[Bug 50553] New: SetEnvironmentVariableW function sets last error on deleting non-existent variable

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=50553

            Bug ID: 50553
           Summary: SetEnvironmentVariableW function sets last error on
                    deleting non-existent variable
           Product: Wine
           Version: 6.0
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: kernel32
          Assignee: wine-bugs at winehq.org
          Reporter: topin89 at mail.ru
      Distribution: ---

This code

```
//gcc test.c -o test.exe && ./test.exe
#include <windows.h>
#include <stdio.h>

int main(int argc, char *argv[]){
    BOOL result;

    result = SetEnvironmentVariableW(L"PERL5LIB", NULL);
    printf("result: %u, last error: %d\n", result, GetLastError());
    SetLastError(0);

    result = SetEnvironmentVariableW(L"PERL5LIB", "SomeValue");
    printf("result: %u, last error: %d\n", result, GetLastError());
    SetLastError(0);

    result = SetEnvironmentVariableW(L"PERL5LIB", NULL);
    printf("result: %u, last error: %d\n", result, GetLastError());
    SetLastError(0);

    result = SetEnvironmentVariableW(L"PERL5LIB", NULL);
    printf("result: %u, last error: %d\n", result, GetLastError());
    SetLastError(0);

    return 0;
}
```

compiled with Mingw-w64 gcc
and running from command line and MSYS console gives this in Windows 10:

```
result: 1, last error: 0
result: 1, last error: 0
result: 1, last error: 0
result: 1, last error: 0
```

and this in Kubuntu 20.04.1 with winehq-staging 6.0:

```
<snip fixmes>
result: 0, last error: 203
result: 1, last error: 0
result: 1, last error: 0
result: 0, last error: 203
```

Error 203 is ERROR_ENVVAR_NOT_FOUND, btw. So, in Win 10 deleting already
deleted environmental variable doesn't lead to error, in Wine it is.

This alone prevents git.exe (and probably many more apps) to work correctly. In
file git-for-windows-repo/compat/mingw.c

there is this function,

```
int mingw_putenv(const char *namevalue)
{
    int size;
    wchar_t *wide, *equal;
    BOOL result;

    if (!namevalue || !*namevalue)
        return 0;

    size = strlen(namevalue) * 2 + 1;
    wide = calloc(size, sizeof(wchar_t));
    if (!wide)
        die("Out of memory, (tried to allocate %u wchar_t's)", size);
    xutftowcs(wide, namevalue, size);
    equal = wcschr(wide, L'=');
    if (!equal)
        result = SetEnvironmentVariableW(wide, NULL);
    else {
        *equal = L'\0';
        result = SetEnvironmentVariableW(wide, equal + 1);
    }
    free(wide);

    if (!result)
        errno = err_win_to_posix(GetLastError());

    return result ? 0 : -1;
}
```

This line :

```
result = SetEnvironmentVariableW(wide, NULL);
```

sets error on removing non-existent `PERL5LIB` and that leads to result == 0
which in turn leads to premature exit in `err_win_to_posix(GetLastError())`.

In this particular case, for some reason last error sets to 0 instead of 203.
Another bug probably, I'll report it later.

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