provider/aws: main route table refresh handles VPC being gone [GH-1806]

CHANGELOG.md

@@ -118,6 +118,8 @@ BUG FIXES:
   * provider/aws: Block devices can be encrypted [GH-1718]
   * provider/aws: ASG health check grace period can be updated in-place [GH-1682]
   * provider/aws: ELB security groups can be updated in-place [GH-1662]
+  * provider/aws: `aws_main_route_table_association` can be deleted
+      manually [GH-1806]
   * provider/openstack: region config is not required [GH-1441]
   * provider/openstack: `enable_dhcp` for networking subnet should be bool [GH-1741]
   * provisioner/remote-exec: add random number to uploaded script path so

builtin/providers/aws/resource_aws_main_route_table_association.go

@@ -76,7 +76,7 @@ func resourceAwsMainRouteTableAssociationRead(d *schema.ResourceData, meta inter
 		return err
 	}
 
-	if *mainAssociation.RouteTableAssociationID != d.Id() {
+	if mainAssociation == nil || *mainAssociation.RouteTableAssociationID != d.Id() {
 		// It seems it doesn't exist anymore, so clear the ID
 		d.SetId("")
 	}
@@ -135,6 +135,9 @@ func findMainRouteTableAssociation(conn *ec2.EC2, vpcId string) (*ec2.RouteTable
 	if err != nil {
 		return nil, err
 	}
+	if mainRouteTable == nil {
+		return nil, nil
+	}
 
 	for _, a := range mainRouteTable.Associations {
 		if *a.Main {
@@ -159,10 +162,7 @@ func findMainRouteTable(conn *ec2.EC2, vpcId string) (*ec2.RouteTable, error) {
 	if err != nil {
 		return nil, err
 	} else if len(routeResp.RouteTables) != 1 {
-		return nil, fmt.Errorf(
-			"Expected to find a single main routing table for VPC: %s, but found %d",
-			vpcId,
-			len(routeResp.RouteTables))
+		return nil, nil
 	}
 
 	return routeResp.RouteTables[0], nil