fix(completions): correctly insert cursor position (#408)

The cursor was being inserted in a strange matter, which made the
modified ast not have a `__cursor__()` function, so we couldn't find the
cursor.

Really, all we need to do is insert the cursor on its own line between
the line.

For example, if you were to put the cursor into the middle of this line
of code

```elixir
Enum.map(some_list, fn row ->   end)
```

It would insert the cursor like so

```elixir
Enum.map(some_list, fn row ->
__cursor__()
end)
```

Fixes #406

flake.nix

@@ -115,7 +115,7 @@
             src = self.outPath;
             inherit version elixir;
             pname = "next-ls-deps";
-            hash = "sha256-9LKtrNvNU8swcaaW3OuOCNKCa76+mvtu7MsWuy204/E=";
+            hash = "sha256-aGVoJJPK+2phB9HLoIp50Qz0s+3tA9PU+yg8nvOGNRY=";
             mixEnv = "prod";
           };
 

lib/next_ls.ex

@@ -581,7 +581,10 @@ defmodule NextLS do
       document
       |> List.update_at(position.line, fn row ->
         {front, back} = String.split_at(row, position.character)
-        String.slice(front, -1..1) <> "__cursor__()" <> back
+        # all we need to do is insert the cursor so we can find the spot to then
+        # calculate the environment, it doens't really matter if its valid code,
+        # it probably isn't already
+        front <> "\n__cursor__()\n" <> back
       end)
       |> Enum.join("\n")
 

mix.lock

@@ -47,7 +47,7 @@
   "req": {:hex, :req, "0.4.0", "1c759054dd64ef1b1a0e475c2d2543250d18f08395d3174c371b7746984579ce", [:mix], [{:brotli, "~> 0.3.1", [hex: :brotli, repo: "hexpm", optional: true]}, {:ezstd, "~> 1.0", [hex: :ezstd, repo: "hexpm", optional: true]}, {:finch, "~> 0.9", [hex: :finch, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}, {:mime, "~> 1.6 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:nimble_csv, "~> 1.0", [hex: :nimble_csv, repo: "hexpm", optional: true]}, {:plug, "~> 1.0", [hex: :plug, repo: "hexpm", optional: true]}], "hexpm", "f53eadc32ebefd3e5d50390356ec3a59ed2b8513f7da8c6c3f2e14040e9fe989"},
   "schematic": {:hex, :schematic, "0.2.1", "0b091df94146fd15a0a343d1bd179a6c5a58562527746dadd09477311698dbb1", [:mix], [{:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "0b255d65921e38006138201cd4263fd8bb807d9dfc511074615cd264a571b3b1"},
   "sourceror": {:hex, :sourceror, "1.0.2", "c5e86fdc14881f797749d1fe5df017ca66727a8146e7ee3e736605a3df78f3e6", [:mix], [], "hexpm", "832335e87d0913658f129d58b2a7dc0490ddd4487b02de6d85bca0169ec2bd79"},
-  "spitfire": {:git, "https://github.com/elixir-tools/spitfire.git", "26e68d4b184caf32ccee840ef0e862c911ff51ef", []},
+  "spitfire": {:git, "https://github.com/elixir-tools/spitfire.git", "d39f91d6e66f70cb3093bad4947d7e46bba40b43", []},
   "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.7", "354c321cf377240c7b8716899e182ce4890c5938111a1296add3ec74cf1715df", [:make, :mix, :rebar3], [], "hexpm", "fe4c190e8f37401d30167c8c405eda19469f34577987c76dde613e838bbc67f8"},
   "styler": {:hex, :styler, "0.8.1", "f3c0f65023e4bfbf7e7aa752d128b8475fdabfd30f96ee7314b84480cc56e788", [:mix], [], "hexpm", "1aa48d3aa689a639289af3d8254d40e068e98c083d6e5e3d1a695e71a147b344"},
   "telemetry": {:hex, :telemetry, "1.2.1", "68fdfe8d8f05a8428483a97d7aab2f268aaff24b49e0f599faa091f1d4e7f61c", [:rebar3], [], "hexpm", "dad9ce9d8effc621708f99eac538ef1cbe05d6a874dd741de2e689c47feafed5"},

priv/monkey/_next_ls_private_compiler.ex

@@ -254,11 +254,6 @@ defmodule :_next_ls_private_formatter do
     ins: [text: :green, space: :green_background]
   ]
 
-  @callback features(Keyword.t()) :: [sigils: [atom()], extensions: [binary()]]
-
-  @callback format(String.t(), Keyword.t()) :: String.t()
-
-  @impl true
   def run(args) do
     cwd = File.cwd!()
     {opts, args} = OptionParser.parse!(args, strict: @switches)