go/types: unexport the GoVersion configuration option for Go 1.17

The GoVersion field was added to types.Config as part of the work on
type parameters. Specifically, it was added to be consistent with
cmd/compile/internal/types2, which requires such an option.

This configuration option is useful, but is also non-trivial and did not
go through the proposal process. Unexport it for Go 1.17; we can create
a proposal to export it for Go 1.18.

Fixes #46296

Change-Id: Id82d8a7096887dcfc404c4d6d8da9c761b316609
Reviewed-on: https://go-review.googlesource.com/c/go/+/323430
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

@@ -101,12 +101,12 @@ type ImporterFrom interface {
 // A Config specifies the configuration for type checking.
 // The zero value for Config is a ready-to-use default configuration.
 type Config struct {
-	// GoVersion describes the accepted Go language version. The string
+	// goVersion describes the accepted Go language version. The string
 	// must follow the format "go%d.%d" (e.g. "go1.12") or it must be
 	// empty; an empty string indicates the latest language version.
 	// If the format is invalid, invoking the type checker will cause a
 	// panic.
-	GoVersion string
+	goVersion string
 
 	// If IgnoreFuncBodies is set, function bodies are not
 	// type-checked.

src/go/types/check.go

@@ -179,9 +179,9 @@ func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Ch
 		info = new(Info)
 	}
 
-	version, err := parseGoVersion(conf.GoVersion)
+	version, err := parseGoVersion(conf.goVersion)
 	if err != nil {
-		panic(fmt.Sprintf("invalid Go version %q (%v)", conf.GoVersion, err))
+		panic(fmt.Sprintf("invalid Go version %q (%v)", conf.goVersion, err))
 	}
 
 	return &Checker{

src/go/types/check_test.go

@@ -240,7 +240,7 @@ func checkFiles(t *testing.T, sizes Sizes, goVersion string, filenames []string,
 	// typecheck and collect typechecker errors
 	var conf Config
 	conf.Sizes = sizes
-	conf.GoVersion = goVersion
+	SetGoVersion(&conf, goVersion)
 
 	// special case for importC.src
 	if len(filenames) == 1 {

src/go/types/stdlib_test.go

@@ -134,7 +134,8 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 		// parse and type-check file
 		file, err := parser.ParseFile(fset, filename, nil, 0)
 		if err == nil {
-			conf := Config{GoVersion: goVersion, Importer: stdLibImporter}
+			conf := Config{Importer: stdLibImporter}
+			SetGoVersion(&conf, goVersion)
 			_, err = conf.Check(filename, fset, []*ast.File{file}, nil)
 		}
 

src/go/types/types_test.go

@@ -11,3 +11,9 @@ import "sync/atomic"
 // for tests where we may want to have a consistent
 // numbering for each individual test case.
 func ResetId() { atomic.StoreUint32(&lastId, 0) }
+
+// SetGoVersion sets the unexported goVersion field on config, so that tests
+// which assert on behavior for older Go versions can set it.
+func SetGoVersion(config *Config, goVersion string) {
+	config.goVersion = goVersion
+}