go/types, types2: don't panic for invalid assignments of comma-ok expressions
The relevant code was broken with CL 478218. Before that CL,
Checker.assignVar used to return the assigned type, or nil,
in case of failure. Checker.recordCommaOkTypes used to take
two types (not two operands), and if one of those types was
nil, it would simply not record. CL 478218, lost that (nil)
signal.
This change consistently reports an assignment check failure
by setting x.mode to invalid for initVar and assignVar and
then tests if x.mode != invalid before recording a comma-ok
expression.
Fixes #59371.
Change-Id: I193815ff3e4b43e3e510fe25bd0e72e0a6a816c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/486135 Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com>
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