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Ensure casting to typmod -1 generates a RelabelType.

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Fix the code changed by commit 5c056b0c2 so that we always generate
RelabelType, not something else, for a cast to unspecified typmod.
Otherwise planner optimizations might not happen.

It appears we missed this point because the previous experiments were
done on type numeric: the parser undesirably generates a call on the
numeric() length-coercion function, but then numeric_support()
optimizes that down to a RelabelType, so that everything seems fine.
It misbehaves for types that have a non-optimized length coercion
function, such as bpchar.

Per report from John Naylor.  Back-patch to all supported branches,
as the previous patch eventually was.  Unfortunately, that no longer
includes 9.6 ... we really shouldn't put this type of change into a
nearly-EOL branch.

Discussion: https://postgr.es/m/CAFBsxsEfbFHEkouc+FSj+3K1sHipLPbEC67L0SAe-9-da8QtYg@mail.gmail.com
This commit is contained in:
Tom Lane
2021-12-16 15:36:02 -05:00
parent aadbf825b7
commit da0d8a4545
3 changed files with 61 additions and 1 deletions
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10
src/backend/parser/parse_coerce.c
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@ -763,7 +763,15 @@ coerce_type_typmod(Node *node, Oid targetTypeId, int32 targetTypMod,
if (hideInputCoercion)
hide_coercion_node(node);
pathtype = find_typmod_coercion_function(targetTypeId, &funcId);
/*
* A negative typmod means that no actual coercion is needed, but we still
* want a RelabelType to ensure that the expression exposes the intended
* typmod.
*/
if (targetTypMod < 0)
pathtype = COERCION_PATH_NONE;
else
pathtype = find_typmod_coercion_function(targetTypeId, &funcId);
if (pathtype != COERCION_PATH_NONE)
{