Code review for protransform patches.

Fix loss of previous expression-simplification work when a transform
function fires: we must not simply revert to untransformed input tree.
Instead build a dummy FuncExpr node to pass to the transform function.
This has the additional advantage of providing a simpler, more uniform
API for transform functions.

Move documentation to a somewhat less buried spot, relocate some
poorly-placed code, be more wary of null constants and invalid typmod
values, add an opr_sanity check on protransform function signatures,
and some other minor cosmetic adjustments.

Note: although this patch touches pg_proc.h, no need for catversion
bump, because the changes are cosmetic and don't actually change the
intended catalog contents.

1 files changed, 11 insertions, 12 deletions

diff --git a/src/backend/utils/adt/varbit.c b/src/backend/utils/adt/varbit.c
index 1227e5a5082..e74e062338d 100644
--- a/src/backend/utils/adt/varbit.c
+++ b/src/backend/utils/adt/varbit.c
@@ -19,7 +19,6 @@
 #include "access/htup.h"
 #include "libpq/pqformat.h"
 #include "nodes/nodeFuncs.h"
-#include "parser/parse_clause.h"
 #include "utils/array.h"
 #include "utils/varbit.h"
 
@@ -649,31 +648,31 @@ varbit_send(PG_FUNCTION_ARGS)
 
 /*
  * varbit_transform()
- * Flatten calls to our length coercion function that leave the new maximum
- * length >= the previous maximum length.  We ignore the isExplicit argument,
- * which only affects truncation.
+ * Flatten calls to varbit's length coercion function that set the new maximum
+ * length >= the previous maximum length.  We can ignore the isExplicit
+ * argument, since that only affects truncation cases.
  */
 Datum
 varbit_transform(PG_FUNCTION_ARGS)
 {
 	FuncExpr   *expr = (FuncExpr *) PG_GETARG_POINTER(0);
-	Node	   *typmod;
 	Node	   *ret = NULL;
+	Node	   *typmod;
 
-	if (!IsA(expr, FuncExpr))
-		PG_RETURN_POINTER(ret);
+	Assert(IsA(expr, FuncExpr));
+	Assert(list_length(expr->args) >= 2);
 
-	Assert(list_length(expr->args) == 3);
-	typmod = lsecond(expr->args);
+	typmod = (Node *) lsecond(expr->args);
 
-	if (IsA(typmod, Const))
+	if (IsA(typmod, Const) && !((Const *) typmod)->constisnull)
 	{
-		Node	   *source = linitial(expr->args);
+		Node	   *source = (Node *) linitial(expr->args);
 		int32		new_typmod = DatumGetInt32(((Const *) typmod)->constvalue);
 		int32		old_max = exprTypmod(source);
 		int32		new_max = new_typmod;
 
-		if (new_max <= 0 || (old_max >= 0 && old_max <= new_max))
+		/* Note: varbit() treats typmod 0 as invalid, so we do too */
+		if (new_max <= 0 || (old_max > 0 && old_max <= new_max))
 			ret = relabel_to_typmod(source, new_typmod);
 	}