Issue error on SET outside transaction block in some cases

Issue error for SET LOCAL/CONSTRAINTS/TRANSACTION outside a transaction
block, as they have no effect.

Per suggestion from Morten Hustveit

doc/src/sgml/ref/set.sgml

@@ -110,10 +110,9 @@ SET [ SESSION | LOCAL ] TIME ZONE { <replaceable class="PARAMETER">timezone</rep
      <para>
       Specifies that the command takes effect for only the current
       transaction.  After <command>COMMIT</> or <command>ROLLBACK</>,
-      the session-level setting takes effect again.  Note that
-      <command>SET LOCAL</> will appear to have no effect if it is
-      executed outside a <command>BEGIN</> block, since the
-      transaction will end immediately.
+      the session-level setting takes effect again.
+      <productname>PostgreSQL</productname> reports an error if
+      <command>SET LOCAL</> is used outside a transaction block.
      </para>
     </listitem>
    </varlistentry>

doc/src/sgml/ref/set_constraints.sgml

@@ -102,7 +102,7 @@ SET CONSTRAINTS { ALL | <replaceable class="parameter">name</replaceable> [, ...
    current transaction. Thus, if you execute this command outside of a
    transaction block
    (<command>BEGIN</command>/<command>COMMIT</command> pair), it will
-   not appear to have any effect.
+   generate an error.
   </para>
  </refsect1>
 

doc/src/sgml/ref/set_transaction.sgml

@@ -184,9 +184,8 @@ SET SESSION CHARACTERISTICS AS TRANSACTION <replaceable class="parameter">transa
 
   <para>
    If <command>SET TRANSACTION</command> is executed without a prior
-   <command>START TRANSACTION</command> or  <command>BEGIN</command>,
-   it will appear to have no effect, since the transaction will immediately
-   end.
+   <command>START TRANSACTION</command> or <command>BEGIN</command>,
+   it will generate an error.
   </para>
 
   <para>

src/backend/tcop/utility.c

@@ -688,7 +688,7 @@ standard_ProcessUtility(Node *parsetree,
 			break;
 
 		case T_VariableSetStmt:
-			ExecSetVariableStmt((VariableSetStmt *) parsetree);
+			ExecSetVariableStmt((VariableSetStmt *) parsetree, isTopLevel);
 			break;
 
 		case T_VariableShowStmt:
@@ -754,6 +754,7 @@ standard_ProcessUtility(Node *parsetree,
 			break;
 
 		case T_ConstraintsSetStmt:
+			RequireTransactionChain(isTopLevel, "SET CONSTRAINTS");
 			AfterTriggerSetState((ConstraintsSetStmt *) parsetree);
 			break;
 

src/backend/utils/misc/guc.c

@@ -6252,7 +6252,7 @@ flatten_set_variable_args(const char *name, List *args)
  * SET command
  */
 void
-ExecSetVariableStmt(VariableSetStmt *stmt)
+ExecSetVariableStmt(VariableSetStmt *stmt, bool isTopLevel)
 {
 	GucAction	action = stmt->is_local ? GUC_ACTION_LOCAL : GUC_ACTION_SET;
 
@@ -6260,6 +6260,8 @@ ExecSetVariableStmt(VariableSetStmt *stmt)
 	{
 		case VAR_SET_VALUE:
 		case VAR_SET_CURRENT:
+			if (stmt->is_local)
+				RequireTransactionChain(isTopLevel, "SET LOCAL");
 			(void) set_config_option(stmt->name,
 									 ExtractSetVariableArgs(stmt),
 									 (superuser() ? PGC_SUSET : PGC_USERSET),
@@ -6269,7 +6271,6 @@ ExecSetVariableStmt(VariableSetStmt *stmt)
 									 0);
 			break;
 		case VAR_SET_MULTI:
-
 			/*
 			 * Special-case SQL syntaxes.  The TRANSACTION and SESSION
 			 * CHARACTERISTICS cases effectively set more than one variable
@@ -6281,6 +6282,8 @@ ExecSetVariableStmt(VariableSetStmt *stmt)
 			{
 				ListCell   *head;
 
+				RequireTransactionChain(isTopLevel, "SET TRANSACTION");
+
 				foreach(head, stmt->args)
 				{
 					DefElem    *item = (DefElem *) lfirst(head);
@@ -6329,6 +6332,8 @@ ExecSetVariableStmt(VariableSetStmt *stmt)
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 							 errmsg("SET LOCAL TRANSACTION SNAPSHOT is not implemented")));
+
+				RequireTransactionChain(isTopLevel, "SET TRANSACTION");
 				Assert(IsA(con, A_Const));
 				Assert(nodeTag(&con->val) == T_String);
 				ImportSnapshot(strVal(&con->val));
@@ -6338,7 +6343,13 @@ ExecSetVariableStmt(VariableSetStmt *stmt)
 					 stmt->name);
 			break;
 		case VAR_SET_DEFAULT:
+			if (stmt->is_local)
+				RequireTransactionChain(isTopLevel, "SET LOCAL");
+			/* fall through */
 		case VAR_RESET:
+			if (strcmp(stmt->name, "transaction_isolation") == 0)
+				RequireTransactionChain(isTopLevel, "RESET TRANSACTION");
+
 			(void) set_config_option(stmt->name,
 									 NULL,
 									 (superuser() ? PGC_SUSET : PGC_USERSET),

src/include/utils/guc.h

@@ -334,7 +334,7 @@ extern void SetPGVariable(const char *name, List *args, bool is_local);
 extern void GetPGVariable(const char *name, DestReceiver *dest);
 extern TupleDesc GetPGVariableResultDesc(const char *name);
 
-extern void ExecSetVariableStmt(VariableSetStmt *stmt);
+extern void ExecSetVariableStmt(VariableSetStmt *stmt, bool isTopLevel);
 extern char *ExtractSetVariableArgs(VariableSetStmt *stmt);
 
 extern void ProcessGUCArray(ArrayType *array,

src/test/regress/expected/guc.out

@@ -29,6 +29,7 @@ SELECT '2006-08-13 12:34:56'::timestamptz;
 
 -- SET LOCAL has no effect outside of a transaction
 SET LOCAL vacuum_cost_delay TO 50;
+ERROR:  SET LOCAL can only be used in transaction blocks
 SHOW vacuum_cost_delay;
  vacuum_cost_delay 
 -------------------
@@ -36,6 +37,7 @@ SHOW vacuum_cost_delay;
 (1 row)
 
 SET LOCAL datestyle = 'SQL';
+ERROR:  SET LOCAL can only be used in transaction blocks
 SHOW datestyle;
  DateStyle 
 -----------