[dev.typeparams] cmd/compile/internal/types2: move instance.go contents into named.go (cleanup)

This just moves the code around the instance type into named.go
where it belongs. While at it, also removed some left-over references
to instance types (which are gone). Removed instance.go.

Change-Id: I302a86ca50675b0be54f6138fa47f48f00f9c98f
Reviewed-on: https://go-review.googlesource.com/c/go/+/338469
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/instance.go

@@ -1,42 +0,0 @@
-// Copyright 2011 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package types2
-
-// TODO(rfindley): move this code to named.go.
-
-import "cmd/compile/internal/syntax"
-
-// instance holds position information for use in lazy instantiation.
-//
-// TODO(rfindley): come up with a better name for this type, now that its usage
-// has changed.
-type instance struct {
-	pos     syntax.Pos   // position of type instantiation; for error reporting only
-	posList []syntax.Pos // position of each targ; for error reporting only
-}
-
-// expand ensures that the underlying type of n is instantiated.
-// The underlying type will be Typ[Invalid] if there was an error.
-func (n *Named) expand() {
-	if n.instance != nil {
-		// n must be loaded before instantiation, in order to have accurate
-		// tparams. This is done implicitly by the call to n.TParams, but making it
-		// explicit is harmless: load is idempotent.
-		n.load()
-		inst := n.check.instantiate(n.instance.pos, n.orig.underlying, n.TParams().list(), n.targs, n.instance.posList)
-		n.underlying = inst
-		n.fromRHS = inst
-		n.instance = nil
-	}
-}
-
-// expand expands uninstantiated named types and leaves all other types alone.
-// expand does not recurse.
-func expand(typ Type) Type {
-	if t, _ := typ.(*Named); t != nil {
-		t.expand()
-	}
-	return typ
-}

src/cmd/compile/internal/types2/named.go

@@ -4,7 +4,10 @@
 
 package types2
 
-import "sync"
+import (
+	"cmd/compile/internal/syntax"
+	"sync"
+)
 
 // TODO(gri) Clean up Named struct below; specifically the fromRHS field (can we use underlying?).
 
@@ -252,3 +255,36 @@ func (n *Named) setUnderlying(typ Type) {
 		n.underlying = typ
 	}
 }
+
+// instance holds position information for use in lazy instantiation.
+//
+// TODO(rfindley): come up with a better name for this type, now that its usage
+// has changed.
+type instance struct {
+	pos     syntax.Pos   // position of type instantiation; for error reporting only
+	posList []syntax.Pos // position of each targ; for error reporting only
+}
+
+// expand ensures that the underlying type of n is instantiated.
+// The underlying type will be Typ[Invalid] if there was an error.
+func (n *Named) expand() {
+	if n.instance != nil {
+		// n must be loaded before instantiation, in order to have accurate
+		// tparams. This is done implicitly by the call to n.TParams, but making it
+		// explicit is harmless: load is idempotent.
+		n.load()
+		inst := n.check.instantiate(n.instance.pos, n.orig.underlying, n.TParams().list(), n.targs, n.instance.posList)
+		n.underlying = inst
+		n.fromRHS = inst
+		n.instance = nil
+	}
+}
+
+// expand expands uninstantiated named types and leaves all other types alone.
+// expand does not recurse.
+func expand(typ Type) Type {
+	if t, _ := typ.(*Named); t != nil {
+		t.expand()
+	}
+	return typ
+}

src/cmd/compile/internal/types2/predicates.go

@@ -57,9 +57,6 @@ func isNumericOrString(typ Type) bool { return is(typ, IsNumeric|IsString) }
 func isTyped(typ Type) bool {
 	// isTyped is called with types that are not fully
 	// set up. Must not call asBasic()!
-	// A *Named or *instance type is always typed, so
-	// we only need to check if we have a true *Basic
-	// type.
 	t, _ := typ.(*Basic)
 	return t == nil || t.info&IsUntyped == 0
 }
@@ -328,9 +325,6 @@ func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
 	case *TypeParam:
 		// nothing to do (x and y being equal is caught in the very beginning of this function)
 
-	// case *instance:
-	//	unreachable since types are expanded
-
 	case *top:
 		// Either both types are theTop in which case the initial x == y check
 		// will have caught them. Otherwise they are not identical.

src/cmd/compile/internal/types2/unify.go

@@ -459,9 +459,6 @@ func (u *unifier) nify(x, y Type, p *ifacePair) bool {
 		// are identical if they originate in the same declaration.
 		return x == y
 
-	// case *instance:
-	//	unreachable since types are expanded
-
 	case nil:
 		// avoid a crash in case of nil type