revert: "fix(lsp): use buffer scheme for files not stored on disk" (#22604)

Although using `buffer://` for unsaved file buffers fixes issues with
language servers like eclipse.jdt.ls or ansible-language-server, it
breaks completion and signature help for clangd.

A regression is worse than a fix for something else, so this reverts
commit 896d672736.

The spec change is also still in dicussion, see
https://github.com/microsoft/language-server-protocol/pull/1679#discussion_r1130704886

runtime/lua/vim/lsp.lua

@@ -369,7 +369,7 @@ do
   --- @field offset_encoding "utf-8"|"utf-16"|"utf-32"
   ---
   --- @class CTBufferState
-  --- @field uri string uri of the buffer
+  --- @field name string name of the buffer
   --- @field lines string[] snapshot of buffer lines from last didChange
   --- @field lines_tmp string[]
   --- @field pending_changes table[] List of debounced changes in incremental sync mode
@@ -488,12 +488,8 @@ do
     if buf_state then
       buf_state.refs = buf_state.refs + 1
     else
-      local uri = vim.uri_from_bufnr(bufnr)
-      if not uv.fs_stat(api.nvim_buf_get_name(bufnr)) then
-        uri = uri:gsub('^file://', 'buffer://')
-      end
       buf_state = {
-        uri = uri,
+        name = api.nvim_buf_get_name(bufnr),
         lines = {},
         lines_tmp = {},
         pending_changes = {},
@@ -508,26 +504,12 @@ do
   end
 
   ---@private
-  ---@param client table
-  ---@param bufnr integer
-  ---@return string uri
-  function changetracking._get_uri(client, bufnr)
+  function changetracking._get_and_set_name(client, bufnr, name)
     local state = state_by_group[get_group(client)] or {}
     local buf_state = (state.buffers or {})[bufnr]
-    return assert(buf_state.uri, 'Must have an URI set')
-  end
-
-  ---@private
-  ---@param client table
-  ---@param bufnr integer
-  ---@param uri string
-  ---@return string uri
-  function changetracking._get_and_set_uri(client, bufnr, uri)
-    local state = state_by_group[get_group(client)] or {}
-    local buf_state = (state.buffers or {})[bufnr]
-    local old_uri = buf_state.uri
-    buf_state.uri = uri
-    return old_uri
+    local old_name = buf_state.name
+    buf_state.name = name
+    return old_name
   end
 
   ---@private
@@ -614,7 +596,7 @@ do
         { text = buf_get_full_text(bufnr) },
       }
     end
-    local uri = buf_state.uri
+    local uri = vim.uri_from_bufnr(bufnr)
     for _, client in pairs(state.clients) do
       if not client.is_stopped() and lsp.buf_is_attached(bufnr, client.id) then
         client.notify('textDocument/didChange', {
@@ -727,14 +709,11 @@ local function text_document_did_open_handler(bufnr, client)
     return
   end
   local filetype = nvim_buf_get_option(bufnr, 'filetype')
-  local uri = vim.uri_from_bufnr(bufnr)
-  if not uv.fs_stat(api.nvim_buf_get_name(bufnr)) then
-    uri = uri:gsub('^file://', 'buffer://')
-  end
+
   local params = {
     textDocument = {
       version = 0,
-      uri = uri,
+      uri = vim.uri_from_bufnr(bufnr),
       languageId = client.config.get_language_id(bufnr, filetype),
       text = buf_get_full_text(bufnr),
     },
@@ -1611,13 +1590,8 @@ local function text_document_did_save_handler(bufnr)
   local text = once(buf_get_full_text)
   for_each_buffer_client(bufnr, function(client)
     local name = api.nvim_buf_get_name(bufnr)
-    local old_uri = changetracking._get_and_set_uri(client, bufnr, uri)
-    if old_uri and name ~= old_uri then
-      client.notify('textDocument/didClose', {
-        textDocument = {
-          uri = old_uri,
-        },
-      })
+    local old_name = changetracking._get_and_set_name(client, bufnr, name)
+    if old_name and name ~= old_name then
       client.notify('textDocument/didOpen', {
         textDocument = {
           version = 0,
@@ -1720,12 +1694,8 @@ function lsp.buf_attach_client(bufnr, client_id)
         end)
       end,
       on_detach = function()
+        local params = { textDocument = { uri = uri } }
         for_each_buffer_client(bufnr, function(client, _)
-          local params = {
-            textDocument = {
-              uri = changetracking._get_uri(client, bufnr),
-            },
-          }
           changetracking.reset_buf(client, bufnr)
           if vim.tbl_get(client.server_capabilities, 'textDocumentSync', 'openClose') then
             client.notify('textDocument/didClose', params)