(renderer) keymap bugfix

lua/u/renderer.lua

@@ -1,4 +1,4 @@
-local Signal = require('u.tracker').Signal
+function _G.URendererOpFuncSwallow() end
 
 local M = {}
 local H = {}
@@ -243,12 +243,20 @@ function Renderer:render(tree) -- {{{
           for lhs, _ in pairs(tag.attributes[mode .. 'map'] or {}) do
             -- Force creating an extmark if there are key handlers. To accurately
             -- sense the bounds of the text, we need an extmark:
-            vim.keymap.set(
+            vim.keymap.set(mode, lhs, function()
-              mode,
+              local result = self:_expr_map_callback(mode, lhs)
-              lhs,
+              -- If the handler indicates that it wants to swallow the event,
-              function() return self:_expr_map_callback(mode, lhs) end,
+              -- we have to convert that intention into something compatible
-              { buffer = self.bufnr, expr = true, replace_keycodes = true }
+              -- with expr-mappings, which don't support '<Nop>' (they try to
-            )
+              -- execute the literal characters). We'll use the 'g@' operator
+              -- to do that, forwarding the event to an operatorfunc that does
+              -- nothing:
+              if result == '' then
+                vim.go.operatorfunc = 'v:lua.URendererOpFuncSwallow'
+                return 'g@ '
+              end
+              return result
+            end, { buffer = self.bufnr, expr = true, replace_keycodes = true })
           end
         end
 
@@ -509,7 +517,7 @@ function TreeBuilder:put_h(name, attributes, children)
   return self
 end
 
---- @param fn fun(TreeBuilder): any
+--- @param fn fun(tb: u.renderer.TreeBuilder): any
 --- @return u.renderer.TreeBuilder
 function TreeBuilder:nest(fn)
   local nested_writer = TreeBuilder.new()