Fix losing session ref when stepping without being stopped

lua/dap.lua

@@ -410,6 +410,8 @@ local function select_config_and_run(opts)
 end
 
 
+--- Get the first stopped session.
+--- If no session is stopped, it returns the active session or next in sessions.
 ---@return Session|nil
 local function first_stopped_session()
   if session and session.stopped_thread_id then
@@ -420,7 +422,11 @@ local function first_stopped_session()
       return s
     end
   end
-  return nil
+  if session then
+    return session
+  end
+  local _, s = next(sessions)
+  return s
 end
 
 

tests/integration_spec.lua

@@ -356,6 +356,12 @@ describe('dap with fake server', function()
     local session = run_and_wait_until_initialized(callable_config, server)
     assert.are.same(session.config.x, 1)
   end)
+
+  it("step does nothing if session is not stopped", function()
+    local session = run_and_wait_until_initialized(config, server)
+    dap.step_over()
+    assert.are.same(session, dap.session())
+  end)
 end)
 
 describe('session disconnect', function()