From 8bf8719c1b908a2cae5e6bc7801e4c9c37915883 Mon Sep 17 00:00:00 2001 From: Andrey Rachitskiy Date: Fri, 28 Aug 2026 12:33:47 +0500 Subject: [PATCH] Fold constant XmlExpr in eval_const_expressions IS DOCUMENT was left as XmlExpr even with a Const argument, so CASE still simplified unused WHEN results and could execute xpath() during planning. That started failing for SQL-language functions once they began using custom plans. Bug: #19487 Author: Andrey Rachitskiy Reported-by: Ilya Portnov Discussion: https://www.postgresql.org/message-id/19487-367258bc497b923a%40postgresql.org Backpatch-through: 18 --- src/backend/optimizer/util/clauses.c | 6 ++++++ src/test/regress/expected/xml.out | 10 ++++++++++ src/test/regress/sql/xml.sql | 5 +++++ 3 files changed, 21 insertions(+) diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c index 8da4ed617b5..0294a956fb2 100644 --- a/src/backend/optimizer/util/clauses.c +++ b/src/backend/optimizer/util/clauses.c @@ -3679,6 +3679,7 @@ eval_const_expressions_mutator(Node *node, case T_ArrayExpr: case T_RowExpr: case T_MinMaxExpr: + case T_XmlExpr: { /* * Generic handling for node types whose own processing is @@ -3693,6 +3694,11 @@ eval_const_expressions_mutator(Node *node, * Treating MinMaxExpr this way amounts to assuming that the * btree comparison function it calls is immutable; see the * reasoning in contain_mutable_functions_walker. + * + * XmlExpr is treated as immutable by that walker too, so fold + * it here. Otherwise a constant IS DOCUMENT left in CASE + * WHEN can still allow unused arms (e.g. xpath()) to be + * simplified and fail at plan time. */ /* Copy the node and const-simplify its arguments */ diff --git a/src/test/regress/expected/xml.out b/src/test/regress/expected/xml.out index fb3e0ec41b2..fd189a8fa97 100644 --- a/src/test/regress/expected/xml.out +++ b/src/test/regress/expected/xml.out @@ -713,6 +713,16 @@ LINE 1: SELECT '<>' IS NOT DOCUMENT; DETAIL: line 1: StartTag: invalid element name <> ^ +-- Fold IS DOCUMENT constants so CASE does not run unused xpath() at plan time. +SELECT CASE WHEN ('2019-12-16T00:00:00.000'::xml) IS DOCUMENT + THEN (xpath('/*/text()', '2019-12-16T00:00:00.000'::xml))[1]::text + ELSE ('2019-12-16T00:00:00.000'::xml)::text +END; + case +------------------------- + 2019-12-16T00:00:00.000 +(1 row) + SELECT xmlagg(data) FROM xmltest; xmlagg -------------------------------------- diff --git a/src/test/regress/sql/xml.sql b/src/test/regress/sql/xml.sql index aafd39433a6..93a3dee92aa 100644 --- a/src/test/regress/sql/xml.sql +++ b/src/test/regress/sql/xml.sql @@ -185,6 +185,11 @@ SELECT xml '' IS NOT DOCUMENT; SELECT xml 'abc' IS NOT DOCUMENT; SELECT '<>' IS NOT DOCUMENT; +-- Fold IS DOCUMENT constants so CASE does not run unused xpath() at plan time. +SELECT CASE WHEN ('2019-12-16T00:00:00.000'::xml) IS DOCUMENT + THEN (xpath('/*/text()', '2019-12-16T00:00:00.000'::xml))[1]::text + ELSE ('2019-12-16T00:00:00.000'::xml)::text +END; SELECT xmlagg(data) FROM xmltest; SELECT xmlagg(data) FROM xmltest WHERE id > 10; -- 2.53.0