Code.Fragment.container_cursor_to_quoted/1 can't return aliases when cursor at alias line.

[scottming]

Is this a bug?

iex(2)> s = "defmodule Mymodule do\n  alias Foo.Bar\n"                                     
"defmodule Mymodule do\n  alias Foo.Bar\n"
iex(3)> s |> Future.Code.Fragment.container_cursor_to_quoted
{:ok,
 {:defmodule, [line: 1],
  [
    {:__aliases__, [line: 1], [:Mymodule]},
    [
      do: {:__block__, [],
       [
         {:alias, [line: 2], [{:__aliases__, [line: 2], [:Foo, :Bar]}]},
         {:__cursor__, [line: 3], []}
       ]}
    ]
  ]}}
iex(4)> s = "defmodule MyModule do\n  alias Project.Structs.User"
"defmodule MyModule do\n  alias Project.Structs.User"
iex(5)> s |> Future.Code.Fragment.container_cursor_to_quoted     
{:ok,
 {:defmodule, [line: 1],
  [
    {:__aliases__, [line: 1], [:MyModule]},
    [do: {:alias, [line: 2], [{:__cursor__, [line: 2], []}]}]
  ]}}
iex(6)> 

I'm trying to copy some code to the Lexical repo: lexical-lsp/lexical#217

But I can't extract the aliases with this line: "defmodule MyModule do\n alias Project.Structs.User"

[josevalim]

Can you tell me the macro task you are trying to do? The container cursor to quoted returns the parent, in this case the parent is the do block. cursor_context will tell you that you are in an alias. So you always look at cursor_context first, and then you use container to disambiguate or to get more context. Does that make sense?

[scottming]

o, I see; thanks for the quick reply. I'm trying to build an alias mapping, with your suggestion, I think I can use cursor_context + container_cursor_to_quoted to archive that.

[josevalim]

Building the mapping is not something the Elixir tools will help, unfortunately. We want to tackle that in #12645.

if you want the AST until the current cursor, then you can always append a new line and call container_cursor_to_quoted. But using Elixir sense and private APIs may still be the best way to achieve that :(

[scottming]

Yes, I have noticed this.

I cannot handle this defmodule MyModule do\n alias Project.Structs.User, as: MyUser with cursor_context + container_cursor_to_quoted. Let me try adding a new line first.):

[scottming]

@josevalim
Hi, José, we already built our alias_mapping, and we think we found a bug.

iex(1)> Code.Fragment.container_cursor_to_quoted("%Struct{field: 1, fie\n")
{:error,
 {[line: 1, column: 17],
  "unexpected expression after keyword list. Keyword lists must always come last in lists and maps. Therefore, this is not allowed:\n\n    [some: :value, :another]\n    %{some: :value, another => value}\n\nInstead, reorder it to be the last entry:\n\n    [:another, some: :value]\n    %{another => value, some: :value}\n\nSyntax error after: ",
  "','"}}

%Struct{field: 1, fie\n this line should not fail the AST parsing, right?

[sabiwara]

%Struct{field: 1, fie\n this line should not fail the AST parsing, right?

I think\n is the issue here: keyword keys must be immediately followed by : without any whitespace. The following are syntax errors:

%{field : 1}

%{field
: 1}

[sabiwara]

Added to the syntax reference.

[scottming]

@sabiwara

Thanks, but if this case cannot be handled by container_cursor_to_quoted, then we have to do something special for when the cursor is in struct arguments, like not adding a new line.

cc @scohen

[josevalim]

IIRC, the new line is a temporary solution until #12645 is in place. My suggestion is for you to add a newline and then, if it fails to parse, try again without the newline.