[PATCH v6 4/4] Do not rely on `getenv ("HOME")`'s path conversion

[Corinna Vinschen]

On Apr  4 17:07, Johannes Schindelin wrote:
> In the very early code path where `dll_crt0_1 ()` calls
> `user_shared->initialize ()`, the Cygwin runtime calls `internal_pwsid ()`
> to initialize the user name in preparation for reading the `fstab` file.
> 
> In case `db_home: env` is defined in `/etc/nsswitch.conf`, we need to
> look at the environment variable `HOME` and use it, if set.

I'm a bit puzzled by this.  HOME is not a Windows variable.  You're
usually not supposed to set it to Windows values, but to the POSIX
value.  I'm aware that Cygwin makes the conversion, too, for historical
reasons.

But why on earth would you set a variable you have under your own
control, and which only makes sense in a POSIX environment, to a Windows
value?  Why should we actually support this scenario for such a special
case?

> When all of this happens, though, the `pinfo_init ()` function has had no
> change to run yet (and therefore, `environ_init ()`). At this stage,

  chance

> therefore, `getenv ()`'s `findenv_func ()` call still finds `getearly ()`
> and we get the _verbatim_ value of `HOME`. That is, the Windows form.
> But we need the "POSIX" form.
> [...]
> Let's detect when the `HOME` value is still in Windows format in
> `fetch_home_env ()`, and convert it in that case.
> 
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  winsup/cygwin/uinfo.cc | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/winsup/cygwin/uinfo.cc b/winsup/cygwin/uinfo.cc
> index 5e2d88bcd7..bc9e926159 100644
> --- a/winsup/cygwin/uinfo.cc
> +++ b/winsup/cygwin/uinfo.cc
> @@ -929,7 +929,13 @@ fetch_home_env (void)
>    /* If `HOME` is set, prefer it */
>    const char *home = getenv ("HOME");
>    if (home)
> -    return strdup (home);
> +    {
> +      /* In the very early code path of `user_info::initialize ()`, the value
> +         of the environment variable `HOME` is still in its Windows form. */
> +      if (isdrive (home))

While the description is clear on the colon problem, shouldn't this
catch UNC paths as well?  I. e., just check for strchr(home, '\\')?

> +	return (char *) cygwin_create_path (CCP_WIN_A_TO_POSIX, home);


> +      return strdup (home);
> +    }
> 
>    /* If `HOME` is unset, fall back to `HOMEDRIVE``HOMEPATH`
>       (without a directory separator, as `HOMEPATH` starts with one). */
> --
> 2.40.0.windows.1