feat(roslyn_ls): support override completion and refresh diagnostics #4050

Problem:
- Diagnostics were only refreshed for the current buffer, not all buffers
  managed by the client. In multi-file C# projects, this left diagnostics
  stale unless the user switched buffers.
- Roslyn did not handle override method completion correctly.

Solution:
- Added `roslyn.client.completionComplexEdit` handler to apply edits for
  override completions.
- Added `refresh_diagnostics` function, called on project initialization
  and on `BufWritePost` / `InsertLeave` events, to proactively pull
  diagnostics for all client buffers.

Rationale:
- Roslyn LSP primarily uses pull-based diagnostics. Neovim currently
  only triggers diagnostic pulls on text changes in the active buffer.
  This makes `debounce_text_changes` insufficient for Roslyn, as changes
  in one file can affect diagnostics across the entire solution.
- The autocmds act as a server-specific workaround to mimic an
  “on-save/on-idle” pull model.

1 files changed, 62 insertions, 7 deletions

diff --git a/lsp/roslyn_ls.lua b/lsp/roslyn_ls.lua
index b7437da5..0469e1ad 100644
--- a/lsp/roslyn_ls.lua
+++ b/lsp/roslyn_ls.lua
@@ -22,6 +22,8 @@
 local uv = vim.uv
 local fs = vim.fs
 
+local group = vim.api.nvim_create_augroup('lspconfig.roslyn_ls', { clear = true })
+
 ---@param client vim.lsp.Client
 ---@param target string
 local function on_init_sln(client, target)
@@ -44,19 +46,30 @@ local function on_init_project(client, project_files)
   })
 end
 
+---@param client vim.lsp.Client
+local function refresh_diagnostics(client)
+  local buffers = vim.lsp.get_buffers_by_client_id(client.id)
+  for _, buf in ipairs(buffers) do
+    if vim.api.nvim_buf_is_loaded(buf) then
+      client:request(
+        vim.lsp.protocol.Methods.textDocument_diagnostic,
+        { textDocument = vim.lsp.util.make_text_document_params(buf) },
+        nil,
+        buf
+      )
+    end
+  end
+end
+
 local function roslyn_handlers()
   return {
     ['workspace/projectInitializationComplete'] = function(_, _, ctx)
       vim.notify('Roslyn project initialization complete', vim.log.levels.INFO, { title = 'roslyn_ls' })
-
-      local buffers = vim.lsp.get_buffers_by_client_id(ctx.client_id)
       local client = assert(vim.lsp.get_client_by_id(ctx.client_id))
-      for _, buf in ipairs(buffers) do
-        client:request(vim.lsp.protocol.Methods.textDocument_diagnostic, {
-          textDocument = vim.lsp.util.make_text_document_params(buf),
-        }, nil, buf)
-      end
+      refresh_diagnostics(client)
+      return vim.NIL
     end,
+
     ['workspace/_roslyn_projectHasUnresolvedDependencies'] = function()
       vim.notify('Detected missing dependencies. Run `dotnet restore` command.', vim.log.levels.ERROR, {
         title = 'roslyn_ls',
@@ -105,6 +118,31 @@ return {
   },
   filetypes = { 'cs' },
   handlers = roslyn_handlers(),
+
+  commands = {
+    ['roslyn.client.completionComplexEdit'] = function(command, ctx)
+      local client = assert(vim.lsp.get_client_by_id(ctx.client_id))
+      local args = command.arguments or {}
+      local uri, edit = args[1], args[2]
+
+      if uri and edit and edit.newText and edit.range then
+        local workspace_edit = {
+          changes = {
+            [uri.uri] = {
+              {
+                range = edit.range,
+                newText = edit.newText,
+              },
+            },
+          },
+        }
+        vim.lsp.util.apply_workspace_edit(workspace_edit, client.offset_encoding)
+      else
+        vim.notify('roslyn_ls: completionComplexEdit args not understood: ' .. vim.inspect(args), vim.log.levels.WARN)
+      end
+    end,
+  },
+
   root_dir = function(bufnr, cb)
     local bufname = vim.api.nvim_buf_get_name(bufnr)
     -- don't try to find sln or csproj for files from libraries
@@ -147,6 +185,23 @@ return {
       end
     end,
   },
+
+  on_attach = function(client, bufnr)
+    -- avoid duplicate autocmds for same buffer
+    if vim.api.nvim_get_autocmds({ buffer = bufnr, group = group })[1] then
+      return
+    end
+
+    vim.api.nvim_create_autocmd({ 'BufWritePost', 'InsertLeave' }, {
+      group = group,
+      buffer = bufnr,
+      callback = function()
+        refresh_diagnostics(client)
+      end,
+      desc = 'roslyn_ls: refresh diagnostics',
+    })
+  end,
+
   capabilities = {
     -- HACK: Doesn't show any diagnostics if we do not set this to true
     textDocument = {