Do not load modules for xref purposes, instead use BEAM info

Signed-off-by: José Valim <[email protected]>

Author: José Valim

lib/mix/lib/mix/tasks/xref.ex

@@ -160,28 +160,45 @@ defmodule Mix.Tasks.Xref do
 
   defp unreachable(pair_fun) do
     excludes = excludes()
-
     each_source_entries(&source_warnings(&1, excludes), pair_fun)
   end
 
   defp source_warnings(source, excludes) do
     source(runtime_dispatches: runtime_dispatches) = source
 
     for {module, func_arity_lines} <- runtime_dispatches,
+        exports = load_exports(module),
         {{func, arity}, lines} <- func_arity_lines,
-        warning = unreachable_mfa(module, func, arity, lines, excludes),
+        warning = unreachable_mfa(exports, module, func, arity, lines, excludes),
         do: warning
   end
 
-  defp unreachable_mfa(module, func, arity, lines, excludes) do
+  defp load_exports(module) do
+    if :code.is_loaded(module) do
+      # If the module is loaded, we will use the faster function_exported?/3 check
+      module
+    else
+      # Otherwise we get all exports from :beam_lib to avoid loading modules
+      with file when is_list(file) <- :code.which(module),
+           {:ok, {^module, [exports: exports]}} <- :beam_lib.chunks(file, [:exports]) do
+        exports
+      else
+        _ -> :unknown_module
+      end
+    end
+  end
+
+  defp unreachable_mfa(exports, module, func, arity, lines, excludes) do
     cond do
       excluded?(module, func, arity, excludes) ->
         nil
       skip?(module, func, arity) ->
         nil
-      not Code.ensure_loaded?(module) ->
+      exports == :unknown_module ->
         {Enum.sort(lines), :unknown_module, module, func, arity}
-      not function_exported?(module, func, arity) ->
+      is_atom(exports) and not function_exported?(module, func, arity) ->
+        {Enum.sort(lines), :unknown_function, module, func, arity}
+      is_list(exports) and not {func, arity} in exports ->
         {Enum.sort(lines), :unknown_function, module, func, arity}
       true ->
         nil
@@ -276,7 +293,7 @@ defmodule Mix.Tasks.Xref do
   defp source_calls_for_filter(source, filter) do
     runtime_dispatches = source(source, :runtime_dispatches)
     compile_dispatches = source(source, :compile_dispatches)
-    dispatches = Stream.concat(runtime_dispatches, compile_dispatches)
+    dispatches = runtime_dispatches ++ compile_dispatches
 
     calls =
       for {module, func_arity_lines} <- dispatches,

lib/mix/test/mix/tasks/xref_test.exs

@@ -129,25 +129,46 @@ defmodule Mix.Tasks.XrefTest do
 
   test "warnings: handles multiple modules in one file" do
     assert_warnings """
-    defmodule A do
+    defmodule A1 do
       def a, do: A2.no_func
       def b, do: A2.a
     end
 
     defmodule A2 do
-      def a, do: A.no_func
-      def b, do: A.b
+      def a, do: A1.no_func
+      def b, do: A1.b
     end
     """, """
     warning: function A2.no_func/0 is undefined or private
       lib/a.ex:2
 
-    warning: function A.no_func/0 is undefined or private
+    warning: function A1.no_func/0 is undefined or private
       lib/a.ex:7
 
     """
   end
 
+  test "warnings: doesn't load unloaded modules" do
+    assert_warnings """
+    defmodule A1 do
+      @compile {:autoload, false}
+      @on_load :init
+      def init do
+        raise "oops"
+      end
+    end
+
+    defmodule A2 do
+      def a, do: A1.no_func
+      def b, do: A1.init
+    end
+    """, """
+    warning: function A1.no_func/0 is undefined or private
+      lib/a.ex:10
+
+    """
+  end
+
   test "warnings: groups multiple warnings in one file" do
     assert_warnings """
     defmodule A do