From 6a507bad18a4fb184792a4b36c0f8bd675ce172e Mon Sep 17 00:00:00 2001
From: "neovim-backports[bot]"
 <175700243+neovim-backports[bot]@users.noreply.github.com>
Date: Mon, 17 Nov 2025 08:49:19 -0800
Subject: [PATCH] =?UTF-8?q?fix(vim.fs):=20abspath(".")=20returns=20"/?=
 =?UTF-8?q?=E2=80=A6/."=20(#36584)?=
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fix(vim.fs): abspath(".") returns "/…/." #36583

(cherry picked from commit 1f9d9cb2e56c484562960d6088ac877322500600)

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>
---
 runtime/lua/vim/fs.lua          |  9 +++++++--
 test/functional/lua/fs_spec.lua | 24 +++++++++++++++++-------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/runtime/lua/vim/fs.lua b/runtime/lua/vim/fs.lua
index c4c75558f2..338b4c94b0 100644
--- a/runtime/lua/vim/fs.lua
+++ b/runtime/lua/vim/fs.lua
@@ -437,7 +437,7 @@ function M.root(source, marker)
   for _, mark in ipairs(markers) do
     local paths = M.find(mark, {
       upward = true,
-      path = vim.fn.fnamemodify(path, ':p:h'),
+      path = M.abspath(path),
     })
 
     if #paths ~= 0 then
@@ -747,6 +747,8 @@ end
 --- @param path string Path
 --- @return string Absolute path
 function M.abspath(path)
+  -- TODO(justinmk): mark f_fnamemodify as API_FAST and use it, ":p:h" should be safe...
+
   vim.validate('path', path, 'string')
 
   -- Expand ~ to user's home directory
@@ -773,7 +775,10 @@ function M.abspath(path)
   -- Convert cwd path separator to `/`
   cwd = cwd:gsub(os_sep, '/')
 
-  -- Prefix is not needed for expanding relative paths, as `cwd` already contains it.
+  if path == '.' then
+    return cwd
+  end
+  -- Prefix is not needed for expanding relative paths, `cwd` already contains it.
   return M.joinpath(cwd, path)
 end
 
diff --git a/test/functional/lua/fs_spec.lua b/test/functional/lua/fs_spec.lua
index fd75077ae9..9a86aa6d04 100644
--- a/test/functional/lua/fs_spec.lua
+++ b/test/functional/lua/fs_spec.lua
@@ -412,23 +412,31 @@ describe('vim.fs', function()
       )
     end)
 
-    it('uses cwd for unnamed buffers', function()
+    it('returns CWD (absolute path) for unnamed buffers', function()
+      assert(n.fn.isabsolutepath(test_source_path) == 1)
       command('new')
-      eq(test_source_path, exec_lua([[return vim.fs.root(0, 'CMakePresets.json')]]))
+      eq(
+        t.fix_slashes(test_source_path),
+        t.fix_slashes(exec_lua([[return vim.fs.root(0, 'CMakePresets.json')]]))
+      )
     end)
 
-    it("uses cwd for buffers with non-empty 'buftype'", function()
+    it("returns CWD (absolute path) for buffers with non-empty 'buftype'", function()
+      assert(n.fn.isabsolutepath(test_source_path) == 1)
       command('new')
       command('set buftype=nofile')
       command('file lua://')
-      eq(test_source_path, exec_lua([[return vim.fs.root(0, 'CMakePresets.json')]]))
+      eq(
+        t.fix_slashes(test_source_path),
+        t.fix_slashes(exec_lua([[return vim.fs.root(0, 'CMakePresets.json')]]))
+      )
     end)
 
-    it('returns an absolute path for an invalid filename', function()
+    it('returns CWD (absolute path) if no match is found', function()
       assert(n.fn.isabsolutepath(test_source_path) == 1)
       eq(
         t.fix_slashes(test_source_path),
-        t.fix_slashes(exec_lua([[return vim.fs.root('file://asd', 'CMakePresets.json')]]))
+        t.fix_slashes(exec_lua([[return vim.fs.root('file://bogus', 'CMakePresets.json')]]))
       )
     end)
   end)
@@ -612,7 +620,9 @@ describe('vim.fs', function()
     local cwd = assert(t.fix_slashes(assert(vim.uv.cwd())))
     local home = t.fix_slashes(assert(vim.uv.os_homedir()))
 
-    it('works', function()
+    it('expands relative paths', function()
+      assert(n.fn.isabsolutepath(cwd) == 1)
+      eq(cwd, vim.fs.abspath('.'))
       eq(cwd .. '/foo', vim.fs.abspath('foo'))
       eq(cwd .. '/././foo', vim.fs.abspath('././foo'))
       eq(cwd .. '/.././../foo', vim.fs.abspath('.././../foo'))