fix(lsp): incorrect rendering of markdown codeblock #40861

Problem:
LSP hover erroneously drops blank lines before a 4-space-indented
codeblock, which is not valid Markdown. This causes incorrect parsing
and wrong display.

Solution:
Fix `split_lines` so that it doesn't drop the blank line just before
a 4-space-indented codeblock.

fix https://github.com/neovim/neovim/issues/40860

(cherry picked from commit 317c5ddda6)

runtime/lua/vim/lsp/util.lua

@@ -92,18 +92,29 @@ end
 ---
 --- @param s string Multiline string
 --- @param no_blank boolean? Drop blank lines for each @param/@return (except one empty line
---- separating each). Workaround for https://github.com/LuaLS/lua-language-server/issues/2333
+--- separating each, and before a codeblock).
+--- Workaround for https://github.com/LuaLS/lua-language-server/issues/2333
 local function split_lines(s, no_blank)
   s = string.gsub(s, '\r\n?', '\n')
+  local raw = vim.split(s, '\n', { plain = true, trimempty = true })
+
+  --- @return boolean # true if line begins a (4-space-indented) codeblock. #40860
+  local function codeblock(l)
+    return l:find('^    ') or l:find('^\t')
+  end
+
   local lines = {}
   local in_desc = true -- Main description block, before seeing any @foo.
-  for line in vim.gsplit(s, '\n', { plain = true, trimempty = true }) do
+  for i, line in ipairs(raw) do
     local start_annotation = not not line:find('^ ?%@.?[pr]')
     in_desc = (not start_annotation) and in_desc or false
     if start_annotation and no_blank and not (lines[#lines] or ''):find('^%s*$') then
       table.insert(lines, '') -- Separate each @foo with a blank line.
     end
-    if in_desc or not no_blank or not line:find('^%s*$') then
+
+    local blank = line:find('^%s*$')
+    local keep_blank = blank and codeblock(raw[i + 1] or '') -- Keep if it precedes a codeblock. #40860
+    if in_desc or not no_blank or not blank or keep_blank then
       table.insert(lines, line)
     end
   end

test/functional/plugin/lsp/util_spec.lua

@@ -1209,7 +1209,7 @@ describe('vim.lsp.util', function()
       local r = exec_lua(function()
         local hover_data = {
           kind = 'markdown',
-          value = '```lua\nfunction vim.api.nvim_buf_attach(buffer: integer, send_buffer: boolean, opts: vim.api.keyset.buf_attach)\n  -> boolean\n```\n\n---\n\n Activates buffer-update events. Example:\n\n\n\n ```lua\n events = {}\n vim.api.nvim_buf_attach(0, false, {\n   on_lines = function(...)\n     table.insert(events, {...})\n   end,\n })\n ```\n\n\n @see `nvim_buf_detach()`\n @see `api-buffer-updates-lua`\n@*param* `buffer` — Buffer handle, or 0 for current buffer\n\n\n\n@*param* `send_buffer` — True if whole buffer.\n Else the first notification will be `nvim_buf_changedtick_event`.\n\n\n@*param* `opts` — Optional parameters.\n\n - on_lines: Lua callback. Args:\n   - the string "lines"\n   - buffer handle\n   - b:changedtick\n@*return* — False if foo;\n\n otherwise True.\n\n@see foo\n@see bar\n\n',
+          value = '```lua\nfunction vim.api.nvim_buf_attach(buffer: integer, send_buffer: boolean, opts: vim.api.keyset.buf_attach)\n  -> boolean\n```\n\n---\n\n Activates buffer-update events. Example:\n\n\n\n ```lua\n events = {}\n vim.api.nvim_buf_attach(0, false, {\n   on_lines = function(...)\n     table.insert(events, {...})\n   end,\n })\n ```\n\n\n @see `nvim_buf_detach()`\n @see `api-buffer-updates-lua`\n@*param* `buffer` — Buffer handle, or 0 for current buffer\n\n\n\n@*param* `send_buffer` — True if whole buffer.\n Else the first notification will be `nvim_buf_changedtick_event`.\n\n\n@*param* `opts` — Optional parameters.\n\n - on_lines: Lua callback. Args:\n   - the string "lines"\n   - buffer handle\n   - b:changedtick\n@*return* — False if foo;\n\n otherwise True.\n\n@see foo\n@see bar\n\nExample:\n\n    iex> params = %{title: "", topics: []}\n\n    iex> changeset.changes[:topics]\n',
         }
         return vim.lsp.util.convert_input_to_markdown_lines(hover_data)
       end)
@@ -1256,6 +1256,12 @@ describe('vim.lsp.util', function()
         ' otherwise True.',
         '@see foo',
         '@see bar',
+        -- Blank line preceding a 4-space-indented codeblock is required, per Markdown spec. #40860
+        'Example:',
+        '',
+        '    iex> params = %{title: "", topics: []}',
+        '',
+        '    iex> changeset.changes[:topics]',
       }
       eq(expected, r)
     end)