Ensure that the result of evaluating a function during constant-expression

simplification gets detoasted before it is incorporated into a Const node.
Otherwise, if an immutable function were to return a TOAST pointer (an
unlikely case, but it can be made to happen), we would end up with a plan
that depends on the continued existence of the out-of-line toast datum.

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index 9173fc7a6e9930bacdbf5847054a7835581ba35a..72fe3b62de5eb0342bcbf9c1f6cf19cfc2e920df 100644 (file)
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2662,9 +2662,20 @@ evaluate_expr(Expr *expr, Oid result_type)
        /* Get back to outer memory context */
        MemoryContextSwitchTo(oldcontext);
 
-       /* Must copy result out of sub-context used by expression eval */
+       /*
+        * Must copy result out of sub-context used by expression eval.
+        *
+        * Also, if it's varlena, forcibly detoast it.  This protects us against
+        * storing TOAST pointers into plans that might outlive the referenced
+        * data.
+        */
        if (!const_is_null)
-               const_val = datumCopy(const_val, resultTypByVal, resultTypLen);
+       {
+               if (resultTypLen == -1)
+                       const_val = PointerGetDatum(PG_DETOAST_DATUM_COPY(const_val));
+               else
+                       const_val = datumCopy(const_val, resultTypByVal, resultTypLen);
+       }
 
        /* Release all the junk we just created */
        FreeExecutorState(estate);