fix(variables): handle changing child var ref

Variable references can change at any time. If a variable was hidden and
re-opened with one of its child var refs changed which was previously
opened, the render would always be invalidated due to state not
containing the variables. This change makes sure that the expanded
variables are always monitored.

See #47

lua/dapui/components/variables.lua

@@ -103,6 +103,12 @@ function Variables:render(render_state, parent_ref, variables, indent)
       local child_vars = self.state:variables(variable.variablesReference)
       if not child_vars then
         render_state:invalidate()
+        -- Happens when the parent component is collapsed and the variable
+        -- reference changes when re-opened.  The name is recorded as opened
+        -- but the variable reference is not yet monitored.
+        if not self.state:is_monitored(variable.variablesReference) then
+          self.state:monitor(variable.variablesReference)
+        end
         return
       else
         self:_get_child_component(variable.name):render(

lua/dapui/render/loop.lua

@@ -103,7 +103,6 @@ function M.run(element_names)
             end
           end
         end
-      else
       end
     end
   end

lua/dapui/state.lua

@@ -161,6 +161,10 @@ function UIState:monitor(var_ref)
   end)
 end
 
+function UIState:is_monitored(var_ref)
+  return self._monitored_vars[var_ref] ~= nil
+end
+
 function UIState:stop_monitor(var_ref)
   self._monitored_vars[var_ref] = (self._monitored_vars[var_ref] or 1) - 1
   if self._monitored_vars[var_ref] then

tests/unit/components/variables_spec.lua

@@ -16,6 +16,9 @@ describe("checking variables", function()
       monitor = function(_, ref)
         monitored[ref] = true
       end,
+      is_monitored = function(_, ref)
+        return monitored[ref] ~= nil
+      end,
       stop_monitor = function(_, ref)
         monitored[ref] = nil
       end,
@@ -182,6 +185,22 @@ describe("checking variables", function()
       local render_state = render.new_state()
       local component = Variables(mock_state)
 
+      local vars = mock_state:variables(1)
+      component:render(render_state, 1, vars)
+      render_state.mappings["expand"][1][1]()
+      render_state = render.new_state()
+      mock_state.variables = function()
+        return nil
+      end
+      vars[1].variablesReference = 10
+      component:render(render_state, 1, vars)
+      assert.True(monitored[10])
+    end)
+
+    it("monitors child var when variable reference is changed", function()
+      local render_state = render.new_state()
+      local component = Variables(mock_state)
+
       local vars = mock_state:variables(1)
       component:render(render_state, 1, vars)
       render_state.mappings["expand"][1][1]()