Specify the orverride import order

There are some situations where the order that resources are overridden is
critical. We have gotten lucky up until now that a strategy of "deepest first"
was good enough. This will let us force the order when two or more resources
depend on a specific ordering.

products/compute/terraform.yaml

@@ -105,9 +105,12 @@ overrides: !ruby/object:Provider::ResourceOverrides
         default_from_api: true
         custom_flatten: 'templates/terraform/custom_flatten/name_from_self_link.erb'
       sourceImage: !ruby/object:Provider::Terraform::PropertyOverride
+        # sourceImage must be overridden first because it creates the 'image' property
+        override_order: -1
         name: image
         diff_suppress_func: 'diskImageDiffSuppress'
       image: !ruby/object:Provider::Terraform::PropertyOverride
+        override_order: 5
         description: |
           The image from which to initialize this disk. This can be
           one of: the image's `self_link`, `projects/{project}/global/images/{image}`,

provider/property_override.rb

@@ -20,6 +20,16 @@ module Provider
   class PropertyOverride < Api::Object
     attr_reader :new_type
 
+    # Ordering of imports can be important so this property can make the
+    # ordering more deterministic. It supports positive or negative numbers
+    # with the lowest number getting imported first.
+    # The default is equal to the negative depth of the metric. This makes
+    # sure that more deeply nested fields happen first.
+    #   eg:
+    # sourceSnapshotEncryptionKey.rawKey has an order of -2
+    # sourceSnapshotEncryptionKey has an order of -1
+    attr_reader :override_order
+
     include Api::Type::Fields
     # To allow overrides for type-specific fields, include those type's
     # fields with an 'include' directive here.

provider/resource_overrides.rb

@@ -112,7 +112,7 @@ def override_properties(api_object, override)
       # before we have applied the overrides to its child properties (and
       # therefore can no longer find the child property, since the
       # parent name has changed)
-      sorted_props = override.properties.sort_by { |path, _| -path.count('.') }
+      sorted_props = override.properties.sort_by { |path, p| p.override_order || -path.count('.') }
       sorted_props.each do |property_path, property_override|
         check_property_value "properties['#{property_path}']",
                              property_override, Provider::PropertyOverride