Find references for atoms (#1404)

This change indexes atoms in the references table and 
adds support for finding atoms in the references provider.

apps/els_lsp/src/els_dt_references.erl

@@ -61,7 +61,8 @@
     | record
     | include
     | include_lib
-    | behaviour.
+    | behaviour
+    | atom.
 -export_type([poi_category/0]).
 
 %%==============================================================================
@@ -185,4 +186,6 @@ kind_to_category(Kind) when Kind =:= include ->
 kind_to_category(Kind) when Kind =:= include_lib ->
     include_lib;
 kind_to_category(Kind) when Kind =:= behaviour ->
-    behaviour.
+    behaviour;
+kind_to_category(Kind) when Kind =:= atom ->
+    atom.

apps/els_lsp/src/els_indexing.erl

@@ -140,7 +140,9 @@ index_references(Id, Uri, POIs, Version) ->
         %% Behaviour
         behaviour,
         %% Type
-        type_application
+        type_application,
+        %% Atom
+        atom
     ],
     [
         index_reference(Id, Uri, POI, Version)

apps/els_lsp/src/els_references_provider.erl

@@ -142,7 +142,8 @@ find_references(Uri, #{kind := module}) ->
     Refs = find_references_to_module(Uri),
     [location(U, R) || #{uri := U, range := R} <- Refs];
 find_references(_Uri, #{kind := Kind, id := Name}) when
-    Kind =:= behaviour
+    Kind =:= behaviour;
+    Kind =:= atom
 ->
     find_references_for_id(Kind, Name);
 find_references(_Uri, _POI) ->

apps/els_lsp/src/els_text_search.erl

@@ -39,6 +39,8 @@ extract_pattern({include, Id}) ->
 extract_pattern({include_lib, Id}) ->
     include_id(Id);
 extract_pattern({behaviour, Name}) ->
+    Name;
+extract_pattern({atom, Name}) ->
     Name.
 
 -spec include_id(string()) -> string().

apps/els_lsp/test/els_references_SUITE.erl

@@ -32,6 +32,7 @@
     type_local/1,
     type_remote/1,
     type_included/1,
+    atom/1,
     refresh_after_watched_file_deleted/1,
     refresh_after_watched_file_changed/1,
     refresh_after_watched_file_added/1,
@@ -555,6 +556,32 @@ type_included(Config) ->
     assert_locations(Locations, ExpectedLocations),
     ok.
 
+-spec atom(config()) -> ok.
+atom(Config) ->
+    Uri = ?config(code_navigation_uri, Config),
+    %% References for the `code_navigation_extra' atom
+    #{result := Locations} = els_client:references(Uri, 85, 5),
+    ExpectedLocations = [
+        #{
+            uri => Uri,
+            range => #{from => {85, 3}, to => {85, 24}}
+        },
+        #{
+            uri => Uri,
+            range => #{from => {86, 14}, to => {86, 35}}
+        },
+        #{
+            uri => Uri,
+            range => #{from => {132, 36}, to => {132, 57}}
+        },
+        #{
+            uri => Uri,
+            range => #{from => {134, 35}, to => {134, 56}}
+        }
+    ],
+    assert_locations(Locations, ExpectedLocations),
+    ok.
+
 -spec refresh_after_watched_file_deleted(config()) -> ok.
 refresh_after_watched_file_deleted(Config) ->
     %% Before