There is an issue with how the engine computes the aliases when the
resource is a child and doesn't have `Parent` set on the alias spec
(and the parent doesn't have any aliases).
```python
class FooResource(pulumi.ComponentResource):
def __init__(self, name, opts=None):
super().__init__("my:module:FooResource", name, None, opts)
class ComponentResource(pulumi.ComponentResource):
def __init__(self, name, opts=None):
super().__init__("my:module:ComponentResource", name, None, opts)
FooResource("childrenamed", pulumi.ResourceOptions(
parent=self,
aliases=[pulumi.Alias(name="child")]
))
```
In the example above, `ComponentResource` has a child `FooResource`
which was renamed from `child` to `childrenamed`.
The engine does not compute the correct alias:
```
expected: urn:pulumi:stack::project::my:module:ComponentResource$my:module:FooResource::child
actual: urn:pulumi:stack::project::my:module:FooResource::child
```
The problem is due to:
117955ce14/pkg/resource/deploy/step_generator.go (L370-L382)
... and:
117955ce14/sdk/go/common/resource/alias.go (L24-L26)
Because the alias spec doesn't have `parent` specified, the parent type
is not being included the computed alias URN.
Existing tests such as https://github.com/pulumi/pulumi/tree/master/tests/integration/aliases/python/rename_component_and_child
didn't catch the problem because the alias specifies both the `name` and
`parent`:
117955ce14/tests/integration/aliases/python/rename_component_and_child/step2/__main__.py (L15)
In this case, specifying `parent` on the alias shouldn't be necessary.
However, even after removing `parent` from the alias spec, the test
still succeeds because the parent itself has an alias:
117955ce14/tests/integration/aliases/python/rename_component_and_child/step2/__main__.py (L18)
... and parent aliases are inherited as part of a child's aliases, so we
still get an alias that works from the inheritance.
If we change the test to make no changes to the parent such that it
doesn't have any aliases, then we get the failure as we'd expect.
A similar problem will happen when retyping a child.
**Fix**
The fix involves using the child's parent in the calculated alias URN
when `Parent` isn't specified for the alias.
As part of this, we need to properly handled `NoParent` because right
now the engine is not correctly using it. The struct representing an
alias in the engine does not have a `NoParent` field:
117955ce14/sdk/go/common/resource/alias.go (L8-L15)
And therefore does not copy it over in the gRPC request:
117955ce14/pkg/resource/deploy/source_eval.go (L1082-L1088)
Instead, the `Alias` struct has an incorrect `NoParent` method which
returns `true` if the `Parent` field has a value of `""`:
117955ce14/sdk/go/common/resource/alias.go (L24-L26)
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