From fb180287d0d3068b5873f4a7a39f506b4d52086d Mon Sep 17 00:00:00 2001
From: "Justin M. Keyes" <justinkz@gmail.com>
Date: Sat, 15 Aug 2026 13:15:37 -0400
Subject: [PATCH] fix(cwd): nvim_win_set_buf of :bcd buf, changes caller CWD
 #41329

Problem:
Setting a :bcd buffer into another window, modifies the caller's CWD.

    local b = vim.api.nvim_create_buf(true, true)
    vim.api.nvim_buf_call(b, function() vim.cmd.bcd('..') end)
    vim.cmd('vsplit')
    vim.api.nvim_win_set_buf(vim.fn.win_getid(2), b)

    :echo haslocaldir(0) haslocaldir(-1,0) haslocaldir(-1,-1,0)
    0 0 0
    :echo getcwd() ==# getcwd(-1,-1)
    0

Analysis:
`ctx_dirs_save` only saves CWD if it predicts the switch can change it.
But win_set_buf() replaces the target window's buffer *after* the
switch, which cannot be "predicted" from `ctx_dirs_save`.

Solution:
Always snapshot whenever the switch enters another window.
Skipping `os_dirname` was a micro-optimization.
---
 src/nvim/context.c                  | 15 +++++----------
 test/functional/ex_cmds/cd_spec.lua | 12 ++++++++++++
 2 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/src/nvim/context.c b/src/nvim/context.c
index 27fa060de6..df77828a17 100644
--- a/src/nvim/context.c
+++ b/src/nvim/context.c
@@ -338,15 +338,8 @@ static void ctx_dirs_save(CtxSwitch *cs, win_T *wp, tabpage_T *tp, buf_T *buf)
     cs->cs_tp_localdir = tp->tp_localdir == NULL ? NULL : xstrdup(tp->tp_localdir);
   }
 
-  // Getting and setting directory can be slow on some systems, only do this when the current or
-  // target window/tab have a local directory or 'acd' is set, or if kCtxKeepDirs was set.
   char cwd[MAXPATHL];
-  if ((cs->cs_flags & kCtxKeepDirs)
-      || (curwin != wp
-          && (curwin->w_localdir != NULL || wp->w_localdir != NULL
-              || curbuf->b_localdir != NULL || wp->w_buffer->b_localdir != NULL
-              || (curtab != tp && (curtab->tp_localdir != NULL || tp->tp_localdir != NULL))
-              || p_acd))) {
+  if ((cs->cs_flags & kCtxKeepDirs) || curwin != wp) {
     if (os_dirname(cwd, MAXPATHL) == OK) {
       cs->cs_cwd = xstrdup(cwd);  // allocated on demand: keeps CtxSwitch small
     }
@@ -392,17 +385,19 @@ static void ctx_dirs_restore(CtxSwitch *cs)
   }
   XFREE_CLEAR(cs->cs_globaldir);
 
-  // Restore the CWD itself.
+  // Restore the CWD itself. After an explicit chdir, ctx_restore() re-derives it instead.
   if (cs->cs_apply_acd) {
     xfree(cs->cs_save_sfname);
     do_autochdir();
-  } else if (cs->cs_cwd != NULL) {
+  } else if (cs->cs_cwd != NULL && ((cs->cs_flags & kCtxKeepDirs) || !_ctx_did_chdir)) {
     os_chdir(cs->cs_cwd);
     if (cs->cs_save_sfname != NULL) {
       xfree(curbuf->b_sfname);
       curbuf->b_sfname = cs->cs_save_sfname;
       curbuf->b_fname = curbuf->b_sfname;
     }
+  } else {
+    xfree(cs->cs_save_sfname);
   }
   XFREE_CLEAR(cs->cs_cwd);
 }
diff --git a/test/functional/ex_cmds/cd_spec.lua b/test/functional/ex_cmds/cd_spec.lua
index fb1193379d..df2d7a4817 100644
--- a/test/functional/ex_cmds/cd_spec.lua
+++ b/test/functional/ex_cmds/cd_spec.lua
@@ -603,6 +603,18 @@ describe('cd during temp context-switch', function()
     command('wincmd w')
     eq({ startdir, startdir }, { cwd(), cwd(-1, -1) })
     command('only')
+
+    -- Setting a :bcd buffer into another window, should not modify the caller's CWD.
+    local bcdbuf = call('nvim_create_buf', true, true)
+    n.exec_lua(function(b, d)
+      vim.api.nvim_buf_call(b, function()
+        vim.cmd.bcd(d)
+      end)
+    end, bcdbuf, bufdir)
+    command('split')
+    call('nvim_win_set_buf', call('win_getid', 2), bcdbuf)
+    eq({ bufdir, startdir, startdir }, { cwd(-1, -1, bcdbuf), cwd(), cwd(-1, -1) })
+    command('only')
   end)
 end)