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Commitff4597a

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Allow "SET list_guc TO NULL" to specify setting the GUC to empty.
We have never had a SET syntax that allows setting a GUC_LIST_INPUTparameter to be an empty list. A locution such asSET search_path = '';doesn't mean that; it means setting the GUC to contain a single itemthat is an empty string. (For search_path the net effect is much thesame, because search_path ignores invalid schema names and '' must beinvalid.) This is confusing, not least because configuration-fileentries and the set_config() function can easily produce empty-listvalues.We considered making the empty-string syntax do this, but that wouldforeclose ever allowing empty-string items to be valid in list GUCs.While there isn't any obvious use-case for that today, it feels likethe kind of restriction that might hurt someday. Instead, let'saccept the forbidden-up-to-now value NULL and treat that as meaning anempty list. (An objection to this could be "what if we someday wantto allow NULL as a GUC value?". That seems unlikely though, and evenif we did allow it for scalar GUCs, we could continue to treat it asmeaning an empty list for list GUCs.)Author: Tom Lane <tgl@sss.pgh.pa.us>Reviewed-by: Andrei Klychkov <andrew.a.klychkov@gmail.com>Reviewed-by: Jim Jones <jim.jones@uni-muenster.de>Discussion:https://postgr.es/m/CA+mfrmwsBmYsJayWjc8bJmicxc3phZcHHY=yW5aYe=P-1d_4bg@mail.gmail.com
1 parent93b7ab5 commitff4597a

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12 files changed

+135
-17
lines changed

12 files changed

+135
-17
lines changed

‎doc/src/sgml/ref/alter_system.sgml‎

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -84,6 +84,8 @@ ALTER SYSTEM RESET ALL
8484
constants, identifiers, numbers, or comma-separated lists of
8585
these, as appropriate for the particular parameter.
8686
Values that are neither numbers nor valid identifiers must be quoted.
87+
If the parameter accepts a list of values, <literal>NULL</literal>
88+
can be written to specify an empty list.
8789
<literal>DEFAULT</literal> can be written to specify removing the
8890
parameter and its value from <filename>postgresql.auto.conf</filename>.
8991
</para>
@@ -136,7 +138,15 @@ ALTER SYSTEM SET wal_level = replica;
136138
in <filename>postgresql.conf</filename>:
137139
<programlisting>
138140
ALTER SYSTEM RESET wal_level;
139-
</programlisting></para>
141+
</programlisting>
142+
</para>
143+
144+
<para>
145+
Set the list of preloaded extension modules to be empty:
146+
<programlisting>
147+
ALTER SYSTEM SET shared_preload_libraries TO NULL;
148+
</programlisting>
149+
</para>
140150
</refsect1>
141151

142152
<refsect1>

‎doc/src/sgml/ref/set.sgml‎

Lines changed: 20 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -21,8 +21,8 @@ PostgreSQL documentation
2121

2222
<refsynopsisdiv>
2323
<synopsis>
24-
SET [ SESSION | LOCAL ] <replaceable class="parameter">configuration_parameter</replaceable> { TO | = } { <replaceable class="parameter">value</replaceable>| '<replaceable class="parameter">value</replaceable>' | DEFAULT }
25-
SET [ SESSION | LOCAL ] TIME ZONE { <replaceable class="parameter">value</replaceable> |'<replaceable class="parameter">value</replaceable>' |LOCAL | DEFAULT }
24+
SET [ SESSION | LOCAL ] <replaceable class="parameter">configuration_parameter</replaceable> { TO | = } { <replaceable class="parameter">value</replaceable>[, ...] | DEFAULT }
25+
SET [ SESSION | LOCAL ] TIME ZONE { <replaceable class="parameter">value</replaceable> | LOCAL | DEFAULT }
2626
</synopsis>
2727
</refsynopsisdiv>
2828

@@ -123,7 +123,7 @@ SET [ SESSION | LOCAL ] TIME ZONE { <replaceable class="parameter">value</replac
123123
<term><replaceable class="parameter">configuration_parameter</replaceable></term>
124124
<listitem>
125125
<para>
126-
Name of a settablerun-time parameter. Available parameters are
126+
Name of a settableconfiguration parameter. Available parameters are
127127
documented in <xref linkend="runtime-config"/> and below.
128128
</para>
129129
</listitem>
@@ -133,9 +133,12 @@ SET [ SESSION | LOCAL ] TIME ZONE { <replaceable class="parameter">value</replac
133133
<term><replaceable class="parameter">value</replaceable></term>
134134
<listitem>
135135
<para>
136-
New value of parameter. Values can be specified as string
136+
New value oftheparameter. Values can be specified as string
137137
constants, identifiers, numbers, or comma-separated lists of
138138
these, as appropriate for the particular parameter.
139+
Values that are neither numbers nor valid identifiers must be quoted.
140+
If the parameter accepts a list of values, <literal>NULL</literal>
141+
can be written to specify an empty list.
139142
<literal>DEFAULT</literal> can be written to specify
140143
resetting the parameter to its default value (that is, whatever
141144
value it would have had if no <command>SET</command> had been executed
@@ -283,6 +286,19 @@ SELECT setseed(<replaceable>value</replaceable>);
283286
Set the schema search path:
284287
<programlisting>
285288
SET search_path TO my_schema, public;
289+
</programlisting>
290+
Note that this is not the same as
291+
<programlisting>
292+
SET search_path TO 'my_schema, public';
293+
</programlisting>
294+
which would have the effect of setting <varname>search_path</varname>
295+
to contain a single, probably-nonexistent schema name.
296+
</para>
297+
298+
<para>
299+
Set the list of temporary tablespace names to be empty:
300+
<programlisting>
301+
SET temp_tablespaces TO NULL;
286302
</programlisting>
287303
</para>
288304

‎src/backend/parser/gram.y‎

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1716,6 +1716,26 @@ generic_set:
17161716
n->location = @3;
17171717
$$ = n;
17181718
}
1719+
| var_name TO NULL_P
1720+
{
1721+
VariableSetStmt *n = makeNode(VariableSetStmt);
1722+
1723+
n->kind = VAR_SET_VALUE;
1724+
n->name = $1;
1725+
n->args = list_make1(makeNullAConst(@3));
1726+
n->location = @3;
1727+
$$ = n;
1728+
}
1729+
| var_name '=' NULL_P
1730+
{
1731+
VariableSetStmt *n = makeNode(VariableSetStmt);
1732+
1733+
n->kind = VAR_SET_VALUE;
1734+
n->name = $1;
1735+
n->args = list_make1(makeNullAConst(@3));
1736+
n->location = @3;
1737+
$$ = n;
1738+
}
17191739
| var_name TO DEFAULT
17201740
{
17211741
VariableSetStmt *n = makeNode(VariableSetStmt);

‎src/backend/utils/adt/ruleutils.c‎

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3087,7 +3087,8 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
30873087
* string literals. (The elements may be double-quoted as-is,
30883088
* but we can't just feed them to the SQL parser; it would do
30893089
* the wrong thing with elements that are zero-length or
3090-
* longer than NAMEDATALEN.)
3090+
* longer than NAMEDATALEN.) Also, we need a special case for
3091+
* empty lists.
30913092
*
30923093
* Variables that are not so marked should just be emitted as
30933094
* simple string literals. If the variable is not known to
@@ -3105,6 +3106,9 @@ pg_get_functiondef(PG_FUNCTION_ARGS)
31053106
/* this shouldn't fail really */
31063107
elog(ERROR,"invalid list syntax in proconfig item");
31073108
}
3109+
/* Special case: represent an empty list as NULL */
3110+
if (namelist==NIL)
3111+
appendStringInfoString(&buf,"NULL");
31083112
foreach(lc,namelist)
31093113
{
31103114
char*curname= (char*)lfirst(lc);

‎src/backend/utils/adt/varlena.c‎

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2753,7 +2753,7 @@ SplitIdentifierString(char *rawstring, char separator,
27532753
nextp++;/* skip leading whitespace */
27542754

27552755
if (*nextp=='\0')
2756-
return true;/*allowempty string */
2756+
return true;/* empty string represents empty list */
27572757

27582758
/* At the top of the loop, we are at start of a new identifier. */
27592759
do
@@ -2880,7 +2880,7 @@ SplitDirectoriesString(char *rawstring, char separator,
28802880
nextp++;/* skip leading whitespace */
28812881

28822882
if (*nextp=='\0')
2883-
return true;/*allowempty string */
2883+
return true;/* empty string represents empty list */
28842884

28852885
/* At the top of the loop, we are at start of a new directory. */
28862886
do
@@ -3001,7 +3001,7 @@ SplitGUCList(char *rawstring, char separator,
30013001
nextp++;/* skip leading whitespace */
30023002

30033003
if (*nextp=='\0')
3004-
return true;/*allowempty string */
3004+
return true;/* empty string represents empty list */
30053005

30063006
/* At the top of the loop, we are at start of a new identifier. */
30073007
do

‎src/backend/utils/misc/guc_funcs.c‎

Lines changed: 32 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -210,12 +210,29 @@ flatten_set_variable_args(const char *name, List *args)
210210
else
211211
flags=0;
212212

213-
/* Complain if list input and non-list variable */
214-
if ((flags&GUC_LIST_INPUT)==0&&
215-
list_length(args)!=1)
216-
ereport(ERROR,
217-
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
218-
errmsg("SET %s takes only one argument",name)));
213+
/*
214+
* Handle special cases for list input.
215+
*/
216+
if (flags&GUC_LIST_INPUT)
217+
{
218+
/* NULL represents an empty list. */
219+
if (list_length(args)==1)
220+
{
221+
Node*arg= (Node*)linitial(args);
222+
223+
if (IsA(arg,A_Const)&&
224+
((A_Const*)arg)->isnull)
225+
returnpstrdup("");
226+
}
227+
}
228+
else
229+
{
230+
/* Complain if list input and non-list variable. */
231+
if (list_length(args)!=1)
232+
ereport(ERROR,
233+
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
234+
errmsg("SET %s takes only one argument",name)));
235+
}
219236

220237
initStringInfo(&buf);
221238

@@ -246,6 +263,12 @@ flatten_set_variable_args(const char *name, List *args)
246263
elog(ERROR,"unrecognized node type: %d", (int)nodeTag(arg));
247264
con= (A_Const*)arg;
248265

266+
/* Complain if NULL is used with a non-list variable. */
267+
if (con->isnull)
268+
ereport(ERROR,
269+
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
270+
errmsg("NULL is an invalid value for %s",name)));
271+
249272
switch (nodeTag(&con->val))
250273
{
251274
caseT_Integer:
@@ -269,6 +292,9 @@ flatten_set_variable_args(const char *name, List *args)
269292
Datuminterval;
270293
char*intervalout;
271294

295+
/* gram.y ensures this is only reachable for TIME ZONE */
296+
Assert(!(flags&GUC_LIST_QUOTE));
297+
272298
typenameTypeIdAndMod(NULL,typeName,&typoid,&typmod);
273299
Assert(typoid==INTERVALOID);
274300

‎src/bin/pg_dump/dumputils.c‎

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -781,7 +781,7 @@ SplitGUCList(char *rawstring, char separator,
781781
nextp++;/* skip leading whitespace */
782782

783783
if (*nextp=='\0')
784-
return true;/*allowempty string */
784+
return true;/* empty string represents empty list */
785785

786786
/* At the top of the loop, we are at start of a new identifier. */
787787
do
@@ -893,6 +893,7 @@ makeAlterConfigCommand(PGconn *conn, const char *configitem,
893893
* elements as string literals. (The elements may be double-quoted as-is,
894894
* but we can't just feed them to the SQL parser; it would do the wrong
895895
* thing with elements that are zero-length or longer than NAMEDATALEN.)
896+
* Also, we need a special case for empty lists.
896897
*
897898
* Variables that are not so marked should just be emitted as simple
898899
* string literals. If the variable is not known to
@@ -908,6 +909,9 @@ makeAlterConfigCommand(PGconn *conn, const char *configitem,
908909
/* this shouldn't fail really */
909910
if (SplitGUCList(pos,',',&namelist))
910911
{
912+
/* Special case: represent an empty list as NULL */
913+
if (*namelist==NULL)
914+
appendPQExpBufferStr(buf,"NULL");
911915
for (nameptr=namelist;*nameptr;nameptr++)
912916
{
913917
if (nameptr!=namelist)

‎src/bin/pg_dump/pg_dump.c‎

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -13764,7 +13764,8 @@ dumpFunc(Archive *fout, const FuncInfo *finfo)
1376413764
* and then quote the elements as string literals. (The elements may
1376513765
* be double-quoted as-is, but we can't just feed them to the SQL
1376613766
* parser; it would do the wrong thing with elements that are
13767-
* zero-length or longer than NAMEDATALEN.)
13767+
* zero-length or longer than NAMEDATALEN.) Also, we need a special
13768+
* case for empty lists.
1376813769
*
1376913770
* Variables that are not so marked should just be emitted as simple
1377013771
* string literals. If the variable is not known to
@@ -13780,6 +13781,9 @@ dumpFunc(Archive *fout, const FuncInfo *finfo)
1378013781
/* this shouldn't fail really */
1378113782
if (SplitGUCList(pos, ',', &namelist))
1378213783
{
13784+
/* Special case: represent an empty list as NULL */
13785+
if (*namelist == NULL)
13786+
appendPQExpBufferStr(q, "NULL");
1378313787
for (nameptr = namelist; *nameptr; nameptr++)
1378413788
{
1378513789
if (nameptr != namelist)

‎src/test/regress/expected/guc.out‎

Lines changed: 22 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -31,6 +31,28 @@ SELECT '2006-08-13 12:34:56'::timestamptz;
3131
2006-08-13 12:34:56-07
3232
(1 row)
3333

34+
-- Check handling of list GUCs
35+
SET search_path = 'pg_catalog', Foo, 'Bar', '';
36+
SHOW search_path;
37+
search_path
38+
----------------------------
39+
pg_catalog, foo, "Bar", ""
40+
(1 row)
41+
42+
SET search_path = null; -- means empty list
43+
SHOW search_path;
44+
search_path
45+
-------------
46+
47+
(1 row)
48+
49+
SET search_path = null, null; -- syntax error
50+
ERROR: syntax error at or near ","
51+
LINE 1: SET search_path = null, null;
52+
^
53+
SET enable_seqscan = null; -- error
54+
ERROR: NULL is an invalid value for enable_seqscan
55+
RESET search_path;
3456
-- SET LOCAL has no effect outside of a transaction
3557
SET LOCAL vacuum_cost_delay TO 50;
3658
WARNING: SET LOCAL can only be used in transaction blocks

‎src/test/regress/expected/rules.out‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3572,6 +3572,7 @@ CREATE FUNCTION func_with_set_params() RETURNS integer
35723572
SET extra_float_digits TO 2
35733573
SET work_mem TO '4MB'
35743574
SET datestyle to iso, mdy
3575+
SET temp_tablespaces to NULL
35753576
SET local_preload_libraries TO "Mixed/Case", 'c:/''a"/path', '', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'
35763577
IMMUTABLE STRICT;
35773578
SELECT pg_get_functiondef('func_with_set_params()'::regprocedure);
@@ -3585,6 +3586,7 @@ SELECT pg_get_functiondef('func_with_set_params()'::regprocedure);
35853586
SET extra_float_digits TO '2' +
35863587
SET work_mem TO '4MB' +
35873588
SET "DateStyle" TO 'iso, mdy' +
3589+
SET temp_tablespaces TO NULL +
35883590
SET local_preload_libraries TO 'Mixed/Case', 'c:/''a"/path', '', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'+
35893591
AS $function$select 1;$function$ +
35903592

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