Re: [PATCH 5/5] gdbsupport: add path_join function

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 14 Apr 2022 16:01:37 -0400
> From: Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>
> Cc: Simon Marchi <simon.marchi@efficios.com>
> 
> From: Simon Marchi <simon.marchi@efficios.com>
> 
> In this review [1], Eli pointed out that we should be careful when
> concatenating file names to avoid duplicated slashes.  On Windows, a
> double slash at the beginning of a file path has a special meaning.  So
> naively concatenating "/"  and "foo/bar" would give "//foo/bar", which
> would not give the desired results.  We already have a few spots doing:
> 
>   if (first_path ends with a slash)
>     path = first_path + second_path
>   else
>     path = first_path + slash + second_path
> 
> In general, I think it's nice to avoid superfluous slashes in file
> paths, since they might end up visible to the user and look a bit
> unprofessional.
> 
> Introduce the path_join function that can be used to join multiple path
> components together (along with unit tests).

Thanks.

> +static void
> +test ()
> +{
> +  std::string s;
> +
> +  s = ::path_join ("/foo", "bar", nullptr);
> +  SELF_CHECK (s == "/foo/bar");
> +
> +  s = ::path_join ("/foo", "/bar", nullptr);
> +  SELF_CHECK (s == "/foo/bar");
> +
> +  s = ::path_join ("/", "bar", nullptr);
> +  SELF_CHECK (s == "/bar");
> +
> +  s = ::path_join ("foo/", "/bar", nullptr);
> +  SELF_CHECK (s == "foo/bar");
> +
> +  s = ::path_join ("foo", "bar", "", nullptr);
> +  SELF_CHECK (s == "foo/bar");
> +
> +  s = ::path_join ("", "/foo", nullptr);
> +  SELF_CHECK (s == "/foo");
> +
> +  s = ::path_join ("", "foo", nullptr);
> +  SELF_CHECK (s == "foo");
> +
> +  s = ::path_join ("foo", "", "bar", nullptr);
> +  SELF_CHECK (s == "foo/bar");
> +
> +  s = ::path_join ("foo", "", nullptr);
> +  SELF_CHECK (s == "foo");
> +
> +  s = ::path_join ("foo/", "", nullptr);
> +  SELF_CHECK (s == "foo/");

Suggest to add a couple of Windows-specific tests here: one which
starts with "d:/" instead of just "/", and another with backslashes.

> +std::string
> +path_join (const char *component...)
> +{
> +  std::string path = component;
> +
> +  auto skip_leading_dir_seps = [] (const char *s)
> +    {
> +      while (*s == '/')
> +	++s;
> +
> +      return s;
> +    };
> +
> +  va_list args;
> +  va_start (args, component);
> +
> +  const char *c = va_arg (args, const char *);
> +  while (c != nullptr)
> +    {
> +      if (!path.empty ())
> +	c = skip_leading_dir_seps (c);
> +
> +      if (*c != '\0')
> +	{
> +	  if (!path.empty () && path.back () != '/')
> +	    path += '/';
> +
> +	  path += c;
> +	}
> +
> +      c = va_arg (args, const char *);
> +    }
> +
> +  va_end (args);
> +
> +  return path;
> +}

I think this should use IS_DIR_SEPARATOR (or override the '=' and '!='
operators), to support Windows file names with backslashes.