v3-allow-SET-to-an-empty-list.patch

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 3d6e6bdbfd2..27ba1920e68 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -3086,9 +3086,10 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
 				 * rules used there aren't exactly like SQL's, we have to
 				 * break the list value apart and then quote the elements as
 				 * string literals.  (The elements may be double-quoted as-is,
-				 * but we can't just feed them to the SQL parser; it would do
-				 * the wrong thing with elements that are zero-length or
-				 * longer than NAMEDATALEN.)
+				 * but we can't just feed them to the SQL parser that way; it
+				 * would truncate elements that are longer than NAMEDATALEN,
+				 * which would be wrong if they're paths.)  Also, we need a
+				 * special case for empty lists.
 				 *
 				 * Variables that are not so marked should just be emitted as
 				 * simple string literals.  If the variable is not known to
@@ -3106,6 +3107,9 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
 						/* this shouldn't fail really */
 						elog(ERROR, "invalid list syntax in proconfig item");
 					}
+					/* Special case: represent an empty list as '' */
+					if (namelist == NIL)
+						appendStringInfoString(&buf, "''");
 					foreach(lc, namelist)
 					{
 						char	   *curname = (char *) lfirst(lc);
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 2c398cd9e5c..d5ef492ee41 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -2753,7 +2753,7 @@ SplitIdentifierString(char *rawstring, char separator,
 		nextp++;				/* skip leading whitespace */
 
 	if (*nextp == '\0')
-		return true;			/* allow empty string */
+		return true;			/* empty string represents empty list */
 
 	/* At the top of the loop, we are at start of a new identifier. */
 	do
@@ -2777,6 +2777,8 @@ SplitIdentifierString(char *rawstring, char separator,
 				nextp = endp;
 			}
 			/* endp now points at the terminating quote */
+			if (curname == endp)
+				return false;	/* empty quoted name not allowed */
 			nextp = endp + 1;
 		}
 		else
@@ -2880,7 +2882,7 @@ SplitDirectoriesString(char *rawstring, char separator,
 		nextp++;				/* skip leading whitespace */
 
 	if (*nextp == '\0')
-		return true;			/* allow empty string */
+		return true;			/* empty string represents empty list */
 
 	/* At the top of the loop, we are at start of a new directory. */
 	do
@@ -2904,6 +2906,8 @@ SplitDirectoriesString(char *rawstring, char separator,
 				nextp = endp;
 			}
 			/* endp now points at the terminating quote */
+			if (curname == endp)
+				return false;	/* empty quoted name not allowed */
 			nextp = endp + 1;
 		}
 		else
@@ -3001,7 +3005,7 @@ SplitGUCList(char *rawstring, char separator,
 		nextp++;				/* skip leading whitespace */
 
 	if (*nextp == '\0')
-		return true;			/* allow empty string */
+		return true;			/* empty string represents empty list */
 
 	/* At the top of the loop, we are at start of a new identifier. */
 	do
@@ -3025,6 +3029,8 @@ SplitGUCList(char *rawstring, char separator,
 				nextp = endp;
 			}
 			/* endp now points at the terminating quote */
+			if (curname == endp)
+				return false;	/* empty quoted name not allowed */
 			nextp = endp + 1;
 		}
 		else
diff --git a/src/backend/utils/misc/guc_funcs.c b/src/backend/utils/misc/guc_funcs.c
index b9e26982abd..a0557d164d8 100644
--- a/src/backend/utils/misc/guc_funcs.c
+++ b/src/backend/utils/misc/guc_funcs.c
@@ -210,12 +210,30 @@ flatten_set_variable_args(const char *name, List *args)
 	else
 		flags = 0;
 
-	/* Complain if list input and non-list variable */
-	if ((flags & GUC_LIST_INPUT) == 0 &&
-		list_length(args) != 1)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("SET %s takes only one argument", name)));
+	/*
+	 * Handle special cases for list input.
+	 */
+	if (flags & GUC_LIST_INPUT)
+	{
+		/* A single empty-string item is treated as an empty list. */
+		if (list_length(args) == 1)
+		{
+			Node	   *arg = (Node *) linitial(args);
+
+			if (IsA(arg, A_Const) &&
+				nodeTag(&((A_Const *) arg)->val) == T_String &&
+				*strVal(&((A_Const *) arg)->val) == '\0')
+				return pstrdup("");
+		}
+	}
+	else
+	{
+		/* Complain if list input and non-list variable. */
+		if (list_length(args) != 1)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("SET %s takes only one argument", name)));
+	}
 
 	initStringInfo(&buf);
 
@@ -269,6 +287,9 @@ flatten_set_variable_args(const char *name, List *args)
 					Datum		interval;
 					char	   *intervalout;
 
+					/* gram.y ensures this is only reachable for TIME ZONE */
+					Assert(!(flags & GUC_LIST_QUOTE));
+
 					typenameTypeIdAndMod(NULL, typeName, &typoid, &typmod);
 					Assert(typoid == INTERVALOID);
 
@@ -286,9 +307,17 @@ flatten_set_variable_args(const char *name, List *args)
 				else
 				{
 					/*
-					 * Plain string literal or identifier.  For quote mode,
+					 * Plain string literal or identifier.  In a list GUC,
+					 * disallow empty-string elements (so that the preceding
+					 * hack for empty lists is unambiguous).  For quote mode,
 					 * quote it if it's not a vanilla identifier.
 					 */
+					if ((flags & GUC_LIST_INPUT) && *val == '\0')
+						ereport(ERROR,
+								(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+								 errmsg("SET %s does not accept empty-string elements",
+										name)));
+
 					if (flags & GUC_LIST_QUOTE)
 						appendStringInfoString(&buf, quote_identifier(val));
 					else
diff --git a/src/bin/pg_dump/dumputils.c b/src/bin/pg_dump/dumputils.c
index 05b84c0d6e7..00a369c8861 100644
--- a/src/bin/pg_dump/dumputils.c
+++ b/src/bin/pg_dump/dumputils.c
@@ -781,7 +781,7 @@ SplitGUCList(char *rawstring, char separator,
 		nextp++;				/* skip leading whitespace */
 
 	if (*nextp == '\0')
-		return true;			/* allow empty string */
+		return true;			/* empty string represents empty list */
 
 	/* At the top of the loop, we are at start of a new identifier. */
 	do
@@ -805,6 +805,8 @@ SplitGUCList(char *rawstring, char separator,
 				nextp = endp;
 			}
 			/* endp now points at the terminating quote */
+			if (curname == endp)
+				return false;	/* empty quoted name not allowed */
 			nextp = endp + 1;
 		}
 		else
@@ -891,8 +893,9 @@ makeAlterConfigCommand(PGconn *conn, const char *configitem,
 	 * array.  However, because the quoting rules used there aren't exactly
 	 * like SQL's, we have to break the list value apart and then quote the
 	 * elements as string literals.  (The elements may be double-quoted as-is,
-	 * but we can't just feed them to the SQL parser; it would do the wrong
-	 * thing with elements that are zero-length or longer than NAMEDATALEN.)
+	 * but we can't just feed them to the SQL parser that way; it would
+	 * truncate elements that are longer than NAMEDATALEN, which would be
+	 * wrong if they're paths.)  Also, we need a special case for empty lists.
 	 *
 	 * Variables that are not so marked should just be emitted as simple
 	 * string literals.  If the variable is not known to
@@ -908,6 +911,9 @@ makeAlterConfigCommand(PGconn *conn, const char *configitem,
 		/* this shouldn't fail really */
 		if (SplitGUCList(pos, ',', &namelist))
 		{
+			/* Special case: represent an empty list as '' */
+			if (*namelist == NULL)
+				appendPQExpBufferStr(buf, "''");
 			for (nameptr = namelist; *nameptr; nameptr++)
 			{
 				if (nameptr != namelist)
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index bea793456f9..9d36a6a5aaf 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -13699,8 +13699,9 @@ dumpFunc(Archive *fout, const FuncInfo *finfo)
 		 * aren't exactly like SQL's, we have to break the list value apart
 		 * and then quote the elements as string literals.  (The elements may
 		 * be double-quoted as-is, but we can't just feed them to the SQL
-		 * parser; it would do the wrong thing with elements that are
-		 * zero-length or longer than NAMEDATALEN.)
+		 * parser that way; it would truncate elements that are longer than
+		 * NAMEDATALEN, which would be wrong if they're paths.)  Also, we need
+		 * a special case for empty lists.
 		 *
 		 * Variables that are not so marked should just be emitted as simple
 		 * string literals.  If the variable is not known to
@@ -13716,6 +13717,9 @@ dumpFunc(Archive *fout, const FuncInfo *finfo)
 			/* this shouldn't fail really */
 			if (SplitGUCList(pos, ',', &namelist))
 			{
+				/* Special case: represent an empty list as '' */
+				if (*namelist == NULL)
+					appendPQExpBufferStr(q, "''");
 				for (nameptr = namelist; *nameptr; nameptr++)
 				{
 					if (nameptr != namelist)
diff --git a/src/test/regress/expected/guc.out b/src/test/regress/expected/guc.out
index 7f9e29c765c..e49e609415b 100644
--- a/src/test/regress/expected/guc.out
+++ b/src/test/regress/expected/guc.out
@@ -31,6 +31,24 @@ SELECT '2006-08-13 12:34:56'::timestamptz;
  2006-08-13 12:34:56-07
 (1 row)
 
+-- Check handling of list GUCs
+SET search_path = 'pg_catalog', Foo, 'Bar';
+SHOW search_path;
+      search_path       
+------------------------
+ pg_catalog, foo, "Bar"
+(1 row)
+
+SET search_path = '';  -- means empty list
+SHOW search_path;
+ search_path 
+-------------
+ 
+(1 row)
+
+SET search_path = '', 'foo';  -- error, empty list elements not OK
+ERROR:  SET search_path does not accept empty-string elements
+RESET search_path;
 -- SET LOCAL has no effect outside of a transaction
 SET LOCAL vacuum_cost_delay TO 50;
 WARNING:  SET LOCAL can only be used in transaction blocks
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 35e8aad7701..43d5cf10266 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3549,21 +3549,23 @@ CREATE FUNCTION func_with_set_params() RETURNS integer
     SET extra_float_digits TO 2
     SET work_mem TO '4MB'
     SET datestyle to iso, mdy
-    SET local_preload_libraries TO "Mixed/Case", 'c:/''a"/path', '', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'
+    SET temp_tablespaces to ''
+    SET local_preload_libraries TO "Mixed/Case", 'c:/''a"/path', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'
     IMMUTABLE STRICT;
 SELECT pg_get_functiondef('func_with_set_params()'::regprocedure);
-                                                                            pg_get_functiondef                                                                            
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
- CREATE OR REPLACE FUNCTION public.func_with_set_params()                                                                                                                +
-  RETURNS integer                                                                                                                                                        +
-  LANGUAGE sql                                                                                                                                                           +
-  IMMUTABLE STRICT                                                                                                                                                       +
-  SET search_path TO 'pg_catalog'                                                                                                                                        +
-  SET extra_float_digits TO '2'                                                                                                                                          +
-  SET work_mem TO '4MB'                                                                                                                                                  +
-  SET "DateStyle" TO 'iso, mdy'                                                                                                                                          +
-  SET local_preload_libraries TO 'Mixed/Case', 'c:/''a"/path', '', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'+
- AS $function$select 1;$function$                                                                                                                                        +
+                                                                          pg_get_functiondef                                                                          
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ CREATE OR REPLACE FUNCTION public.func_with_set_params()                                                                                                            +
+  RETURNS integer                                                                                                                                                    +
+  LANGUAGE sql                                                                                                                                                       +
+  IMMUTABLE STRICT                                                                                                                                                   +
+  SET search_path TO 'pg_catalog'                                                                                                                                    +
+  SET extra_float_digits TO '2'                                                                                                                                      +
+  SET work_mem TO '4MB'                                                                                                                                              +
+  SET "DateStyle" TO 'iso, mdy'                                                                                                                                      +
+  SET temp_tablespaces TO ''                                                                                                                                         +
+  SET local_preload_libraries TO 'Mixed/Case', 'c:/''a"/path', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'+
+ AS $function$select 1;$function$                                                                                                                                    +
  
 (1 row)
 
diff --git a/src/test/regress/sql/guc.sql b/src/test/regress/sql/guc.sql
index f65f84a2632..65630135f18 100644
--- a/src/test/regress/sql/guc.sql
+++ b/src/test/regress/sql/guc.sql
@@ -12,6 +12,14 @@ SHOW vacuum_cost_delay;
 SHOW datestyle;
 SELECT '2006-08-13 12:34:56'::timestamptz;
 
+-- Check handling of list GUCs
+SET search_path = 'pg_catalog', Foo, 'Bar';
+SHOW search_path;
+SET search_path = '';  -- means empty list
+SHOW search_path;
+SET search_path = '', 'foo';  -- error, empty list elements not OK
+RESET search_path;
+
 -- SET LOCAL has no effect outside of a transaction
 SET LOCAL vacuum_cost_delay TO 50;
 SHOW vacuum_cost_delay;
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
index fdd3ff1d161..5c5ff5e9cca 100644
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1217,7 +1217,8 @@ CREATE FUNCTION func_with_set_params() RETURNS integer
     SET extra_float_digits TO 2
     SET work_mem TO '4MB'
     SET datestyle to iso, mdy
-    SET local_preload_libraries TO "Mixed/Case", 'c:/''a"/path', '', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'
+    SET temp_tablespaces to ''
+    SET local_preload_libraries TO "Mixed/Case", 'c:/''a"/path', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'
     IMMUTABLE STRICT;
 SELECT pg_get_functiondef('func_with_set_params()'::regprocedure);