fix(vim.system): resolve executable paths on windows

Fixes #31107

runtime/lua/vim/_system.lua

@@ -230,6 +230,8 @@ local function default_handler(stream, text, bucket)
   end
 end
 
+local is_win = vim.fn.has('win32') == 1
+
 local M = {}
 
 --- @param cmd string
@@ -238,6 +240,13 @@ local M = {}
 --- @param on_error fun()
 --- @return uv.uv_process_t, integer
 local function spawn(cmd, opts, on_exit, on_error)
+  if is_win then
+    local cmd1 = vim.fn.exepath(cmd)
+    if cmd1 ~= '' then
+      cmd = cmd1
+    end
+  end
+
   local handle, pid_or_err = uv.spawn(cmd, opts, on_exit)
   if not handle then
     on_error()

src/nvim/eval.lua

@@ -2165,6 +2165,7 @@ M.funcs = {
       If {expr} starts with "./" the |current-directory| is used.
 
     ]=],
+    fast = true,
     name = 'exepath',
     params = { { 'expr', 'string' } },
     signature = 'exepath({expr})',

test/functional/lua/system_spec.lua

@@ -9,7 +9,7 @@ local function system_sync(cmd, opts)
   return exec_lua(function()
     local obj = vim.system(cmd, opts)
 
-    if opts.timeout then
+    if opts and opts.timeout then
       -- Minor delay before calling wait() so the timeout uv timer can have a headstart over the
       -- internal call to vim.wait() in wait().
       vim.wait(10)
@@ -75,7 +75,7 @@ describe('vim.system', function()
 
   it('kill processes', function()
     exec_lua(function()
-      local signal
+      local signal --- @type integer?
       local cmd = vim.system({ 'cat', '-' }, { stdin = true }, function(r)
         signal = r.signal
       end) -- run forever
@@ -112,4 +112,12 @@ describe('vim.system', function()
     )
     eq(true, exec_lua([[return _G.processed]]))
   end)
+
+  if t.is_os('win') then
+    it('can resolve windows command extentions.', function()
+      t.write_file('test.bat', 'echo hello world')
+      system_sync({ 'chmod', '+x', 'test.bat' })
+      system_sync({ './test' })
+    end)
+  end
 end)