startup: allow lua files as session one

src/nvim/main.c

@@ -1069,9 +1069,14 @@ static void command_line_scan(mparm_T *parmp)
               } else {
                 a = argv[0];
               }
-              size_t s_size = STRLEN(a) + 4;
+
+              size_t s_size = STRLEN(a) + 9;
               char *s = xmalloc(s_size);
-              snprintf(s, s_size, "so %s", a);
+              if (path_with_extension(a, "lua")) {
+                snprintf(s, s_size, "luafile %s", a);
+              } else {
+                snprintf(s, s_size, "so %s", a);
+              }
               parmp->cmds_tofree[parmp->n_commands] = true;
               parmp->commands[parmp->n_commands++] = s;
             } else {

test/functional/core/startup_spec.lua

@@ -493,3 +493,27 @@ describe('user config init', function()
     end)
   end)
 end)
+
+describe('user session', function()
+  local xhome = 'Xhome'
+  local pathsep = helpers.get_pathsep()
+  local session_file = table.concat({xhome, 'session.lua'}, pathsep)
+
+  before_each(function()
+    rmdir(xhome)
+
+    mkdir(xhome)
+    write_file(session_file, [[
+      vim.g.lua_session = 1
+    ]])
+  end)
+
+  after_each(function()
+    rmdir(xhome)
+  end)
+
+  it('loads session from the provided lua file', function()
+    clear{ args={'-S', session_file }, env={ HOME=xhome }}
+    eq(1, eval('g:lua_session'))
+  end)
+end)