I think that the root cause for this issue would be in the create_scan_plan handling of pseudoconstant quals when creating a foreign-join (or custom-join) plan.
Yes exactly. In create_scan_plan, we are supposed to extract all the pseudoconstant clauses and use them as one-time quals in a gating Result node. Currently we check against rel->baserestrictinfo and ppi_clauses for the pseudoconstant clauses. But for scans of foreign joins, we do not have any restriction clauses in these places and thus the gating Result node as well as the pseudoconstant clauses would just be lost.
I looked at Nishant's patch. IIUC it treats the pseudoconstant clauses as local conditions. While it can fix the wrong results issue, I think maybe it's better to still treat the pseudoconstant clauses as one-time quals in a gating node. So I wonder if we can store the restriction clauses for foreign joins in ForeignPath, just as what we do for normal JoinPath, and then check against them for pseudoconstant clauses in create_scan_plan, something like attached.
BTW, while going through the codes I noticed one place in add_foreign_final_paths that uses NULL for List *. I changed it to NIL.
