Extract file from doc entry if available

The documentation could be in an include file, then the file in
the moduledoc anno would be different than the file in the
doc anno.

Normally this does not matter except for when we need to create
a warning for a broken link.

lib/ex_doc/formatter/html.ex

@@ -98,6 +98,7 @@ defmodule ExDoc.Formatter.HTML do
                 [
                   id: id,
                   line: child_node.doc_line,
+                  file: child_node.source_path,
                   current_kfa: {:function, child_node.name, child_node.arity}
                 ]
 
@@ -115,6 +116,7 @@ defmodule ExDoc.Formatter.HTML do
                 [
                   id: id,
                   line: child_node.doc_line,
+                  file: child_node.source_path,
                   current_kfa: {child_node.type, child_node.name, child_node.arity}
                 ]
 

lib/ex_doc/retriever.ex

@@ -236,6 +236,7 @@ defmodule ExDoc.Retriever do
     {:docs_v1, _, _, content_type, _, module_metadata, _} = module_data.docs
     {{type, name, arity}, anno, signature, source_doc, metadata} = doc_element
     doc_line = anno_line(anno)
+    source = anno_file(anno, source)
 
     annotations =
       annotations_for_docs.(metadata) ++
@@ -310,6 +311,7 @@ defmodule ExDoc.Retriever do
     {:docs_v1, _, _, content_type, _, module_metadata, _} = module_data.docs
     {{kind, name, arity}, anno, _signature, source_doc, metadata} = callback
     doc_line = anno_line(anno)
+    source = anno_file(anno, source)
 
     signature = signature(callback_data.signature)
     specs = callback_data.specs
@@ -355,6 +357,7 @@ defmodule ExDoc.Retriever do
     {:docs_v1, _, _, content_type, _, module_metadata, _} = module_data.docs
     {{_, name, arity}, anno, _signature, source_doc, metadata} = type_entry
     doc_line = anno_line(anno)
+    source = anno_file(anno, source)
     annotations = annotations_from_metadata(metadata, module_metadata)
 
     type_data = module_data.language.type_data(type_entry, module_data)
@@ -406,6 +409,15 @@ defmodule ExDoc.Retriever do
   defp anno_line(line) when is_integer(line), do: abs(line)
   defp anno_line(anno), do: anno |> :erl_anno.line() |> abs()
 
+  defp anno_file(anno, source) do
+    case :erl_anno.file(anno) do
+      :undefined ->
+        source
+      file ->
+        %{ url: source.url, path: Path.join(Path.dirname(source.path), file) }
+    end
+  end
+
   defp source_link(%{path: _, url: nil}, _line), do: nil
 
   defp source_link(source, line) do