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.

2 files changed, 17 insertions, 0 deletions

diff --git a/src/test/regress/expected/opr_sanity.out b/src/test/regress/expected/opr_sanity.out
index 7815b0d7be4..110ea4111f9 100644
--- a/src/test/regress/expected/opr_sanity.out
+++ b/src/test/regress/expected/opr_sanity.out
@@ -330,6 +330,16 @@ WHERE proargmodes IS NOT NULL AND proargnames IS NOT NULL AND
 -----+---------
 (0 rows)
 
+-- Check for protransform functions with the wrong signature
+SELECT p1.oid, p1.proname, p2.oid, p2.proname
+FROM pg_proc AS p1, pg_proc AS p2
+WHERE p2.oid = p1.protransform AND
+    (p2.prorettype != 'internal'::regtype OR p2.proretset OR p2.pronargs != 1
+     OR p2.proargtypes[0] != 'internal'::regtype);
+ oid | proname | oid | proname 
+-----+---------+-----+---------
+(0 rows)
+
 -- Insist that all built-in pg_proc entries have descriptions
 SELECT p1.oid, p1.proname
 FROM pg_proc as p1 LEFT JOIN pg_description as d
diff --git a/src/test/regress/sql/opr_sanity.sql b/src/test/regress/sql/opr_sanity.sql
index 3ed6366bfc0..a3be0c1114f 100644
--- a/src/test/regress/sql/opr_sanity.sql
+++ b/src/test/regress/sql/opr_sanity.sql
@@ -256,6 +256,13 @@ FROM pg_proc as p1
 WHERE proargmodes IS NOT NULL AND proargnames IS NOT NULL AND
     array_length(proargmodes,1) <> array_length(proargnames,1);
 
+-- Check for protransform functions with the wrong signature
+SELECT p1.oid, p1.proname, p2.oid, p2.proname
+FROM pg_proc AS p1, pg_proc AS p2
+WHERE p2.oid = p1.protransform AND
+    (p2.prorettype != 'internal'::regtype OR p2.proretset OR p2.pronargs != 1
+     OR p2.proargtypes[0] != 'internal'::regtype);
+
 -- Insist that all built-in pg_proc entries have descriptions
 SELECT p1.oid, p1.proname
 FROM pg_proc as p1 LEFT JOIN pg_description as d