go/types, types2: correctly include comparable in type set intersection
The comparable bit was handled incorrectly. This CL establishes
a clear invariant for a type set's terms and its comparable bit
and correctly uses the bit when computing term intersections.
Relevant changes:
- Introduce a new function intersectTermLists that does the
correct intersection computation.
Minor:
- Moved the comparable bit after terms in _TypeSet to make it
clearer that they belong together.
- Simplify and clarify _TypeSet.IsAll predicate.
- Remove the IsTypeSet predicate which was only used for error
reporting in union.go, and use the existing predicates instead.
- Rename/introduce local variables in computeInterfaceTypeSet
for consistency and to avoid confusion.
- Update some tests whose output has changed because the comparable
bit is now only set if we have have the set of all types.
For instance, for interface{comparable; int} the type set doesn't
set the comparable bit because the intersection of comparable and
int is just int; etc.
- Add many more comments to make the code clearer.
Fixes #51472.
Change-Id: I8a5661eb1693a41a17ce5f70d7e10774301f38ab
Reviewed-on: https://go-review.googlesource.com/c/go/+/390025
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org> Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>