapstructure:provisioningState tag. This is a bug", res.Parsed))
 	}
 }
+
+// Resource group names can be capitalised, but we store them in lowercase.
+// Use a custom diff function to avoid creation of new resources.
+func resourceAzurermResourceGroupNameDiffSuppress(k, old, new string, d *schema.ResourceData) bool {
+	return strings.ToLower(old) == strings.ToLower(new)
+}

builtin/providers/azurerm/resource_arm_storage_account.go

@@ -33,9 +33,10 @@ func resourceArmStorageAccount() *schema.Resource {
 			},
 
 			"resource_group_name": {
-				Type:     schema.TypeString,
-				Required: true,
-				ForceNew: true,
+				Type:             schema.TypeString,
+				Required:         true,
+				ForceNew:         true,
+				DiffSuppressFunc: resourceAzurermResourceGroupNameDiffSuppress,
 			},
 
 			"location": {