From 183b3acedab90390d07036bfd532481acd71cd1d Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 20 Sep 2021 11:48:52 -0400 Subject: [PATCH] Don't elide casting to typmod -1. Casting a value that's already of a type with a specific typmod to an unspecified typmod doesn't do anything so far as run-time behavior is concerned. However, it really ought to change the exposed type of the expression to match. Up to now, coerce_type_typmod hasn't bothered with that, which creates gotchas in contexts such as recursive unions. If for example one side of the union is numeric(18,3), but it needs to be plain numeric to match the other side, there's no direct way to express that. This is easy enough to fix, by inserting a RelabelType to update the exposed type of the expression. However, it's a bit nervous-making to change this behavior, because it's stood for a really long time. But no complaints have emerged about 14beta3, so go ahead and back-patch. Back-patch of 5c056b0c2 into previous supported branches. Discussion: https://postgr.es/m/CABNQVagu3bZGqiTjb31a8D5Od3fUMs7Oh3gmZMQZVHZ=uWWWfQ@mail.gmail.com Discussion: https://postgr.es/m/1488389.1631984807@sss.pgh.pa.us --- src/backend/parser/parse_coerce.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-) diff --git a/src/backend/parser/parse_coerce.c b/src/backend/parser/parse_coerce.c index c69cac40151..7d5cdeaa179 100644 --- a/src/backend/parser/parse_coerce.c +++ b/src/backend/parser/parse_coerce.c @@ -739,26 +739,38 @@ coerce_type_typmod(Node *node, Oid targetTypeId, int32 targetTypMod, CoercionPathType pathtype; Oid funcId; - /* - * A negative typmod is assumed to mean that no coercion is wanted. Also, - * skip coercion if already done. - */ - if (targetTypMod < 0 || targetTypMod == exprTypmod(node)) + /* Skip coercion if already done */ + if (targetTypMod == exprTypmod(node)) return node; + /* Suppress display of nested coercion steps */ + if (hideInputCoercion) + hide_coercion_node(node); + pathtype = find_typmod_coercion_function(targetTypeId, &funcId); if (pathtype != COERCION_PATH_NONE) { - /* Suppress display of nested coercion steps */ - if (hideInputCoercion) - hide_coercion_node(node); - node = build_coercion_expression(node, pathtype, funcId, targetTypeId, targetTypMod, cformat, location, isExplicit); } + else + { + /* + * We don't need to perform any actual coercion step, but we should + * apply a RelabelType to ensure that the expression exposes the + * intended typmod. + */ + RelabelType *rt; + + rt = makeRelabelType((Expr *) node, targetTypeId, targetTypMod, + exprCollation(node), + cformat); + rt->location = location; + node = (Node *) rt; + } return node; } -- 2.39.5