os_nodetype: open fd with O_NONBLOCK (#5515)

Closes #5267

Helped-by: oni-link <knil.ino@gmail.com>

src/nvim/os/fs.c

@@ -163,7 +163,11 @@ int os_nodetype(const char *name)
   // saves us the hassle.
 
   int nodetype = NODE_WRITABLE;
-  int fd = os_open(name, O_RDONLY, 0);
+  int fd = os_open(name, O_RDONLY
+#ifdef O_NONBLOCK
+                   | O_NONBLOCK
+#endif
+                   , 0);
   switch (uv_guess_handle(fd)) {
     case UV_TTY:         // FILE_TYPE_CHAR
       nodetype = NODE_WRITABLE;

test/functional/ex_cmds/write_spec.lua

@@ -1,20 +1,26 @@
--- Specs for :write
-
 local helpers = require('test.functional.helpers')(after_each)
-local eq, eval, clear, write_file, execute, source =
+local eq, eval, clear, write_file, execute, source, insert =
   helpers.eq, helpers.eval, helpers.clear, helpers.write_file,
-	helpers.execute, helpers.source
+  helpers.execute, helpers.source, helpers.insert
 
 if helpers.pending_win32(pending) then return end
 
 describe(':write', function()
-  after_each(function()
+  local function cleanup()
     os.remove('test_bkc_file.txt')
     os.remove('test_bkc_link.txt')
+    os.remove('test_fifo')
+  end
+  before_each(function()
+    clear()
+    cleanup()
+  end)
+  after_each(function()
+    cleanup()
   end)
 
   it('&backupcopy=auto preserves symlinks', function()
-    clear('--cmd', 'set backupcopy=auto')
+    execute('set backupcopy=auto')
     write_file('test_bkc_file.txt', 'content0')
     execute("silent !ln -s test_bkc_file.txt test_bkc_link.txt")
     source([[
@@ -27,7 +33,7 @@ describe(':write', function()
   end)
 
   it('&backupcopy=no replaces symlink with new file', function()
-    clear('--cmd', 'set backupcopy=no')
+    execute('set backupcopy=no')
     write_file('test_bkc_file.txt', 'content0')
     execute("silent !ln -s test_bkc_file.txt test_bkc_link.txt")
     source([[
@@ -38,4 +44,23 @@ describe(':write', function()
     eq(eval("['content0']"), eval("readfile('test_bkc_file.txt')"))
     eq(eval("['content1']"), eval("readfile('test_bkc_link.txt')"))
   end)
+
+  it("appends FIFO file", function()
+    if eval("executable('mkfifo')") == 0 then
+      pending('missing "mkfifo" command', function()end)
+      return
+    end
+
+    local text = "some fifo text from write_spec"
+    assert(os.execute("mkfifo test_fifo"))
+    insert(text)
+
+    -- Blocks until a consumer reads the FIFO.
+    execute("write >> test_fifo")
+
+    -- Read the FIFO, this will unblock the :write above.
+    local fifo = assert(io.open("test_fifo"))
+    eq(text.."\n", fifo:read("*all"))
+    fifo:close()
+  end)
 end)