*Context*
Since Elixir 1.13, Macro.Env.fetch_alias/2 has existed as a mechanism to
resolve an alias to its fully-qualified name. This has the limitation,
however, that you cannot use the actual alias in the lookup.
iex> alias Foo.Bar, as: Baz
iex> Macro.Env.fetch_alias(__ENV__, :Baz)
{:ok, Foo.Bar}
iex> Macro.Env.fetch_alias(__ENV__, Baz)
:error
There is not a mechanism to go the other way without relying on the private
aliases field in a Macro.Env struct.
*Proposal*
Introduce a new function, Macro.Env.fetch_aliased_as/2, that is able to
look up the name that a module is aliased as. Additionally, extend the
behavior of both Macro.Env.fetch_aliased_as/2 and Macro.Env.fetch_alias/2
to accept qualified atoms.
iex> alias Foo.Bar, as: Baz
Baz
iex> Macro.Env.fetch_alias(__ENV__, :Baz)
{:ok, Foo.Bar}
iex> Macro.Env.fetch_alias(__ENV__, Baz)
{:ok, Foo.Bar}
iex> Macro.Env.fetch_alias(__ENV__, :Unknown)
:error
iex> Macro.Env.fetch_aliased_as(__ENV__, :"Foo.Bar")
{:ok, Baz}
iex> Macro.Env.fetch_aliased_as(__ENV__, Foo.Bar}
{:ok, Baz}
iex> Macro.Env.fetch_aliased_as(__ENV__, Foo.Unknown)
:error
I'll submit a PR shortly for this change, but am happy to wait for any
discussion that might happen here before it's acted on.
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