Try to find a workspace by external ID before removing it

When a workspace name is changed out side of TF, we should still be able
to find it using it's external ID. So we first try that before we delete
the workspace from the state.

tfe/resource_tfe_workspace.go

@@ -176,13 +176,48 @@ func resourceTFEWorkspaceRead(d *schema.ResourceData, meta interface{}) error {
 
 	log.Printf("[DEBUG] Read configuration of workspace: %s", name)
 	workspace, err := tfeClient.Workspaces.Read(ctx, organization, name)
-	if err != nil {
-		if err == tfe.ErrResourceNotFound {
+	if err != nil && err != tfe.ErrResourceNotFound {
+		return fmt.Errorf("Error reading configuration of workspace %s: %v", name, err)
+	}
+
+	// If we cannot find the workspace, it either doesn't exist anymore or is
+	// renamed. To make sure the workspace is really gone before we delete it
+	// from our state, we will list all workspaces and try to find it using
+	// the external ID.
+	if err == tfe.ErrResourceNotFound {
+		// Set the workspace to nil so we can check if we found one later.
+		workspace = nil
+
+		options := tfe.WorkspaceListOptions{}
+		externalID := d.Get("external_id").(string)
+		for {
+			wl, err := tfeClient.Workspaces.List(ctx, organization, options)
+			if err != nil {
+				return fmt.Errorf("Error retrieving workspaces: %v", err)
+			}
+
+			for _, w := range wl.Items {
+				if externalID == w.ID {
+					workspace = w
+					break
+				}
+			}
+
+			// Exit the loop if we found the workspace or have seen all pages.
+			if workspace != nil || wl.CurrentPage >= wl.TotalPages {
+				break
+			}
+
+			// Update the page number to get the next page.
+			options.PageNumber = wl.NextPage
+		}
+
+		// Return if we didn't find a matching workspace.
+		if workspace == nil {
 			log.Printf("[DEBUG] Workspace %s does no longer exist", name)
 			d.SetId("")
 			return nil
 		}
-		return fmt.Errorf("Error reading configuration of workspace %s: %v", name, err)
 	}
 
 	// Update the config.