LSP: Move default buf callbacks to vim.lsp.callbacks (#11452)

- In the process, refactored focusable_preview to a util function.
- Add text for locations_to_items of the current line.
- Improve location callback to handle multiple return values by using
set_qflist.
- Remove update_tagstack and leave note for future travelers.

5 files changed, 300 insertions, 307 deletions

diff --git a/runtime/lua/vim/lsp.lua b/runtime/lua/vim/lsp.lua
index 928d19177a..82f4fda66f 100644
--- a/runtime/lua/vim/lsp.lua
+++ b/runtime/lua/vim/lsp.lua
@@ -1,4 +1,4 @@
-local default_callbacks = require 'vim.lsp.default_callbacks'
+local default_callbacks = require 'vim.lsp.callbacks'
 local log = require 'vim.lsp.log'
 local lsp_rpc = require 'vim.lsp.rpc'
 local protocol = require 'vim.lsp.protocol'
@@ -13,7 +13,7 @@ local validate = vim.validate
 
 local lsp = {
   protocol = protocol;
-  default_callbacks = default_callbacks;
+  callbacks = default_callbacks;
   buf = require'vim.lsp.buf';
   util = util;
   -- Allow raw RPC access.
@@ -469,7 +469,7 @@ function lsp.start_client(config)
   function client.request(method, params, callback)
     if not callback then
       callback = resolve_callback(method)
-        or error(string.format("request callback is empty and no default was found for client %s", client.name))
+        or error("not found: request callback for client "..client.name)
     end
     local _ = log.debug() and log.debug(log_prefix, "client.request", client_id, method, params, callback)
     -- TODO keep these checks or just let it go anyway?
diff --git a/runtime/lua/vim/lsp/buf.lua b/runtime/lua/vim/lsp/buf.lua
index 51295e5570..a6a05fb095 100644
--- a/runtime/lua/vim/lsp/buf.lua
+++ b/runtime/lua/vim/lsp/buf.lua
@@ -3,7 +3,6 @@ local validate = vim.validate
 local api = vim.api
 local vfn = vim.fn
 local util = require 'vim.lsp.util'
-local log = require 'vim.lsp.log'
 local list_extend = vim.list_extend
 
 local M = {}
@@ -16,270 +15,68 @@ local function npcall(fn, ...)
   return ok_or_nil(pcall(fn, ...))
 end
 
-local function err_message(...)
-  api.nvim_err_writeln(table.concat(vim.tbl_flatten{...}))
-  api.nvim_command("redraw")
-end
-
-local function find_window_by_var(name, value)
-  for _, win in ipairs(api.nvim_list_wins()) do
-    if npcall(api.nvim_win_get_var, win, name) == value then
-      return win
-    end
-  end
-end
-
 local function request(method, params, callback)
-  --  TODO(ashkan) enable this.
-  --  callback = vim.lsp.default_callbacks[method] or callback
   validate {
     method = {method, 's'};
-    callback = {callback, 'f'};
+    callback = {callback, 'f', true};
   }
-  return vim.lsp.buf_request(0, method, params, function(err, _, result, client_id)
-    local _ = log.debug() and log.debug("vim.lsp.buf", method, client_id, err, result)
-    if err then error(tostring(err)) end
-    return callback(err, method, result, client_id)
-  end)
-end
-
-local function focusable_preview(method, params, fn)
-  if npcall(api.nvim_win_get_var, 0, method) then
-    return api.nvim_command("wincmd p")
-  end
-
-  local bufnr = api.nvim_get_current_buf()
-  do
-    local win = find_window_by_var(method, bufnr)
-    if win then
-      api.nvim_set_current_win(win)
-      api.nvim_command("stopinsert")
-      return
-    end
-  end
-  return request(method, params, function(_, _, result, _)
-      -- TODO(ashkan) could show error in preview...
-    local lines, filetype, opts = fn(result)
-    if lines then
-      local _, winnr = util.open_floating_preview(lines, filetype, opts)
-      api.nvim_win_set_var(winnr, method, bufnr)
-    end
-  end)
+  return vim.lsp.buf_request(0, method, params, callback)
 end
 
 function M.hover()
   local params = util.make_position_params()
-  focusable_preview('textDocument/hover', params, function(result)
-    if not (result and result.contents) then return end
-
-    local markdown_lines = util.convert_input_to_markdown_lines(result.contents)
-    markdown_lines = util.trim_empty_lines(markdown_lines)
-    if vim.tbl_isempty(markdown_lines) then
-      return { 'No information available' }
-    end
-    return markdown_lines, util.try_trim_markdown_code_blocks(markdown_lines)
-  end)
+  request('textDocument/hover', params)
 end
 
 function M.peek_definition()
   local params = util.make_position_params()
-  request('textDocument/peekDefinition', params, function(_, _, result, _)
-    if not (result and result[1]) then return end
-    local loc = result[1]
-    local bufnr = vim.uri_to_bufnr(loc.uri) or error("couldn't find file "..tostring(loc.uri))
-    local start = loc.range.start
-    local finish = loc.range["end"]
-    util.open_floating_peek_preview(bufnr, start, finish, { offset_x = 1 })
-    local headbuf = util.open_floating_preview({"Peek:"}, nil, {
-      offset_y = -(finish.line - start.line);
-      width = finish.character - start.character + 2;
-    })
-    -- TODO(ashkan) change highlight group?
-    api.nvim_buf_add_highlight(headbuf, -1, 'Keyword', 0, -1)
-  end)
+  request('textDocument/peekDefinition', params)
 end
 
 
-local function update_tagstack()
-  local bufnr = api.nvim_get_current_buf()
-  local line = vfn.line('.')
-  local col = vfn.col('.')
-  local tagname = vfn.expand('<cWORD>')
-  local item = { bufnr = bufnr, from = { bufnr, line, col, 0 }, tagname = tagname }
-  local winid = vfn.win_getid()
-  local tagstack = vfn.gettagstack(winid)
-  local action
-  if tagstack.length == tagstack.curidx then
-    action = 'r'
-    tagstack.items[tagstack.curidx] = item
-  elseif tagstack.length > tagstack.curidx then
-    action = 'r'
-    if tagstack.curidx > 1 then
-      tagstack.items = table.insert(tagstack.items[tagstack.curidx - 1], item)
-    else
-      tagstack.items = { item }
-    end
-  else
-    action = 'a'
-    tagstack.items = { item }
-  end
-  tagstack.curidx = tagstack.curidx + 1
-  vfn.settagstack(winid, tagstack, action)
-end
-local function handle_location(result)
-  -- We can sometimes get a list of locations, so set the first value as the
-  -- only value we want to handle
-  -- TODO(ashkan) was this correct^? We could use location lists.
-  if result[1] ~= nil then
-    result = result[1]
-  end
-  if result.uri == nil then
-    err_message('[LSP] Could not find a valid location')
-    return
-  end
-  local bufnr = vim.uri_to_bufnr(result.uri)
-  update_tagstack()
-  api.nvim_set_current_buf(bufnr)
-  local row = result.range.start.line
-  local col = result.range.start.character
-  local line = api.nvim_buf_get_lines(0, row, row+1, true)[1]
-  col = #line:sub(1, col)
-  api.nvim_win_set_cursor(0, {row + 1, col})
-  return true
-end
-local function location_callback(_, method, result)
-  if result == nil or vim.tbl_isempty(result) then
-    local _ = log.info() and log.info(method, 'No location found')
-    return nil
-  end
-  return handle_location(result)
-end
-
 function M.declaration()
   local params = util.make_position_params()
-  request('textDocument/declaration', params, location_callback)
+  request('textDocument/declaration', params)
 end
 
 function M.definition()
   local params = util.make_position_params()
-  request('textDocument/definition', params, location_callback)
+  request('textDocument/definition', params)
 end
 
 function M.type_definition()
   local params = util.make_position_params()
-  request('textDocument/typeDefinition', params, location_callback)
+  request('textDocument/typeDefinition', params)
 end
 
 function M.implementation()
   local params = util.make_position_params()
-  request('textDocument/implementation', params, location_callback)
-end
-
---- Convert SignatureHelp response to preview contents.
--- https://microsoft.github.io/language-server-protocol/specifications/specification-3-14/#textDocument_signatureHelp
-local function signature_help_to_preview_contents(input)
-  if not input.signatures then
-    return
-  end
-  --The active signature. If omitted or the value lies outside the range of
-  --`signatures` the value defaults to zero or is ignored if `signatures.length
-  --=== 0`. Whenever possible implementors should make an active decision about
-  --the active signature and shouldn't rely on a default value.
-  local contents = {}
-  local active_signature = input.activeSignature or 0
-  -- If the activeSignature is not inside the valid range, then clip it.
-  if active_signature >= #input.signatures then
-    active_signature = 0
-  end
-  local signature = input.signatures[active_signature + 1]
-  if not signature then
-    return
-  end
-  list_extend(contents, vim.split(signature.label, '\n', true))
-  if signature.documentation then
-    util.convert_input_to_markdown_lines(signature.documentation, contents)
-  end
-  if input.parameters then
-    local active_parameter = input.activeParameter or 0
-    -- If the activeParameter is not inside the valid range, then clip it.
-    if active_parameter >= #input.parameters then
-      active_parameter = 0
-    end
-    local parameter = signature.parameters and signature.parameters[active_parameter]
-    if parameter then
-      --[=[
-      --Represents a parameter of a callable-signature. A parameter can
-      --have a label and a doc-comment.
-      interface ParameterInformation {
-        --The label of this parameter information.
-        --
-        --Either a string or an inclusive start and exclusive end offsets within its containing
-        --signature label. (see SignatureInformation.label). The offsets are based on a UTF-16
-        --string representation as `Position` and `Range` does.
-        --
-        --*Note*: a label of type string should be a substring of its containing signature label.
-        --Its intended use case is to highlight the parameter label part in the `SignatureInformation.label`.
-        label: string | [number, number];
-        --The human-readable doc-comment of this parameter. Will be shown
-        --in the UI but can be omitted.
-        documentation?: string | MarkupContent;
-      }
-      --]=]
-      -- TODO highlight parameter
-      if parameter.documentation then
-        util.convert_input_to_markdown_lines(parameter.documentation, contents)
-      end
-    end
-  end
-  return contents
+  request('textDocument/implementation', params)
 end
 
 function M.signature_help()
   local params = util.make_position_params()
-  focusable_preview('textDocument/signatureHelp', params, function(result)
-    if not (result and result.signatures and result.signatures[1]) then
-      return { 'No signature available' }
-    end
-
-    -- TODO show empty popup when signatures is empty?
-    local lines = signature_help_to_preview_contents(result)
-    lines = util.trim_empty_lines(lines)
-    if vim.tbl_isempty(lines) then
-      return { 'No signature available' }
-    end
-    return lines, util.try_trim_markdown_code_blocks(lines)
-  end)
+  request('textDocument/signatureHelp', params)
 end
 
 -- TODO(ashkan) ?
 function M.completion(context)
   local params = util.make_position_params()
   params.context = context
-  return request('textDocument/completion', params, function(_, _, result)
-    if vim.tbl_isempty(result or {}) then return end
-    local row, col = unpack(api.nvim_win_get_cursor(0))
-    local line = assert(api.nvim_buf_get_lines(0, row-1, row, false)[1])
-    local line_to_cursor = line:sub(col+1)
-
-    local matches = util.text_document_completion_list_to_complete_items(result, line_to_cursor)
-    vim.fn.complete(col, matches)
-  end)
+  return request('textDocument/completion', params)
 end
 
 function M.formatting(options)
   validate { options = {options, 't', true} }
   options = vim.tbl_extend('keep', options or {}, {
-    tabSize = api.nvim_buf_get_option(0, 'tabstop');
-    insertSpaces = api.nvim_buf_get_option(0, 'expandtab');
+    tabSize = vim.bo.tabstop;
+    insertSpaces = vim.bo.expandtab;
   })
   local params = {
     textDocument = { uri = vim.uri_from_bufnr(0) };
     options = options;
   }
-  return request('textDocument/formatting', params, function(_, _, result)
-    if not result then return end
-    util.apply_text_edits(result)
-  end)
+  return request('textDocument/formatting', params)
 end
 
 function M.range_formatting(options, start_pos, end_pos)
@@ -289,8 +86,8 @@ function M.range_formatting(options, start_pos, end_pos)
     end_pos = {end_pos, 't', true};
   }
   options = vim.tbl_extend('keep', options or {}, {
-    tabSize = api.nvim_buf_get_option(0, 'tabstop');
-    insertSpaces = api.nvim_buf_get_option(0, 'expandtab');
+    tabSize = vim.bo.tabstop;
+    insertSpaces = vim.bo.expandtab;
   })
   local A = list_extend({}, start_pos or api.nvim_buf_get_mark(0, '<'))
   local B = list_extend({}, end_pos or api.nvim_buf_get_mark(0, '>'))
@@ -299,10 +96,10 @@ function M.range_formatting(options, start_pos, end_pos)
   B[1] = B[1] - 1
   -- account for encoding.
   if A[2] > 0 then
-    A = {A[1], util.character_offset(0, unpack(A))}
+    A = {A[1], util.character_offset(0, A[1], A[2])}
   end
   if B[2] > 0 then
-    B = {B[1], util.character_offset(0, unpack(B))}
+    B = {B[1], util.character_offset(0, B[1], B[2])}
   end
   local params = {
     textDocument = { uri = vim.uri_from_bufnr(0) };
@@ -312,10 +109,7 @@ function M.range_formatting(options, start_pos, end_pos)
     };
     options = options;
   }
-  return request('textDocument/rangeFormatting', params, function(_, _, result)
-    if not result then return end
-    util.apply_text_edits(result)
-  end)
+  return request('textDocument/rangeFormatting', params)
 end
 
 function M.rename(new_name)
@@ -325,10 +119,7 @@ function M.rename(new_name)
   new_name = new_name or npcall(vfn.input, "New Name: ")
   if not (new_name and #new_name > 0) then return end
   params.newName = new_name
-  request('textDocument/rename', params, function(_, _, result)
-    if not result then return end
-    util.apply_workspace_edit(result)
-  end)
+  request('textDocument/rename', params)
 end
 
 function M.references(context)
@@ -338,11 +129,7 @@ function M.references(context)
     includeDeclaration = true;
   }
   params[vim.type_idx] = vim.types.dictionary
-  request('textDocument/references', params, function(_, _, result)
-    if not result then return end
-    util.set_qflist(result)
-    vim.api.nvim_command("copen")
-  end)
+  request('textDocument/references', params)
 end
 
 return M
diff --git a/runtime/lua/vim/lsp/callbacks.lua b/runtime/lua/vim/lsp/callbacks.lua
new file mode 100644
index 0000000000..4fc3f74519
--- /dev/null
+++ b/runtime/lua/vim/lsp/callbacks.lua
@@ -0,0 +1,223 @@
+local log = require 'vim.lsp.log'
+local protocol = require 'vim.lsp.protocol'
+local util = require 'vim.lsp.util'
+local vim = vim
+local api = vim.api
+
+local M = {}
+
+local function err_message(...)
+  api.nvim_err_writeln(table.concat(vim.tbl_flatten{...}))
+  api.nvim_command("redraw")
+end
+
+M['workspace/applyEdit'] = function(_, _, workspace_edit)
+  if not workspace_edit then return end
+  -- TODO(ashkan) Do something more with label?
+  if workspace_edit.label then
+    print("Workspace edit", workspace_edit.label)
+  end
+  util.apply_workspace_edit(workspace_edit.edit)
+end
+
+M['textDocument/publishDiagnostics'] = function(_, _, result)
+  if not result then return end
+  local uri = result.uri
+  local bufnr = vim.uri_to_bufnr(uri)
+  if not bufnr then
+    err_message("LSP.publishDiagnostics: Couldn't find buffer for ", uri)
+    return
+  end
+  util.buf_clear_diagnostics(bufnr)
+  util.buf_diagnostics_save_positions(bufnr, result.diagnostics)
+  util.buf_diagnostics_underline(bufnr, result.diagnostics)
+  util.buf_diagnostics_virtual_text(bufnr, result.diagnostics)
+  -- util.set_loclist(result.diagnostics)
+end
+
+M['textDocument/references'] = function(_, _, result)
+  if not result then return end
+  util.set_qflist(result)
+  api.nvim_command("copen")
+  api.nvim_command("wincmd p")
+end
+
+M['textDocument/rename'] = function(_, _, result)
+  if not result then return end
+  util.apply_workspace_edit(result)
+end
+
+M['textDocument/rangeFormatting'] = function(_, _, result)
+  if not result then return end
+  util.apply_text_edits(result)
+end
+
+M['textDocument/formatting'] = function(_, _, result)
+  if not result then return end
+  util.apply_text_edits(result)
+end
+
+M['textDocument/completion'] = function(_, _, result)
+  if vim.tbl_isempty(result or {}) then return end
+  local row, col = unpack(api.nvim_win_get_cursor(0))
+  local line = assert(api.nvim_buf_get_lines(0, row-1, row, false)[1])
+  local line_to_cursor = line:sub(col+1)
+
+  local matches = util.text_document_completion_list_to_complete_items(result, line_to_cursor)
+  vim.fn.complete(col, matches)
+end
+
+M['textDocument/hover'] = function(_, method, result)
+  util.focusable_preview(method, function()
+    if not (result and result.contents) then
+      return { 'No information available' }
+    end
+    local markdown_lines = util.convert_input_to_markdown_lines(result.contents)
+    markdown_lines = util.trim_empty_lines(markdown_lines)
+    if vim.tbl_isempty(markdown_lines) then
+      return { 'No information available' }
+    end
+    return markdown_lines, util.try_trim_markdown_code_blocks(markdown_lines)
+  end)
+end
+
+local function location_callback(_, method, result)
+  if result == nil or vim.tbl_isempty(result) then
+    local _ = log.info() and log.info(method, 'No location found')
+    return nil
+  end
+  util.jump_to_location(result[1])
+  if #result > 1 then
+    util.set_qflist(result)
+    api.nvim_command("copen")
+    api.nvim_command("wincmd p")
+  end
+end
+
+M['textDocument/declaration'] = location_callback
+M['textDocument/definition'] = location_callback
+M['textDocument/typeDefinition'] = location_callback
+M['textDocument/implementation'] = location_callback
+
+--- Convert SignatureHelp response to preview contents.
+-- https://microsoft.github.io/language-server-protocol/specifications/specification-3-14/#textDocument_signatureHelp
+local function signature_help_to_preview_contents(input)
+  if not input.signatures then
+    return
+  end
+  --The active signature. If omitted or the value lies outside the range of
+  --`signatures` the value defaults to zero or is ignored if `signatures.length
+  --=== 0`. Whenever possible implementors should make an active decision about
+  --the active signature and shouldn't rely on a default value.
+  local contents = {}
+  local active_signature = input.activeSignature or 0
+  -- If the activeSignature is not inside the valid range, then clip it.
+  if active_signature >= #input.signatures then
+    active_signature = 0
+  end
+  local signature = input.signatures[active_signature + 1]
+  if not signature then
+    return
+  end
+  vim.list_extend(contents, vim.split(signature.label, '\n', true))
+  if signature.documentation then
+    util.convert_input_to_markdown_lines(signature.documentation, contents)
+  end
+  if input.parameters then
+    local active_parameter = input.activeParameter or 0
+    -- If the activeParameter is not inside the valid range, then clip it.
+    if active_parameter >= #input.parameters then
+      active_parameter = 0
+    end
+    local parameter = signature.parameters and signature.parameters[active_parameter]
+    if parameter then
+      --[=[
+      --Represents a parameter of a callable-signature. A parameter can
+      --have a label and a doc-comment.
+      interface ParameterInformation {
+        --The label of this parameter information.
+        --
+        --Either a string or an inclusive start and exclusive end offsets within its containing
+        --signature label. (see SignatureInformation.label). The offsets are based on a UTF-16
+        --string representation as `Position` and `Range` does.
+        --
+        --*Note*: a label of type string should be a substring of its containing signature label.
+        --Its intended use case is to highlight the parameter label part in the `SignatureInformation.label`.
+        label: string | [number, number];
+        --The human-readable doc-comment of this parameter. Will be shown
+        --in the UI but can be omitted.
+        documentation?: string | MarkupContent;
+      }
+      --]=]
+      -- TODO highlight parameter
+      if parameter.documentation then
+        util.convert_input_to_markdown_lines(parameter.documentation, contents)
+      end
+    end
+  end
+  return contents
+end
+
+M['textDocument/signatureHelp'] = function(_, method, result)
+  util.focusable_preview(method, function()
+    if not (result and result.signatures and result.signatures[1]) then
+      return { 'No signature available' }
+    end
+    -- TODO show popup when signatures is empty?
+    local lines = signature_help_to_preview_contents(result)
+    lines = util.trim_empty_lines(lines)
+    if vim.tbl_isempty(lines) then
+      return { 'No signature available' }
+    end
+    return lines, util.try_trim_markdown_code_blocks(lines)
+  end)
+end
+
+M['textDocument/peekDefinition'] = function(_, _, result, _)
+  if not (result and result[1]) then return end
+  local loc = result[1]
+  local bufnr = vim.uri_to_bufnr(loc.uri) or error("not found: "..tostring(loc.uri))
+  local start = loc.range.start
+  local finish = loc.range["end"]
+  util.open_floating_peek_preview(bufnr, start, finish, { offset_x = 1 })
+  local headbuf = util.open_floating_preview({"Peek:"}, nil, {
+    offset_y = -(finish.line - start.line);
+    width = finish.character - start.character + 2;
+  })
+  -- TODO(ashkan) change highlight group?
+  api.nvim_buf_add_highlight(headbuf, -1, 'Keyword', 0, -1)
+end
+
+local function log_message(_, _, result, client_id)
+  local message_type = result.type
+  local message = result.message
+  local client = vim.lsp.get_client_by_id(client_id)
+  local client_name = client and client.name or string.format("id=%d", client_id)
+  if not client then
+    err_message("LSP[", client_name, "] client has shut down after sending the message")
+  end
+  if message_type == protocol.MessageType.Error then
+    err_message("LSP[", client_name, "] ", message)
+  else
+    local message_type_name = protocol.MessageType[message_type]
+    api.nvim_out_write(string.format("LSP[%s][%s] %s\n", client_name, message_type_name, message))
+  end
+  return result
+end
+
+M['window/showMessage'] = log_message
+M['window/logMessage'] = log_message
+
+-- Add boilerplate error validation and logging for all of these.
+for k, fn in pairs(M) do
+  M[k] = function(err, method, params, client_id)
+    local _ = log.debug() and log.debug('default_callback', method, { params = params, client_id = client_id, err = err })
+    if err then
+      error(tostring(err))
+    end
+    return fn(err, method, params, client_id)
+  end
+end
+
+return M
+-- vim:sw=2 ts=2 et
diff --git a/runtime/lua/vim/lsp/default_callbacks.lua b/runtime/lua/vim/lsp/default_callbacks.lua
deleted file mode 100644
index 2a891e7d1d..0000000000
--- a/runtime/lua/vim/lsp/default_callbacks.lua
+++ /dev/null
@@ -1,69 +0,0 @@
-local log = require 'vim.lsp.log'
-local protocol = require 'vim.lsp.protocol'
-local util = require 'vim.lsp.util'
-local api = vim.api
-
-local M = {}
-
-local function err_message(...)
-  api.nvim_err_writeln(table.concat(vim.tbl_flatten{...}))
-  api.nvim_command("redraw")
-end
-
-M['workspace/applyEdit'] = function(_, _, workspace_edit)
-  if not workspace_edit then return end
-  -- TODO(ashkan) Do something more with label?
-  if workspace_edit.label then
-    print("Workspace edit", workspace_edit.label)
-  end
-  util.apply_workspace_edit(workspace_edit.edit)
-end
-
-M['textDocument/publishDiagnostics'] = function(_, _, result)
-  if not result then return end
-  local uri = result.uri
-  local bufnr = vim.uri_to_bufnr(uri)
-  if not bufnr then
-    err_message("LSP.publishDiagnostics: Couldn't find buffer for ", uri)
-    return
-  end
-  util.buf_clear_diagnostics(bufnr)
-  util.buf_diagnostics_save_positions(bufnr, result.diagnostics)
-  util.buf_diagnostics_underline(bufnr, result.diagnostics)
-  util.buf_diagnostics_virtual_text(bufnr, result.diagnostics)
-  -- util.set_loclist(result.diagnostics)
-end
-
-local function log_message(_, _, result, client_id)
-  local message_type = result.type
-  local message = result.message
-  local client = vim.lsp.get_client_by_id(client_id)
-  local client_name = client and client.name or string.format("id=%d", client_id)
-  if not client then
-    err_message("LSP[", client_name, "] client has shut down after sending the message")
-  end
-  if message_type == protocol.MessageType.Error then
-    err_message("LSP[", client_name, "] ", message)
-  else
-    local message_type_name = protocol.MessageType[message_type]
-    api.nvim_out_write(string.format("LSP[%s][%s] %s\n", client_name, message_type_name, message))
-  end
-  return result
-end
-
-M['window/showMessage'] = log_message
-M['window/logMessage'] = log_message
-
--- Add boilerplate error validation and logging for all of these.
-for k, fn in pairs(M) do
-  M[k] = function(err, method, params, client_id)
-    local _ = log.debug() and log.debug('default_callback', method, { params = params, client_id = client_id, err = err })
-    if err then
-      error(tostring(err))
-    end
-    return fn(err, method, params, client_id)
-  end
-end
-
-return M
--- vim:sw=2 ts=2 et
diff --git a/runtime/lua/vim/lsp/util.lua b/runtime/lua/vim/lsp/util.lua
index 2dfcdfc70c..6e0d3fd4ee 100644
--- a/runtime/lua/vim/lsp/util.lua
+++ b/runtime/lua/vim/lsp/util.lua
@@ -2,6 +2,7 @@ local protocol = require 'vim.lsp.protocol'
 local vim = vim
 local validate = vim.validate
 local api = vim.api
+local list_extend = vim.list_extend
 
 local M = {}
 
@@ -10,7 +11,13 @@ local function split_lines(value)
   return split(value, '\n', true)
 end
 
-local list_extend = vim.list_extend
+local function ok_or_nil(status, ...)
+  if not status then return end
+  return ...
+end
+local function npcall(fn, ...)
+  return ok_or_nil(pcall(fn, ...))
+end
 
 --- Find the longest shared prefix between prefix and word.
 -- e.g. remove_prefix("123tes", "testing") == "ting"
@@ -303,6 +310,50 @@ function M.make_floating_popup_options(width, height, opts)
   }
 end
 
+function M.jump_to_location(location)
+  if location.uri == nil then return end
+  local bufnr = vim.uri_to_bufnr(location.uri)
+  -- TODO(ashkan) use tagfunc here to update tagstack.
+  api.nvim_set_current_buf(bufnr)
+  local row = location.range.start.line
+  local col = location.range.start.character
+  local line = api.nvim_buf_get_lines(0, row, row+1, true)[1]
+  col = vim.str_byteindex(line, col)
+  api.nvim_win_set_cursor(0, {row + 1, col})
+  return true
+end
+
+local function find_window_by_var(name, value)
+  for _, win in ipairs(api.nvim_list_wins()) do
+    if npcall(api.nvim_win_get_var, win, name) == value then
+      return win
+    end
+  end
+end
+
+-- Check if a window with `unique_name` tagged is associated with the current
+-- buffer. If not, make a new preview.
+--
+-- fn()'s return values will be passed directly to open_floating_preview in the
+-- case that a new floating window should be created.
+function M.focusable_preview(unique_name, fn)
+  if npcall(api.nvim_win_get_var, 0, unique_name) then
+    return api.nvim_command("wincmd p")
+  end
+  local bufnr = api.nvim_get_current_buf()
+  do
+    local win = find_window_by_var(unique_name, bufnr)
+    if win then
+      api.nvim_set_current_win(win)
+      api.nvim_command("stopinsert")
+      return
+    end
+  end
+  local pbufnr, pwinnr = M.open_floating_preview(fn())
+  api.nvim_win_set_var(pwinnr, unique_name, bufnr)
+  return pbufnr, pwinnr
+end
+
 function M.open_floating_preview(contents, filetype, opts)
   validate {
     contents = { contents, 't' };
@@ -609,12 +660,13 @@ function M.locations_to_items(locations)
           if pos.character > #line then
             col = #line
           else
-            col =  vim.str_byteindex(line, pos.character)
+            col = vim.str_byteindex(line, pos.character)
           end
           table.insert(items, {
             filename = fname,
             lnum = row + 1,
             col = col + 1;
+            text = line;
           })
         end
       end