[dev.typeparams] go/types: (TypeParam) SetBound -> SetConstraint

This is a straightforward port of CL 338196 to go/types, minus the
deprecated TypeParam.Bound() method (since it is not needed), plus an
adjustment for methodset.go.

Change-Id: Ie372bfeec245094102a2c3257a43499d75981447
Reviewed-on: https://go-review.googlesource.com/c/go/+/339675
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

8 files changed, 20 insertions, 23 deletions

diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index ecb9920a81..aae05438cd 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -826,7 +826,7 @@ func (check *Checker) applyTypeFunc(f func(Type) Type, x Type) Type {
 		// type and collect possible result types at the same time.
 		var rtypes []Type
 		var tildes []bool
-		if !tp.Bound().is(func(typ Type, tilde bool) bool {
+		if !tp.iface().is(func(typ Type, tilde bool) bool {
 			if r := f(typ); r != nil {
 				rtypes = append(rtypes, r)
 				tildes = append(tildes, tilde)
diff --git a/src/go/types/call.go b/src/go/types/call.go
index 16b8e4eb7c..da2f319a4a 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -482,7 +482,7 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
 			var why string
 			if tpar := asTypeParam(x.typ); tpar != nil {
 				// Type parameter bounds don't specify fields, so don't mention "field".
-				if tname := tpar.Bound().obj; tname != nil {
+				if tname := tpar.iface().obj; tname != nil {
 					why = check.sprintf("interface %s has no method %s", tname.name, sel)
 				} else {
 					why = check.sprintf("type bound for %s has no method %s", x.typ, sel)
diff --git a/src/go/types/instantiate.go b/src/go/types/instantiate.go
index 2e6c20723b..6d56eb7ea2 100644
--- a/src/go/types/instantiate.go
+++ b/src/go/types/instantiate.go
@@ -162,7 +162,7 @@ func (check *Checker) verify(pos token.Pos, tparams []*TypeName, targs []Type, p
 // 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 token.Pos, targ Type, tpar *TypeParam, smap *substMap) bool {
-	iface := tpar.Bound()
+	iface := tpar.iface()
 	if iface.Empty() {
 		return true // no type bound
 	}
@@ -176,7 +176,7 @@ func (check *Checker) satisfies(pos token.Pos, targ Type, tpar *TypeParam, smap
 	// if iface is comparable, targ must be comparable
 	// TODO(gri) the error messages needs to be better, here
 	if iface.IsComparable() && !Comparable(targ) {
-		if tpar := asTypeParam(targ); tpar != nil && tpar.Bound().typeSet().IsTop() {
+		if tpar := asTypeParam(targ); tpar != nil && tpar.iface().typeSet().IsTop() {
 			check.softErrorf(atPos(pos), _Todo, "%s has no constraints", targ)
 			return false
 		}
@@ -222,7 +222,7 @@ func (check *Checker) satisfies(pos token.Pos, targ Type, tpar *TypeParam, smap
 	// If targ is itself a type parameter, each of its possible types, but at least one, must be in the
 	// 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()
+		targBound := targ.iface()
 		if targBound.typeSet().types == nil {
 			check.softErrorf(atPos(pos), _Todo, "%s does not satisfy %s (%s has no type constraints)", targ, tpar.bound, targ)
 			return false
diff --git a/src/go/types/lookup.go b/src/go/types/lookup.go
index 6d38db4523..7cab336dbe 100644
--- a/src/go/types/lookup.go
+++ b/src/go/types/lookup.go
@@ -190,7 +190,7 @@ func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (o
 				}
 
 			case *TypeParam:
-				if i, m := t.Bound().typeSet().LookupMethod(pkg, name); m != nil {
+				if i, m := t.iface().typeSet().LookupMethod(pkg, name); m != nil {
 					assert(m.typ != nil)
 					index = concat(e.index, i)
 					if obj != nil || e.multiples {
diff --git a/src/go/types/methodset.go b/src/go/types/methodset.go
index 491917d6bc..1462601d58 100644
--- a/src/go/types/methodset.go
+++ b/src/go/types/methodset.go
@@ -160,7 +160,7 @@ func NewMethodSet(T Type) *MethodSet {
 				mset = mset.add(t.typeSet().methods, e.index, true, e.multiples)
 
 			case *TypeParam:
-				mset = mset.add(t.Bound().typeSet().methods, e.index, true, e.multiples)
+				mset = mset.add(t.iface().typeSet().methods, e.index, true, e.multiples)
 			}
 		}
 
diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index 579d35da42..f9cac34a03 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/predicates.go
@@ -113,7 +113,7 @@ func comparable(T Type, seen map[Type]bool) bool {
 	case *Array:
 		return comparable(t.elem, seen)
 	case *TypeParam:
-		return t.Bound().IsComparable()
+		return t.iface().IsComparable()
 	}
 	return false
 }
diff --git a/src/go/types/type.go b/src/go/types/type.go
index 2ad89d9705..5819dd290c 100644
--- a/src/go/types/type.go
+++ b/src/go/types/type.go
@@ -56,7 +56,7 @@ func optype(typ Type) Type {
 		// for a type parameter list of the form:
 		// (type T interface { type T }).
 		// See also issue #39680.
-		if a := t.Bound().typeSet().types; a != nil && a != typ {
+		if a := t.iface().typeSet().types; a != nil && a != typ {
 			// If we have a union with a single entry, ignore
 			// any tilde because under(~t) == under(t).
 			if u, _ := a.(*Union); u != nil && u.NumTerms() == 1 {
diff --git a/src/go/types/typeparam.go b/src/go/types/typeparam.go
index 8cb44ea25e..33a516c209 100644
--- a/src/go/types/typeparam.go
+++ b/src/go/types/typeparam.go
@@ -74,23 +74,20 @@ func (t *TypeParam) Constraint() Type {
 	return t.bound
 }
 
-// Bound returns the underlying type of the type parameter's
-// constraint.
-// Deprecated for external use. Use Constraint instead.
-func (t *TypeParam) Bound() *Interface {
-	if iface, _ := under(t.Constraint()).(*Interface); iface != nil {
-		return iface
+// SetConstraint sets the type constraint for t.
+func (t *TypeParam) SetConstraint(bound Type) {
+	if bound == nil {
+		panic("types2.TypeParam.SetConstraint: bound must not be nil")
 	}
-	return &emptyInterface
+	t.bound = bound
 }
 
-// TODO(rfindley): document the SetBound methods.
-
-func (t *TypeParam) SetBound(bound Type) {
-	if bound == nil {
-		panic("internal error: bound must not be nil")
+// iface returns the constraint interface of t.
+func (t *TypeParam) iface() *Interface {
+	if iface, _ := under(t.Constraint()).(*Interface); iface != nil {
+		return iface
 	}
-	t.bound = bound
+	return &emptyInterface
 }
 
 func (t *TypeParam) Underlying() Type { return t }
@@ -135,5 +132,5 @@ func bindTParams(list []*TypeName) *TypeParams {
 // Implementation
 
 func (t *TypeParam) underIs(f func(Type) bool) bool {
-	return t.Bound().typeSet().underIs(f)
+	return t.iface().typeSet().underIs(f)
 }