fix(difftool): fully resolve symlinks when comparing paths #36147

Fixes issue on mac where it was constantly reloading buffers as paths
were not being normalized and resolved correctly (in relation to buffer
name).

Quickfix entry:
/var/folders/pt/2s7dzyw12v36tsslrghfgpkr0000gn/T/git-difftool.m95lj8/right/app.vue

Buffer name:
/private/var/folders/pt/2s7dzyw12v36tsslrghfgpkr0000gn/T/git-difftool.m95lj8/right/app.vue

/var was synlinked to /private/var and this was not being properly
handled.

Also added lazy redraw to avoid too many redraws when this happens in
future and added test for symlink handling.

Signed-off-by: Tomas Slusny <slusnucky@gmail.com>

runtime/lua/vim/_core/util.lua

@@ -5,12 +5,20 @@ local M = {}
 --- @param file string
 --- @return number buffer number of the edited buffer
 M.edit_in = function(winnr, file)
+  local function resolved_path(path)
+    if not path or path == '' then
+      return ''
+    end
+    return vim.fn.resolve(vim.fs.abspath(path))
+  end
+
   return vim.api.nvim_win_call(winnr, function()
-    local current = vim.fs.abspath(vim.api.nvim_buf_get_name(vim.api.nvim_win_get_buf(winnr)))
+    local current_buf = vim.api.nvim_win_get_buf(winnr)
+    local current = resolved_path(vim.api.nvim_buf_get_name(current_buf))
 
     -- Check if the current buffer is already the target file
-    if current == (file and vim.fs.abspath(file) or '') then
-      return vim.api.nvim_get_current_buf()
+    if current == resolved_path(file) then
+      return current_buf
     end
 
     -- Read the file into the buffer

runtime/pack/dist/opt/nvim.difftool/lua/difftool.lua

@@ -140,14 +140,16 @@ local function diff_dirs_diffr(left_dir, right_dir, opt)
       elseif right_exists then
         status = 'A'
       end
+      local left = vim.fn.resolve(vim.fs.abspath(modified_left))
+      local right = vim.fn.resolve(vim.fs.abspath(modified_right))
       table.insert(qf_entries, {
-        filename = modified_right,
+        filename = right,
         text = status,
         user_data = {
           diff = true,
           rel = vim.fs.relpath(left_dir, modified_left),
-          left = vim.fs.abspath(modified_left),
-          right = vim.fs.abspath(modified_right),
+          left = left,
+          right = right,
         },
       })
     end
@@ -426,7 +428,7 @@ function M.open(left, right, opt)
   layout.group = vim.api.nvim_create_augroup('nvim.difftool.events', { clear = true })
   local hl_id = vim.api.nvim_create_namespace('nvim.difftool.hl')
 
-  local function get_diff_entry()
+  local function get_diff_entry(bufnr)
     --- @type {idx: number, items: table[], size: number}
     local qf_info = vim.fn.getqflist({ idx = 0, items = 1, size = 1 })
     if qf_info.size == 0 then
@@ -434,7 +436,12 @@ function M.open(left, right, opt)
     end
 
     local entry = qf_info.items[qf_info.idx]
-    if not entry or not entry.user_data or not entry.user_data.diff then
+    if
+      not entry
+      or not entry.user_data
+      or not entry.user_data.diff
+      or (bufnr and entry.bufnr ~= bufnr)
+    then
       return nil
     end
 
@@ -466,14 +473,16 @@ function M.open(left, right, opt)
   vim.api.nvim_create_autocmd('BufWinEnter', {
     group = layout.group,
     pattern = '*',
-    callback = function()
-      local entry = get_diff_entry()
+    callback = function(args)
+      local entry = get_diff_entry(args.buf)
       if not entry then
         return
       end
 
+      vim.w.lazyredraw = true
       vim.schedule(function()
         diff_files(entry.user_data.left, entry.user_data.right, true)
+        vim.w.lazyredraw = false
       end)
     end,
   })

test/functional/plugin/difftool_spec.lua

@@ -61,6 +61,31 @@ describe('nvim.difftool', function()
     )
   end)
 
+  it('handles symlinks', function()
+    -- Create a symlink in right dir pointing to file2.txt in left dir
+    local symlink_path = vim.fs.joinpath(testdir_right, 'file2.txt')
+    local target_path = vim.fs.joinpath('..', testdir_left, 'file2.txt')
+    assert(vim.uv.fs_symlink(target_path, symlink_path) == true)
+    finally(function()
+      os.remove(symlink_path)
+    end)
+    assert(fn.getftype(symlink_path) == 'link')
+
+    -- Run difftool
+    command(('DiffTool %s %s'):format(testdir_left, testdir_right))
+    local qflist = fn.getqflist()
+    local entries = {}
+    for _, item in ipairs(qflist) do
+      table.insert(entries, { text = item.text, rel = item.user_data and item.user_data.rel })
+    end
+
+    -- file2.txt should not be reported as added or deleted anymore
+    eq({
+      { text = 'M', rel = 'file1.txt' },
+      { text = 'A', rel = 'file3.txt' },
+    }, entries)
+  end)
+
   it('has autocmds when diff window is opened', function()
     command(('DiffTool %s %s'):format(testdir_left, testdir_right))
     local autocmds = fn.nvim_get_autocmds({ group = 'nvim.difftool.events' })