feat: apply changes as text edits using LSP utils (#18)

* feat: apply changes as text edits using LSP utils

This means we can leverage all of the work that was done in the LSP
client to preserve marks, cursor position, etc

* log: add trace logging to debug performance

* feat: use the same diff -> TextEdit technique for bad LSP servers

Some LSP servers simply return a single TextEdit that replaces the whole
buffer. This is bad for extmarks, cursor, and if the buffer is open in
multiple windows the non-active window will jump to the top. We can
detect that situation and apply the same vim.diff logic to convert it
into more granular TextEdits.

1 files changed, 22 insertions, 15 deletions

diff --git a/lua/conform/init.lua b/lua/conform/init.lua
index b47d43e..4a6b226 100644
--- a/lua/conform/init.lua
+++ b/lua/conform/init.lua
@@ -52,6 +52,25 @@ M.formatters = {}
 
 M.notify_on_error = true
 
+---@private
+M.original_apply_text_edits = vim.lsp.util.apply_text_edits
+
+local function apply_text_edits(text_edits, bufnr, offset_encoding)
+  if
+    #text_edits == 1
+    and text_edits[1].range.start.line == 0
+    and text_edits[1].range.start.character == 0
+    and text_edits[1].range["end"].line == vim.api.nvim_buf_line_count(bufnr) + 1
+    and text_edits[1].range["end"].character == 0
+  then
+    local original_lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, true)
+    local new_lines = vim.split(text_edits[1].newText, "\n", { plain = true })
+    require("conform.runner").apply_format(bufnr, original_lines, new_lines, nil, false)
+  else
+    M.original_apply_text_edits(text_edits, bufnr, offset_encoding)
+  end
+end
+
 M.setup = function(opts)
   opts = opts or {}
 
@@ -100,17 +119,9 @@ M.setup = function(opts)
     require("conform.health").show_window()
   end, { desc = "Show information about Conform formatters" })
 
-  ---@diagnostic disable-next-line: duplicate-set-field
-  vim.lsp.handlers["textDocument/formatting"] = function(_, result, ctx, _)
-    if not result then
-      return
-    end
-    local client = vim.lsp.get_client_by_id(ctx.client_id)
-    assert(client)
-    local restore = require("conform.util").save_win_positions(ctx.bufnr)
-    vim.lsp.util.apply_text_edits(result, ctx.bufnr, client.offset_encoding)
-    restore()
-  end
+  -- Monkey patch lsp.util.apply_text_edits to handle LSP clients that replace the entire buffer
+  -- during formatting. This is unfortunately the best place to shim that logic in.
+  vim.lsp.util.apply_text_edits = apply_text_edits
 end
 
 ---@param bufnr integer
@@ -289,11 +300,7 @@ M.format = function(opts)
     end
   elseif opts.lsp_fallback and supports_lsp_format(opts.bufnr) then
     log.debug("Running LSP formatter on %s", vim.api.nvim_buf_get_name(opts.bufnr))
-    local restore = require("conform.util").save_win_positions(opts.bufnr)
     vim.lsp.buf.format(opts)
-    if not opts.async then
-      restore()
-    end
   elseif any_formatters_configured and not opts.quiet then
     vim.notify("No formatters found for buffer. See :ConformInfo", vim.log.levels.WARN)
   else