go/types: compute effective Go version independent of token.Pos
Previously, the Checker.allowVersion method would use a token.Pos
to try to infer which file of the current package the checker
was "in". This proved fragile when type-checking syntax that
had been modified or synthesized and whose positions were invalid.
This change records the effective version in the checker state
(checker.environment.version). Just like other aspects of the
environment, the version changes from one file to the next
and must be saved and restored with each check.later closure.
Similarly, declInfo captures and temporarily reinstates
the effective version when checking each object.
+ Test of position independence in go/types and types2
+ Test of panic avoidance in go/types
Fixes golang/go#69477
Fixes golang/go#69338
Change-Id: Ic06f9d88151c64a4f7848f8942d08e3c312cdd6f
Reviewed-on: https://go-review.googlesource.com/c/go/+/613735
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>