Convert JavaScript string column to Elixir (#467)

* Fix column/index wording

* Convert JavaScript string column to Elixir

assets/js/cell/live_editor.js

@@ -238,9 +238,9 @@ class LiveEditor {
 
     this.editor.getModel().__getHover = (model, position) => {
       const line = model.getLineContent(position.lineNumber);
-      const index = position.column - 1;
+      const column = position.column;
 
-      return this.__asyncIntellisenseRequest("details", { line, index })
+      return this.__asyncIntellisenseRequest("details", { line, column })
         .then((response) => {
           const contents = response.contents.map((content) => ({
             value: content,

lib/livebook/intellisense.ex

@@ -31,8 +31,8 @@ defmodule Livebook.Intellisense do
     %{items: items}
   end
 
-  def handle_request({:details, line, index}, binding, env) do
-    get_details(line, index, binding, env)
+  def handle_request({:details, line, column}, binding, env) do
+    get_details(line, column, binding, env)
   end
 
   def handle_request({:format, code}, _binding, _env) do
@@ -140,12 +140,12 @@ defmodule Livebook.Intellisense do
 
   @doc """
   Returns detailed information about identifier being
-  at `index` in `line`.
+  in `column` in `line`.
   """
-  @spec get_details(String.t(), non_neg_integer(), Code.binding(), Macro.Env.t()) ::
+  @spec get_details(String.t(), pos_integer(), Code.binding(), Macro.Env.t()) ::
           Livebook.Runtime.details() | nil
-  def get_details(line, index, binding, env) do
-    {from, to} = subject_range(line, index)
+  def get_details(line, column, binding, env) do
+    {from, to} = subject_range(line, column)
 
     if from < to do
       subject = binary_part(line, from, to - from)
@@ -170,9 +170,9 @@ defmodule Livebook.Intellisense do
   @closing_identifier '?!'
   @punctuation @non_closing_punctuation ++ @closing_punctuation
 
-  defp subject_range(line, index) do
-    {left, right} = String.split_at(line, index)
-    bytes_until_index = byte_size(left)
+  defp subject_range(line, column) do
+    {left, right} = String.split_at(line, column)
+    bytes_until_column = byte_size(left)
 
     left =
       left
@@ -187,7 +187,7 @@ defmodule Livebook.Intellisense do
       |> consume_until(@space ++ @operators ++ @punctuation, @closing_identifier)
       |> List.to_string()
 
-    {bytes_until_index - byte_size(left), bytes_until_index + byte_size(right)}
+    {bytes_until_column - byte_size(left), bytes_until_column + byte_size(right)}
   end
 
   defp consume_until(acc \\ [], chars, stop, stop_include)

lib/livebook/js_interop.ex

@@ -40,6 +40,21 @@ defmodule Livebook.JSInterop do
     apply_to_code_units(ops, Enum.slice(code_units, n..-1))
   end
 
+  @doc """
+  Returns a column number in the Elixir string corresponding to
+  the given column interpreted in terms of UTF-16 code units as
+  JavaScript does.
+  """
+  @spec convert_column_to_elixir(pos_integer(), String.t()) :: pos_integer()
+  def convert_column_to_elixir(column, line) do
+    line
+    |> string_to_utf16_code_units()
+    |> Enum.take(column - 1)
+    |> utf16_code_units_to_string()
+    |> String.length()
+    |> Kernel.+(1)
+  end
+
   # ---
 
   defp string_to_utf16_code_units(string) do

lib/livebook/runtime.ex

@@ -72,9 +72,9 @@ defprotocol Livebook.Runtime do
   @type completion_item_kind :: :function | :module | :type | :variable | :field
 
   @typedoc """
-  Looks up more details about an identifier found at `index` in `line`.
+  Looks up more details about an identifier found in `column` in `line`.
   """
-  @type details_request :: {:details, line :: String.t(), index :: non_neg_integer()}
+  @type details_request :: {:details, line :: String.t(), column :: pos_integer()}
 
   @type details_response :: %{
           range: %{

lib/livebook_web/live/session_live.ex

@@ -632,8 +632,9 @@ defmodule LivebookWeb.SessionLive do
         %{"type" => "completion", "hint" => hint} ->
           {:completion, hint}
 
-        %{"type" => "details", "line" => line, "index" => index} ->
-          {:details, line, index}
+        %{"type" => "details", "line" => line, "column" => column} ->
+          column = Livebook.JSInterop.convert_column_to_elixir(column, line)
+          {:details, line, column}
 
         %{"type" => "format", "code" => code} ->
           {:format, code}

test/livebook/js_interop_test.exs

@@ -43,4 +43,27 @@ defmodule Livebook.JSInteropTest do
       assert JSInterop.apply_delta_to_string(delta, string) == " cats"
     end
   end
+
+  describe "convert_column_to_elixir/2" do
+    test "keeps the column as is for ASCII characters" do
+      column = 4
+      line = "String.replace"
+      assert JSInterop.convert_column_to_elixir(column, line) == 4
+    end
+
+    test "shifts the column given characters spanning multiple UTF-16 code units" do
+      # 🚀 consists of 2 UTF-16 code units, so JavaScript assumes "🚀".length is 2
+      column = 7
+      line = "🚀🚀 String.replace"
+      assert JSInterop.convert_column_to_elixir(column, line) == 5
+    end
+
+    test "returns proper column if a middle UTF-16 code unit is given" do
+      # 🚀 consists of 2 UTF-16 code units, so JavaScript assumes "🚀".length is 2
+      # 3th and 4th code unit correspond to the second 🚀
+      column = 3
+      line = "🚀🚀 String.replace"
+      assert JSInterop.convert_column_to_elixir(column, line) == 2
+    end
+  end
 end