Fix incorrect logic in plpgsql for cleanup after evaluation of non-simple

expressions.  We need to deal with this when handling subscripts in an array
assignment, and also when catching an exception.  In an Assert-enabled build
these omissions led to Assert failures, but I think in a normal build the
only consequence would be short-term memory leakage; which may explain why
this wasn't reported from the field long ago.

Back-patch to all supported versions.  7.4 doesn't have exceptions, but
otherwise these bugs go all the way back.

Heikki Linnakangas and Tom Lane

src/pl/plpgsql/src/pl_exec.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.262 2010/08/09 02:25:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_exec.c,v 1.263 2010/08/09 18:50:10 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1099,6 +1099,9 @@ exec_stmt_block(PLpgSQL_execstate *estate, PLpgSQL_stmt_block *block)
 			 */
 			SPI_restore_connection();
 
+			/* Must clean up the econtext too */
+			exec_eval_cleanup(estate);
+
 			/* Look for a matching exception handler */
 			foreach(e, block->exceptions->exc_list)
 			{
@@ -2701,6 +2704,9 @@ plpgsql_estate_setup(PLpgSQL_execstate *estate,
  *
  * NB: the result of the evaluation is no longer valid after this is done,
  * unless it is a pass-by-value datatype.
+ *
+ * NB: if you change this code, see also the hacks in exec_assign_value's
+ * PLPGSQL_DTYPE_ARRAYELEM case.
  * ----------
  */
 static void
@@ -3464,6 +3470,10 @@ exec_assign_expr(PLpgSQL_execstate *estate, PLpgSQL_datum *target,
 
 /* ----------
  * exec_assign_value			Put a value into a target field
+ *
+ * Note: in some code paths, this may leak memory in the eval_econtext;
+ * we assume that will be cleaned up later by exec_eval_cleanup.  We cannot
+ * call exec_eval_cleanup here for fear of destroying the input Datum value.
  * ----------
  */
 static void
@@ -3714,6 +3724,9 @@ exec_assign_value(PLpgSQL_execstate *estate,
 
 		case PLPGSQL_DTYPE_ARRAYELEM:
 			{
+				/*
+				 * Target is an element of an array
+				 */
 				int			nsubscripts;
 				int			i;
 				PLpgSQL_expr *subscripts[MAXDIM];
@@ -3729,10 +3742,19 @@ exec_assign_value(PLpgSQL_execstate *estate,
 							coerced_value;
 				ArrayType  *oldarrayval;
 				ArrayType  *newarrayval;
+				SPITupleTable *save_eval_tuptable;
+
+				/*
+				 * We need to do subscript evaluation, which might require
+				 * evaluating general expressions; and the caller might have
+				 * done that too in order to prepare the input Datum.  We
+				 * have to save and restore the caller's SPI_execute result,
+				 * if any.
+				 */
+				save_eval_tuptable = estate->eval_tuptable;
+				estate->eval_tuptable = NULL;
 
 				/*
-				 * Target is an element of an array
-				 *
 				 * To handle constructs like x[1][2] := something, we have to
 				 * be prepared to deal with a chain of arrayelem datums. Chase
 				 * back to find the base array datum, and save the subscript
@@ -3786,8 +3808,23 @@ exec_assign_value(PLpgSQL_execstate *estate,
 						ereport(ERROR,
 								(errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
 								 errmsg("array subscript in assignment must not be null")));
+
+					/*
+					 * Clean up in case the subscript expression wasn't simple.
+					 * We can't do exec_eval_cleanup, but we can do this much
+					 * (which is safe because the integer subscript value is
+					 * surely pass-by-value), and we must do it in case the
+					 * next subscript expression isn't simple either.
+					 */
+					if (estate->eval_tuptable != NULL)
+						SPI_freetuptable(estate->eval_tuptable);
+					estate->eval_tuptable = NULL;
 				}
 
+				/* Now we can restore caller's SPI_execute result if any. */
+				Assert(estate->eval_tuptable == NULL);
+				estate->eval_tuptable = save_eval_tuptable;
+
 				/* Coerce source value to match array element type. */
 				coerced_value = exec_simple_cast_value(value,
 													   valtype,

src/test/regress/expected/plpgsql.out

@@ -3945,6 +3945,49 @@ SELECT * FROM leaker_1(true);
 
 DROP FUNCTION leaker_1(bool);
 DROP FUNCTION leaker_2(bool);
+-- Test for appropriate cleanup of non-simple expression evaluations
+-- (bug in all versions prior to August 2010)
+CREATE FUNCTION nonsimple_expr_test() RETURNS text[] AS $$
+DECLARE
+  arr text[];
+  lr text;
+  i integer;
+BEGIN
+  arr := array[array['foo','bar'], array['baz', 'quux']];
+  lr := 'fool';
+  i := 1;
+  -- use sub-SELECTs to make expressions non-simple
+  arr[(SELECT i)][(SELECT i+1)] := (SELECT lr);
+  RETURN arr;
+END;
+$$ LANGUAGE plpgsql;
+SELECT nonsimple_expr_test();
+   nonsimple_expr_test   
+-------------------------
+ {{foo,fool},{baz,quux}}
+(1 row)
+
+DROP FUNCTION nonsimple_expr_test();
+CREATE FUNCTION nonsimple_expr_test() RETURNS integer AS $$
+declare
+   i integer NOT NULL := 0;
+begin
+  begin
+    i := (SELECT NULL::integer);  -- should throw error
+  exception
+    WHEN OTHERS THEN
+      i := (SELECT 1::integer);
+  end;
+  return i;
+end;
+$$ LANGUAGE plpgsql;
+SELECT nonsimple_expr_test();
+ nonsimple_expr_test 
+---------------------
+                   1
+(1 row)
+
+DROP FUNCTION nonsimple_expr_test();
 -- Test handling of string literals.
 set standard_conforming_strings = off;
 create or replace function strtest() returns text as $$

src/test/regress/sql/plpgsql.sql

@@ -3150,6 +3150,46 @@ SELECT * FROM leaker_1(true);
 DROP FUNCTION leaker_1(bool);
 DROP FUNCTION leaker_2(bool);
 
+-- Test for appropriate cleanup of non-simple expression evaluations
+-- (bug in all versions prior to August 2010)
+
+CREATE FUNCTION nonsimple_expr_test() RETURNS text[] AS $$
+DECLARE
+  arr text[];
+  lr text;
+  i integer;
+BEGIN
+  arr := array[array['foo','bar'], array['baz', 'quux']];
+  lr := 'fool';
+  i := 1;
+  -- use sub-SELECTs to make expressions non-simple
+  arr[(SELECT i)][(SELECT i+1)] := (SELECT lr);
+  RETURN arr;
+END;
+$$ LANGUAGE plpgsql;
+
+SELECT nonsimple_expr_test();
+
+DROP FUNCTION nonsimple_expr_test();
+
+CREATE FUNCTION nonsimple_expr_test() RETURNS integer AS $$
+declare
+   i integer NOT NULL := 0;
+begin
+  begin
+    i := (SELECT NULL::integer);  -- should throw error
+  exception
+    WHEN OTHERS THEN
+      i := (SELECT 1::integer);
+  end;
+  return i;
+end;
+$$ LANGUAGE plpgsql;
+
+SELECT nonsimple_expr_test();
+
+DROP FUNCTION nonsimple_expr_test();
+
 -- Test handling of string literals.
 
 set standard_conforming_strings = off;