DocumentSymbols provider handles compilation errors gracefully (#186)

Rather than throwing an exception (which causes the spawned process to crash)
the DocumentSymbols provider will now simply return an error.

This is beneficial because this is very much an expected error and thus it is
confusing to show the exception in the logs. Possibly there are also performance
benefits to this as well.

Ideally the DocumentSymbols provider could still return valid symbols in this
case, but that is currently infeasible.

Author: axelson

apps/language_server/lib/language_server/providers/document_symbols.ex

@@ -17,23 +17,32 @@ defmodule ElixirLS.LanguageServer.Providers.DocumentSymbols do
   ]
 
   def symbols(uri, text, hierarchical) do
-    symbols = list_symbols(text)
+    case list_symbols(text) do
+      {:ok, symbols} ->
+        {:ok, build_symbols(symbols, uri, hierarchical)}
 
-    symbols =
-      if hierarchical do
-        Enum.map(symbols, &build_symbol_information_hierarchical(uri, &1))
-      else
-        symbols
-        |> Enum.map(&build_symbol_information_flat(uri, &1))
-        |> List.flatten()
-      end
+      {:error, :compilation_error} ->
+        {:error, :server_error, "[DocumentSymbols] Compilation error while parsing source file"}
+    end
+  end
 
-    {:ok, symbols}
+  defp build_symbols(symbols, uri, hierarchical)
+
+  defp build_symbols(symbols, uri, true) do
+    Enum.map(symbols, &build_symbol_information_hierarchical(uri, &1))
+  end
+
+  defp build_symbols(symbols, uri, false) do
+    symbols
+    |> Enum.map(&build_symbol_information_flat(uri, &1))
+    |> List.flatten()
   end
 
   defp list_symbols(src) do
-    Code.string_to_quoted!(src, columns: true, line: 0)
-    |> extract_modules()
+    case Code.string_to_quoted(src, columns: true, line: 0) do
+      {:ok, quoted_form} -> {:ok, extract_modules(quoted_form)}
+      {:error, _error} -> {:error, :compilation_error}
+    end
   end
 
   # Identify and extract the module symbol, and the symbols contained within the module

apps/language_server/test/providers/document_symbols_test.exs

@@ -2395,4 +2395,19 @@ defmodule ElixirLS.LanguageServer.Providers.DocumentSymbolsTest do
              }
            ]
   end
+
+  test "handles a file with compilation errors by returning an empty list" do
+    uri = "file://project/test.exs"
+
+    text = """
+    defmodule A do
+      def hello do
+        Hello.hi(
+      end
+    end
+    """
+
+    assert {:error, :server_error, message} = DocumentSymbols.symbols(uri, text, true)
+    assert String.contains?(message, "Compilation error")
+  end
 end