feat(lsp): multi-client support for signature_help

Signatures can be cycled using `<C-s>` when the user enters the floating
window.

4 files changed, 162 insertions, 89 deletions

diff --git a/runtime/doc/lsp.txt b/runtime/doc/lsp.txt
index 6e5c85c019..87df1e06d6 100644
--- a/runtime/doc/lsp.txt
+++ b/runtime/doc/lsp.txt
@@ -1911,7 +1911,7 @@ make_floating_popup_options({width}, {height}, {opts})
                   |vim.lsp.util.open_floating_preview.Opts|.
 
     Return: ~
-        (`table`) Options
+        (`vim.api.keyset.win_config`)
 
                                        *vim.lsp.util.make_formatting_params()*
 make_formatting_params({options})
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index f82cf4453e..3ed1442a96 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -209,6 +209,8 @@ LSP
   `textDocument/rangesFormatting` request).
 • |vim.lsp.buf.code_action()| actions show client name when there are multiple
   clients.
+• |vim.lsp.buf.signature_help()| can now cycle through different signatures
+  using `<C-s>` and also support multiple clients.
 
 LUA
 
diff --git a/runtime/lua/vim/lsp/buf.lua b/runtime/lua/vim/lsp/buf.lua
index 152226a757..6d7597c5ff 100644
--- a/runtime/lua/vim/lsp/buf.lua
+++ b/runtime/lua/vim/lsp/buf.lua
@@ -258,6 +258,33 @@ function M.implementation(opts)
   get_locations(ms.textDocument_implementation, opts)
 end
 
+--- @param results table<integer,{err: lsp.ResponseError?, result: lsp.SignatureHelp?}>
+local function process_signature_help_results(results)
+  local signatures = {} --- @type [vim.lsp.Client,lsp.SignatureInformation][]
+
+  -- Pre-process results
+  for client_id, r in pairs(results) do
+    local err = r.err
+    local client = assert(lsp.get_client_by_id(client_id))
+    if err then
+      vim.notify(
+        client.name .. ': ' .. tostring(err.code) .. ': ' .. err.message,
+        vim.log.levels.ERROR
+      )
+      api.nvim_command('redraw')
+    else
+      local result = r.result --- @type lsp.SignatureHelp
+      if result and result.signatures and result.signatures[1] then
+        for _, sig in ipairs(result.signatures) do
+          signatures[#signatures + 1] = { client, sig }
+        end
+      end
+    end
+  end
+
+  return signatures
+end
+
 local sig_help_ns = api.nvim_create_namespace('vim_lsp_signature_help')
 
 --- @class vim.lsp.buf.signature_help.Opts : vim.lsp.util.open_floating_preview.Opts
@@ -270,58 +297,79 @@ local sig_help_ns = api.nvim_create_namespace('vim_lsp_signature_help')
 function M.signature_help(config)
   local method = ms.textDocument_signatureHelp
 
-  config = config or {}
+  config = config and vim.deepcopy(config) or {}
   config.focus_id = method
 
-  lsp.buf_request(0, method, client_positional_params(), function(err, result, ctx)
-    local client = assert(vim.lsp.get_client_by_id(ctx.client_id))
-
-    if err then
-      vim.notify(
-        client.name .. ': ' .. tostring(err.code) .. ': ' .. err.message,
-        vim.log.levels.ERROR
-      )
-      api.nvim_command('redraw')
-      return
-    end
-
+  lsp.buf_request_all(0, method, client_positional_params(), function(results, ctx)
     if api.nvim_get_current_buf() ~= ctx.bufnr then
       -- Ignore result since buffer changed. This happens for slow language servers.
       return
     end
 
-    -- When use `autocmd CompleteDone <silent><buffer> lua vim.lsp.buf.signature_help()` to call signatureHelp handler
-    -- If the completion item doesn't have signatures It will make noise. Change to use `print` that can use `<silent>` to ignore
-    if not result or not result.signatures or not result.signatures[1] then
+    local signatures = process_signature_help_results(results)
+
+    if not next(signatures) then
       if config.silent ~= true then
         print('No signature help available')
       end
       return
     end
 
-    local triggers =
-      vim.tbl_get(client.server_capabilities, 'signatureHelpProvider', 'triggerCharacters')
-
     local ft = vim.bo[ctx.bufnr].filetype
-    local lines, hl = util.convert_signature_help_to_markdown_lines(result, ft, triggers)
-    if not lines or vim.tbl_isempty(lines) then
-      if config.silent ~= true then
-        print('No signature help available')
+    local total = #signatures
+    local idx = 0
+
+    --- @param update_win? integer
+    local function show_signature(update_win)
+      idx = (idx % total) + 1
+      local client, result = signatures[idx][1], signatures[idx][2]
+      --- @type string[]?
+      local triggers =
+        vim.tbl_get(client.server_capabilities, 'signatureHelpProvider', 'triggerCharacters')
+      local lines, hl =
+        util.convert_signature_help_to_markdown_lines({ signatures = { result } }, ft, triggers)
+      if not lines then
+        return
       end
-      return
+
+      local sfx = total > 1 and string.format(' (%d/%d) (<C-s> to cycle)', idx, total) or ''
+      local title = string.format('Signature Help: %s%s', client.name, sfx)
+      if config.border then
+        config.title = title
+      else
+        table.insert(lines, 1, '# ' .. title)
+        if hl then
+          hl[1] = hl[1] + 1
+          hl[3] = hl[3] + 1
+        end
+      end
+
+      config._update_win = update_win
+
+      local buf, win = util.open_floating_preview(lines, 'markdown', config)
+
+      if hl then
+        vim.api.nvim_buf_clear_namespace(buf, sig_help_ns, 0, -1)
+        vim.hl.range(
+          buf,
+          sig_help_ns,
+          'LspSignatureActiveParameter',
+          { hl[1], hl[2] },
+          { hl[3], hl[4] }
+        )
+      end
+      return buf, win
     end
 
-    local fbuf = util.open_floating_preview(lines, 'markdown', config)
+    local fbuf, fwin = show_signature()
 
-    -- Highlight the active parameter.
-    if hl then
-      vim.hl.range(
-        fbuf,
-        sig_help_ns,
-        'LspSignatureActiveParameter',
-        { hl[1], hl[2] },
-        { hl[3], hl[4] }
-      )
+    if total > 1 then
+      vim.keymap.set('n', '<C-s>', function()
+        show_signature(fwin)
+      end, {
+        buffer = fbuf,
+        desc = 'Cycle next signature',
+      })
     end
   end)
 end
diff --git a/runtime/lua/vim/lsp/util.lua b/runtime/lua/vim/lsp/util.lua
index 763cd940c3..4ca4239127 100644
--- a/runtime/lua/vim/lsp/util.lua
+++ b/runtime/lua/vim/lsp/util.lua
@@ -737,7 +737,7 @@ function M.convert_signature_help_to_markdown_lines(signature_help, ft, triggers
   if active_signature >= #signature_help.signatures or active_signature < 0 then
     active_signature = 0
   end
-  local signature = signature_help.signatures[active_signature + 1]
+  local signature = vim.deepcopy(signature_help.signatures[active_signature + 1])
   local label = signature.label
   if ft then
     -- wrap inside a code block for proper rendering
@@ -804,9 +804,11 @@ function M.convert_signature_help_to_markdown_lines(signature_help, ft, triggers
       active_offset[2] = active_offset[2] + #contents[1]
     end
 
-    active_hl = {}
-    list_extend(active_hl, get_pos_from_offset(active_offset[1], contents) or {})
-    list_extend(active_hl, get_pos_from_offset(active_offset[2], contents) or {})
+    local a_start = get_pos_from_offset(active_offset[1], contents)
+    local a_end = get_pos_from_offset(active_offset[2], contents)
+    if a_start and a_end then
+      active_hl = { a_start[1], a_start[2], a_end[1], a_end[2] }
+    end
   end
 
   return contents, active_hl
@@ -818,7 +820,7 @@ end
 ---@param width integer window width (in character cells)
 ---@param height integer window height (in character cells)
 ---@param opts? vim.lsp.util.open_floating_preview.Opts
----@return table Options
+---@return vim.api.keyset.win_config
 function M.make_floating_popup_options(width, height, opts)
   validate('opts', opts, 'table', true)
   opts = opts or {}
@@ -1500,6 +1502,8 @@ end
 ---   to display the full window height.
 --- (default: `'auto'`)
 --- @field anchor_bias? 'auto'|'above'|'below'
+---
+--- @field _update_win? integer
 
 --- Shows contents in a floating window.
 ---
@@ -1521,43 +1525,49 @@ function M.open_floating_preview(contents, syntax, opts)
 
   local bufnr = api.nvim_get_current_buf()
 
-  -- check if this popup is focusable and we need to focus
-  if opts.focus_id and opts.focusable ~= false and opts.focus then
-    -- Go back to previous window if we are in a focusable one
-    local current_winnr = api.nvim_get_current_win()
-    if vim.w[current_winnr][opts.focus_id] then
-      api.nvim_command('wincmd p')
-      return bufnr, current_winnr
-    end
-    do
-      local win = find_window_by_var(opts.focus_id, bufnr)
-      if win and api.nvim_win_is_valid(win) and vim.fn.pumvisible() == 0 then
-        -- focus and return the existing buf, win
-        api.nvim_set_current_win(win)
-        api.nvim_command('stopinsert')
-        return api.nvim_win_get_buf(win), win
+  local floating_winnr = opts._update_win
+
+  -- Create/get the buffer
+  local floating_bufnr --- @type integer
+  if floating_winnr then
+    floating_bufnr = api.nvim_win_get_buf(floating_winnr)
+  else
+    -- check if this popup is focusable and we need to focus
+    if opts.focus_id and opts.focusable ~= false and opts.focus then
+      -- Go back to previous window if we are in a focusable one
+      local current_winnr = api.nvim_get_current_win()
+      if vim.w[current_winnr][opts.focus_id] then
+        api.nvim_command('wincmd p')
+        return bufnr, current_winnr
+      end
+      do
+        local win = find_window_by_var(opts.focus_id, bufnr)
+        if win and api.nvim_win_is_valid(win) and vim.fn.pumvisible() == 0 then
+          -- focus and return the existing buf, win
+          api.nvim_set_current_win(win)
+          api.nvim_command('stopinsert')
+          return api.nvim_win_get_buf(win), win
+        end
       end
     end
-  end
 
-  -- check if another floating preview already exists for this buffer
-  -- and close it if needed
-  local existing_float = vim.b[bufnr].lsp_floating_preview
-  if existing_float and api.nvim_win_is_valid(existing_float) then
-    api.nvim_win_close(existing_float, true)
+    -- check if another floating preview already exists for this buffer
+    -- and close it if needed
+    local existing_float = vim.b[bufnr].lsp_floating_preview
+    if existing_float and api.nvim_win_is_valid(existing_float) then
+      api.nvim_win_close(existing_float, true)
+    end
+    floating_bufnr = api.nvim_create_buf(false, true)
   end
 
-  -- Create the buffer
-  local floating_bufnr = api.nvim_create_buf(false, true)
-
   -- Set up the contents, using treesitter for markdown
   local do_stylize = syntax == 'markdown' and vim.g.syntax_on ~= nil
+
   if do_stylize then
     local width = M._make_floating_popup_size(contents, opts)
     contents = M._normalize_markdown(contents, { width = width })
     vim.bo[floating_bufnr].filetype = 'markdown'
     vim.treesitter.start(floating_bufnr)
-    api.nvim_buf_set_lines(floating_bufnr, 0, -1, false, contents)
   else
     -- Clean up input: trim empty lines
     contents = vim.split(table.concat(contents, '\n'), '\n', { trimempty = true })
@@ -1565,19 +1575,47 @@ function M.open_floating_preview(contents, syntax, opts)
     if syntax then
       vim.bo[floating_bufnr].syntax = syntax
     end
-    api.nvim_buf_set_lines(floating_bufnr, 0, -1, true, contents)
   end
 
-  -- Compute size of float needed to show (wrapped) lines
-  if opts.wrap then
-    opts.wrap_at = opts.wrap_at or api.nvim_win_get_width(0)
+  vim.bo[floating_bufnr].modifiable = true
+  api.nvim_buf_set_lines(floating_bufnr, 0, -1, false, contents)
+
+  if floating_winnr then
+    api.nvim_win_set_config(floating_winnr, {
+      border = opts.border,
+      title = opts.title,
+    })
   else
-    opts.wrap_at = nil
-  end
-  local width, height = M._make_floating_popup_size(contents, opts)
+    -- Compute size of float needed to show (wrapped) lines
+    if opts.wrap then
+      opts.wrap_at = opts.wrap_at or api.nvim_win_get_width(0)
+    else
+      opts.wrap_at = nil
+    end
+
+    -- TODO(lewis6991): These function assume the current window to determine options,
+    -- therefore it won't work for opts._update_win and the current window if the floating
+    -- window
+    local width, height = M._make_floating_popup_size(contents, opts)
+    local float_option = M.make_floating_popup_options(width, height, opts)
 
-  local float_option = M.make_floating_popup_options(width, height, opts)
-  local floating_winnr = api.nvim_open_win(floating_bufnr, false, float_option)
+    floating_winnr = api.nvim_open_win(floating_bufnr, false, float_option)
+
+    api.nvim_buf_set_keymap(
+      floating_bufnr,
+      'n',
+      'q',
+      '<cmd>bdelete<cr>',
+      { silent = true, noremap = true, nowait = true }
+    )
+    close_preview_autocmd(opts.close_events, floating_winnr, { floating_bufnr, bufnr })
+
+    -- save focus_id
+    if opts.focus_id then
+      api.nvim_win_set_var(floating_winnr, opts.focus_id, bufnr)
+    end
+    api.nvim_buf_set_var(bufnr, 'lsp_floating_preview', floating_winnr)
+  end
 
   if do_stylize then
     vim.wo[floating_winnr].conceallevel = 2
@@ -1590,21 +1628,6 @@ function M.open_floating_preview(contents, syntax, opts)
   vim.bo[floating_bufnr].modifiable = false
   vim.bo[floating_bufnr].bufhidden = 'wipe'
 
-  api.nvim_buf_set_keymap(
-    floating_bufnr,
-    'n',
-    'q',
-    '<cmd>bdelete<cr>',
-    { silent = true, noremap = true, nowait = true }
-  )
-  close_preview_autocmd(opts.close_events, floating_winnr, { floating_bufnr, bufnr })
-
-  -- save focus_id
-  if opts.focus_id then
-    api.nvim_win_set_var(floating_winnr, opts.focus_id, bufnr)
-  end
-  api.nvim_buf_set_var(bufnr, 'lsp_floating_preview', floating_winnr)
-
   return floating_bufnr, floating_winnr
 end