[dev.typeparams] cmd/compile/internal/types2: implement type sets with term lists

This CL resolves several known issues and TODOs.

- Represent type sets with term lists and using term list abstractions.

- Represent Unions internally as a list of (syntactical) terms.
  Use term operations to print terms and detect overlapping union
  entries.

- Compute type sets corresponding to unions lazily, on demand.

- Adjust code throughout.

- Adjusted error check in test/typeparam/mincheck.dir/main.go
  to make test pass.

Change-Id: Ib36fb7e1d343c2b6aec51d304f0f7d1ad415f999
Reviewed-on: https://go-review.googlesource.com/c/go/+/338310
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 1 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/types2/unify.go b/src/cmd/compile/internal/types2/unify.go
index aa9a23d243..75b9a12197 100644
--- a/src/cmd/compile/internal/types2/unify.go
+++ b/src/cmd/compile/internal/types2/unify.go
@@ -361,9 +361,6 @@ func (u *unifier) nify(x, y Type, p *ifacePair) bool {
 				u.nify(x.results, y.results, p)
 		}
 
-	case *Union:
-		panic("unimplemented: unification with type sets described by types")
-
 	case *Interface:
 		// Two interface types are identical if they have the same set of methods with
 		// the same names and identical function types. Lower-case method names from
@@ -371,7 +368,7 @@ func (u *unifier) nify(x, y Type, p *ifacePair) bool {
 		if y, ok := y.(*Interface); ok {
 			xset := x.typeSet()
 			yset := y.typeSet()
-			if !Identical(xset.types, yset.types) {
+			if !xset.terms.equal(yset.terms) {
 				return false
 			}
 			a := xset.methods