feat: Add dry_run option and report if buffer was/would be changed by formatters (#273)

* feat: add dry_run option and pass return values for if buffer would be modified

* fix: implement dry_run for blocking calls to lsp formatter

* refactor: change `changed` variable to `did_edit`

* docs: Update README

* fix: address PR comments

* fix: small cleanups

---------

Co-authored-by: Steven Arcangeli <stevearc@stevearc.com>

1 files changed, 33 insertions, 8 deletions

diff --git a/lua/conform/lsp_format.lua b/lua/conform/lsp_format.lua
index cd6e429..f49e15f 100644
--- a/lua/conform/lsp_format.lua
+++ b/lua/conform/lsp_format.lua
@@ -4,7 +4,7 @@ local util = require("vim.lsp.util")
 
 local M = {}
 
-local function apply_text_edits(text_edits, bufnr, offset_encoding)
+local function apply_text_edits(text_edits, bufnr, offset_encoding, dry_run)
   if
     #text_edits == 1
     and text_edits[1].range.start.line == 0
@@ -19,9 +19,19 @@ local function apply_text_edits(text_edits, bufnr, offset_encoding)
       table.remove(new_lines)
     end
     log.debug("Converting full-file LSP format to piecewise format")
-    require("conform.runner").apply_format(bufnr, original_lines, new_lines, nil, false)
+    return require("conform.runner").apply_format(
+      bufnr,
+      original_lines,
+      new_lines,
+      nil,
+      false,
+      dry_run
+    )
+  elseif dry_run then
+    return #text_edits > 0
   else
     vim.lsp.util.apply_text_edits(text_edits, bufnr, offset_encoding)
+    return #text_edits > 0
   end
 end
 
@@ -56,7 +66,7 @@ function M.get_format_clients(options)
 end
 
 ---@param options table
----@param callback fun(err?: string)
+---@param callback fun(err?: string, did_edit?: boolean)
 function M.format(options, callback)
   options = options or {}
   if not options.bufnr or options.bufnr == 0 then
@@ -84,9 +94,10 @@ function M.format(options, callback)
   if options.async then
     local changedtick = vim.b[bufnr].changedtick
     local do_format
+    local did_edit = false
     do_format = function(idx, client)
       if not client then
-        return callback()
+        return callback(nil, did_edit)
       end
       local params = set_range(client, util.make_formatting_params(options.formatting_options))
       local auto_id = vim.api.nvim_create_autocmd("LspDetach", {
@@ -112,21 +123,35 @@ function M.format(options, callback)
             )
           )
         else
-          apply_text_edits(result, ctx.bufnr, client.offset_encoding)
+          local this_did_edit =
+            apply_text_edits(result, ctx.bufnr, client.offset_encoding, options.dry_run)
           changedtick = vim.b[bufnr].changedtick
 
-          do_format(next(clients, idx))
+          if options.dry_run and this_did_edit then
+            callback(nil, true)
+          else
+            did_edit = did_edit or this_did_edit
+            do_format(next(clients, idx))
+          end
         end
       end, bufnr)
     end
     do_format(next(clients))
   else
     local timeout_ms = options.timeout_ms or 1000
+    local did_edit = false
     for _, client in pairs(clients) do
       local params = set_range(client, util.make_formatting_params(options.formatting_options))
       local result, err = client.request_sync(method, params, timeout_ms, bufnr)
       if result and result.result then
-        apply_text_edits(result.result, bufnr, client.offset_encoding)
+        local this_did_edit =
+          apply_text_edits(result.result, bufnr, client.offset_encoding, options.dry_run)
+        did_edit = did_edit or this_did_edit
+
+        if options.dry_run and did_edit then
+          callback(nil, true)
+          return true
+        end
       elseif err then
         if not options.quiet then
           vim.notify(string.format("[LSP][%s] %s", client.name, err), vim.log.levels.WARN)
@@ -134,7 +159,7 @@ function M.format(options, callback)
         return callback(string.format("[LSP][%s] %s", client.name, err))
       end
     end
-    callback()
+    callback(nil, did_edit)
   end
 end