fix(startup): server fails if $NVIM_APPNAME is relative dir #30310

Problem:
If $NVIM_APPNAME is a relative dir path, Nvim fails to start its
primary/default server, and `v:servername` is empty.
Root cause is d34c64e342dfba9248d1055e702d02620a1b31a8, but this wasn't
noticed until 96128a5076b7 started reporting the error more loudly.

Solution:
- `server_address_new`: replace slashes "/" in the appname before using
  it as a servername.
- `vim_mktempdir`: always prefer the system-wide top-level "nvim.user/"
  directory. That isn't intended to be specific to NVIM_APPNAME; rather,
  each *subdirectory* ("nvim.user/xxx") is owned by each Nvim instance.
  Nvim "apps" can be identified by the server socket(s) stored in those
  per-Nvim subdirs.

fix #30256

5 files changed, 26 insertions, 19 deletions

diff --git a/test/functional/core/fileio_spec.lua b/test/functional/core/fileio_spec.lua
index 073041fced..d33710a63d 100644
--- a/test/functional/core/fileio_spec.lua
+++ b/test/functional/core/fileio_spec.lua
@@ -321,11 +321,11 @@ end)
 describe('tmpdir', function()
   local tmproot_pat = [=[.*[/\\]nvim%.[^/\\]+]=]
   local testlog = 'Xtest_tmpdir_log'
-  local os_tmpdir
+  local os_tmpdir ---@type string
 
   before_each(function()
     -- Fake /tmp dir so that we can mess it up.
-    os_tmpdir = vim.uv.fs_mkdtemp(vim.fs.dirname(t.tmpname(false)) .. '/nvim_XXXXXXXXXX')
+    os_tmpdir = assert(vim.uv.fs_mkdtemp(vim.fs.dirname(t.tmpname(false)) .. '/nvim_XXXXXXXXXX'))
   end)
 
   after_each(function()
@@ -414,15 +414,4 @@ describe('tmpdir', function()
     rm_tmpdir()
     eq('E5431: tempdir disappeared (3 times)', api.nvim_get_vvar('errmsg'))
   end)
-
-  it('$NVIM_APPNAME relative path', function()
-    clear({
-      env = {
-        NVIM_APPNAME = 'a/b',
-        NVIM_LOG_FILE = testlog,
-        TMPDIR = os_tmpdir,
-      },
-    })
-    matches([=[.*[/\\]a%%b%.[^/\\]+]=], fn.tempname())
-  end)
 end)
diff --git a/test/functional/vimscript/server_spec.lua b/test/functional/core/server_spec.lua
index 85a179b3d5..0ec11169e9 100644
--- a/test/functional/vimscript/server_spec.lua
+++ b/test/functional/core/server_spec.lua
@@ -154,7 +154,7 @@ describe('server', function()
     clear_serverlist()
 
     -- Address without slashes is a "name" which is appended to a generated path. #8519
-    matches([[.*[/\\]xtest1%.2%.3%.4[^/\\]*]], fn.serverstart('xtest1.2.3.4'))
+    matches([[[/\\]xtest1%.2%.3%.4[^/\\]*]], fn.serverstart('xtest1.2.3.4'))
     clear_serverlist()
 
     eq('Vim:Failed to start server: invalid argument', pcall_err(fn.serverstart, '127.0.0.1:65536')) -- invalid port
@@ -273,6 +273,6 @@ describe('startup --listen', function()
 
     -- Address without slashes is a "name" which is appended to a generated path. #8519
     clear({ args = { '--listen', 'test-name' } })
-    matches([[.*[/\\]test%-name[^/\\]*]], api.nvim_get_vvar('servername'))
+    matches([[[/\\]test%-name[^/\\]*]], api.nvim_get_vvar('servername'))
   end)
 end)
diff --git a/test/functional/options/defaults_spec.lua b/test/functional/options/defaults_spec.lua
index ca4a6eaca7..ad94ef1206 100644
--- a/test/functional/options/defaults_spec.lua
+++ b/test/functional/options/defaults_spec.lua
@@ -915,7 +915,7 @@ describe('stdpath()', function()
     assert_alive() -- Check for crash. #8393
   end)
 
-  it('supports $NVIM_APPNAME', function()
+  it('$NVIM_APPNAME', function()
     local appname = 'NVIM_APPNAME_TEST' .. ('_'):rep(106)
     clear({ env = { NVIM_APPNAME = appname, NVIM_LOG_FILE = testlog } })
     eq(appname, fn.fnamemodify(fn.stdpath('config'), ':t'))
@@ -957,6 +957,25 @@ describe('stdpath()', function()
     test_appname('a/b\\c', 0)
   end)
 
+  it('$NVIM_APPNAME relative path', function()
+    local tmpdir = t.tmpname(false)
+    t.mkdir(tmpdir)
+
+    clear({
+      args_rm = { '--listen' },
+      env = {
+        NVIM_APPNAME = 'relative/appname',
+        NVIM_LOG_FILE = testlog,
+        TMPDIR = tmpdir,
+      },
+    })
+
+    t.matches(vim.pesc(tmpdir), fn.tempname():gsub('\\', '/'))
+    t.assert_nolog('tempdir', testlog, 100)
+    t.assert_nolog('TMPDIR', testlog, 100)
+    t.matches([=[[/\\]relative%-appname.[^/\\]+]=], api.nvim_get_vvar('servername'))
+  end)
+
   describe('returns a String', function()
     describe('with "config"', function()
       it('knows XDG_CONFIG_HOME', function()
diff --git a/test/functional/testnvim.lua b/test/functional/testnvim.lua
index 66ce6daacb..d74e8055ef 100644
--- a/test/functional/testnvim.lua
+++ b/test/functional/testnvim.lua
@@ -14,8 +14,7 @@ local is_os = t.is_os
 local ok = t.ok
 local sleep = uv.sleep
 
---- This module uses functions from the context of the test session, i.e. in the context of the
---- nvim being tests.
+--- Functions executing in the current nvim session/process being tested.
 local M = {}
 
 local runtime_set = 'set runtimepath^=./build/lib/nvim/'
diff --git a/test/testutil.lua b/test/testutil.lua
index abfc10e806..19e297c503 100644
--- a/test/testutil.lua
+++ b/test/testutil.lua
@@ -16,7 +16,7 @@ local function shell_quote(str)
   return str
 end
 
---- This module uses functions from the context of the test runner.
+--- Functions executing in the context of the test runner (not the current nvim test session).
 --- @class test.testutil
 local M = {
   paths = Paths,