Fix to_char() to use ASCII-only case-folding rules where appropriate.

formatting.c used locale-dependent case folding rules in some code paths
where the result isn't supposed to be locale-dependent, for example
to_char(timestamp, 'DAY').  Since the source data is always just ASCII
in these cases, that usually didn't matter ... but it does matter in
Turkish locales, which have unusual treatment of "i" and "I".  To confuse
matters even more, the misbehavior was only visible in UTF8 encoding,
because in single-byte encodings we used pg_toupper/pg_tolower which
don't have locale-specific behavior for ASCII characters.  Fix by providing
intentionally ASCII-only case-folding functions and using these where
appropriate.  Per bug #7913 from Adnan Dursun.  Back-patch to all active
branches, since it's been like this for a long time.

src/backend/utils/adt/formatting.c

@@ -1492,12 +1492,7 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
-		char	   *p;
-
-		result = pnstrdup(buff, nbytes);
-
-		for (p = result; *p; p++)
-			*p = pg_ascii_tolower((unsigned char) *p);
+		result = asc_tolower(buff, nbytes);
 	}
 #ifdef USE_WIDE_UPPER_LOWER
 	else if (pg_database_encoding_max_length() > 1)
@@ -1617,12 +1612,7 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
-		char	   *p;
-
-		result = pnstrdup(buff, nbytes);
-
-		for (p = result; *p; p++)
-			*p = pg_ascii_toupper((unsigned char) *p);
+		result = asc_toupper(buff, nbytes);
 	}
 #ifdef USE_WIDE_UPPER_LOWER
 	else if (pg_database_encoding_max_length() > 1)
@@ -1743,23 +1733,7 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 	/* C/POSIX collations use this path regardless of database encoding */
 	if (lc_ctype_is_c(collid))
 	{
-		char	   *p;
-
-		result = pnstrdup(buff, nbytes);
-
-		for (p = result; *p; p++)
-		{
-			char		c;
-
-			if (wasalnum)
-				*p = c = pg_ascii_tolower((unsigned char) *p);
-			else
-				*p = c = pg_ascii_toupper((unsigned char) *p);
-			/* we don't trust isalnum() here */
-			wasalnum = ((c >= 'A' && c <= 'Z') ||
-						(c >= 'a' && c <= 'z') ||
-						(c >= '0' && c <= '9'));
-		}
+		result = asc_initcap(buff, nbytes);
 	}
 #ifdef USE_WIDE_UPPER_LOWER
 	else if (pg_database_encoding_max_length() > 1)
@@ -1886,6 +1860,87 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 	return result;
 }
 
+/*
+ * ASCII-only lower function
+ *
+ * We pass the number of bytes so we can pass varlena and char*
+ * to this function.  The result is a palloc'd, null-terminated string.
+ */
+char *
+asc_tolower(const char *buff, size_t nbytes)
+{
+	char	   *result;
+	char	   *p;
+
+	if (!buff)
+		return NULL;
+
+	result = pnstrdup(buff, nbytes);
+
+	for (p = result; *p; p++)
+		*p = pg_ascii_tolower((unsigned char) *p);
+
+	return result;
+}
+
+/*
+ * ASCII-only upper function
+ *
+ * We pass the number of bytes so we can pass varlena and char*
+ * to this function.  The result is a palloc'd, null-terminated string.
+ */
+char *
+asc_toupper(const char *buff, size_t nbytes)
+{
+	char	   *result;
+	char	   *p;
+
+	if (!buff)
+		return NULL;
+
+	result = pnstrdup(buff, nbytes);
+
+	for (p = result; *p; p++)
+		*p = pg_ascii_toupper((unsigned char) *p);
+
+	return result;
+}
+
+/*
+ * ASCII-only initcap function
+ *
+ * We pass the number of bytes so we can pass varlena and char*
+ * to this function.  The result is a palloc'd, null-terminated string.
+ */
+char *
+asc_initcap(const char *buff, size_t nbytes)
+{
+	char	   *result;
+	char	   *p;
+	int			wasalnum = false;
+
+	if (!buff)
+		return NULL;
+
+	result = pnstrdup(buff, nbytes);
+
+	for (p = result; *p; p++)
+	{
+		char		c;
+
+		if (wasalnum)
+			*p = c = pg_ascii_tolower((unsigned char) *p);
+		else
+			*p = c = pg_ascii_toupper((unsigned char) *p);
+		/* we don't trust isalnum() here */
+		wasalnum = ((c >= 'A' && c <= 'Z') ||
+					(c >= 'a' && c <= 'z') ||
+					(c >= '0' && c <= '9'));
+	}
+
+	return result;
+}
+
 /* convenience routines for when the input is null-terminated */
 
 static char *
@@ -1906,6 +1961,20 @@ str_initcap_z(const char *buff, Oid collid)
 	return str_initcap(buff, strlen(buff), collid);
 }
 
+static char *
+asc_tolower_z(const char *buff)
+{
+	return asc_tolower(buff, strlen(buff));
+}
+
+static char *
+asc_toupper_z(const char *buff)
+{
+	return asc_toupper(buff, strlen(buff));
+}
+
+/* asc_initcap_z is not currently needed */
+
 
 /* ----------
  * Skip TM / th in FROM_CHAR
@@ -2418,7 +2487,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				INVALID_FOR_INTERVAL;
 				if (tmtcTzn(in))
 				{
-					char	   *p = str_tolower_z(tmtcTzn(in), collid);
+					/* We assume here that timezone names aren't localized */
+					char	   *p = asc_tolower_z(tmtcTzn(in));
 
 					strcpy(s, p);
 					pfree(p);
@@ -2465,7 +2535,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 					strcpy(s, str_toupper_z(localized_full_months[tm->tm_mon - 1], collid));
 				else
 					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
-						 str_toupper_z(months_full[tm->tm_mon - 1], collid));
+						 asc_toupper_z(months_full[tm->tm_mon - 1]));
 				s += strlen(s);
 				break;
 			case DCH_Month:
@@ -2475,7 +2545,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				if (S_TM(n->suffix))
 					strcpy(s, str_initcap_z(localized_full_months[tm->tm_mon - 1], collid));
 				else
-					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9, months_full[tm->tm_mon - 1]);
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
+							months_full[tm->tm_mon - 1]);
 				s += strlen(s);
 				break;
 			case DCH_month:
@@ -2485,10 +2556,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				if (S_TM(n->suffix))
 					strcpy(s, str_tolower_z(localized_full_months[tm->tm_mon - 1], collid));
 				else
-				{
-					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9, months_full[tm->tm_mon - 1]);
-					*s = pg_tolower((unsigned char) *s);
-				}
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
+							asc_tolower_z(months_full[tm->tm_mon - 1]));
 				s += strlen(s);
 				break;
 			case DCH_MON:
@@ -2498,7 +2567,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				if (S_TM(n->suffix))
 					strcpy(s, str_toupper_z(localized_abbrev_months[tm->tm_mon - 1], collid));
 				else
-					strcpy(s, str_toupper_z(months[tm->tm_mon - 1], collid));
+					strcpy(s, asc_toupper_z(months[tm->tm_mon - 1]));
 				s += strlen(s);
 				break;
 			case DCH_Mon:
@@ -2518,10 +2587,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				if (S_TM(n->suffix))
 					strcpy(s, str_tolower_z(localized_abbrev_months[tm->tm_mon - 1], collid));
 				else
-				{
-					strcpy(s, months[tm->tm_mon - 1]);
-					*s = pg_tolower((unsigned char) *s);
-				}
+					strcpy(s, asc_tolower_z(months[tm->tm_mon - 1]));
 				s += strlen(s);
 				break;
 			case DCH_MM:
@@ -2536,7 +2602,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 					strcpy(s, str_toupper_z(localized_full_days[tm->tm_wday], collid));
 				else
 					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
-							str_toupper_z(days[tm->tm_wday], collid));
+							asc_toupper_z(days[tm->tm_wday]));
 				s += strlen(s);
 				break;
 			case DCH_Day:
@@ -2544,7 +2610,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				if (S_TM(n->suffix))
 					strcpy(s, str_initcap_z(localized_full_days[tm->tm_wday], collid));
 				else
-					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9, days[tm->tm_wday]);
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
+							days[tm->tm_wday]);
 				s += strlen(s);
 				break;
 			case DCH_day:
@@ -2552,10 +2619,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				if (S_TM(n->suffix))
 					strcpy(s, str_tolower_z(localized_full_days[tm->tm_wday], collid));
 				else
-				{
-					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9, days[tm->tm_wday]);
-					*s = pg_tolower((unsigned char) *s);
-				}
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
+							asc_tolower_z(days[tm->tm_wday]));
 				s += strlen(s);
 				break;
 			case DCH_DY:
@@ -2563,7 +2628,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				if (S_TM(n->suffix))
 					strcpy(s, str_toupper_z(localized_abbrev_days[tm->tm_wday], collid));
 				else
-					strcpy(s, str_toupper_z(days_short[tm->tm_wday], collid));
+					strcpy(s, asc_toupper_z(days_short[tm->tm_wday]));
 				s += strlen(s);
 				break;
 			case DCH_Dy:
@@ -2579,10 +2644,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
 				if (S_TM(n->suffix))
 					strcpy(s, str_tolower_z(localized_abbrev_days[tm->tm_wday], collid));
 				else
-				{
-					strcpy(s, days_short[tm->tm_wday]);
-					*s = pg_tolower((unsigned char) *s);
-				}
+					strcpy(s, asc_tolower_z(days_short[tm->tm_wday]));
 				s += strlen(s);
 				break;
 			case DCH_DDD:
@@ -4690,12 +4752,12 @@ NUM_processor(FormatNode *node, NUMDesc *Num, char *inout, char *number,
 				case NUM_rn:
 					if (IS_FILLMODE(Np->Num))
 					{
-						strcpy(Np->inout_p, str_tolower_z(Np->number_p, collid));
+						strcpy(Np->inout_p, asc_tolower_z(Np->number_p));
 						Np->inout_p += strlen(Np->inout_p) - 1;
 					}
 					else
 					{
-						sprintf(Np->inout_p, "%15s", str_tolower_z(Np->number_p, collid));
+						sprintf(Np->inout_p, "%15s", asc_tolower_z(Np->number_p));
 						Np->inout_p += strlen(Np->inout_p) - 1;
 					}
 					break;

src/include/utils/formatting.h

@@ -24,6 +24,10 @@ extern char *str_tolower(const char *buff, size_t nbytes, Oid collid);
 extern char *str_toupper(const char *buff, size_t nbytes, Oid collid);
 extern char *str_initcap(const char *buff, size_t nbytes, Oid collid);
 
+extern char *asc_tolower(const char *buff, size_t nbytes);
+extern char *asc_toupper(const char *buff, size_t nbytes);
+extern char *asc_initcap(const char *buff, size_t nbytes);
+
 extern Datum timestamp_to_char(PG_FUNCTION_ARGS);
 extern Datum timestamptz_to_char(PG_FUNCTION_ARGS);
 extern Datum interval_to_char(PG_FUNCTION_ARGS);