Introduce "builtin" collation provider.

New provider for collations, like "libc" or "icu", but without any
external dependency.

Initially, the only locale supported by the builtin provider is "C",
which is identical to the libc provider's "C" locale. The libc
provider's "C" locale has always been treated as a special case that
uses an internal implementation, without using libc at all -- so the
new builtin provider uses the same implementation.

The builtin provider's locale is independent of the server environment
variables LC_COLLATE and LC_CTYPE. Using the builtin provider, the
database collation locale can be "C" while LC_COLLATE and LC_CTYPE are
set to "en_US", which is impossible with the libc provider.

By offering a new builtin provider, it clarifies that the semantics of
a collation using this provider will never depend on libc, and makes
it easier to document the behavior.

Discussion: https://postgr.es/m/ab925f69-5f9d-f85e-b87c-bd2a44798659@joeconway.com
Discussion: https://postgr.es/m/dd9261f4-7a98-4565-93ec-336c1c110d90@manitou-mail.org
Discussion: https://postgr.es/m/ff4c2f2f9c8fc7ca27c1c24ae37ecaeaeaff6b53.camel%40j-davis.com
Reviewed-by: Daniel Vérité, Peter Eisentraut, Jeremy Schneider

1 files changed, 103 insertions, 20 deletions

diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 77d5752dc8e..39390fbe4eb 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -1268,7 +1268,18 @@ lookup_collation_cache(Oid collation, bool set_flags)
 			elog(ERROR, "cache lookup failed for collation %u", collation);
 		collform = (Form_pg_collation) GETSTRUCT(tp);
 
-		if (collform->collprovider == COLLPROVIDER_LIBC)
+		if (collform->collprovider == COLLPROVIDER_BUILTIN)
+		{
+			Datum		datum;
+			const char *colllocale;
+
+			datum = SysCacheGetAttrNotNull(COLLOID, tp, Anum_pg_collation_colllocale);
+			colllocale = TextDatumGetCString(datum);
+
+			cache_entry->collate_is_c = true;
+			cache_entry->ctype_is_c = (strcmp(colllocale, "C") == 0);
+		}
+		else if (collform->collprovider == COLLPROVIDER_LIBC)
 		{
 			Datum		datum;
 			const char *collcollate;
@@ -1319,16 +1330,30 @@ lc_collate_is_c(Oid collation)
 	if (collation == DEFAULT_COLLATION_OID)
 	{
 		static int	result = -1;
-		char	   *localeptr;
-
-		if (default_locale.provider == COLLPROVIDER_ICU)
-			return false;
+		const char *localeptr;
 
 		if (result >= 0)
 			return (bool) result;
-		localeptr = setlocale(LC_COLLATE, NULL);
-		if (!localeptr)
-			elog(ERROR, "invalid LC_COLLATE setting");
+
+		if (default_locale.provider == COLLPROVIDER_BUILTIN)
+		{
+			result = true;
+			return (bool) result;
+		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+		{
+			result = false;
+			return (bool) result;
+		}
+		else if (default_locale.provider == COLLPROVIDER_LIBC)
+		{
+			localeptr = setlocale(LC_CTYPE, NULL);
+			if (!localeptr)
+				elog(ERROR, "invalid LC_CTYPE setting");
+		}
+		else
+			elog(ERROR, "unexpected collation provider '%c'",
+				 default_locale.provider);
 
 		if (strcmp(localeptr, "C") == 0)
 			result = true;
@@ -1372,16 +1397,29 @@ lc_ctype_is_c(Oid collation)
 	if (collation == DEFAULT_COLLATION_OID)
 	{
 		static int	result = -1;
-		char	   *localeptr;
-
-		if (default_locale.provider == COLLPROVIDER_ICU)
-			return false;
+		const char *localeptr;
 
 		if (result >= 0)
 			return (bool) result;
-		localeptr = setlocale(LC_CTYPE, NULL);
-		if (!localeptr)
-			elog(ERROR, "invalid LC_CTYPE setting");
+
+		if (default_locale.provider == COLLPROVIDER_BUILTIN)
+		{
+			localeptr = default_locale.info.builtin.locale;
+		}
+		else if (default_locale.provider == COLLPROVIDER_ICU)
+		{
+			result = false;
+			return (bool) result;
+		}
+		else if (default_locale.provider == COLLPROVIDER_LIBC)
+		{
+			localeptr = setlocale(LC_CTYPE, NULL);
+			if (!localeptr)
+				elog(ERROR, "invalid LC_CTYPE setting");
+		}
+		else
+			elog(ERROR, "unexpected collation provider '%c'",
+				 default_locale.provider);
 
 		if (strcmp(localeptr, "C") == 0)
 			result = true;
@@ -1519,10 +1557,10 @@ pg_newlocale_from_collation(Oid collid)
 
 	if (collid == DEFAULT_COLLATION_OID)
 	{
-		if (default_locale.provider == COLLPROVIDER_ICU)
-			return &default_locale;
-		else
+		if (default_locale.provider == COLLPROVIDER_LIBC)
 			return (pg_locale_t) 0;
+		else
+			return &default_locale;
 	}
 
 	cache_entry = lookup_collation_cache(collid, false);
@@ -1547,7 +1585,19 @@ pg_newlocale_from_collation(Oid collid)
 		result.provider = collform->collprovider;
 		result.deterministic = collform->collisdeterministic;
 
-		if (collform->collprovider == COLLPROVIDER_LIBC)
+		if (collform->collprovider == COLLPROVIDER_BUILTIN)
+		{
+			const char *locstr;
+
+			datum = SysCacheGetAttrNotNull(COLLOID, tp, Anum_pg_collation_colllocale);
+			locstr = TextDatumGetCString(datum);
+
+			builtin_validate_locale(GetDatabaseEncoding(), locstr);
+
+			result.info.builtin.locale = MemoryContextStrdup(TopMemoryContext,
+															 locstr);
+		}
+		else if (collform->collprovider == COLLPROVIDER_LIBC)
 		{
 			const char *collcollate;
 			const char *collctype pg_attribute_unused();
@@ -1626,7 +1676,11 @@ pg_newlocale_from_collation(Oid collid)
 
 			collversionstr = TextDatumGetCString(datum);
 
-			datum = SysCacheGetAttrNotNull(COLLOID, tp, collform->collprovider == COLLPROVIDER_ICU ? Anum_pg_collation_colllocale : Anum_pg_collation_collcollate);
+			Assert(collform->collprovider != COLLPROVIDER_BUILTIN);
+			if (collform->collprovider == COLLPROVIDER_LIBC)
+				datum = SysCacheGetAttrNotNull(COLLOID, tp, Anum_pg_collation_collcollate);
+			else
+				datum = SysCacheGetAttrNotNull(COLLOID, tp, Anum_pg_collation_colllocale);
 
 			actual_versionstr = get_collation_actual_version(collform->collprovider,
 															 TextDatumGetCString(datum));
@@ -1677,6 +1731,10 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
+	/* the builtin collation provider is not versioned */
+	if (collprovider == COLLPROVIDER_BUILTIN)
+		return NULL;
+
 #ifdef USE_ICU
 	if (collprovider == COLLPROVIDER_ICU)
 	{
@@ -2443,6 +2501,31 @@ pg_strnxfrm_prefix(char *dest, size_t destsize, const char *src,
 	return result;
 }
 
+const char *
+builtin_validate_locale(int encoding, const char *locale)
+{
+	const char *canonical_name = NULL;
+	int			required_encoding = -1;
+
+	if (strcmp(locale, "C") == 0)
+		canonical_name = "C";
+
+	if (!canonical_name)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("invalid locale name \"%s\" for builtin provider",
+						locale)));
+
+	if (required_encoding >= 0 && encoding != required_encoding)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("encoding \"%s\" does not match locale \"%s\"",
+						pg_encoding_to_char(encoding), locale)));
+
+	return canonical_name;
+}
+
+
 #ifdef USE_ICU
 
 /*