[dev.typeparams] go/types: move instance.go contents into named.go (cleanup)

This is a port of CL 338469 to go/types.

Change-Id: I3ee655fa2dc7e789f210c8dec171b3358c4ff132
Reviewed-on: https://go-review.googlesource.com/c/go/+/339677
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>

4 files changed, 39 insertions, 54 deletions

diff --git a/src/go/types/instance.go b/src/go/types/instance.go
deleted file mode 100644
index 1223c9f6f1..0000000000
--- a/src/go/types/instance.go
+++ /dev/null
@@ -1,44 +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 types
-
-// TODO(rfindley): move this code to named.go.
-
-import "go/token"
-
-// 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     token.Pos   // position of type instantiation; for error reporting only
-	posList []token.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.
-// TODO(rfindley): expand would be a better name for this method, but conflicts
-// with the existing concept of lazy expansion. Need to reconcile this.
-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
-}
diff --git a/src/go/types/named.go b/src/go/types/named.go
index 87eaa3179e..fc53783ab8 100644
--- a/src/go/types/named.go
+++ b/src/go/types/named.go
@@ -4,7 +4,10 @@
 
 package types
 
-import "sync"
+import (
+	"go/token"
+	"sync"
+)
 
 // TODO(rfindley) Clean up Named struct below; specifically the fromRHS field (can we use underlying?).
 
@@ -252,3 +255,38 @@ 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     token.Pos   // position of type instantiation; for error reporting only
+	posList []token.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.
+// TODO(rfindley): expand would be a better name for this method, but conflicts
+// with the existing concept of lazy expansion. Need to reconcile this.
+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
+}
diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index f9cac34a03..23924693fd 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/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.
diff --git a/src/go/types/unify.go b/src/go/types/unify.go
index da57e533cc..90a5cf7c72 100644
--- a/src/go/types/unify.go
+++ b/src/go/types/unify.go
@@ -456,9 +456,6 @@ 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