Ensure variables live across calls in generate_series(numeric, numeric).

In generate_series_step_numeric(), the variables "start_num"
and "stop_num" may be potentially freed until the next call.
So they should be put in the location which can survive across calls.
But previously they were not, and which could cause incorrect
behavior of generate_series(numeric, numeric). This commit fixes
this problem by copying them on multi_call_memory_ctx.

Andrew Gierth

src/backend/utils/adt/numeric.c

@@ -1325,11 +1325,16 @@ generate_series_step_numeric(PG_FUNCTION_ARGS)
 
 		/*
 		 * Use fctx to keep state from call to call. Seed current with the
-		 * original start value.
+		 * original start value. We must copy the start_num and stop_num
+		 * values rather than pointing to them, since we may have detoasted
+		 * them in the per-call context.
 		 */
-		init_var_from_num(start_num, &fctx->current);
-		init_var_from_num(stop_num, &fctx->stop);
+		init_var(&fctx->current);
+		init_var(&fctx->stop);
 		init_var(&fctx->step);
+
+		set_var_from_num(start_num, &fctx->current);
+		set_var_from_num(stop_num, &fctx->stop);
 		set_var_from_var(&steploc, &fctx->step);
 
 		funcctx->user_fctx = fctx;

src/test/regress/expected/numeric.out

@@ -1461,3 +1461,41 @@ select (i / (10::numeric ^ 131071))::numeric(1,0)
        9
 (4 rows)
 
+-- Check usage with variables
+select * from generate_series(1::numeric, 3::numeric) i, generate_series(i,3) j;
+ i | j 
+---+---
+ 1 | 1
+ 1 | 2
+ 1 | 3
+ 2 | 2
+ 2 | 3
+ 3 | 3
+(6 rows)
+
+select * from generate_series(1::numeric, 3::numeric) i, generate_series(1,i) j;
+ i | j 
+---+---
+ 1 | 1
+ 2 | 1
+ 2 | 2
+ 3 | 1
+ 3 | 2
+ 3 | 3
+(6 rows)
+
+select * from generate_series(1::numeric, 3::numeric) i, generate_series(1,5,i) j;
+ i | j 
+---+---
+ 1 | 1
+ 1 | 2
+ 1 | 3
+ 1 | 4
+ 1 | 5
+ 2 | 1
+ 2 | 3
+ 2 | 5
+ 3 | 1
+ 3 | 4
+(10 rows)
+

src/test/regress/sql/numeric.sql

@@ -854,3 +854,7 @@ select (i / (10::numeric ^ 131071))::numeric(1,0)
 	from generate_series(6 * (10::numeric ^ 131071),
 			     9 * (10::numeric ^ 131071),
 			     10::numeric ^ 131071) as a(i);
+-- Check usage with variables
+select * from generate_series(1::numeric, 3::numeric) i, generate_series(i,3) j;
+select * from generate_series(1::numeric, 3::numeric) i, generate_series(1,i) j;
+select * from generate_series(1::numeric, 3::numeric) i, generate_series(1,5,i) j;