[BUG] Chaining .? (optional select) produces nested Optional(Optional(...))

[LouisCaubet]

Describe the bug
Chaining multiple .? (optional field select) operations does not work correctly. Each .? in the chain wraps the result in an additional Optional, producing Optional(Optional(Optional(...))) instead of a flat Optional.

For example:

a.?b.?c.?d.orValue("default")

fails at runtime, while the equivalent [?] index syntax works fine:

a[?"b"][?"c"][?"d"].orValue("default")

cel-go seems to handle this correctly: The Go reference implementation unwraps an optional operand before applying qualifiers: https://github.com/google/cel-go/blob/master/interpreter/attributes.go#L1298

To Reproduce
Check which components this affects:

• parser
• checker
• runtime

Sample expression and input that reproduces the issue:

a.?b.?c.?d.orValue("default")

Expected behavior
A clear and concise description of what you expected to happen.

a.?b.?c.?d.orValue("default") should behave the same way as a[?"b"][?"c"][?"d"].orValue("default"), not throw.

[l46kok]

Thanks for the report. This looks like a bug with the soon-to-be legacy runtime. We'll have a fix-out soon. Consider switching over to the planner runtime if you can, which doesn't have this issue.

[LouisCaubet]

Thanks for the quick response. I've confirmed that the planner runtime fixes our issue and will try to get us switched over.