Support C.UTF-8 locale in the new builtin collation provider.

The builtin C.UTF-8 locale has similar semantics to the libc locale of
the same name. That is, code point sort order (fast, memcmp-based)
combined with Unicode semantics for character operations such as
pattern matching, regular expressions, and
LOWER()/INITCAP()/UPPER(). The character semantics are based on
Unicode simple case mappings.

The builtin provider's C.UTF-8 offers several important advantages
over libc:

 * faster sorting -- benefits from additional optimizations such as
   abbreviated keys and varstrfastcmp_c
 * faster case conversion, e.g. LOWER(), at least compared with some
   libc implementations
 * available on all platforms with identical semantics, and the
   semantics are stable, testable, and documentable within a given
   Postgres major version

Being based on memcmp, the builtin C.UTF-8 locale does not offer
natural language sort order. But it is an improvement for most use
cases that might otherwise use libc's "C.UTF-8" locale, as well as
many use cases that use libc's "C" locale.

Discussion: https://postgr.es/m/ff4c2f2f9c8fc7ca27c1c24ae37ecaeaeaff6b53.camel%40j-davis.com
Reviewed-by: Daniel Vérité, Peter Eisentraut, Jeremy Schneider

src/backend/utils/adt/formatting.c

@@ -77,6 +77,8 @@
 
 #include "catalog/pg_collation.h"
 #include "catalog/pg_type.h"
+#include "common/unicode_case.h"
+#include "common/unicode_category.h"
 #include "mb/pg_wchar.h"
 #include "nodes/miscnodes.h"
 #include "parser/scansup.h"
@@ -1679,6 +1681,34 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 		}
 		else
 #endif
+		if (mylocale && mylocale->provider == COLLPROVIDER_BUILTIN)
+		{
+			const char *src = buff;
+			size_t		srclen = nbytes;
+			size_t		dstsize;
+			char	   *dst;
+			size_t		needed;
+
+			Assert(GetDatabaseEncoding() == PG_UTF8);
+
+			/* first try buffer of equal size plus terminating NUL */
+			dstsize = srclen + 1;
+			dst = palloc(dstsize);
+
+			needed = unicode_strlower(dst, dstsize, src, srclen);
+			if (needed + 1 > dstsize)
+			{
+				/* grow buffer if needed and retry */
+				dstsize = needed + 1;
+				dst = repalloc(dst, dstsize);
+				needed = unicode_strlower(dst, dstsize, src, srclen);
+				Assert(needed + 1 == dstsize);
+			}
+
+			Assert(dst[needed] == '\0');
+			result = dst;
+		}
+		else
 		{
 			Assert(!mylocale || mylocale->provider == COLLPROVIDER_LIBC);
 
@@ -1799,6 +1829,34 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 		}
 		else
 #endif
+		if (mylocale && mylocale->provider == COLLPROVIDER_BUILTIN)
+		{
+			const char *src = buff;
+			size_t		srclen = nbytes;
+			size_t		dstsize;
+			char	   *dst;
+			size_t		needed;
+
+			Assert(GetDatabaseEncoding() == PG_UTF8);
+
+			/* first try buffer of equal size plus terminating NUL */
+			dstsize = srclen + 1;
+			dst = palloc(dstsize);
+
+			needed = unicode_strupper(dst, dstsize, src, srclen);
+			if (needed + 1 > dstsize)
+			{
+				/* grow buffer if needed and retry */
+				dstsize = needed + 1;
+				dst = repalloc(dst, dstsize);
+				needed = unicode_strupper(dst, dstsize, src, srclen);
+				Assert(needed + 1 == dstsize);
+			}
+
+			Assert(dst[needed] == '\0');
+			result = dst;
+		}
+		else
 		{
 			Assert(!mylocale || mylocale->provider == COLLPROVIDER_LIBC);
 
@@ -1920,6 +1978,60 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 		}
 		else
 #endif
+		if (mylocale && mylocale->provider == COLLPROVIDER_BUILTIN)
+		{
+			const unsigned char *src = (unsigned char *) buff;
+			size_t		srclen = nbytes;
+			unsigned char *dst;
+			size_t		dstsize;
+			int			srcoff = 0;
+			int			dstoff = 0;
+
+			Assert(GetDatabaseEncoding() == PG_UTF8);
+
+			/* overflow paranoia */
+			if ((srclen + 1) > (INT_MAX / MAX_MULTIBYTE_CHAR_LEN))
+				ereport(ERROR,
+						(errcode(ERRCODE_OUT_OF_MEMORY),
+						 errmsg("out of memory")));
+
+			/* result is at most srclen codepoints plus terminating NUL */
+			dstsize = srclen * MAX_MULTIBYTE_CHAR_LEN + 1;
+			dst = (unsigned char *) palloc(dstsize);
+
+			while (srcoff < nbytes)
+			{
+				pg_wchar	u1 = utf8_to_unicode(src + srcoff);
+				pg_wchar	u2;
+				int			u1len = unicode_utf8len(u1);
+				int			u2len;
+
+				if (wasalnum)
+					u2 = unicode_lowercase_simple(u1);
+				else
+					u2 = unicode_uppercase_simple(u1);
+
+				u2len = unicode_utf8len(u2);
+
+				Assert(dstoff + u2len + 1 <= dstsize);
+
+				wasalnum = pg_u_isalnum(u2, true);
+
+				unicode_to_utf8(u2, dst + dstoff);
+				srcoff += u1len;
+				dstoff += u2len;
+			}
+
+			Assert(dstoff + 1 <= dstsize);
+			*(dst + dstoff) = '\0';
+			dstoff++;
+
+			/* allocate result buffer of the right size and free workspace */
+			result = palloc(dstoff);
+			memcpy(result, dst, dstoff);
+			pfree(dst);
+		}
+		else
 		{
 			Assert(!mylocale || mylocale->provider == COLLPROVIDER_LIBC);
 

src/backend/utils/adt/pg_locale.c

@@ -1270,8 +1270,14 @@ lookup_collation_cache(Oid collation, bool set_flags)
 
 		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 = true;
+			cache_entry->ctype_is_c = (strcmp(colllocale, "C") == 0);
 		}
 		else if (collform->collprovider == COLLPROVIDER_LIBC)
 		{
@@ -1670,7 +1676,6 @@ pg_newlocale_from_collation(Oid collid)
 
 			collversionstr = TextDatumGetCString(datum);
 
-			Assert(collform->collprovider != COLLPROVIDER_BUILTIN);
 			if (collform->collprovider == COLLPROVIDER_LIBC)
 				datum = SysCacheGetAttrNotNull(COLLOID, tp, Anum_pg_collation_collcollate);
 			else
@@ -1725,7 +1730,13 @@ get_collation_actual_version(char collprovider, const char *collcollate)
 {
 	char	   *collversion = NULL;
 
-	/* the builtin collation provider is not versioned */
+	/*
+	 * The only two supported locales (C and C.UTF-8) are both based on memcmp
+	 * and are not expected to change.
+	 *
+	 * Note that the character semantics may change for some locales, but the
+	 * collation version only tracks changes to sort order.
+	 */
 	if (collprovider == COLLPROVIDER_BUILTIN)
 		return NULL;
 
@@ -2505,13 +2516,17 @@ pg_strnxfrm_prefix(char *dest, size_t destsize, const char *src,
 int
 builtin_locale_encoding(const char *locale)
 {
-	if (strcmp(locale, "C") != 0)
-		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("invalid locale name \"%s\" for builtin provider",
-						locale)));
+	if (strcmp(locale, "C") == 0)
+		return -1;
+	if (strcmp(locale, "C.UTF-8") == 0)
+		return PG_UTF8;
 
-	return -1;
+	ereport(ERROR,
+			(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+			 errmsg("invalid locale name \"%s\" for builtin provider",
+					locale)));
+
+	return 0;					/* keep compiler quiet */
 }
 
 
@@ -2525,13 +2540,28 @@ builtin_locale_encoding(const char *locale)
 const char *
 builtin_validate_locale(int encoding, const char *locale)
 {
-	if (strcmp(locale, "C") != 0)
+	const char *canonical_name = NULL;
+	int			required_encoding;
+
+	if (strcmp(locale, "C") == 0)
+		canonical_name = "C";
+	else if (strcmp(locale, "C.UTF-8") == 0 || strcmp(locale, "C.UTF8") == 0)
+		canonical_name = "C.UTF-8";
+
+	if (!canonical_name)
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("invalid locale name \"%s\" for builtin provider",
 						locale)));
 
-	return "C";
+	required_encoding = builtin_locale_encoding(canonical_name);
+	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;
 }