feat(lsp): add buf_detach_client (#16250)

This allows the user to detach an active buffer from the language
client. If no clients remain attached to a buffer, the on_lines callback
is used to cancel nvim_buf_attach.

1 files changed, 46 insertions, 2 deletions

diff --git a/runtime/lua/vim/lsp.lua b/runtime/lua/vim/lsp.lua
index 25cde843a0..00839ec181 100644
--- a/runtime/lua/vim/lsp.lua
+++ b/runtime/lua/vim/lsp.lua
@@ -1112,9 +1112,9 @@ local text_document_did_change_handler
 do
   text_document_did_change_handler = function(_, bufnr, changedtick, firstline, lastline, new_lastline)
 
-    -- Don't do anything if there are no clients attached.
+    -- Detach (nvim_buf_attach) via returning True to on_lines if no clients are attached
     if tbl_isempty(all_buffer_active_clients[bufnr] or {}) then
-      return
+      return true
     end
     util.buf_versions[bufnr] = changedtick
     local compute_change_and_notify = changetracking.prepare(bufnr, firstline, lastline, new_lastline)
@@ -1220,6 +1220,50 @@ function lsp.buf_attach_client(bufnr, client_id)
   return true
 end
 
+--- Detaches client from the specified buffer.
+--- Note: While the server is notified that the text document (buffer)
+--- was closed, it is still able to send notifications should it ignore this notification.
+---
+---@param bufnr number Buffer handle, or 0 for current
+---@param client_id number Client id
+function lsp.buf_detach_client(bufnr, client_id)
+  validate {
+    bufnr     = {bufnr, 'n', true};
+    client_id = {client_id, 'n'};
+  }
+  bufnr = resolve_bufnr(bufnr)
+
+  local client = lsp.get_client_by_id(client_id)
+  if not client or not client.attached_buffers[bufnr] then
+    vim.notify(
+      string.format('Buffer (id: %d) is not attached to client (id: %d). Cannot detach.', client_id, bufnr)
+    )
+    return
+  end
+
+  changetracking.reset_buf(client, bufnr)
+
+  if client.resolved_capabilities.text_document_open_close then
+    local uri = vim.uri_from_bufnr(bufnr)
+    local params = { textDocument = { uri = uri; } }
+    client.notify('textDocument/didClose', params)
+  end
+
+  client.attached_buffers[bufnr] = nil
+  util.buf_versions[bufnr] = nil
+
+  all_buffer_active_clients[bufnr][client_id] = nil
+  if #vim.tbl_keys(all_buffer_active_clients[bufnr]) == 0 then
+    all_buffer_active_clients[bufnr] = nil
+  end
+
+  local namespace = vim.lsp.diagnostic.get_namespace(client_id)
+  vim.diagnostic.reset(namespace, bufnr)
+
+  vim.notify(string.format('Detached buffer (id: %d) from client (id: %d)', bufnr, client_id))
+
+end
+
 --- Checks if a buffer is attached for a particular client.
 ---
 ---@param bufnr (number) Buffer handle, or 0 for current