expr: propagate errors through evaluation and optimization #2234
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jamii
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benesch
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This converts the non-converging fixpoint panic into a graceful error (MaterializeInc#1177). It also tees us up nicely for runtime errors (MaterializeInc#489). This PR is mostly extracted from MaterializeInc#2234, which has already been approved.
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AND, OR, and coalesce all want to evaluate their arguments lazily rather
than eagerly. This has semantic implications when evaluation can error.
For example
coalesce(1, 1 / 0)
does not result in an error, because `1 / 0` is not evaluated,
coalesce(NULL, 1 / 0)
does result in an error, because the `1 / 0` will be evaluated.
This patch installs the necessary plumbing to allow functions to opt-in
to lazy evaluation, and then teaches AND, OR, and coalesce to do so.
This patch allows scalar expressions evaluation to return an error. As optimization might involve evaluating the constituent scalar expressions, optimization can now return errors as well. If such an error is discovered during optimization (i.e., somewhere between plan time and run time), it will be returned to the client. Errors that truly occur at runtime are still replaced with NULLs, as before. A future commit will wire up a separate error pathway for runtime errors.
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Builds on #2233 to propagate errors that occur at optimization time to the client.
This patch allows scalar expressions evaluation to return an error. As
optimization might involve evaluating the constituent scalar
expressions, optimization can now return errors as well. If such an
error is discovered during optimization (i.e., somewhere between plan
time and run time), it will be returned to the client.
Errors that truly occur at runtime are still replaced with NULLs, as
before. A future commit will wire up a separate error pathway for
runtime errors.