feat(lsp): support workspace/foldingRange/refresh #41780

Problem:
Servers cannot request refreshing stale LSP folding ranges after a
project-wide change.

Solution:
Advertise `workspace.foldingRange.refreshSupport` and re-request folding
ranges for active buffers when handling `workspace/foldingRange/refresh`.

AI-assisted

runtime/doc/news.txt

@@ -375,6 +375,8 @@ LSP
 • |vim.lsp.formatexpr()| now falls back to `textDocument/formatting` if the whole
   buffer is being formatted and the language server doesn't support
   `textDocument/rangeFormatting`.
+• Support for `workspace/foldingRange/refresh`:
+  https://microsoft.github.io/language-server-protocol/specifications/lsp/3.18/specification/#workspace_foldingRange_refresh
 
 LUA
 

runtime/lua/vim/lsp/_folding_range.lua

@@ -289,6 +289,26 @@ function State:foldclose(kind, winid)
   end)
 end
 
+--- |lsp-handler| for the method `workspace/foldingRange/refresh`
+---
+--- Refresh requests are sent by the server to indicate a project-wide change
+--- that requires all folding ranges to be re-requested by the client.
+---@param ctx lsp.HandlerContext
+---@internal
+function M.on_refresh(err, _, ctx)
+  if err then
+    return vim.NIL
+  end
+
+  for _, state in pairs(State.active) do
+    if state.client_state[ctx.client_id] then
+      state:refresh(ctx.client_id)
+    end
+  end
+
+  return vim.NIL
+end
+
 ---@param kind lsp.FoldingRangeKind
 ---@param winid? integer
 function M.foldclose(kind, winid)

runtime/lua/vim/lsp/handlers.lua

@@ -673,6 +673,11 @@ RSC['workspace/diagnostic/refresh'] = function(err, result, ctx)
   return vim.lsp.diagnostic.on_refresh(err, result, ctx)
 end
 
+---@see https://microsoft.github.io/language-server-protocol/specification/#workspace_foldingRange_refresh
+RSC['workspace/foldingRange/refresh'] = function(err, result, ctx)
+  return vim.lsp._folding_range.on_refresh(err, result, ctx)
+end
+
 ---@see https://microsoft.github.io/language-server-protocol/specification/#workspace_inlayHint_refresh
 RSC['workspace/inlayHint/refresh'] = function(err, result, ctx)
   return vim.lsp.inlay_hint.on_refresh(err, result, ctx)

runtime/lua/vim/lsp/protocol.lua

@@ -639,6 +639,9 @@ function protocol.make_client_capabilities()
       diagnostics = {
         refreshSupport = true,
       },
+      foldingRange = {
+        refreshSupport = true,
+      },
       fileOperations = {
         dynamicRegistration = false,
         didCreate = false,

test/functional/plugin/lsp/folding_range_spec.lua

@@ -101,13 +101,14 @@ static int foldLevel(linenr_T lnum)
     exec_lua(create_server_definition)
     bufnr = n.api.nvim_get_current_buf()
     client_id = exec_lua(function()
+      _G.folding_ranges = result
       _G.server = _G._create_server({
         capabilities = {
           foldingRangeProvider = true,
         },
         handlers = {
           ['textDocument/foldingRange'] = function(_, _, callback)
-            callback(nil, result)
+            callback(nil, _G.folding_ranges)
           end,
         },
       })
@@ -186,6 +187,31 @@ static int foldLevel(linenr_T lnum)
       }, foldlevels)
     end)
 
+    it('refreshes folding ranges on request', function()
+      local function foldlevels()
+        return exec_lua(function()
+          return { vim.lsp.foldexpr(1), vim.lsp.foldexpr(2), vim.lsp.foldexpr(3) }
+        end)
+      end
+
+      retry(nil, nil, function()
+        eq({ '>1', '<1', '0' }, foldlevels())
+      end)
+
+      exec_lua(function()
+        _G.folding_ranges = { { startLine = 1, endLine = 2 } }
+        vim.lsp._folding_range.on_refresh(
+          nil,
+          nil,
+          { method = 'workspace/foldingRange/refresh', client_id = client_id }
+        )
+      end)
+
+      retry(nil, nil, function()
+        eq({ '0', '>1', '<1' }, foldlevels())
+      end)
+    end)
+
     it('updates folds in all windows', function()
       screen:expect({
         grid = [[