cmd/compile/internal/types2: move typeHash to environment.go

This is a clean port of CL 347560.

Change-Id: I0d56f5a818df1a66e603415d5198d909b0aef228
Reviewed-on: https://go-review.googlesource.com/c/go/+/348573
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

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

@@ -3,7 +3,10 @@
 // license that can be found in the LICENSE file.
 package types2
 
-import "sync"
+import (
+	"bytes"
+	"sync"
+)
 
 // An Environment is an opaque type checking environment. It may be used to
 // share identical type instances across type-checked packages or calls to
@@ -25,7 +28,37 @@ func NewEnvironment() *Environment {
 	}
 }
 
-// TODO(rfindley): move Environment.typeHash here.
+// typeHash returns a string representation of typ, which can be used as an exact
+// type hash: types that are identical produce identical string representations.
+// If typ is a *Named type and targs is not empty, typ is printed as if it were
+// instantiated with targs.
+func (env *Environment) typeHash(typ Type, targs []Type) string {
+	assert(env != nil)
+	assert(typ != nil)
+	var buf bytes.Buffer
+
+	h := newTypeHasher(&buf, env)
+	if named, _ := typ.(*Named); named != nil && len(targs) > 0 {
+		// Don't use WriteType because we need to use the provided targs
+		// and not any targs that might already be with the *Named type.
+		h.typePrefix(named)
+		h.typeName(named.obj)
+		h.typeList(targs)
+	} else {
+		assert(targs == nil)
+		h.typ(typ)
+	}
+
+	if debug {
+		// there should be no instance markers in type hashes
+		for _, b := range buf.Bytes() {
+			assert(b != instanceMarker)
+		}
+	}
+
+	return buf.String()
+}
+
 // typeForHash returns the recorded type for the type hash h, if it exists.
 // If no type exists for h and n is non-nil, n is recorded for h.
 func (env *Environment) typeForHash(h string, n *Named) *Named {

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

@@ -6,10 +6,7 @@
 
 package types2
 
-import (
+import "cmd/compile/internal/syntax"
-	"bytes"
-	"cmd/compile/internal/syntax"
-)
 
 type substMap map[*TypeParam]Type
 
@@ -253,37 +250,6 @@ func (subst *subster) typ(typ Type) Type {
 	return typ
 }
 
-// typeHash returns a string representation of typ, which can be used as an exact
-// type hash: types that are identical produce identical string representations.
-// If typ is a *Named type and targs is not empty, typ is printed as if it were
-// instantiated with targs.
-func (env *Environment) typeHash(typ Type, targs []Type) string {
-	assert(env != nil)
-	assert(typ != nil)
-	var buf bytes.Buffer
-
-	h := newTypeHasher(&buf, env)
-	if named, _ := typ.(*Named); named != nil && len(targs) > 0 {
-		// Don't use WriteType because we need to use the provided targs
-		// and not any targs that might already be with the *Named type.
-		h.typePrefix(named)
-		h.typeName(named.obj)
-		h.typeList(targs)
-	} else {
-		assert(targs == nil)
-		h.typ(typ)
-	}
-
-	if debug {
-		// there should be no instance markers in type hashes
-		for _, b := range buf.Bytes() {
-			assert(b != instanceMarker)
-		}
-	}
-
-	return buf.String()
-}
-
 // typOrNil is like typ but if the argument is nil it is replaced with Typ[Invalid].
 // A nil type may appear in pathological cases such as type T[P any] []func(_ T([]_))
 // where an array/slice element is accessed before it is set up.