From a7abe78c11dd7213978bc9edc20ff76feb57da0d Mon Sep 17 00:00:00 2001
From: Lukasz Samson <lukaszsamson@gmail.com>
Date: Sat, 11 Jul 2026 12:12:23 +0200
Subject: [PATCH] completion: restore bitstring modifier suggestions

---
 lib/elixir_sense/core/source.ex                     | 13 ++++++++++++-
 .../providers/completion/completion_engine.ex       | 13 ++++++++++++-
 test/elixir_sense/core/source_test.exs              |  4 ++++
 .../providers/completion/suggestions_test.exs       |  4 ++++
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/lib/elixir_sense/core/source.ex b/lib/elixir_sense/core/source.ex
index 8cb039d9..ca9102f2 100644
--- a/lib/elixir_sense/core/source.ex
+++ b/lib/elixir_sense/core/source.ex
@@ -735,7 +735,7 @@ defmodule ElixirSense.Core.Source do
   def concat_module_parts([], _, _), do: :error
 
   def bitstring_options(prefix) do
-    case Code.Fragment.container_cursor_to_quoted(prefix, columns: true) do
+    case bitstring_quoted(prefix) do
       {:ok, quoted} ->
         path = Macro.path(quoted, &match?({:__cursor__, _, []}, &1))
 
@@ -764,6 +764,17 @@ defmodule ElixirSense.Core.Source do
     end
   end
 
+  # A modifier prefix can be an Elixir reserved word (for example, `in`). In
+  # that case Code.Fragment fails before it has a chance to insert its cursor.
+  # Retrying with an identifier suffix makes the fragment parseable without
+  # changing the original text returned to the completion engine.
+  defp bitstring_quoted(prefix) do
+    case Code.Fragment.container_cursor_to_quoted(prefix, columns: true) do
+      {:error, _} -> Code.Fragment.container_cursor_to_quoted(prefix <> "_", columns: true)
+      result -> result
+    end
+  end
+
   # Strip binary `-` operator wrappers introduced when typing `big-uns` etc.
   # Mirrors remove_operators/2 from elixir-ls completion_engine.ex (commit 98e983d).
   defp bitstring_remove_operators([{op, _, [_, previous]} = head | tail], previous)
diff --git a/lib/elixir_sense/providers/completion/completion_engine.ex b/lib/elixir_sense/providers/completion/completion_engine.ex
index 47c11892..ccde4c72 100644
--- a/lib/elixir_sense/providers/completion/completion_engine.ex
+++ b/lib/elixir_sense/providers/completion/completion_engine.ex
@@ -998,7 +998,7 @@ defmodule ElixirSense.Providers.Completion.CompletionEngine do
   end
 
   defp container_context(code, env, metadata, cursor_position) do
-    case Code.Fragment.container_cursor_to_quoted(code) do
+    case container_cursor_to_quoted(code) do
       {:ok, quoted} ->
         case Macro.path(quoted, &match?({:__cursor__, _, []}, &1)) do
           [cursor, {:%{}, _, pairs}, {:%, _, [struct_module_ast, _map]} | _] ->
@@ -1056,6 +1056,17 @@ defmodule ElixirSense.Providers.Completion.CompletionEngine do
     end
   end
 
+  # A modifier prefix can be an Elixir reserved word (for example, `in`). In
+  # that case Code.Fragment fails before it has a chance to insert its cursor.
+  # Retrying with an identifier suffix makes the fragment parseable without
+  # affecting the original completion hint.
+  defp container_cursor_to_quoted(code) do
+    case Code.Fragment.container_cursor_to_quoted(code) do
+      {:error, _} -> Code.Fragment.container_cursor_to_quoted(code ++ ~c"_")
+      result -> result
+    end
+  end
+
   defp remove_operators([{op, _, [_, previous]} = head | tail], previous) when op in [:-],
     do: remove_operators(tail, head)
 
diff --git a/test/elixir_sense/core/source_test.exs b/test/elixir_sense/core/source_test.exs
index d286e55b..433e28ed 100644
--- a/test/elixir_sense/core/source_test.exs
+++ b/test/elixir_sense/core/source_test.exs
@@ -1229,6 +1229,10 @@ defmodule ElixirSense.Core.SourceTest do
       assert "int" == bitstring_options(text)
     end
 
+    test "single line reserved word prefix" do
+      assert "in" == bitstring_options("<<ident::in")
+    end
+
     test "single line multiple" do
       text = "<<ident::integer, some::"
       assert "" == bitstring_options(text)
diff --git a/test/elixir_sense/providers/completion/suggestions_test.exs b/test/elixir_sense/providers/completion/suggestions_test.exs
index adf2431f..2c9bccf2 100644
--- a/test/elixir_sense/providers/completion/suggestions_test.exs
+++ b/test/elixir_sense/providers/completion/suggestions_test.exs
@@ -4710,6 +4710,10 @@ defmodule ElixirSense.Providers.Completion.SuggestionTest do
   end
 
   test "bitstring options" do
+    assert [%{name: "integer", type: :bitstring_option}] =
+             ElixirSense.suggestions("<<x::in", 1, 8)
+             |> Enum.filter(&(&1.type == :bitstring_option))
+
     buffer = """
     defmodule ElixirSenseExample.OtherModule do
       alias ElixirSenseExample.SameModule