[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, 18 insertions, 9 deletions

diff --git a/src/cmd/compile/internal/types2/typeparam.go b/src/cmd/compile/internal/types2/typeparam.go
index 2614f467b1..27e6e35588 100644
--- a/src/cmd/compile/internal/types2/typeparam.go
+++ b/src/cmd/compile/internal/types2/typeparam.go
@@ -67,7 +67,7 @@ func (t *TypeParam) Constraint() Type {
 		if n, _ := t.bound.(*Named); n != nil {
 			pos = n.obj.pos
 		}
-		computeTypeSet(t.check, pos, iface)
+		computeInterfaceTypeSet(t.check, pos, iface)
 	}
 	return t.bound
 }
@@ -80,14 +80,6 @@ func (t *TypeParam) SetConstraint(bound Type) {
 	t.bound = bound
 }
 
-// iface returns the constraint interface of t.
-func (t *TypeParam) iface() *Interface {
-	if iface, _ := under(t.Constraint()).(*Interface); iface != nil {
-		return iface
-	}
-	return &emptyInterface
-}
-
 // Bound returns the constraint interface of t.
 // Deprecated. Only here for the compiler.
 // TODO(gri) remove in favor of uses of Constraint.
@@ -136,6 +128,23 @@ func bindTParams(list []*TypeName) *TypeParams {
 // ----------------------------------------------------------------------------
 // Implementation
 
+// iface returns the constraint interface of t.
+func (t *TypeParam) iface() *Interface {
+	if iface, _ := under(t.Constraint()).(*Interface); iface != nil {
+		return iface
+	}
+	return &emptyInterface
+}
+
+// structuralType returns the structural type of the type parameter's constraint; or nil.
+func (t *TypeParam) structuralType() Type {
+	return t.iface().typeSet().structuralType()
+}
+
+func (t *TypeParam) is(f func(*term) bool) bool {
+	return t.iface().typeSet().is(f)
+}
+
 func (t *TypeParam) underIs(f func(Type) bool) bool {
 	return t.iface().typeSet().underIs(f)
 }