From b98b8b9b5be2ccbfc5aaf2a983fe5d439f91bc94 Mon Sep 17 00:00:00 2001
From: Rob Findley <rfindley@google.com>
Date: Fri, 16 Jul 2021 09:21:36 -0400
Subject: [PATCH] [dev.typeparams] go/types: remove unused *Checker arguments
 (cleanup)

This is a straightforward port of CL 331512 to go/types. API usage in
methodset.go was also updated.

Change-Id: I6701265c9d2ae40eb9aa0ea5f00c98ce3516edab
Reviewed-on: https://go-review.googlesource.com/c/go/+/335009
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>
---
 src/go/types/api.go         |  4 ++--
 src/go/types/builtins.go    |  6 ++---
 src/go/types/call.go        |  4 ++--
 src/go/types/conversions.go |  6 ++---
 src/go/types/expr.go        |  6 ++---
 src/go/types/infer.go       |  4 ++--
 src/go/types/interface.go   |  2 +-
 src/go/types/lookup.go      | 45 +++++++++++++++----------------------
 src/go/types/methodset.go   |  7 +-----
 src/go/types/operand.go     |  8 +++----
 src/go/types/predicates.go  | 40 ++++++++++++---------------------
 src/go/types/stmt.go        |  4 ++--
 src/go/types/unify.go       |  9 ++++----
 13 files changed, 59 insertions(+), 86 deletions(-)

diff --git a/src/go/types/api.go b/src/go/types/api.go
index 2815a6d027..6c0ceb7b7c 100644
--- a/src/go/types/api.go
+++ b/src/go/types/api.go
@@ -422,11 +422,11 @@ func Implements(V Type, T *Interface) bool {
 // Identical reports whether x and y are identical types.
 // Receivers of Signature types are ignored.
 func Identical(x, y Type) bool {
-	return (*Checker)(nil).identical(x, y)
+	return identical(x, y, true, nil)
 }
 
 // IdenticalIgnoreTags reports whether x and y are identical types if tags are ignored.
 // Receivers of Signature types are ignored.
 func IdenticalIgnoreTags(x, y Type) bool {
-	return (*Checker)(nil).identicalIgnoreTags(x, y)
+	return identical(x, y, false, nil)
 }
diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
index 5670790856..e976e76cf1 100644
--- a/src/go/types/builtins.go
+++ b/src/go/types/builtins.go
@@ -286,7 +286,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 		}
 
 		// both argument types must be identical
-		if !check.identical(x.typ, y.typ) {
+		if !Identical(x.typ, y.typ) {
 			check.invalidArg(x, _InvalidComplex, "mismatched types %s and %s", x.typ, y.typ)
 			return
 		}
@@ -351,7 +351,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 			return
 		}
 
-		if !check.identical(dst, src) {
+		if !Identical(dst, src) {
 			check.invalidArg(x, _InvalidCopy, "arguments to copy %s and %s have different element types %s and %s", x, &y, dst, src)
 			return
 		}
@@ -644,7 +644,7 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 
 		base := derefStructPtr(x.typ)
 		sel := selx.Sel.Name
-		obj, index, indirect := check.lookupFieldOrMethod(base, false, check.pkg, sel)
+		obj, index, indirect := LookupFieldOrMethod(base, false, check.pkg, sel)
 		switch obj.(type) {
 		case nil:
 			check.invalidArg(x, _MissingFieldOrMethod, "%s has no single field %s", base, sel)
diff --git a/src/go/types/call.go b/src/go/types/call.go
index cef5e9fc59..4e5b98a12e 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -470,7 +470,7 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
 
 	check.instantiatedOperand(x)
 
-	obj, index, indirect = check.lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
+	obj, index, indirect = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
 	if obj == nil {
 		switch {
 		case index != nil:
@@ -500,7 +500,7 @@ func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
 				} else {
 					changeCase = string(unicode.ToUpper(r)) + sel[1:]
 				}
-				if obj, _, _ = check.lookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, changeCase); obj != nil {
+				if obj, _, _ = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, changeCase); obj != nil {
 					why += ", but does have " + changeCase
 				}
 			}
diff --git a/src/go/types/conversions.go b/src/go/types/conversions.go
index ad6d3eef10..a1fcdd4fd8 100644
--- a/src/go/types/conversions.go
+++ b/src/go/types/conversions.go
@@ -94,7 +94,7 @@ func (x *operand) convertibleTo(check *Checker, T Type, reason *string) bool {
 	V := x.typ
 	Vu := under(V)
 	Tu := under(T)
-	if check.identicalIgnoreTags(Vu, Tu) {
+	if IdenticalIgnoreTags(Vu, Tu) {
 		return true
 	}
 
@@ -102,7 +102,7 @@ func (x *operand) convertibleTo(check *Checker, T Type, reason *string) bool {
 	// have identical underlying types if tags are ignored"
 	if V, ok := V.(*Pointer); ok {
 		if T, ok := T.(*Pointer); ok {
-			if check.identicalIgnoreTags(under(V.base), under(T.base)) {
+			if IdenticalIgnoreTags(under(V.base), under(T.base)) {
 				return true
 			}
 		}
@@ -143,7 +143,7 @@ func (x *operand) convertibleTo(check *Checker, T Type, reason *string) bool {
 	if s := asSlice(V); s != nil {
 		if p := asPointer(T); p != nil {
 			if a := asArray(p.Elem()); a != nil {
-				if check.identical(s.Elem(), a.Elem()) {
+				if Identical(s.Elem(), a.Elem()) {
 					if check == nil || check.allowVersion(check.pkg, 1, 17) {
 						return true
 					}
diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index c8adea45e2..edd7caf1c9 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -955,7 +955,7 @@ func (check *Checker) binary(x *operand, e ast.Expr, lhs, rhs ast.Expr, op token
 		return
 	}
 
-	if !check.identical(x.typ, y.typ) {
+	if !Identical(x.typ, y.typ) {
 		// only report an error if we have valid types
 		// (otherwise we had an error reported elsewhere already)
 		if x.typ != Typ[Invalid] && y.typ != Typ[Invalid] {
@@ -1281,7 +1281,7 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 					xkey := keyVal(x.val)
 					if asInterface(utyp.key) != nil {
 						for _, vtyp := range visited[xkey] {
-							if check.identical(vtyp, x.typ) {
+							if Identical(vtyp, x.typ) {
 								duplicate = true
 								break
 							}
@@ -1468,7 +1468,7 @@ func (check *Checker) typeAssertion(at positioner, x *operand, xtyp *Interface,
 	}
 	var msg string
 	if wrongType != nil {
-		if check.identical(method.typ, wrongType.typ) {
+		if Identical(method.typ, wrongType.typ) {
 			msg = fmt.Sprintf("missing method %s (%s has pointer receiver)", method.name, method.name)
 		} else {
 			msg = fmt.Sprintf("wrong type for method %s (have %s, want %s)", method.name, wrongType.typ, method.typ)
diff --git a/src/go/types/infer.go b/src/go/types/infer.go
index dda188ef10..9faf7b7520 100644
--- a/src/go/types/infer.go
+++ b/src/go/types/infer.go
@@ -93,7 +93,7 @@ func (check *Checker) infer(posn positioner, tparams []*TypeName, targs []Type,
 	// Unify parameter and argument types for generic parameters with typed arguments
 	// and collect the indices of generic parameters with untyped arguments.
 	// Terminology: generic parameter = function parameter with a type-parameterized type
-	u := newUnifier(check, false)
+	u := newUnifier(false)
 	u.x.init(tparams)
 
 	// Set the type arguments which we know already.
@@ -369,7 +369,7 @@ func (check *Checker) inferB(tparams []*TypeName, targs []Type, report bool) (ty
 
 	// Setup bidirectional unification between those structural bounds
 	// and the corresponding type arguments (which may be nil!).
-	u := newUnifier(check, false)
+	u := newUnifier(false)
 	u.x.init(tparams)
 	u.y = u.x // type parameters between LHS and RHS of unification are identical
 
diff --git a/src/go/types/interface.go b/src/go/types/interface.go
index 3a4da569ab..73fde3421a 100644
--- a/src/go/types/interface.go
+++ b/src/go/types/interface.go
@@ -212,7 +212,7 @@ func newTypeSet(check *Checker, pos token.Pos, ityp *Interface) *TypeSet {
 			}
 			// check != nil
 			check.later(func() {
-				if !check.allowVersion(m.pkg, 1, 14) || !check.identical(m.typ, other.Type()) {
+				if !check.allowVersion(m.pkg, 1, 14) || !Identical(m.typ, other.Type()) {
 					check.errorf(atPos(pos), _DuplicateDecl, "duplicate method %s", m.name)
 					check.errorf(atPos(mpos[other.(*Func)]), _DuplicateDecl, "\tother declaration of %s", m.name) // secondary error, \t indented
 				}
diff --git a/src/go/types/lookup.go b/src/go/types/lookup.go
index cdd2f1bd51..70e3b4281d 100644
--- a/src/go/types/lookup.go
+++ b/src/go/types/lookup.go
@@ -8,6 +8,11 @@ package types
 
 import "go/token"
 
+// Internal use of LookupFieldOrMethod: If the obj result is a method
+// associated with a concrete (non-interface) type, the method's signature
+// may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
+// the method's type.
+
 // LookupFieldOrMethod looks up a field or method with given package and name
 // in T and returns the corresponding *Var or *Func, an index sequence, and a
 // bool indicating if there were any pointer indirections on the path to the
@@ -35,19 +40,6 @@ import "go/token"
 //	the method's formal receiver base type, nor was the receiver addressable.
 //
 func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
-	return (*Checker)(nil).lookupFieldOrMethod(T, addressable, pkg, name)
-}
-
-// Internal use of Checker.lookupFieldOrMethod: If the obj result is a method
-// associated with a concrete (non-interface) type, the method's signature
-// may not be fully set up. Call Checker.objDecl(obj, nil) before accessing
-// the method's type.
-// TODO(gri) Now that we provide the *Checker, we can probably remove this
-// caveat by calling Checker.objDecl from lookupFieldOrMethod. Investigate.
-
-// lookupFieldOrMethod is like the external version but completes interfaces
-// as necessary.
-func (check *Checker) lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
 	// Methods cannot be associated to a named pointer type
 	// (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
@@ -57,7 +49,7 @@ func (check *Checker) lookupFieldOrMethod(T Type, addressable bool, pkg *Package
 	// not have found it for T (see also issue 8590).
 	if t := asNamed(T); t != nil {
 		if p, _ := t.Underlying().(*Pointer); p != nil {
-			obj, index, indirect = check.rawLookupFieldOrMethod(p, false, pkg, name)
+			obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name)
 			if _, ok := obj.(*Func); ok {
 				return nil, nil, false
 			}
@@ -65,7 +57,7 @@ func (check *Checker) lookupFieldOrMethod(T Type, addressable bool, pkg *Package
 		}
 	}
 
-	return check.rawLookupFieldOrMethod(T, addressable, pkg, name)
+	return lookupFieldOrMethod(T, addressable, pkg, name)
 }
 
 // TODO(gri) The named type consolidation and seen maps below must be
@@ -73,10 +65,9 @@ func (check *Checker) lookupFieldOrMethod(T Type, addressable bool, pkg *Package
 //           types always have only one representation (even when imported
 //           indirectly via different packages.)
 
-// rawLookupFieldOrMethod should only be called by lookupFieldOrMethod and missingMethod.
-func (check *Checker) rawLookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
+// lookupFieldOrMethod should only be called by LookupFieldOrMethod and missingMethod.
+func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
 	// WARNING: The code in this function is extremely subtle - do not modify casually!
-	//          This function and NewMethodSet should be kept in sync.
 
 	if name == "_" {
 		return // blank fields/methods are never found
@@ -226,7 +217,7 @@ func (check *Checker) rawLookupFieldOrMethod(T Type, addressable bool, pkg *Pack
 			return
 		}
 
-		current = check.consolidateMultiples(next)
+		current = consolidateMultiples(next)
 	}
 
 	return nil, nil, false // not found
@@ -243,7 +234,7 @@ type embeddedType struct {
 // consolidateMultiples collects multiple list entries with the same type
 // into a single entry marked as containing multiples. The result is the
 // consolidated list.
-func (check *Checker) consolidateMultiples(list []embeddedType) []embeddedType {
+func consolidateMultiples(list []embeddedType) []embeddedType {
 	if len(list) <= 1 {
 		return list // at most one entry - nothing to do
 	}
@@ -251,7 +242,7 @@ func (check *Checker) consolidateMultiples(list []embeddedType) []embeddedType {
 	n := 0                     // number of entries w/ unique type
 	prev := make(map[Type]int) // index at which type was previously seen
 	for _, e := range list {
-		if i, found := check.lookupType(prev, e.typ); found {
+		if i, found := lookupType(prev, e.typ); found {
 			list[i].multiples = true
 			// ignore this entry
 		} else {
@@ -263,14 +254,14 @@ func (check *Checker) consolidateMultiples(list []embeddedType) []embeddedType {
 	return list[:n]
 }
 
-func (check *Checker) lookupType(m map[Type]int, typ Type) (int, bool) {
+func lookupType(m map[Type]int, typ Type) (int, bool) {
 	// fast path: maybe the types are equal
 	if i, found := m[typ]; found {
 		return i, true
 	}
 
 	for t, i := range m {
-		if check.identical(t, typ) {
+		if Identical(t, typ) {
 			return i, true
 		}
 	}
@@ -336,7 +327,7 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
 			// to see if they can be made to match.
 			// TODO(gri) is this always correct? what about type bounds?
 			// (Alternative is to rename/subst type parameters and compare.)
-			u := newUnifier(check, true)
+			u := newUnifier(true)
 			u.x.init(ftyp.tparams)
 			if !u.unify(ftyp, mtyp) {
 				return m, f
@@ -351,12 +342,12 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
 	Vn := asNamed(Vd)
 	for _, m := range T.typeSet().methods {
 		// TODO(gri) should this be calling lookupFieldOrMethod instead (and why not)?
-		obj, _, _ := check.rawLookupFieldOrMethod(V, false, m.pkg, m.name)
+		obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name)
 
 		// Check if *V implements this method of T.
 		if obj == nil {
 			ptr := NewPointer(V)
-			obj, _, _ = check.rawLookupFieldOrMethod(ptr, false, m.pkg, m.name)
+			obj, _, _ = lookupFieldOrMethod(ptr, false, m.pkg, m.name)
 			if obj != nil {
 				return m, obj.(*Func)
 			}
@@ -412,7 +403,7 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
 		// to see if they can be made to match.
 		// TODO(gri) is this always correct? what about type bounds?
 		// (Alternative is to rename/subst type parameters and compare.)
-		u := newUnifier(check, true)
+		u := newUnifier(true)
 		u.x.init(ftyp.rparams)
 		if !u.unify(ftyp, mtyp) {
 			return m, f
diff --git a/src/go/types/methodset.go b/src/go/types/methodset.go
index 53c0b71dfd..491917d6bc 100644
--- a/src/go/types/methodset.go
+++ b/src/go/types/methodset.go
@@ -190,12 +190,7 @@ func NewMethodSet(T Type) *MethodSet {
 			}
 		}
 
-		// It's ok to call consolidateMultiples with a nil *Checker because
-		// MethodSets are not used internally (outside debug mode). When used
-		// externally, interfaces are expected to be completed and then we do
-		// not need a *Checker to complete them when (indirectly) calling
-		// Checker.identical via consolidateMultiples.
-		current = (*Checker)(nil).consolidateMultiples(next)
+		current = consolidateMultiples(next)
 	}
 
 	if len(base) == 0 {
diff --git a/src/go/types/operand.go b/src/go/types/operand.go
index 81dc66e800..1d0f5b80b6 100644
--- a/src/go/types/operand.go
+++ b/src/go/types/operand.go
@@ -240,7 +240,7 @@ func (x *operand) assignableTo(check *Checker, T Type, reason *string) (bool, er
 	}
 
 	// x's type is identical to T
-	if check.identical(V, T) {
+	if Identical(V, T) {
 		return true, 0
 	}
 
@@ -272,7 +272,7 @@ func (x *operand) assignableTo(check *Checker, T Type, reason *string) (bool, er
 
 	// x's type V and T have identical underlying types
 	// and at least one of V or T is not a named type
-	if check.identical(Vu, Tu) && (!isNamed(V) || !isNamed(T)) {
+	if Identical(Vu, Tu) && (!isNamed(V) || !isNamed(T)) {
 		return true, 0
 	}
 
@@ -281,7 +281,7 @@ func (x *operand) assignableTo(check *Checker, T Type, reason *string) (bool, er
 		if m, wrongType := check.missingMethod(V, Ti, true); m != nil /* Implements(V, Ti) */ {
 			if reason != nil {
 				if wrongType != nil {
-					if check.identical(m.typ, wrongType.typ) {
+					if Identical(m.typ, wrongType.typ) {
 						*reason = fmt.Sprintf("missing method %s (%s has pointer receiver)", m.name, m.name)
 					} else {
 						*reason = fmt.Sprintf("wrong type for method %s (have %s, want %s)", m.Name(), wrongType.typ, m.typ)
@@ -300,7 +300,7 @@ func (x *operand) assignableTo(check *Checker, T Type, reason *string) (bool, er
 	// type, x's type V and T have identical element types,
 	// and at least one of V or T is not a named type
 	if Vc, ok := Vu.(*Chan); ok && Vc.dir == SendRecv {
-		if Tc, ok := Tu.(*Chan); ok && check.identical(Vc.elem, Tc.elem) {
+		if Tc, ok := Tu.(*Chan); ok && Identical(Vc.elem, Tc.elem) {
 			return !isNamed(V) || !isNamed(T), _InvalidChanAssign
 		}
 	}
diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index 2524ad0367..c3c168647d 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/predicates.go
@@ -147,18 +147,6 @@ func hasNil(typ Type) bool {
 	return false
 }
 
-// identical reports whether x and y are identical types.
-// Receivers of Signature types are ignored.
-func (check *Checker) identical(x, y Type) bool {
-	return check.identical0(x, y, true, nil)
-}
-
-// identicalIgnoreTags reports whether x and y are identical types if tags are ignored.
-// Receivers of Signature types are ignored.
-func (check *Checker) identicalIgnoreTags(x, y Type) bool {
-	return check.identical0(x, y, false, nil)
-}
-
 // An ifacePair is a node in a stack of interface type pairs compared for identity.
 type ifacePair struct {
 	x, y *Interface
@@ -170,7 +158,7 @@ func (p *ifacePair) identical(q *ifacePair) bool {
 }
 
 // For changes to this code the corresponding changes should be made to unifier.nify.
-func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
+func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
 	// types must be expanded for comparison
 	x = expandf(x)
 	y = expandf(y)
@@ -194,13 +182,13 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 		if y, ok := y.(*Array); ok {
 			// If one or both array lengths are unknown (< 0) due to some error,
 			// assume they are the same to avoid spurious follow-on errors.
-			return (x.len < 0 || y.len < 0 || x.len == y.len) && check.identical0(x.elem, y.elem, cmpTags, p)
+			return (x.len < 0 || y.len < 0 || x.len == y.len) && identical(x.elem, y.elem, cmpTags, p)
 		}
 
 	case *Slice:
 		// Two slice types are identical if they have identical element types.
 		if y, ok := y.(*Slice); ok {
-			return check.identical0(x.elem, y.elem, cmpTags, p)
+			return identical(x.elem, y.elem, cmpTags, p)
 		}
 
 	case *Struct:
@@ -215,7 +203,7 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 					if f.embedded != g.embedded ||
 						cmpTags && x.Tag(i) != y.Tag(i) ||
 						!f.sameId(g.pkg, g.name) ||
-						!check.identical0(f.typ, g.typ, cmpTags, p) {
+						!identical(f.typ, g.typ, cmpTags, p) {
 						return false
 					}
 				}
@@ -226,7 +214,7 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 	case *Pointer:
 		// Two pointer types are identical if they have identical base types.
 		if y, ok := y.(*Pointer); ok {
-			return check.identical0(x.base, y.base, cmpTags, p)
+			return identical(x.base, y.base, cmpTags, p)
 		}
 
 	case *Tuple:
@@ -237,7 +225,7 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 				if x != nil {
 					for i, v := range x.vars {
 						w := y.vars[i]
-						if !check.identical0(v.typ, w.typ, cmpTags, p) {
+						if !identical(v.typ, w.typ, cmpTags, p) {
 							return false
 						}
 					}
@@ -255,9 +243,9 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 		// parameter names.
 		if y, ok := y.(*Signature); ok {
 			return x.variadic == y.variadic &&
-				check.identicalTParams(x.tparams, y.tparams, cmpTags, p) &&
-				check.identical0(x.params, y.params, cmpTags, p) &&
-				check.identical0(x.results, y.results, cmpTags, p)
+				identicalTParams(x.tparams, y.tparams, cmpTags, p) &&
+				identical(x.params, y.params, cmpTags, p) &&
+				identical(x.results, y.results, cmpTags, p)
 		}
 
 	case *Union:
@@ -325,7 +313,7 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 				}
 				for i, f := range a {
 					g := b[i]
-					if f.Id() != g.Id() || !check.identical0(f.typ, g.typ, cmpTags, q) {
+					if f.Id() != g.Id() || !identical(f.typ, g.typ, cmpTags, q) {
 						return false
 					}
 				}
@@ -336,14 +324,14 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 	case *Map:
 		// Two map types are identical if they have identical key and value types.
 		if y, ok := y.(*Map); ok {
-			return check.identical0(x.key, y.key, cmpTags, p) && check.identical0(x.elem, y.elem, cmpTags, p)
+			return identical(x.key, y.key, cmpTags, p) && identical(x.elem, y.elem, cmpTags, p)
 		}
 
 	case *Chan:
 		// Two channel types are identical if they have identical value types
 		// and the same direction.
 		if y, ok := y.(*Chan); ok {
-			return x.dir == y.dir && check.identical0(x.elem, y.elem, cmpTags, p)
+			return x.dir == y.dir && identical(x.elem, y.elem, cmpTags, p)
 		}
 
 	case *Named:
@@ -376,13 +364,13 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 	return false
 }
 
-func (check *Checker) identicalTParams(x, y []*TypeName, cmpTags bool, p *ifacePair) bool {
+func identicalTParams(x, y []*TypeName, cmpTags bool, p *ifacePair) bool {
 	if len(x) != len(y) {
 		return false
 	}
 	for i, x := range x {
 		y := y[i]
-		if !check.identical0(x.typ.(*TypeParam).bound, y.typ.(*TypeParam).bound, cmpTags, p) {
+		if !identical(x.typ.(*TypeParam).bound, y.typ.(*TypeParam).bound, cmpTags, p) {
 			return false
 		}
 	}
diff --git a/src/go/types/stmt.go b/src/go/types/stmt.go
index afef833490..53fccb0a64 100644
--- a/src/go/types/stmt.go
+++ b/src/go/types/stmt.go
@@ -265,7 +265,7 @@ L:
 			// look for duplicate types for a given value
 			// (quadratic algorithm, but these lists tend to be very short)
 			for _, vt := range seen[val] {
-				if check.identical(v.typ, vt.typ) {
+				if Identical(v.typ, vt.typ) {
 					check.errorf(&v, _DuplicateCase, "duplicate case %s in expression switch", &v)
 					check.error(atPos(vt.pos), _DuplicateCase, "\tprevious case") // secondary error, \t indented
 					continue L
@@ -289,7 +289,7 @@ L:
 		// look for duplicate types
 		// (quadratic algorithm, but type switches tend to be reasonably small)
 		for t, other := range seen {
-			if T == nil && t == nil || T != nil && t != nil && check.identical(T, t) {
+			if T == nil && t == nil || T != nil && t != nil && Identical(T, t) {
 				// talk about "case" rather than "type" because of nil case
 				Ts := "nil"
 				if T != nil {
diff --git a/src/go/types/unify.go b/src/go/types/unify.go
index 43189d3b69..762000db32 100644
--- a/src/go/types/unify.go
+++ b/src/go/types/unify.go
@@ -8,6 +8,7 @@ package types
 
 import (
 	"bytes"
+	"fmt"
 	"sort"
 )
 
@@ -37,7 +38,6 @@ import (
 // and the respective types inferred for each type parameter.
 // A unifier is created by calling newUnifier.
 type unifier struct {
-	check *Checker
 	exact bool
 	x, y  tparamsList // x and y must initialized via tparamsList.init
 	types []Type      // inferred types, shared by x and y
@@ -48,8 +48,8 @@ type unifier struct {
 // exactly. If exact is not set, a named type's underlying type
 // is considered if unification would fail otherwise, and the
 // direction of channels is ignored.
-func newUnifier(check *Checker, exact bool) *unifier {
-	u := &unifier{check: check, exact: exact}
+func newUnifier(exact bool) *unifier {
+	u := &unifier{exact: exact}
 	u.x.unifier = u
 	u.y.unifier = u
 	return u
@@ -452,8 +452,7 @@ func (u *unifier) nify(x, y Type, p *ifacePair) bool {
 		// avoid a crash in case of nil type
 
 	default:
-		u.check.dump("### u.nify(%s, %s), u.x.tparams = %s", x, y, u.x.tparams)
-		unreachable()
+		panic(fmt.Sprintf("### u.nify(%s, %s), u.x.tparams = %s", x, y, u.x.tparams))
 	}
 
 	return false