Fix the MSVC build for versions 2015 and later.

Visual Studio 2015 and later versions should still be able to do the same
as Visual Studio 2012, but the declaration of locale_name is missing in
_locale_t, causing the code compilation to fail, hence this falls back
instead on to enumerating all system locales by using EnumSystemLocalesEx
to find the required locale name.  If the input argument is in Unix-style
then we can get ISO Locale name directly by using GetLocaleInfoEx() with
LCType as LOCALE_SNAME.

In passing, change the documentation references of the now obsolete links.

Note that this problem occurs only with NLS enabled builds.

Author: Juan José Santamaría Flecha, Davinder Singh and Amit Kapila
Reviewed-by: Ranier Vilela and Amit Kapila
Backpatch-through: 9.5
Discussion: https://postgr.es/m/CAHzhFSFoJEWezR96um4-rg5W6m2Rj9Ud2CNZvV4NWc9tXV7aXQ@mail.gmail.com

Author: Amit Kapila

src/backend/utils/adt/pg_locale.c

@@ -234,6 +234,7 @@ pg_perm_setlocale(int category, const char *locale)
 			result = IsoLocaleName(locale);
 			if (result == NULL)
 				result = (char *) locale;
+			elog(DEBUG3, "IsoLocaleName() executed; locale: \"%s\"", result);
 #endif							/* WIN32 */
 			break;
 #endif							/* LC_MESSAGES */
@@ -971,65 +972,234 @@ cache_locale_time(void)
  * string.  Furthermore, msvcr110.dll changed the undocumented _locale_t
  * content to carry locale names instead of locale identifiers.
  *
- * MinGW headers declare _create_locale(), but msvcrt.dll lacks that symbol.
- * IsoLocaleName() always fails in a MinGW-built postgres.exe, so only
- * Unix-style values of the lc_messages GUC can elicit localized messages.  In
- * particular, every lc_messages setting that initdb can select automatically
- * will yield only C-locale messages.  XXX This could be fixed by running the
- * fully-qualified locale name through a lookup table.
+ * Visual Studio 2015 should still be able to do the same as Visual Studio
+ * 2012, but the declaration of locale_name is missing in _locale_t, causing
+ * this code compilation to fail, hence this falls back instead on to
+ * enumerating all system locales by using EnumSystemLocalesEx to find the
+ * required locale name.  If the input argument is in Unix-style then we can
+ * get ISO Locale name directly by using GetLocaleInfoEx() with LCType as
+ * LOCALE_SNAME.
+ *
+ * MinGW headers declare _create_locale(), but msvcrt.dll lacks that symbol in
+ * releases before Windows 8. IsoLocaleName() always fails in a MinGW-built
+ * postgres.exe, so only Unix-style values of the lc_messages GUC can elicit
+ * localized messages. In particular, every lc_messages setting that initdb
+ * can select automatically will yield only C-locale messages. XXX This could
+ * be fixed by running the fully-qualified locale name through a lookup table.
  *
  * This function returns a pointer to a static buffer bearing the converted
  * name or NULL if conversion fails.
  *
- * [1] http://msdn.microsoft.com/en-us/library/windows/desktop/dd373763.aspx
- * [2] http://msdn.microsoft.com/en-us/library/windows/desktop/dd373814.aspx
+ * [1] https://docs.microsoft.com/en-us/windows/win32/intl/locale-identifiers
+ * [2] https://docs.microsoft.com/en-us/windows/win32/intl/locale-names
+ */
+
+#if _MSC_VER >= 1900
+/*
+ * Callback function for EnumSystemLocalesEx() in get_iso_localename().
+ *
+ * This function enumerates all system locales, searching for one that matches
+ * an input with the format: <Language>[_<Country>], e.g.
+ * English[_United States]
+ *
+ * The input is a three wchar_t array as an LPARAM. The first element is the
+ * locale_name we want to match, the second element is an allocated buffer
+ * where the Unix-style locale is copied if a match is found, and the third
+ * element is the search status, 1 if a match was found, 0 otherwise.
+ */
+static BOOL CALLBACK
+search_locale_enum(LPWSTR pStr, DWORD dwFlags, LPARAM lparam)
+{
+	wchar_t		test_locale[LOCALE_NAME_MAX_LENGTH];
+	wchar_t   **argv;
+
+	(void) (dwFlags);
+
+	argv = (wchar_t **) lparam;
+	*argv[2] = (wchar_t) 0;
+
+	memset(test_locale, 0, sizeof(test_locale));
+
+	/* Get the name of the <Language> in English */
+	if (GetLocaleInfoEx(pStr, LOCALE_SENGLISHLANGUAGENAME,
+						test_locale, LOCALE_NAME_MAX_LENGTH))
+	{
+		/*
+		 * If the enumerated locale does not have a hyphen ("en") OR  the
+		 * lc_message input does not have an underscore ("English"), we only
+		 * need to compare the <Language> tags.
+		 */
+		if (wcsrchr(pStr, '-') == NULL || wcsrchr(argv[0], '_') == NULL)
+		{
+			if (_wcsicmp(argv[0], test_locale) == 0)
+			{
+				wcscpy(argv[1], pStr);
+				*argv[2] = (wchar_t) 1;
+				return FALSE;
+			}
+		}
+
+		/*
+		 * We have to compare a full <Language>_<Country> tag, so we append
+		 * the underscore and name of the country/region in English, e.g.
+		 * "English_United States".
+		 */
+		else
+		{
+			size_t		len;
+
+			wcscat(test_locale, L"_");
+			len = wcslen(test_locale);
+			if (GetLocaleInfoEx(pStr, LOCALE_SENGLISHCOUNTRYNAME,
+								test_locale + len,
+								LOCALE_NAME_MAX_LENGTH - len))
+			{
+				if (_wcsicmp(argv[0], test_locale) == 0)
+				{
+					wcscpy(argv[1], pStr);
+					*argv[2] = (wchar_t) 1;
+					return FALSE;
+				}
+			}
+		}
+	}
+
+	return TRUE;
+}
+
+/*
+ * This function converts a Windows locale name to an ISO formatted version
+ * for Visual Studio 2015 or greater.
+ *
+ * Returns NULL, if no valid conversion was found.
  */
 static char *
-IsoLocaleName(const char *winlocname)
+get_iso_localename(const char *winlocname)
 {
-#ifdef _MSC_VER
-	static char iso_lc_messages[32];
-	_locale_t	loct = NULL;
+	wchar_t		wc_locale_name[LOCALE_NAME_MAX_LENGTH];
+	wchar_t		buffer[LOCALE_NAME_MAX_LENGTH];
+	static char iso_lc_messages[LOCALE_NAME_MAX_LENGTH];
+	char	   *period;
+	int			len;
+	int			ret_val;
 
-	if (pg_strcasecmp("c", winlocname) == 0 ||
-		pg_strcasecmp("posix", winlocname) == 0)
+	/*
+	 * Valid locales have the following syntax:
+	 * <Language>[_<Country>[.<CodePage>]]
+	 *
+	 * GetLocaleInfoEx can only take locale name without code-page and for the
+	 * purpose of this API the code-page doesn't matter.
+	 */
+	period = strchr(winlocname, '.');
+	if (period != NULL)
+		len = period - winlocname;
+	else
+		len = pg_mbstrlen(winlocname);
+
+	memset(wc_locale_name, 0, sizeof(wc_locale_name));
+	memset(buffer, 0, sizeof(buffer));
+	MultiByteToWideChar(CP_ACP, 0, winlocname, len, wc_locale_name,
+						LOCALE_NAME_MAX_LENGTH);
+
+	/*
+	 * If the lc_messages is already an Unix-style string, we have a direct
+	 * match with LOCALE_SNAME, e.g. en-US, en_US.
+	 */
+	ret_val = GetLocaleInfoEx(wc_locale_name, LOCALE_SNAME, (LPWSTR) &buffer,
+							  LOCALE_NAME_MAX_LENGTH);
+	if (!ret_val)
 	{
-		strcpy(iso_lc_messages, "C");
-		return iso_lc_messages;
+		/*
+		 * Search for a locale in the system that matches language and country
+		 * name.
+		 */
+		wchar_t    *argv[3];
+
+		argv[0] = wc_locale_name;
+		argv[1] = buffer;
+		argv[2] = (wchar_t *) &ret_val;
+		EnumSystemLocalesEx(search_locale_enum, LOCALE_WINDOWS, (LPARAM) argv,
+							NULL);
 	}
 
-	loct = _create_locale(LC_CTYPE, winlocname);
-	if (loct != NULL)
+	if (ret_val)
 	{
 		size_t		rc;
 		char	   *hyphen;
 
 		/* Locale names use only ASCII, any conversion locale suffices. */
-		rc = wchar2char(iso_lc_messages, loct->locinfo->locale_name[LC_CTYPE],
-						sizeof(iso_lc_messages), NULL);
-		_free_locale(loct);
+		rc = wchar2char(iso_lc_messages, buffer, sizeof(iso_lc_messages), NULL);
 		if (rc == -1 || rc == sizeof(iso_lc_messages))
 			return NULL;
 
 		/*
-		 * Since the message catalogs sit on a case-insensitive filesystem, we
-		 * need not standardize letter case here.  So long as we do not ship
-		 * message catalogs for which it would matter, we also need not
-		 * translate the script/variant portion, e.g. uz-Cyrl-UZ to
-		 * uz_UZ@cyrillic.  Simply replace the hyphen with an underscore.
-		 *
-		 * Note that the locale name can be less-specific than the value we
-		 * would derive under earlier Visual Studio releases.  For example,
-		 * French_France.1252 yields just "fr".  This does not affect any of
-		 * the country-specific message catalogs available as of this writing
-		 * (pt_BR, zh_CN, zh_TW).
+		 * Simply replace the hyphen with an underscore.  See comments in
+		 * IsoLocaleName.
 		 */
 		hyphen = strchr(iso_lc_messages, '-');
 		if (hyphen)
 			*hyphen = '_';
 		return iso_lc_messages;
 	}
-#endif							/* _MSC_VER */
+
+	return NULL;
+}
+#endif							/* _MSC_VER >= 1900 */
+
+static char *
+IsoLocaleName(const char *winlocname)
+{
+#if defined(_MSC_VER)
+	static char iso_lc_messages[LOCALE_NAME_MAX_LENGTH];
+
+	if (pg_strcasecmp("c", winlocname) == 0 ||
+		pg_strcasecmp("posix", winlocname) == 0)
+	{
+		strcpy(iso_lc_messages, "C");
+		return iso_lc_messages;
+	}
+	else
+	{
+#if (_MSC_VER >= 1900)			/* Visual Studio 2015 or later */
+		return get_iso_localename(winlocname);
+#else
+		_locale_t	loct;
+
+		loct = _create_locale(LC_CTYPE, winlocname);
+		if (loct != NULL)
+		{
+			size_t		rc;
+			char	   *hyphen;
+
+			/* Locale names use only ASCII, any conversion locale suffices. */
+			rc = wchar2char(iso_lc_messages, loct->locinfo->locale_name[LC_CTYPE],
+							sizeof(iso_lc_messages), NULL);
+			_free_locale(loct);
+			if (rc == -1 || rc == sizeof(iso_lc_messages))
+				return NULL;
+
+			/*
+			 * Since the message catalogs sit on a case-insensitive
+			 * filesystem, we need not standardize letter case here.  So long
+			 * as we do not ship message catalogs for which it would matter,
+			 * we also need not translate the script/variant portion, e.g.
+			 * uz-Cyrl-UZ to uz_UZ@cyrillic.  Simply replace the hyphen with
+			 * an underscore.
+			 *
+			 * Note that the locale name can be less-specific than the value
+			 * we would derive under earlier Visual Studio releases.  For
+			 * example, French_France.1252 yields just "fr".  This does not
+			 * affect any of the country-specific message catalogs available
+			 * as of this writing (pt_BR, zh_CN, zh_TW).
+			 */
+			hyphen = strchr(iso_lc_messages, '-');
+			if (hyphen)
+				*hyphen = '_';
+			return iso_lc_messages;
+		}
+#endif							/* Visual Studio 2015 or later */
+	}
+#endif							/* defined(_MSC_VER) */
 	return NULL;				/* Not supported on this version of msvc/mingw */
 }
 #endif							/* WIN32 && LC_MESSAGES */