feat: try to recover from missing tempdir #22573

Problem:
If vim_tempdir mysteriously goes missing (typically by "antivirus" on
Windows), any plugins using tempname() will be broken for the rest of
the session. #1432 #9833 https://groups.google.com/g/vim_use/c/ef55jNm5czI
Steps:
    mkdir foo
    TMPDIR=./foo nvim
    :echo tempname()
    !rm -r foo
    :echo tempname()
    tempname() still uses the foo path even though it was deleted.

Solution:
- Don't assume that vim_tempdir exists.
- If it goes missing once, retry vim_mktempdir and log (silently) an error.
- If it goes missing again, retry vim_mktempdir and show an error.

Rejected in Vim for performance reasons:
  https://groups.google.com/g/vim_use/c/qgRob9SWDv8/m/FAOFVVcDTv0J
  https://groups.google.com/g/vim_dev/c/cogp-Vye4oo/m/d_SVFXBbnnoJ
But, logging shows that `vim_gettempdir` is not called frequently.

Fixes #1432
Fixes #9833
Fixes #11250
Related: stdpath("run") f50135a32e

test/functional/core/fileio_spec.lua

@@ -15,6 +15,7 @@ local request = helpers.request
 local retry = helpers.retry
 local rmdir = helpers.rmdir
 local matches = helpers.matches
+local meths = helpers.meths
 local mkdir = helpers.mkdir
 local sleep = helpers.sleep
 local read_file = helpers.read_file
@@ -261,13 +262,13 @@ end)
 describe('tmpdir', function()
   local tmproot_pat = [=[.*[/\\]nvim%.[^/\\]+]=]
   local testlog = 'Xtest_tmpdir_log'
-  local faketmp
+  local os_tmpdir
 
   before_each(function()
     -- Fake /tmp dir so that we can mess it up.
-    faketmp = tmpname()
-    os.remove(faketmp)
-    mkdir(faketmp)
+    os_tmpdir = tmpname()
+    os.remove(os_tmpdir)
+    mkdir(os_tmpdir)
   end)
 
   after_each(function()
@@ -275,16 +276,21 @@ describe('tmpdir', function()
     os.remove(testlog)
   end)
 
-  it('failure modes', function()
-    clear({ env={ NVIM_LOG_FILE=testlog, TMPDIR=faketmp, } })
-    assert_nolog('tempdir is not a directory', testlog)
-    assert_nolog('tempdir has invalid permissions', testlog)
-
+  local function get_tmproot()
     -- Tempfiles typically look like: "…/nvim.<user>/xxx/0".
     --  - "…/nvim.<user>/xxx/" is the per-process tmpdir, not shared with other Nvims.
     --  - "…/nvim.<user>/" is the tmpdir root, shared by all Nvims (normally).
     local tmproot = (funcs.tempname()):match(tmproot_pat)
     ok(tmproot:len() > 4, 'tmproot like "nvim.foo"', tmproot)
+    return tmproot
+  end
+
+  it('failure modes', function()
+    clear({ env={ NVIM_LOG_FILE=testlog, TMPDIR=os_tmpdir, } })
+    assert_nolog('tempdir is not a directory', testlog)
+    assert_nolog('tempdir has invalid permissions', testlog)
+
+    local tmproot = get_tmproot()
 
     -- Test how Nvim handles invalid tmpdir root (by hostile users or accidents).
     --
@@ -292,7 +298,7 @@ describe('tmpdir', function()
     expect_exit(command, ':qall!')
     rmdir(tmproot)
     write_file(tmproot, '')  -- Not a directory, vim_mktempdir() should skip it.
-    clear({ env={ NVIM_LOG_FILE=testlog, TMPDIR=faketmp, } })
+    clear({ env={ NVIM_LOG_FILE=testlog, TMPDIR=os_tmpdir, } })
     matches(tmproot_pat, funcs.stdpath('run'))  -- Tickle vim_mktempdir().
     -- Assert that broken tmpdir root was handled.
     assert_log('tempdir root not a directory', testlog, 100)
@@ -303,18 +309,52 @@ describe('tmpdir', function()
     os.remove(tmproot)
     mkdir(tmproot)
     funcs.setfperm(tmproot, 'rwxr--r--')  -- Invalid permissions, vim_mktempdir() should skip it.
-    clear({ env={ NVIM_LOG_FILE=testlog, TMPDIR=faketmp, } })
+    clear({ env={ NVIM_LOG_FILE=testlog, TMPDIR=os_tmpdir, } })
     matches(tmproot_pat, funcs.stdpath('run'))  -- Tickle vim_mktempdir().
     -- Assert that broken tmpdir root was handled.
     assert_log('tempdir root has invalid permissions', testlog, 100)
   end)
 
   it('too long', function()
-    local bigname = ('%s/%s'):format(faketmp, ('x'):rep(666))
+    local bigname = ('%s/%s'):format(os_tmpdir, ('x'):rep(666))
     mkdir(bigname)
     clear({ env={ NVIM_LOG_FILE=testlog, TMPDIR=bigname, } })
     matches(tmproot_pat, funcs.stdpath('run'))  -- Tickle vim_mktempdir().
     local len = (funcs.tempname()):len()
     ok(len > 4 and len < 256, '4 < len < 256', tostring(len))
   end)
+
+  it('disappeared #1432', function()
+    clear({ env={ NVIM_LOG_FILE=testlog, TMPDIR=os_tmpdir, } })
+    assert_nolog('tempdir disappeared', testlog)
+
+    local function rm_tmpdir()
+      local tmpname1 = funcs.tempname()
+      local tmpdir1 = funcs.fnamemodify(tmpname1, ':h')
+      eq(funcs.stdpath('run'), tmpdir1)
+
+      rmdir(tmpdir1)
+      retry(nil, 1000, function()
+        eq(0, funcs.isdirectory(tmpdir1))
+      end)
+      local tmpname2 = funcs.tempname()
+      local tmpdir2 = funcs.fnamemodify(tmpname2, ':h')
+      neq(tmpdir1, tmpdir2)
+    end
+
+    -- Your antivirus hates you...
+    rm_tmpdir()
+    assert_log('tempdir disappeared', testlog, 100)
+    funcs.tempname()
+    funcs.tempname()
+    funcs.tempname()
+    eq('', meths.get_vvar('errmsg'))
+    rm_tmpdir()
+    funcs.tempname()
+    funcs.tempname()
+    funcs.tempname()
+    eq('E5431: tempdir disappeared (2 times)', meths.get_vvar('errmsg'))
+    rm_tmpdir()
+    eq('E5431: tempdir disappeared (3 times)', meths.get_vvar('errmsg'))
+  end)
 end)