[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, 8 insertions, 8 deletions

diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go
index c55d5c093a..fa4a1638b6 100644
--- a/src/cmd/compile/internal/types2/typexpr.go
+++ b/src/cmd/compile/internal/types2/typexpr.go
@@ -147,18 +147,18 @@ func (check *Checker) varType(e syntax.Expr) Type {
 // ordinaryType reports an error if typ is an interface type containing
 // type lists or is (or embeds) the predeclared type comparable.
 func (check *Checker) ordinaryType(pos syntax.Pos, typ Type) {
-	// We don't want to call under() (via Interface) or complete interfaces while we
+	// We don't want to call under() (via asInterface) or complete interfaces while we
 	// are in the middle of type-checking parameter declarations that might belong to
 	// interface methods. Delay this check to the end of type-checking.
 	check.later(func() {
 		if t := asInterface(typ); t != nil {
-			tset := computeTypeSet(check, pos, t) // TODO(gri) is this the correct position?
-			if tset.types != nil {
-				check.softErrorf(pos, "interface contains type constraints (%s)", tset.types)
-				return
-			}
-			if tset.IsComparable() {
-				check.softErrorf(pos, "interface is (or embeds) comparable")
+			tset := computeInterfaceTypeSet(check, pos, t) // TODO(gri) is this the correct position?
+			if !tset.IsMethodSet() {
+				if tset.comparable {
+					check.softErrorf(pos, "interface is (or embeds) comparable")
+				} else {
+					check.softErrorf(pos, "interface contains type constraints")
+				}
 			}
 		}
 	})