refactor(optimizer): record error contexts when casting composite types

[BugenZhao]

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What's changed and what's your intention?

Record contexts for error when recursively calling cast on composite types, to provide better error messages.

Preview:

risingwave/src/frontend/planner_test/tests/testdata/output/cast.yaml

Lines 92 to 115 in fc42233

	- name: composite type cast error message (struct)
	sql: |
	create table t (v struct<a struct<b int>, c bool>);
	select v::struct<d struct<e bytea>, f bool> from t;
	binder_error: |
	Failed to bind expression: CAST(v AS STRUCT<d STRUCT<e BYTEA>, f BOOLEAN>)
	Caused by these errors (recent errors listed first):
	1: cannot cast type "struct<a struct<b integer>, c boolean>" to "struct<d struct<e bytea>, f boolean>"
	2: cannot cast struct field "a" to struct field "d"
	3: cannot cast type "struct<b integer>" to "struct<e bytea>"
	4: cannot cast struct field "b" to struct field "e"
	5: cannot cast type "integer" to "bytea" in Explicit context
	- name: composite type cast error message (map)
	sql: |
	create table t (v map(int, int));
	select v::map(int, bytea) from t;
	binder_error: |
	Failed to bind expression: CAST(v AS MAP(INT,BYTEA))
	Caused by these errors (recent errors listed first):
	1: cannot cast type "map(integer,integer)" to "map(integer,bytea)"
	2: cannot cast map value
	3: cannot cast type "integer" to "bytea" in Explicit context

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Documentation

• My PR needs documentation updates. (Please use the Release note section below to summarize the impact on users)

Release note

If this PR includes changes that directly affect users or other significant modifications relevant to the community, kindly draft a release note to provide a concise summary of these changes. Please prioritize highlighting the impact these changes will have on users.

[BugenZhao]

Not to be confused with cast_map.

[xxchan]

A little confused how it works. So this is an empty leaf CastError? Why it's not shown in the err msg stack? (Why we need it?)

[BugenZhao]

Yes. In error report we'll disregard all empty and repeated entries, so it won't appear.

To preserve the reason for a cast failure, we must return a Result in functions like cast_struct. However, the default error message "cannot cast" is uniformly applied in cast, so we simply return an empty leaf error and let the caller to fill the context.

[xxchan]

It sounds like Result<(), Option<CastError>> 🤪

[xxchan]

very good 👍