From fce6290e0ac18ca2d5cc635adf4c3a77b375a49a Mon Sep 17 00:00:00 2001
From: Rob Findley <rfindley@google.com>
Date: Thu, 15 Jul 2021 23:18:59 -0400
Subject: [PATCH] [dev.typeparams] go/types: remove typeparams wrappers and
 aliases

These wrappers and aliases were necessary when we had different versions
of the API depending on the typeparams build constraint, but now they're
just boilerplate. Remove them.

Notably the documentation for types.Info is restored.

Change-Id: I5363d1d5df47649c2641c03328dfba45b1456278
Reviewed-on: https://go-review.googlesource.com/c/go/+/334895
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                 | 100 +++++++++++++++++++-
 src/go/types/api_test.go            | 123 +++++++++++++++++++++++++
 src/go/types/api_typeparams.go      |  48 ----------
 src/go/types/api_typeparams_test.go | 136 ----------------------------
 src/go/types/check.go               |   4 +-
 src/go/types/decl.go                |   2 +-
 src/go/types/index.go               |   4 +-
 src/go/types/infer.go               |   6 +-
 src/go/types/lookup.go              |   4 +-
 src/go/types/methodset.go           |   4 +-
 src/go/types/predicates.go          |   8 +-
 src/go/types/sanitize.go            |   4 +-
 src/go/types/signature.go           |   4 +-
 src/go/types/sizeof_test.go         |   2 +-
 src/go/types/subst.go               |  16 ++--
 src/go/types/type.go                |  87 +++++++++---------
 src/go/types/typestring.go          |   6 +-
 src/go/types/unify.go               |   6 +-
 18 files changed, 302 insertions(+), 262 deletions(-)
 delete mode 100644 src/go/types/api_typeparams.go
 delete mode 100644 src/go/types/api_typeparams_test.go

diff --git a/src/go/types/api.go b/src/go/types/api.go
index 2bfbb8ce0c..2815a6d027 100644
--- a/src/go/types/api.go
+++ b/src/go/types/api.go
@@ -162,6 +162,102 @@ func srcimporter_setUsesCgo(conf *Config) {
 	conf.go115UsesCgo = true
 }
 
+// Info holds result type information for a type-checked package.
+// Only the information for which a map is provided is collected.
+// If the package has type errors, the collected information may
+// be incomplete.
+type Info struct {
+	// Types maps expressions to their types, and for constant
+	// expressions, also their values. Invalid expressions are
+	// omitted.
+	//
+	// For (possibly parenthesized) identifiers denoting built-in
+	// functions, the recorded signatures are call-site specific:
+	// if the call result is not a constant, the recorded type is
+	// an argument-specific signature. Otherwise, the recorded type
+	// is invalid.
+	//
+	// The Types map does not record the type of every identifier,
+	// only those that appear where an arbitrary expression is
+	// permitted. For instance, the identifier f in a selector
+	// expression x.f is found only in the Selections map, the
+	// identifier z in a variable declaration 'var z int' is found
+	// only in the Defs map, and identifiers denoting packages in
+	// qualified identifiers are collected in the Uses map.
+	Types map[ast.Expr]TypeAndValue
+
+	// Inferred maps calls of parameterized functions that use
+	// type inference to the inferred type arguments and signature
+	// of the function called. The recorded "call" expression may be
+	// an *ast.CallExpr (as in f(x)), or an *ast.IndexExpr (s in f[T]).
+	Inferred map[ast.Expr]Inferred
+
+	// Defs maps identifiers to the objects they define (including
+	// package names, dots "." of dot-imports, and blank "_" identifiers).
+	// For identifiers that do not denote objects (e.g., the package name
+	// in package clauses, or symbolic variables t in t := x.(type) of
+	// type switch headers), the corresponding objects are nil.
+	//
+	// For an embedded field, Defs returns the field *Var it defines.
+	//
+	// Invariant: Defs[id] == nil || Defs[id].Pos() == id.Pos()
+	Defs map[*ast.Ident]Object
+
+	// Uses maps identifiers to the objects they denote.
+	//
+	// For an embedded field, Uses returns the *TypeName it denotes.
+	//
+	// Invariant: Uses[id].Pos() != id.Pos()
+	Uses map[*ast.Ident]Object
+
+	// Implicits maps nodes to their implicitly declared objects, if any.
+	// The following node and object types may appear:
+	//
+	//     node               declared object
+	//
+	//     *ast.ImportSpec    *PkgName for imports without renames
+	//     *ast.CaseClause    type-specific *Var for each type switch case clause (incl. default)
+	//     *ast.Field         anonymous parameter *Var (incl. unnamed results)
+	//
+	Implicits map[ast.Node]Object
+
+	// Selections maps selector expressions (excluding qualified identifiers)
+	// to their corresponding selections.
+	Selections map[*ast.SelectorExpr]*Selection
+
+	// Scopes maps ast.Nodes to the scopes they define. Package scopes are not
+	// associated with a specific node but with all files belonging to a package.
+	// Thus, the package scope can be found in the type-checked Package object.
+	// Scopes nest, with the Universe scope being the outermost scope, enclosing
+	// the package scope, which contains (one or more) files scopes, which enclose
+	// function scopes which in turn enclose statement and function literal scopes.
+	// Note that even though package-level functions are declared in the package
+	// scope, the function scopes are embedded in the file scope of the file
+	// containing the function declaration.
+	//
+	// The following node types may appear in Scopes:
+	//
+	//     *ast.File
+	//     *ast.FuncType
+	//     *ast.BlockStmt
+	//     *ast.IfStmt
+	//     *ast.SwitchStmt
+	//     *ast.TypeSwitchStmt
+	//     *ast.CaseClause
+	//     *ast.CommClause
+	//     *ast.ForStmt
+	//     *ast.RangeStmt
+	//
+	Scopes map[ast.Node]*Scope
+
+	// InitOrder is the list of package-level initializers in the order in which
+	// they must be executed. Initializers referring to variables related by an
+	// initialization dependency appear in topological order, the others appear
+	// in source order. Variables without an initialization expression do not
+	// appear in this list.
+	InitOrder []*Initializer
+}
+
 // The Info struct is found in api_notypeparams.go and api_typeparams.go.
 
 // TypeOf returns the type of expression e, or nil if not found.
@@ -254,9 +350,9 @@ func (tv TypeAndValue) HasOk() bool {
 	return tv.mode == commaok || tv.mode == mapindex
 }
 
-// _Inferred reports the _Inferred type arguments and signature
+// Inferred reports the Inferred type arguments and signature
 // for a parameterized function call that uses type inference.
-type _Inferred struct {
+type Inferred struct {
 	TArgs []Type
 	Sig   *Signature
 }
diff --git a/src/go/types/api_test.go b/src/go/types/api_test.go
index 6a7218d90f..ef248781cc 100644
--- a/src/go/types/api_test.go
+++ b/src/go/types/api_test.go
@@ -389,6 +389,129 @@ func TestTypesInfo(t *testing.T) {
 	}
 }
 
+func TestInferredInfo(t *testing.T) {
+	var tests = []struct {
+		src   string
+		fun   string
+		targs []string
+		sig   string
+	}{
+		{genericPkg + `p0; func f[T any](T); func _() { f(42) }`,
+			`f`,
+			[]string{`int`},
+			`func(int)`,
+		},
+		{genericPkg + `p1; func f[T any](T) T; func _() { f('@') }`,
+			`f`,
+			[]string{`rune`},
+			`func(rune) rune`,
+		},
+		{genericPkg + `p2; func f[T any](...T) T; func _() { f(0i) }`,
+			`f`,
+			[]string{`complex128`},
+			`func(...complex128) complex128`,
+		},
+		{genericPkg + `p3; func f[A, B, C any](A, *B, []C); func _() { f(1.2, new(string), []byte{}) }`,
+			`f`,
+			[]string{`float64`, `string`, `byte`},
+			`func(float64, *string, []byte)`,
+		},
+		{genericPkg + `p4; func f[A, B any](A, *B, ...[]B); func _() { f(1.2, new(byte)) }`,
+			`f`,
+			[]string{`float64`, `byte`},
+			`func(float64, *byte, ...[]byte)`,
+		},
+
+		{genericPkg + `s1; func f[T any, P interface{~*T}](x T); func _(x string) { f(x) }`,
+			`f`,
+			[]string{`string`, `*string`},
+			`func(x string)`,
+		},
+		{genericPkg + `s2; func f[T any, P interface{~*T}](x []T); func _(x []int) { f(x) }`,
+			`f`,
+			[]string{`int`, `*int`},
+			`func(x []int)`,
+		},
+		{genericPkg + `s3; type C[T any] interface{~chan<- T}; func f[T any, P C[T]](x []T); func _(x []int) { f(x) }`,
+			`f`,
+			[]string{`int`, `chan<- int`},
+			`func(x []int)`,
+		},
+		{genericPkg + `s4; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]](x []T); func _(x []int) { f(x) }`,
+			`f`,
+			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
+			`func(x []int)`,
+		},
+
+		{genericPkg + `t1; func f[T any, P interface{~*T}]() T; func _() { _ = f[string] }`,
+			`f`,
+			[]string{`string`, `*string`},
+			`func() string`,
+		},
+		{genericPkg + `t2; type C[T any] interface{~chan<- T}; func f[T any, P C[T]]() []T; func _() { _ = f[int] }`,
+			`f`,
+			[]string{`int`, `chan<- int`},
+			`func() []int`,
+		},
+		{genericPkg + `t3; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T; func _() { _ = f[int] }`,
+			`f`,
+			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
+			`func() []int`,
+		},
+	}
+
+	for _, test := range tests {
+		info := Info{}
+		info.Inferred = make(map[ast.Expr]Inferred)
+		name, err := mayTypecheck(t, "InferredInfo", test.src, &info)
+		if err != nil {
+			t.Errorf("package %s: %v", name, err)
+			continue
+		}
+
+		// look for inferred type arguments and signature
+		var targs []Type
+		var sig *Signature
+		for call, inf := range info.Inferred {
+			var fun ast.Expr
+			switch x := call.(type) {
+			case *ast.CallExpr:
+				fun = x.Fun
+			case *ast.IndexExpr:
+				fun = x.X
+			default:
+				panic(fmt.Sprintf("unexpected call expression type %T", call))
+			}
+			if ExprString(fun) == test.fun {
+				targs = inf.TArgs
+				sig = inf.Sig
+				break
+			}
+		}
+		if targs == nil {
+			t.Errorf("package %s: no inferred information found for %s", name, test.fun)
+			continue
+		}
+
+		// check that type arguments are correct
+		if len(targs) != len(test.targs) {
+			t.Errorf("package %s: got %d type arguments; want %d", name, len(targs), len(test.targs))
+			continue
+		}
+		for i, targ := range targs {
+			if got := targ.String(); got != test.targs[i] {
+				t.Errorf("package %s, %d. type argument: got %s; want %s", name, i, got, test.targs[i])
+				continue
+			}
+		}
+
+		// check that signature is correct
+		if got := sig.String(); got != test.sig {
+			t.Errorf("package %s: got %s; want %s", name, got, test.sig)
+		}
+	}
+}
+
 func TestDefsInfo(t *testing.T) {
 	var tests = []struct {
 		src  string
diff --git a/src/go/types/api_typeparams.go b/src/go/types/api_typeparams.go
deleted file mode 100644
index 864103df63..0000000000
--- a/src/go/types/api_typeparams.go
+++ /dev/null
@@ -1,48 +0,0 @@
-// Copyright 2021 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
-
-import (
-	"go/ast"
-)
-
-type (
-	Inferred  = _Inferred
-	TypeParam = _TypeParam
-)
-
-// NewTypeParam returns a new TypeParam.
-func NewTypeParam(obj *TypeName, index int, bound Type) *TypeParam {
-	return (*Checker)(nil).newTypeParam(obj, index, bound)
-}
-
-func (s *Signature) TParams() []*TypeName           { return s._TParams() }
-func (s *Signature) SetTParams(tparams []*TypeName) { s._SetTParams(tparams) }
-
-func (t *Named) TParams() []*TypeName { return t._TParams() }
-func (t *Named) TArgs() []Type        { return t._TArgs() }
-func (t *Named) SetTArgs(args []Type) { t._SetTArgs(args) }
-
-// Info is documented in api_notypeparams.go.
-type Info struct {
-	Types map[ast.Expr]TypeAndValue
-
-	// Inferred maps calls of parameterized functions that use type inference to
-	// the Inferred type arguments and signature of the function called. The
-	// recorded "call" expression may be an *ast.CallExpr (as in f(x)), or an
-	// *ast.IndexExpr (s in f[T]).
-	Inferred map[ast.Expr]_Inferred
-
-	Defs       map[*ast.Ident]Object
-	Uses       map[*ast.Ident]Object
-	Implicits  map[ast.Node]Object
-	Selections map[*ast.SelectorExpr]*Selection
-	Scopes     map[ast.Node]*Scope
-	InitOrder  []*Initializer
-}
-
-func getInferred(info *Info) map[ast.Expr]_Inferred {
-	return info.Inferred
-}
diff --git a/src/go/types/api_typeparams_test.go b/src/go/types/api_typeparams_test.go
deleted file mode 100644
index d9117b8412..0000000000
--- a/src/go/types/api_typeparams_test.go
+++ /dev/null
@@ -1,136 +0,0 @@
-// Copyright 2021 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_test
-
-import (
-	"fmt"
-	"go/ast"
-	"testing"
-
-	. "go/types"
-)
-
-func TestInferredInfo(t *testing.T) {
-	var tests = []struct {
-		src   string
-		fun   string
-		targs []string
-		sig   string
-	}{
-		{genericPkg + `p0; func f[T any](T); func _() { f(42) }`,
-			`f`,
-			[]string{`int`},
-			`func(int)`,
-		},
-		{genericPkg + `p1; func f[T any](T) T; func _() { f('@') }`,
-			`f`,
-			[]string{`rune`},
-			`func(rune) rune`,
-		},
-		{genericPkg + `p2; func f[T any](...T) T; func _() { f(0i) }`,
-			`f`,
-			[]string{`complex128`},
-			`func(...complex128) complex128`,
-		},
-		{genericPkg + `p3; func f[A, B, C any](A, *B, []C); func _() { f(1.2, new(string), []byte{}) }`,
-			`f`,
-			[]string{`float64`, `string`, `byte`},
-			`func(float64, *string, []byte)`,
-		},
-		{genericPkg + `p4; func f[A, B any](A, *B, ...[]B); func _() { f(1.2, new(byte)) }`,
-			`f`,
-			[]string{`float64`, `byte`},
-			`func(float64, *byte, ...[]byte)`,
-		},
-
-		{genericPkg + `s1; func f[T any, P interface{~*T}](x T); func _(x string) { f(x) }`,
-			`f`,
-			[]string{`string`, `*string`},
-			`func(x string)`,
-		},
-		{genericPkg + `s2; func f[T any, P interface{~*T}](x []T); func _(x []int) { f(x) }`,
-			`f`,
-			[]string{`int`, `*int`},
-			`func(x []int)`,
-		},
-		{genericPkg + `s3; type C[T any] interface{~chan<- T}; func f[T any, P C[T]](x []T); func _(x []int) { f(x) }`,
-			`f`,
-			[]string{`int`, `chan<- int`},
-			`func(x []int)`,
-		},
-		{genericPkg + `s4; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]](x []T); func _(x []int) { f(x) }`,
-			`f`,
-			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
-			`func(x []int)`,
-		},
-
-		{genericPkg + `t1; func f[T any, P interface{~*T}]() T; func _() { _ = f[string] }`,
-			`f`,
-			[]string{`string`, `*string`},
-			`func() string`,
-		},
-		{genericPkg + `t2; type C[T any] interface{~chan<- T}; func f[T any, P C[T]]() []T; func _() { _ = f[int] }`,
-			`f`,
-			[]string{`int`, `chan<- int`},
-			`func() []int`,
-		},
-		{genericPkg + `t3; type C[T any] interface{~chan<- T}; func f[T any, P C[T], Q C[[]*P]]() []T; func _() { _ = f[int] }`,
-			`f`,
-			[]string{`int`, `chan<- int`, `chan<- []*chan<- int`},
-			`func() []int`,
-		},
-	}
-
-	for _, test := range tests {
-		info := Info{}
-		info.Inferred = make(map[ast.Expr]Inferred)
-		name, err := mayTypecheck(t, "InferredInfo", test.src, &info)
-		if err != nil {
-			t.Errorf("package %s: %v", name, err)
-			continue
-		}
-
-		// look for inferred type arguments and signature
-		var targs []Type
-		var sig *Signature
-		for call, inf := range info.Inferred {
-			var fun ast.Expr
-			switch x := call.(type) {
-			case *ast.CallExpr:
-				fun = x.Fun
-			case *ast.IndexExpr:
-				fun = x.X
-			default:
-				panic(fmt.Sprintf("unexpected call expression type %T", call))
-			}
-			if ExprString(fun) == test.fun {
-				targs = inf.TArgs
-				sig = inf.Sig
-				break
-			}
-		}
-		if targs == nil {
-			t.Errorf("package %s: no inferred information found for %s", name, test.fun)
-			continue
-		}
-
-		// check that type arguments are correct
-		if len(targs) != len(test.targs) {
-			t.Errorf("package %s: got %d type arguments; want %d", name, len(targs), len(test.targs))
-			continue
-		}
-		for i, targ := range targs {
-			if got := targ.String(); got != test.targs[i] {
-				t.Errorf("package %s, %d. type argument: got %s; want %s", name, i, got, test.targs[i])
-				continue
-			}
-		}
-
-		// check that signature is correct
-		if got := sig.String(); got != test.sig {
-			t.Errorf("package %s: got %s; want %s", name, got, test.sig)
-		}
-	}
-}
diff --git a/src/go/types/check.go b/src/go/types/check.go
index 3e534de08a..30aa8a9f0c 100644
--- a/src/go/types/check.go
+++ b/src/go/types/check.go
@@ -412,8 +412,8 @@ func (check *Checker) recordCommaOkTypes(x ast.Expr, a [2]Type) {
 func (check *Checker) recordInferred(call ast.Expr, targs []Type, sig *Signature) {
 	assert(call != nil)
 	assert(sig != nil)
-	if m := getInferred(check.Info); m != nil {
-		m[call] = _Inferred{targs, sig}
+	if m := check.Info.Inferred; m != nil {
+		m[call] = Inferred{targs, sig}
 	}
 }
 
diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index 761418c4fb..ac1b3815d2 100644
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -740,7 +740,7 @@ func (check *Checker) collectTypeParams(list *ast.FieldList) (tparams []*TypeNam
 
 	setBoundAt := func(at int, bound Type) {
 		assert(IsInterface(bound))
-		tparams[at].typ.(*_TypeParam).bound = bound
+		tparams[at].typ.(*TypeParam).bound = bound
 	}
 
 	index := 0
diff --git a/src/go/types/index.go b/src/go/types/index.go
index 7c7aa382ff..769626dcc2 100644
--- a/src/go/types/index.go
+++ b/src/go/types/index.go
@@ -123,7 +123,7 @@ func (check *Checker) indexExpr(x *operand, expr *typeparams.IndexExpr) (isFuncI
 				tkey = t.key
 				e = t.elem
 				nmaps++
-			case *_TypeParam:
+			case *TypeParam:
 				check.errorf(x, 0, "type of %s contains a type parameter - cannot index (implementation restriction)", x)
 			case *instance:
 				panic("unimplemented")
@@ -246,7 +246,7 @@ func (check *Checker) sliceExpr(x *operand, e *ast.SliceExpr) {
 		valid = true
 		// x.typ doesn't change
 
-	case *Union, *_TypeParam:
+	case *Union, *TypeParam:
 		check.errorf(x, 0, "generic slice expressions not yet implemented")
 		x.mode = invalid
 		return
diff --git a/src/go/types/infer.go b/src/go/types/infer.go
index ae53f68e48..dda188ef10 100644
--- a/src/go/types/infer.go
+++ b/src/go/types/infer.go
@@ -189,7 +189,7 @@ func (check *Checker) infer(posn positioner, tparams []*TypeName, targs []Type,
 		// only parameter type it can possibly match against is a *TypeParam.
 		// Thus, only consider untyped arguments for generic parameters that
 		// are not of composite types and which don't have a type inferred yet.
-		if tpar, _ := par.typ.(*_TypeParam); tpar != nil && targs[tpar.index] == nil {
+		if tpar, _ := par.typ.(*TypeParam); tpar != nil && targs[tpar.index] == nil {
 			arg := args[i]
 			targ := Default(arg.typ)
 			// The default type for an untyped nil is untyped nil. We must not
@@ -333,7 +333,7 @@ func (w *tpWalker) isParameterized(typ Type) (res bool) {
 	case *Named:
 		return w.isParameterizedList(t.targs)
 
-	case *_TypeParam:
+	case *TypeParam:
 		// t must be one of w.tparams
 		return t.index < len(w.tparams) && w.tparams[t.index].typ == t
 
@@ -382,7 +382,7 @@ func (check *Checker) inferB(tparams []*TypeName, targs []Type, report bool) (ty
 
 	// Unify type parameters with their structural constraints, if any.
 	for _, tpar := range tparams {
-		typ := tpar.typ.(*_TypeParam)
+		typ := tpar.typ.(*TypeParam)
 		sbound := check.structuralType(typ.bound)
 		if sbound != nil {
 			if !u.unify(typ, sbound) {
diff --git a/src/go/types/lookup.go b/src/go/types/lookup.go
index 4ce4b3217c..cdd2f1bd51 100644
--- a/src/go/types/lookup.go
+++ b/src/go/types/lookup.go
@@ -107,7 +107,7 @@ func (check *Checker) rawLookupFieldOrMethod(T Type, addressable bool, pkg *Pack
 		var next []embeddedType // embedded types found at current depth
 
 		// look for (pkg, name) in all types at current depth
-		var tpar *_TypeParam // set if obj receiver is a type parameter
+		var tpar *TypeParam // set if obj receiver is a type parameter
 		for _, e := range current {
 			typ := e.typ
 
@@ -196,7 +196,7 @@ func (check *Checker) rawLookupFieldOrMethod(T Type, addressable bool, pkg *Pack
 					indirect = e.indirect
 				}
 
-			case *_TypeParam:
+			case *TypeParam:
 				if i, m := t.Bound().typeSet().LookupMethod(pkg, name); m != nil {
 					assert(m.typ != nil)
 					index = concat(e.index, i)
diff --git a/src/go/types/methodset.go b/src/go/types/methodset.go
index 71d634bf36..53c0b71dfd 100644
--- a/src/go/types/methodset.go
+++ b/src/go/types/methodset.go
@@ -130,7 +130,7 @@ func NewMethodSet(T Type) *MethodSet {
 				// continue with underlying type, but only if it's not a type parameter
 				// TODO(rFindley): should this use named.under()? Can there be a difference?
 				typ = named.underlying
-				if _, ok := typ.(*_TypeParam); ok {
+				if _, ok := typ.(*TypeParam); ok {
 					continue
 				}
 			}
@@ -159,7 +159,7 @@ func NewMethodSet(T Type) *MethodSet {
 			case *Interface:
 				mset = mset.add(t.typeSet().methods, e.index, true, e.multiples)
 
-			case *_TypeParam:
+			case *TypeParam:
 				mset = mset.add(t.Bound().typeSet().methods, e.index, true, e.multiples)
 			}
 		}
diff --git a/src/go/types/predicates.go b/src/go/types/predicates.go
index 7f6eee8120..2524ad0367 100644
--- a/src/go/types/predicates.go
+++ b/src/go/types/predicates.go
@@ -10,7 +10,7 @@ package types
 // isNamed may be called with types that are not fully set up.
 func isNamed(typ Type) bool {
 	switch typ.(type) {
-	case *Basic, *Named, *_TypeParam, *instance:
+	case *Basic, *Named, *TypeParam, *instance:
 		return true
 	}
 	return false
@@ -128,7 +128,7 @@ func comparable(T Type, seen map[Type]bool) bool {
 		return t.underIs(func(t Type) bool {
 			return comparable(t, seen)
 		})
-	case *_TypeParam:
+	case *TypeParam:
 		return t.Bound().IsComparable()
 	}
 	return false
@@ -356,7 +356,7 @@ func (check *Checker) identical0(x, y Type, cmpTags bool, p *ifacePair) bool {
 			return x.obj == y.obj
 		}
 
-	case *_TypeParam:
+	case *TypeParam:
 		// nothing to do (x and y being equal is caught in the very beginning of this function)
 
 	// case *instance:
@@ -382,7 +382,7 @@ func (check *Checker) identicalTParams(x, y []*TypeName, cmpTags bool, p *ifaceP
 	}
 	for i, x := range x {
 		y := y[i]
-		if !check.identical0(x.typ.(*_TypeParam).bound, y.typ.(*_TypeParam).bound, cmpTags, p) {
+		if !check.identical0(x.typ.(*TypeParam).bound, y.typ.(*TypeParam).bound, cmpTags, p) {
 			return false
 		}
 	}
diff --git a/src/go/types/sanitize.go b/src/go/types/sanitize.go
index df09a6a38f..62b91ef8c3 100644
--- a/src/go/types/sanitize.go
+++ b/src/go/types/sanitize.go
@@ -24,7 +24,7 @@ func sanitizeInfo(info *Info) {
 		}
 	}
 
-	inferred := getInferred(info)
+	inferred := info.Inferred
 	for e, inf := range inferred {
 		changed := false
 		for i, targ := range inf.TArgs {
@@ -147,7 +147,7 @@ func (s sanitizer) typ(typ Type) Type {
 		s.typeList(t.targs)
 		s.funcList(t.methods)
 
-	case *_TypeParam:
+	case *TypeParam:
 		if bound := s.typ(t.bound); bound != t.bound {
 			t.bound = bound
 		}
diff --git a/src/go/types/signature.go b/src/go/types/signature.go
index 9be2cce752..8048ba6519 100644
--- a/src/go/types/signature.go
+++ b/src/go/types/signature.go
@@ -70,7 +70,7 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 				}
 				smap := makeSubstMap(recvTParams, list)
 				for i, tname := range sig.rparams {
-					bound := recvTParams[i].typ.(*_TypeParam).bound
+					bound := recvTParams[i].typ.(*TypeParam).bound
 					// bound is (possibly) parameterized in the context of the
 					// receiver type declaration. Substitute parameters for the
 					// current context.
@@ -78,7 +78,7 @@ func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast
 					//           (no bound == empty interface)
 					if bound != nil {
 						bound = check.subst(tname.pos, bound, smap)
-						tname.typ.(*_TypeParam).bound = bound
+						tname.typ.(*TypeParam).bound = bound
 					}
 				}
 			}
diff --git a/src/go/types/sizeof_test.go b/src/go/types/sizeof_test.go
index 05a171f498..8f5f42b415 100644
--- a/src/go/types/sizeof_test.go
+++ b/src/go/types/sizeof_test.go
@@ -31,7 +31,7 @@ func TestSizeof(t *testing.T) {
 		{Map{}, 16, 32},
 		{Chan{}, 12, 24},
 		{Named{}, 84, 160},
-		{_TypeParam{}, 28, 48},
+		{TypeParam{}, 28, 48},
 		{instance{}, 44, 88},
 		{top{}, 0, 0},
 
diff --git a/src/go/types/subst.go b/src/go/types/subst.go
index 0e2e7f408a..a4852ce86f 100644
--- a/src/go/types/subst.go
+++ b/src/go/types/subst.go
@@ -22,21 +22,21 @@ type substMap struct {
 	// TODO(gri) rewrite that code, get rid of this field, and make this
 	//           struct just the map (proj)
 	targs []Type
-	proj  map[*_TypeParam]Type
+	proj  map[*TypeParam]Type
 }
 
 // makeSubstMap creates a new substitution map mapping tpars[i] to targs[i].
 // If targs[i] is nil, tpars[i] is not substituted.
 func makeSubstMap(tpars []*TypeName, targs []Type) *substMap {
 	assert(len(tpars) == len(targs))
-	proj := make(map[*_TypeParam]Type, len(tpars))
+	proj := make(map[*TypeParam]Type, len(tpars))
 	for i, tpar := range tpars {
 		// We must expand type arguments otherwise *instance
 		// types end up as components in composite types.
 		// TODO(gri) explain why this causes problems, if it does
 		targ := expand(targs[i]) // possibly nil
 		targs[i] = targ
-		proj[tpar.typ.(*_TypeParam)] = targ
+		proj[tpar.typ.(*TypeParam)] = targ
 	}
 	return &substMap{targs, proj}
 }
@@ -49,7 +49,7 @@ func (m *substMap) empty() bool {
 	return len(m.proj) == 0
 }
 
-func (m *substMap) lookup(tpar *_TypeParam) Type {
+func (m *substMap) lookup(tpar *TypeParam) Type {
 	if t := m.proj[tpar]; t != nil {
 		return t
 	}
@@ -128,7 +128,7 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist
 		}
 
 		// stop checking bounds after the first failure
-		if !check.satisfies(pos, targs[i], tname.typ.(*_TypeParam), smap) {
+		if !check.satisfies(pos, targs[i], tname.typ.(*TypeParam), smap) {
 			break
 		}
 	}
@@ -140,7 +140,7 @@ func (check *Checker) instantiate(pos token.Pos, typ Type, targs []Type, poslist
 // parameter tpar (after any of its type parameters have been substituted through smap).
 // A suitable error is reported if the result is false.
 // TODO(gri) This should be a method of interfaces or type sets.
-func (check *Checker) satisfies(pos token.Pos, targ Type, tpar *_TypeParam, smap *substMap) bool {
+func (check *Checker) satisfies(pos token.Pos, targ Type, tpar *TypeParam, smap *substMap) bool {
 	iface := tpar.Bound()
 	if iface.Empty() {
 		return true // no type bound
@@ -232,7 +232,7 @@ func (check *Checker) subst(pos token.Pos, typ Type, smap *substMap) Type {
 	switch t := typ.(type) {
 	case *Basic:
 		return typ // nothing to do
-	case *_TypeParam:
+	case *TypeParam:
 		return smap.lookup(t)
 	}
 
@@ -415,7 +415,7 @@ func (subst *subster) typ(typ Type) Type {
 
 		return named
 
-	case *_TypeParam:
+	case *TypeParam:
 		return subst.smap.lookup(t)
 
 	case *instance:
diff --git a/src/go/types/type.go b/src/go/types/type.go
index 4dcc511b93..7445fa59ab 100644
--- a/src/go/types/type.go
+++ b/src/go/types/type.go
@@ -242,10 +242,10 @@ func NewSignature(recv *Var, params, results *Tuple, variadic bool) *Signature {
 func (s *Signature) Recv() *Var { return s.recv }
 
 // _TParams returns the type parameters of signature s, or nil.
-func (s *Signature) _TParams() []*TypeName { return s.tparams }
+func (s *Signature) TParams() []*TypeName { return s.tparams }
 
 // _SetTParams sets the type parameters of signature s.
-func (s *Signature) _SetTParams(tparams []*TypeName) { s.tparams = tparams }
+func (s *Signature) SetTParams(tparams []*TypeName) { s.tparams = tparams }
 
 // Params returns the parameters of signature s, or nil.
 func (s *Signature) Params() *Tuple { return s.params }
@@ -546,16 +546,16 @@ func (t *Named) _Orig() *Named { return t.orig }
 
 // _TParams returns the type parameters of the named type t, or nil.
 // The result is non-nil for an (originally) parameterized type even if it is instantiated.
-func (t *Named) _TParams() []*TypeName { return t.expand().tparams }
+func (t *Named) TParams() []*TypeName { return t.expand().tparams }
 
 // _SetTParams sets the type parameters of the named type t.
-func (t *Named) _SetTParams(tparams []*TypeName) { t.expand().tparams = tparams }
+func (t *Named) SetTParams(tparams []*TypeName) { t.expand().tparams = tparams }
 
 // _TArgs returns the type arguments after instantiation of the named type t, or nil if not instantiated.
-func (t *Named) _TArgs() []Type { return t.targs }
+func (t *Named) TArgs() []Type { return t.targs }
 
 // SetTArgs sets the type arguments of the named type t.
-func (t *Named) _SetTArgs(args []Type) { t.targs = args }
+func (t *Named) SetTArgs(args []Type) { t.targs = args }
 
 // NumMethods returns the number of explicit methods whose receiver is named type t.
 func (t *Named) NumMethods() int { return len(t.expand().methods) }
@@ -591,8 +591,8 @@ var lastID uint32
 // each call, starting with 1. It may be called concurrently.
 func nextID() uint64 { return uint64(atomic.AddUint32(&lastID, 1)) }
 
-// A _TypeParam represents a type parameter type.
-type _TypeParam struct {
+// A TypeParam represents a type parameter type.
+type TypeParam struct {
 	check *Checker  // for lazy type bound completion
 	id    uint64    // unique id, for debugging only
 	obj   *TypeName // corresponding type name
@@ -600,7 +600,12 @@ type _TypeParam struct {
 	bound Type      // *Named or *Interface; underlying type is always *Interface
 }
 
-func (check *Checker) newTypeParam(obj *TypeName, index int, bound Type) *_TypeParam {
+// NewTypeParam returns a new TypeParam.
+func NewTypeParam(obj *TypeName, index int, bound Type) *TypeParam {
+	return (*Checker)(nil).newTypeParam(obj, index, bound)
+}
+
+func (check *Checker) newTypeParam(obj *TypeName, index int, bound Type) *TypeParam {
 	assert(bound != nil)
 
 	// Always increment lastID, even if it is not used.
@@ -610,14 +615,14 @@ func (check *Checker) newTypeParam(obj *TypeName, index int, bound Type) *_TypeP
 		id = check.nextID
 	}
 
-	typ := &_TypeParam{check: check, id: id, obj: obj, index: index, bound: bound}
+	typ := &TypeParam{check: check, id: id, obj: obj, index: index, bound: bound}
 	if obj.typ == nil {
 		obj.typ = typ
 	}
 	return typ
 }
 
-func (t *_TypeParam) Bound() *Interface {
+func (t *TypeParam) Bound() *Interface {
 	iface := asInterface(t.bound)
 	// use the type bound position if we have one
 	pos := token.NoPos
@@ -717,36 +722,36 @@ type top struct{}
 var theTop = &top{}
 
 // Type-specific implementations of Underlying.
-func (t *Basic) Underlying() Type      { return t }
-func (t *Array) Underlying() Type      { return t }
-func (t *Slice) Underlying() Type      { return t }
-func (t *Struct) Underlying() Type     { return t }
-func (t *Pointer) Underlying() Type    { return t }
-func (t *Tuple) Underlying() Type      { return t }
-func (t *Signature) Underlying() Type  { return t }
-func (t *Interface) Underlying() Type  { return t }
-func (t *Map) Underlying() Type        { return t }
-func (t *Chan) Underlying() Type       { return t }
-func (t *Named) Underlying() Type      { return t.expand().underlying }
-func (t *_TypeParam) Underlying() Type { return t }
-func (t *instance) Underlying() Type   { return t }
-func (t *top) Underlying() Type        { return t }
+func (t *Basic) Underlying() Type     { return t }
+func (t *Array) Underlying() Type     { return t }
+func (t *Slice) Underlying() Type     { return t }
+func (t *Struct) Underlying() Type    { return t }
+func (t *Pointer) Underlying() Type   { return t }
+func (t *Tuple) Underlying() Type     { return t }
+func (t *Signature) Underlying() Type { return t }
+func (t *Interface) Underlying() Type { return t }
+func (t *Map) Underlying() Type       { return t }
+func (t *Chan) Underlying() Type      { return t }
+func (t *Named) Underlying() Type     { return t.expand().underlying }
+func (t *TypeParam) Underlying() Type { return t }
+func (t *instance) Underlying() Type  { return t }
+func (t *top) Underlying() Type       { return t }
 
 // Type-specific implementations of String.
-func (t *Basic) String() string      { return TypeString(t, nil) }
-func (t *Array) String() string      { return TypeString(t, nil) }
-func (t *Slice) String() string      { return TypeString(t, nil) }
-func (t *Struct) String() string     { return TypeString(t, nil) }
-func (t *Pointer) String() string    { return TypeString(t, nil) }
-func (t *Tuple) String() string      { return TypeString(t, nil) }
-func (t *Signature) String() string  { return TypeString(t, nil) }
-func (t *Interface) String() string  { return TypeString(t, nil) }
-func (t *Map) String() string        { return TypeString(t, nil) }
-func (t *Chan) String() string       { return TypeString(t, nil) }
-func (t *Named) String() string      { return TypeString(t, nil) }
-func (t *_TypeParam) String() string { return TypeString(t, nil) }
-func (t *instance) String() string   { return TypeString(t, nil) }
-func (t *top) String() string        { return TypeString(t, nil) }
+func (t *Basic) String() string     { return TypeString(t, nil) }
+func (t *Array) String() string     { return TypeString(t, nil) }
+func (t *Slice) String() string     { return TypeString(t, nil) }
+func (t *Struct) String() string    { return TypeString(t, nil) }
+func (t *Pointer) String() string   { return TypeString(t, nil) }
+func (t *Tuple) String() string     { return TypeString(t, nil) }
+func (t *Signature) String() string { return TypeString(t, nil) }
+func (t *Interface) String() string { return TypeString(t, nil) }
+func (t *Map) String() string       { return TypeString(t, nil) }
+func (t *Chan) String() string      { return TypeString(t, nil) }
+func (t *Named) String() string     { return TypeString(t, nil) }
+func (t *TypeParam) String() string { return TypeString(t, nil) }
+func (t *instance) String() string  { return TypeString(t, nil) }
+func (t *top) String() string       { return TypeString(t, nil) }
 
 // under returns the true expanded underlying type.
 // If it doesn't exist, the result is Typ[Invalid].
@@ -827,7 +832,7 @@ func asNamed(t Type) *Named {
 	return e
 }
 
-func asTypeParam(t Type) *_TypeParam {
-	u, _ := under(t).(*_TypeParam)
+func asTypeParam(t Type) *TypeParam {
+	u, _ := under(t).(*TypeParam)
 	return u
 }
diff --git a/src/go/types/typestring.go b/src/go/types/typestring.go
index fb398de502..d234d86e61 100644
--- a/src/go/types/typestring.go
+++ b/src/go/types/typestring.go
@@ -281,7 +281,7 @@ func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
 			writeTParamList(buf, t.TParams(), qf, visited)
 		}
 
-	case *_TypeParam:
+	case *TypeParam:
 		s := "?"
 		if t.obj != nil {
 			s = t.obj.name
@@ -321,7 +321,7 @@ func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited
 	for i, p := range list {
 		// TODO(rFindley) support 'any' sugar here.
 		var b Type = &emptyInterface
-		if t, _ := p.typ.(*_TypeParam); t != nil && t.bound != nil {
+		if t, _ := p.typ.(*TypeParam); t != nil && t.bound != nil {
 			b = t.bound
 		}
 		if i > 0 {
@@ -334,7 +334,7 @@ func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited
 		}
 		prev = b
 
-		if t, _ := p.typ.(*_TypeParam); t != nil {
+		if t, _ := p.typ.(*TypeParam); t != nil {
 			writeType(buf, t, qf, visited)
 		} else {
 			buf.WriteString(p.name)
diff --git a/src/go/types/unify.go b/src/go/types/unify.go
index bc611db347..43189d3b69 100644
--- a/src/go/types/unify.go
+++ b/src/go/types/unify.go
@@ -99,7 +99,7 @@ func (d *tparamsList) init(tparams []*TypeName) {
 	}
 	if debug {
 		for i, tpar := range tparams {
-			assert(i == tpar.typ.(*_TypeParam).index)
+			assert(i == tpar.typ.(*TypeParam).index)
 		}
 	}
 	d.tparams = tparams
@@ -147,7 +147,7 @@ func (u *unifier) join(i, j int) bool {
 // If typ is a type parameter of d, index returns the type parameter index.
 // Otherwise, the result is < 0.
 func (d *tparamsList) index(typ Type) int {
-	if t, ok := typ.(*_TypeParam); ok {
+	if t, ok := typ.(*TypeParam); ok {
 		if i := t.index; i < len(d.tparams) && d.tparams[i].typ == t {
 			return i
 		}
@@ -439,7 +439,7 @@ func (u *unifier) nify(x, y Type, p *ifacePair) bool {
 			}
 		}
 
-	case *_TypeParam:
+	case *TypeParam:
 		// Two type parameters (which are not part of the type parameters of the
 		// enclosing type as those are handled in the beginning of this function)
 		// are identical if they originate in the same declaration.