go/types: use a global atomic counter for type parameter ids

This is a 1:1 port of CL 309830 to go/types.

Change-Id: Ibf709f8194dd5e93a87145e5f9db674ce93af529
Reviewed-on: https://go-review.googlesource.com/c/go/+/314594
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_test.go

@@ -353,6 +353,7 @@ func TestTypesInfo(t *testing.T) {
 	}
 
 	for _, test := range tests {
+		ResetId() // avoid renumbering of type parameter ids when adding tests
 		if strings.HasPrefix(test.src, genericPkg) && !typeparams.Enabled {
 			continue
 		}

src/go/types/check.go

@@ -86,7 +86,6 @@ type Checker struct {
 	pkg  *Package
 	*Info
 	version version                    // accepted language version
-	nextId  uint64                     // unique Id for type parameters (first valid Id is 1)
 	objMap  map[Object]*declInfo       // maps package-level objects and (non-interface) methods to declaration info
 	impMap  map[importKey]*Package     // maps (import path, source directory) to (complete or fake) package
 	posMap  map[*Interface][]token.Pos // maps interface types to lists of embedded interface positions
@@ -191,7 +190,6 @@ func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Ch
 		pkg:     pkg,
 		Info:    info,
 		version: version,
-		nextId:  1,
 		objMap:  make(map[Object]*declInfo),
 		impMap:  make(map[importKey]*Package),
 		posMap:  make(map[*Interface][]token.Pos),

src/go/types/type.go

@@ -7,6 +7,7 @@ package types
 import (
 	"fmt"
 	"go/token"
+	"sync/atomic"
 )
 
 // A Type represents a type of Go.
@@ -715,6 +716,15 @@ func (t *Named) AddMethod(m *Func) {
 	}
 }
 
+// Note: This is a uint32 rather than a uint64 because the
+// respective 64 bit atomic instructions are not available
+// on all platforms.
+var lastId uint32
+
+// nextId returns a value increasing monotonically by 1 with
+// 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 {
 	check *Checker  // for lazy type bound completion
@@ -727,8 +737,7 @@ type _TypeParam struct {
 // newTypeParam returns a new TypeParam.
 func (check *Checker) newTypeParam(obj *TypeName, index int, bound Type) *_TypeParam {
 	assert(bound != nil)
-	typ := &_TypeParam{check: check, id: check.nextId, obj: obj, index: index, bound: bound}
+	typ := &_TypeParam{check: check, id: nextId(), obj: obj, index: index, bound: bound}
-	check.nextId++
 	if obj.typ == nil {
 		obj.typ = typ
 	}

src/go/types/types_test.go

@@ -0,0 +1,13 @@
+// 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 "sync/atomic"
+
+// Upon calling ResetId, nextId starts with 1 again.
+// It may be called concurrently. This is only needed
+// for tests where we may want to have a consistent
+// numbering for each individual test case.
+func ResetId() { atomic.StoreUint32(&lastId, 0) }