[dev.typeparams] cmd/compile/internal/types2: replace Named, TypeParam methods with functions

This removes two more converter methods in favor of functions.
This further reduces the API surface of types2.Type and matches
the approach taken in go/types.

Change-Id: I3cdd54c5e0d1e7664a69f3697fc081a66315b969
Reviewed-on: https://go-review.googlesource.com/c/go/+/293292
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

13 files changed, 43 insertions, 62 deletions

diff --git a/src/cmd/compile/internal/importer/support.go b/src/cmd/compile/internal/importer/support.go
index cac87745fe..b143913583 100644
--- a/src/cmd/compile/internal/importer/support.go
+++ b/src/cmd/compile/internal/importer/support.go
@@ -127,7 +127,3 @@ type anyType struct{}
 func (t anyType) Underlying() types2.Type { return t }
 func (t anyType) Under() types2.Type      { return t }
 func (t anyType) String() string          { return "any" }
-
-// types2.aType is not exported for now so we need to implemented these here.
-func (anyType) Named() *types2.Named         { return nil }
-func (anyType) TypeParam() *types2.TypeParam { return nil }
diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
index 763122bc5b..16e294d226 100644
--- a/src/cmd/compile/internal/types2/builtins.go
+++ b/src/cmd/compile/internal/types2/builtins.go
@@ -577,7 +577,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 
 	case _Alignof:
 		// unsafe.Alignof(x T) uintptr
-		if x.typ.TypeParam() != nil {
+		if asTypeParam(x.typ) != nil {
 			check.invalidOpf(call, "unsafe.Alignof undefined for %s", x)
 			return
 		}
@@ -638,7 +638,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 
 	case _Sizeof:
 		// unsafe.Sizeof(x T) uintptr
-		if x.typ.TypeParam() != nil {
+		if asTypeParam(x.typ) != nil {
 			check.invalidOpf(call, "unsafe.Sizeof undefined for %s", x)
 			return
 		}
@@ -705,7 +705,7 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 // applyTypeFunc returns nil.
 // If x is not a type parameter, the result is f(x).
 func (check *Checker) applyTypeFunc(f func(Type) Type, x Type) Type {
-	if tp := x.TypeParam(); tp != nil {
+	if tp := asTypeParam(x); tp != nil {
 		// Test if t satisfies the requirements for the argument
 		// type and collect possible result types at the same time.
 		var rtypes []Type
diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index 10db701324..67a76d14fb 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -563,7 +563,7 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
 			check.errorf(e.Sel, "cannot call pointer method %s on %s", sel, x.typ)
 		default:
 			var why string
-			if tpar := x.typ.TypeParam(); tpar != nil {
+			if tpar := asTypeParam(x.typ); tpar != nil {
 				// Type parameter bounds don't specify fields, so don't mention "field".
 				switch obj := tpar.Bound().obj.(type) {
 				case nil:
diff --git a/src/cmd/compile/internal/types2/decl.go b/src/cmd/compile/internal/types2/decl.go
index 59d0a112b1..e9fc08df37 100644
--- a/src/cmd/compile/internal/types2/decl.go
+++ b/src/cmd/compile/internal/types2/decl.go
@@ -559,7 +559,7 @@ func (n0 *Named) Under() Type {
 
 	// If the underlying type of a defined type is not a defined
 	// type, then that is the desired underlying type.
-	n := u.Named()
+	n := asNamed(u)
 	if n == nil {
 		return u // common case
 	}
@@ -573,7 +573,7 @@ func (n0 *Named) Under() Type {
 			u = Typ[Invalid]
 			break
 		}
-		n1 := u.Named()
+		n1 := asNamed(u)
 		if n1 == nil {
 			break // end of chain
 		}
@@ -760,7 +760,7 @@ func (check *Checker) collectMethods(obj *TypeName) {
 
 	// spec: "If the base type is a struct type, the non-blank method
 	// and field names must be distinct."
-	base := obj.typ.Named() // shouldn't fail but be conservative
+	base := asNamed(obj.typ) // shouldn't fail but be conservative
 	if base != nil {
 		if t, _ := base.underlying.(*Struct); t != nil {
 			for _, fld := range t.fields {
diff --git a/src/cmd/compile/internal/types2/expr.go b/src/cmd/compile/internal/types2/expr.go
index 07b23c9eff..57c8896e0d 100644
--- a/src/cmd/compile/internal/types2/expr.go
+++ b/src/cmd/compile/internal/types2/expr.go
@@ -615,7 +615,7 @@ func (check *Checker) convertUntyped(x *operand, target Type) {
 	// TODO(gri) We should not need this because we have the code
 	// for Sum types in convertUntypedInternal. But at least one
 	// test fails. Investigate.
-	if t := target.TypeParam(); t != nil {
+	if t := asTypeParam(target); t != nil {
 		types := t.Bound().allTypes
 		if types == nil {
 			goto Error
diff --git a/src/cmd/compile/internal/types2/lookup.go b/src/cmd/compile/internal/types2/lookup.go
index df25c9cf70..e210850ba0 100644
--- a/src/cmd/compile/internal/types2/lookup.go
+++ b/src/cmd/compile/internal/types2/lookup.go
@@ -54,7 +54,7 @@ func (check *Checker) lookupFieldOrMethod(T Type, addressable bool, pkg *Package
 	// Thus, if we have a named pointer type, proceed with the underlying
 	// pointer type but discard the result if it is a method since we would
 	// not have found it for T (see also issue 8590).
-	if t := T.Named(); t != nil {
+	if t := asNamed(T); t != nil {
 		if p, _ := t.underlying.(*Pointer); p != nil {
 			obj, index, indirect = check.rawLookupFieldOrMethod(p, false, pkg, name)
 			if _, ok := obj.(*Func); ok {
@@ -112,7 +112,7 @@ func (check *Checker) rawLookupFieldOrMethod(T Type, addressable bool, pkg *Pack
 
 			// If we have a named type, we may have associated methods.
 			// Look for those first.
-			if named := typ.Named(); named != nil {
+			if named := asNamed(typ); named != nil {
 				if seen[named] {
 					// We have seen this type before, at a more shallow depth
 					// (note that multiples of this type at the current depth
@@ -142,7 +142,7 @@ func (check *Checker) rawLookupFieldOrMethod(T Type, addressable bool, pkg *Pack
 				// continue with underlying type, but only if it's not a type parameter
 				// TODO(gri) is this what we want to do for type parameters? (spec question)
 				typ = named.Under()
-				if typ.TypeParam() != nil {
+				if asTypeParam(typ) != nil {
 					continue
 				}
 			}
@@ -352,7 +352,7 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
 
 	// A concrete type implements T if it implements all methods of T.
 	Vd, _ := deref(V)
-	Vn := Vd.Named()
+	Vn := asNamed(Vd)
 	for _, m := range T.allMethods {
 		// TODO(gri) should this be calling lookupFieldOrMethod instead (and why not)?
 		obj, _, _ := check.rawLookupFieldOrMethod(V, false, m.pkg, m.name)
diff --git a/src/cmd/compile/internal/types2/operand.go b/src/cmd/compile/internal/types2/operand.go
index dcd29fbce0..238c9b8ee0 100644
--- a/src/cmd/compile/internal/types2/operand.go
+++ b/src/cmd/compile/internal/types2/operand.go
@@ -180,7 +180,7 @@ func operandString(x *operand, qf Qualifier) string {
 			switch {
 			case isGeneric(x.typ):
 				intro = " of generic type "
-			case x.typ.TypeParam() != nil:
+			case asTypeParam(x.typ) != nil:
 				intro = " of type parameter type "
 			default:
 				intro = " of type "
diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index a7972c6928..a48e72b9c4 100644
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -104,7 +104,7 @@ func comparable(T Type, seen map[Type]bool) bool {
 	//     interface{ comparable; type []byte }
 	//
 	// is not comparable because []byte is not comparable.
-	if t := T.TypeParam(); t != nil && optype(t) == theTop {
+	if t := asTypeParam(T); t != nil && optype(t) == theTop {
 		return t.Bound().IsComparable()
 	}
 
diff --git a/src/cmd/compile/internal/types2/subst.go b/src/cmd/compile/internal/types2/subst.go
index 27405d8f41..fc4b228e33 100644
--- a/src/cmd/compile/internal/types2/subst.go
+++ b/src/cmd/compile/internal/types2/subst.go
@@ -146,7 +146,7 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, poslis
 			// 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)
-			if base, isPtr := deref(targ); isPtr && base.TypeParam() != nil {
+			if base, isPtr := deref(targ); isPtr && asTypeParam(base) != nil {
 				check.errorf(pos, "%s has no methods", targ)
 				break
 			}
@@ -179,7 +179,7 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, poslis
 
 		// 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 := targ.TypeParam(); targ != nil {
+		if targ := asTypeParam(targ); targ != nil {
 			targBound := targ.Bound()
 			if targBound.allTypes == nil {
 				check.softErrorf(pos, "%s does not satisfy %s (%s has no type constraints)", targ, tpar.bound, targ)
diff --git a/src/cmd/compile/internal/types2/type.go b/src/cmd/compile/internal/types2/type.go
index f90abba8da..4b6f507393 100644
--- a/src/cmd/compile/internal/types2/type.go
+++ b/src/cmd/compile/internal/types2/type.go
@@ -26,13 +26,6 @@ type Type interface {
 
 	// String returns a string representation of a type.
 	String() string
-
-	// If the receiver for Named and TypeParam is of
-	// the respective type (possibly after unpacking
-	// an instance type), these methods return that
-	// type. Otherwise the result is nil.
-	Named() *Named
-	TypeParam() *TypeParam
 }
 
 // aType implements default type behavior
@@ -43,9 +36,6 @@ func (aType) Underlying() Type { panic("unreachable") }
 func (aType) Under() Type      { panic("unreachable") }
 func (aType) String() string   { panic("unreachable") }
 
-func (aType) Named() *Named         { return nil }
-func (aType) TypeParam() *TypeParam { return nil }
-
 // BasicKind describes the kind of basic type.
 type BasicKind int
 
@@ -209,6 +199,9 @@ type Tuple struct {
 	aType
 }
 
+// TODO(gri) Don't represent empty tuples with a (*Tuple)(nil) pointer;
+//           it's too subtle and causes problems. Use a singleton instead.
+
 // NewTuple returns a new tuple for the given variables.
 func NewTuple(x ...*Var) *Tuple {
 	if len(x) > 0 {
@@ -217,16 +210,6 @@ func NewTuple(x ...*Var) *Tuple {
 	return nil
 }
 
-// We cannot rely on the embedded X() *X methods because (*Tuple)(nil)
-// is a valid *Tuple value but (*Tuple)(nil).X() would panic without
-// these implementations. At the moment we only need X = Basic, Named,
-// but add all because missing one leads to very confusing bugs.
-// TODO(gri) Don't represent empty tuples with a (*Tuple)(nil) pointer;
-//           it's too subtle and causes problems.
-
-func (*Tuple) Named() *Named         { return nil }
-func (*Tuple) TypeParam() *TypeParam { return nil }
-
 // Len returns the number variables of tuple t.
 func (t *Tuple) Len() int {
 	if t != nil {
@@ -730,9 +713,6 @@ func (check *Checker) NewNamed(obj *TypeName, underlying Type, methods []*Func)
 // Obj returns the type name for the named type t.
 func (t *Named) Obj() *TypeName { return t.obj }
 
-// func (t *Named) Named() *Named      // declared below
-func (t *Named) TypeParam() *TypeParam { return t.Under().TypeParam() }
-
 // TODO(gri) Come up with a better representation and API to distinguish
 //           between parameterized instantiated and non-instantiated types.
 
@@ -814,7 +794,7 @@ func (t *TypeParam) Bound() *Interface {
 // result may be the bottom or top type, but it is never
 // the incoming type parameter.
 func optype(typ Type) Type {
-	if t := typ.TypeParam(); t != nil {
+	if t := asTypeParam(typ); t != nil {
 		// If the optype is typ, return the top type as we have
 		// no information. It also prevents infinite recursion
 		// via the TypeParam converter methods. This can happen
@@ -830,9 +810,6 @@ func optype(typ Type) Type {
 	return typ.Under()
 }
 
-// func (t *TypeParam) Named() *Named         // Named does not unpack type parameters
-// func (t *TypeParam) TypeParam() *TypeParam // declared below
-
 // An instance represents an instantiated generic type syntactically
 // (without expanding the instantiation). Type instances appear only
 // during type-checking and are replaced by their fully instantiated
@@ -847,9 +824,6 @@ type instance struct {
 	aType
 }
 
-func (t *instance) Named() *Named         { return t.expand().Named() }
-func (t *instance) TypeParam() *TypeParam { return t.expand().TypeParam() }
-
 // expand returns the instantiated (= expanded) type of t.
 // The result is either an instantiated *Named type, or
 // Typ[Invalid] if there was an error.
@@ -908,9 +882,6 @@ type top struct {
 // theTop is the singleton top type.
 var theTop = &top{}
 
-func (t *Named) Named() *Named             { return t }
-func (t *TypeParam) TypeParam() *TypeParam { return t }
-
 // Type-specific implementations of Underlying.
 func (t *Basic) Underlying() Type     { return t }
 func (t *Array) Underlying() Type     { return t }
@@ -1025,3 +996,17 @@ func asChan(t Type) *Chan {
 	op, _ := optype(t).(*Chan)
 	return op
 }
+
+// If the argument to asNamed and asTypeParam is of the respective types
+// (possibly after expanding an instance type), these methods return that type.
+// Otherwise the result is nil.
+
+func asNamed(t Type) *Named {
+	e, _ := expand(t).(*Named)
+	return e
+}
+
+func asTypeParam(t Type) *TypeParam {
+	u, _ := t.Under().(*TypeParam)
+	return u
+}
diff --git a/src/cmd/compile/internal/types2/typexpr.go b/src/cmd/compile/internal/types2/typexpr.go
index 7ee28abac3..cf9d7c0a40 100644
--- a/src/cmd/compile/internal/types2/typexpr.go
+++ b/src/cmd/compile/internal/types2/typexpr.go
@@ -302,7 +302,7 @@ func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []
 				// Also: Don't report an error via genericType since it will be reported
 				//       again when we type-check the signature.
 				// TODO(gri) maybe the receiver should be marked as invalid instead?
-				if recv := check.genericType(rname, false).Named(); recv != nil {
+				if recv := asNamed(check.genericType(rname, false)); recv != nil {
 					recvTParams = recv.tparams
 				}
 			}
@@ -382,7 +382,7 @@ func (check *Checker) funcType(sig *Signature, recvPar *syntax.Field, tparams []
 		// (ignore invalid types - error was reported before)
 		if t := rtyp; t != Typ[Invalid] {
 			var err string
-			if T := t.Named(); T != nil {
+			if T := asNamed(t); T != nil {
 				// spec: "The type denoted by T is called the receiver base type; it must not
 				// be a pointer or interface type and it must be declared in the same package
 				// as the method."
@@ -575,7 +575,7 @@ func (check *Checker) typInternal(e0 syntax.Expr, def *Named) (T Type) {
 		check.atEnd(func() {
 			if !Comparable(typ.key) {
 				var why string
-				if typ.key.TypeParam() != nil {
+				if asTypeParam(typ.key) != nil {
 					why = " (missing comparable constraint)"
 				}
 				check.errorf(e.Key, "invalid map key type %s%s", typ.key, why)
@@ -644,7 +644,7 @@ func (check *Checker) instantiatedType(x syntax.Expr, targs []syntax.Expr, def *
 	if b == Typ[Invalid] {
 		return b // error already reported
 	}
-	base := b.Named()
+	base := asNamed(b)
 	if base == nil {
 		unreachable() // should have been caught by genericType
 	}
@@ -1045,7 +1045,7 @@ func (a byUniqueTypeName) Less(i, j int) bool { return sortName(a[i]) < sortName
 func (a byUniqueTypeName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
 
 func sortName(t Type) string {
-	if named := t.Named(); named != nil {
+	if named := asNamed(t); named != nil {
 		return named.obj.Id()
 	}
 	return ""
diff --git a/src/cmd/compile/internal/types2/unify.go b/src/cmd/compile/internal/types2/unify.go
index ab19c5a38b..153df9d622 100644
--- a/src/cmd/compile/internal/types2/unify.go
+++ b/src/cmd/compile/internal/types2/unify.go
@@ -211,12 +211,12 @@ func (u *unifier) nify(x, y Type, p *ifacePair) bool {
 		// match a type name against an unnamed type literal, consider
 		// the underlying type of the named type.
 		// (Subtle: We use isNamed to include any type with a name (incl.
-		// basic types and type parameters. We use Named() because we only
+		// basic types and type parameters. We use asNamed because we only
 		// want *Named types.)
 		switch {
-		case !isNamed(x) && y != nil && y.Named() != nil:
+		case !isNamed(x) && y != nil && asNamed(y) != nil:
 			return u.nify(x, y.Under(), p)
-		case x != nil && x.Named() != nil && !isNamed(y):
+		case x != nil && asNamed(x) != nil && !isNamed(y):
 			return u.nify(x.Under(), y, p)
 		}
 	}
diff --git a/src/cmd/compile/internal/types2/universe.go b/src/cmd/compile/internal/types2/universe.go
index dc79902777..994e298a6c 100644
--- a/src/cmd/compile/internal/types2/universe.go
+++ b/src/cmd/compile/internal/types2/universe.go
@@ -255,7 +255,7 @@ func def(obj Object) {
 		return // nothing to do
 	}
 	// fix Obj link for named types
-	if typ := obj.Type().Named(); typ != nil {
+	if typ := asNamed(obj.Type()); typ != nil {
 		typ.obj = obj.(*TypeName)
 	}
 	// exported identifiers go into package unsafe