PG compilation error with Visual Studio 2015/2017/2019

Hi All,

I am working on “pg_locale compilation error with Visual Studio 2017”,
Related threads[1],[2].
We are getting compilation error in static char *IsoLocaleName(const char
*winlocname) function in pg_locale.c file. This function is trying to
convert the locale name into the Unix style. For example, it will change
the locale name "en-US" into "en_US".
It is creating a locale using _locale_t _create_locale( int category, const
char *locale) and then trying to access the name of that locale by pointing
to internal elements of the structure loct->locinfo->locale_name[LC_CTYPE]
but it has been missing from the _locale_t since VS2015 which is causing
the compilation error. I found a few useful APIs that can be used here.

ResolveLocaleName and GetLocaleInfoEx both can take locale in the following
format.
<language>-<REGION>
<language>-<Script>-<REGION>

ResolveLocaleName will try to find the closest matching locale name to the
input locale name even if the input locale name is invalid given that the
<language> is correct.

en-something-YZ => en-US
ex-US => error
Aa-aaaa-aa => aa-ET represents (Afar,Ethiopia)
Aa-aaa-aa => aa-ET

Refer [4] for more details

But in the case of GetLocaleInfoEx, it will only check the format of the
input locale, as mentioned before, if correct it will return the name of
the locale otherwise it will return an error.
For example.

en-something-YZ => error
ex-US => ex-US
aa-aaaa-aa => aa-Aaaa-AA
aa-aaa-aa => error.

Refer [5] for more details.

Currently, it is using _create_locale it behaves similarly to
GetLocaleInfoEx i.e. it also only checks the format only difference is for
a bigger set.
I thought of using GetLocaleInfoEx for the fix because it behaves similarly
to the already existing and a similar issue was resolved earlier using the
same. I have attached the patch, let me know your thoughts.

[1]
https://www.postgresql.org/message-id/e317eec9-d40d-49b9-b776-e89cf1d18c82@postgrespro.ru
[2] https://www.postgresql.org/message-id/23073.1526049547%40sss.pgh.pa.us
[3] https://docs.microsoft.com/en-us/windows/win32/intl/locale-names
[4]
https://docs.microsoft.com/en-us/windows/win32/api/winnls/nf-winnls-resolvelocalename
[5]
https://docs.microsoft.com/en-us/windows/win32/api/winnls/nf-winnls-getlocaleinfoex
--
Regards,
Davinder.
EnterpriseDB: http://www.enterprisedb.com