A view with conditional INSTEAD rules and no unconditional INSTEAD rules or INSTEAD OF triggers is not auto-updatable. Previously we relied on a check in the executor to catch this, but that's problematic since the planner may fail to properly handle such a query and thus return a particularly unhelpful error to the user, before reaching the executor check.
Instead, trap this in the rewriter and report the correct error there. Doing so also allows us to include more useful error detail than the executor check can provide. This doesn't change the existing behaviour of updatable views; it merely ensures that useful error messages are reported when a view isn't updatable.
Per report from Pengzhou Tang, though not adopting that suggested fix. Back-patch to all supported branches.
d751ba5235 Make rewriter prevent auto-updates on views with conditional INSTEAD rules.
src/backend/executor/execMain.c | 8 ++--
src/backend/rewrite/rewriteHandler.c | 60 ++++++++++++++++++++++++---
src/test/regress/expected/updatable_views.out | 21 ++++++++++
src/test/regress/sql/updatable_views.sql | 14 +++++++
4 files changed, 94 insertions(+), 9 deletions(-)