[dev.typeparams] cmd/compile/internal/types2: introduce type set abstraction for interfaces

With this change, interfaces are "completed" on-demand, when needed,
and the respective information (set of all methods, type constraints)
is recorded in a new typeSet data structure.

As a consequence, interfaces don't need to be explicitly completed
anymore and (internal) uses of interfaces have become much simpler.

This change also introduces a new field Interface.complete to indicate
that all methods and embedded elements have been set up. This prevent
the computation and recording (!) of a partial type set for erroneous
programs (if we compute the partial type set and store it, subsequent
type set accesses use the wrong type set which may lead to follow-on
errors).

Change-Id: I1ffc907f7d0fb93b3e987fe5ff9c6fa5cae00d7f
Reviewed-on: https://go-review.googlesource.com/c/go/+/329309
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 7 insertions, 8 deletions

diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index 3ef65c2e92..38bd07b8a2 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -136,6 +136,7 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, poslis
 // satisfies reports whether the type argument targ satisfies the constraint of type parameter
 // parameter tpar (after any of its type parameters have been substituted through smap).
 // A suitable error is reported if the result is false.
+// TODO(gri) This should be a method of interfaces or type sets.
 func (check *Checker) satisfies(pos syntax.Pos, targ Type, tpar *TypeParam, smap *substMap) bool {
 	iface := tpar.Bound()
 	if iface.Empty() {
@@ -150,8 +151,7 @@ func (check *Checker) satisfies(pos syntax.Pos, targ Type, tpar *TypeParam, smap
 
 	// targ must implement iface (methods)
 	// - check only if we have methods
-	check.completeInterface(nopos, iface)
-	if len(iface.allMethods) > 0 {
+	if iface.NumMethods() > 0 {
 		// If the type argument is a pointer to a type parameter, the type argument's
 		// method set is empty.
 		// TODO(gri) is this what we want? (spec question)
@@ -182,7 +182,7 @@ func (check *Checker) satisfies(pos syntax.Pos, targ Type, tpar *TypeParam, smap
 	}
 
 	// targ's underlying type must also be one of the interface types listed, if any
-	if iface.allTypes == nil {
+	if iface.typeSet().types == nil {
 		return true // nothing to do
 	}
 
@@ -190,7 +190,7 @@ func (check *Checker) satisfies(pos syntax.Pos, targ Type, tpar *TypeParam, smap
 	// list of iface types (i.e., the targ type list must be a non-empty subset of the iface types).
 	if targ := asTypeParam(targ); targ != nil {
 		targBound := targ.Bound()
-		if targBound.allTypes == nil {
+		if targBound.typeSet().types == nil {
 			check.softErrorf(pos, "%s does not satisfy %s (%s has no type constraints)", targ, tpar.bound, targ)
 			return false
 		}
@@ -198,7 +198,7 @@ func (check *Checker) satisfies(pos syntax.Pos, targ Type, tpar *TypeParam, smap
 			// TODO(gri) incorporate tilde information!
 			if !iface.isSatisfiedBy(typ) {
 				// TODO(gri) match this error message with the one below (or vice versa)
-				check.softErrorf(pos, "%s does not satisfy %s (%s type constraint %s not found in %s)", targ, tpar.bound, targ, typ, iface.allTypes)
+				check.softErrorf(pos, "%s does not satisfy %s (%s type constraint %s not found in %s)", targ, tpar.bound, targ, typ, iface.typeSet().types)
 				return false
 			}
 			return true
@@ -207,7 +207,7 @@ func (check *Checker) satisfies(pos syntax.Pos, targ Type, tpar *TypeParam, smap
 
 	// Otherwise, targ's type or underlying type must also be one of the interface types listed, if any.
 	if !iface.isSatisfiedBy(targ) {
-		check.softErrorf(pos, "%s does not satisfy %s (%s not found in %s)", targ, tpar.bound, targ, iface.allTypes)
+		check.softErrorf(pos, "%s does not satisfy %s (%s not found in %s)", targ, tpar.bound, targ, iface.typeSet().types)
 		return false
 	}
 
@@ -312,12 +312,11 @@ func (subst *subster) typ(typ Type) Type {
 		methods, mcopied := subst.funcList(t.methods)
 		embeddeds, ecopied := subst.typeList(t.embeddeds)
 		if mcopied || ecopied {
-			iface := &Interface{methods: methods, embeddeds: embeddeds}
+			iface := &Interface{methods: methods, embeddeds: embeddeds, complete: t.complete}
 			if subst.check == nil {
 				panic("internal error: cannot instantiate interfaces yet")
 			}
 			subst.check.posMap[iface] = subst.check.posMap[t] // satisfy completeInterface requirement
-			subst.check.completeInterface(nopos, iface)
 			return iface
 		}