go/types: rename UsesCgo to go115UsesCgo

This API and functionality was added late in the Go 1.15 release
cycle, and use within gopls has revealed some shortcomings. It's
possible (but not decided) that we'll want a different API long-term,
so for now this CL renames UsesCgo to a non-exported name to avoid
long-term commitment under the Go 1 compat guarantee.

Updates #16623.
Updates #39072.

Change-Id: I04bc0c161a84adebe43e926df5df406bc794c3db
Reviewed-on: https://go-review.googlesource.com/c/go/+/237417
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

5 files changed, 16 insertions, 9 deletions

diff --git a/api/go1.15.txt b/api/go1.15.txt
index f16faa0780..b51837cf38 100644
--- a/api/go1.15.txt
+++ b/api/go1.15.txt
@@ -114,7 +114,6 @@ pkg debug/pe, const IMAGE_SUBSYSTEM_XBOX = 14
 pkg debug/pe, const IMAGE_SUBSYSTEM_XBOX ideal-int
 pkg go/printer, const StdFormat = 16
 pkg go/printer, const StdFormat Mode
-pkg go/types, type Config struct, UsesCgo bool
 pkg math/big, method (*Int) FillBytes([]uint8) []uint8
 pkg net, method (*Resolver) LookupIP(context.Context, string, string) ([]IP, error)
 pkg net/url, method (*URL) EscapedFragment() string
diff --git a/src/go/internal/srcimporter/srcimporter.go b/src/go/internal/srcimporter/srcimporter.go
index daef27c8b9..90bb3a9bc1 100644
--- a/src/go/internal/srcimporter/srcimporter.go
+++ b/src/go/internal/srcimporter/srcimporter.go
@@ -20,6 +20,7 @@ import (
 	"path/filepath"
 	"strings"
 	"sync"
+	_ "unsafe" // for go:linkname
 )
 
 // An Importer provides the context for importing packages from source code.
@@ -133,7 +134,7 @@ func (p *Importer) ImportFrom(path, srcDir string, mode types.ImportMode) (*type
 			// build.Context's VFS.
 			conf.FakeImportC = true
 		} else {
-			conf.UsesCgo = true
+			setUsesCgo(&conf)
 			file, err := p.cgo(bp)
 			if err != nil {
 				return nil, err
@@ -260,3 +261,6 @@ func (p *Importer) joinPath(elem ...string) string {
 	}
 	return filepath.Join(elem...)
 }
+
+//go:linkname setUsesCgo go/types.srcimporter_setUsesCgo
+func setUsesCgo(conf *types.Config)
diff --git a/src/go/types/api.go b/src/go/types/api.go
index 7787b88906..1abcd9d951 100644
--- a/src/go/types/api.go
+++ b/src/go/types/api.go
@@ -105,14 +105,14 @@ type Config struct {
 	//          Do not use casually!
 	FakeImportC bool
 
-	// If UsesCgo is set, the type checker expects the
+	// If go115UsesCgo is set, the type checker expects the
 	// _cgo_gotypes.go file generated by running cmd/cgo to be
 	// provided as a package source file. Qualified identifiers
 	// referring to package C will be resolved to cgo-provided
 	// declarations within _cgo_gotypes.go.
 	//
-	// It is an error to set both FakeImportC and UsesCgo.
-	UsesCgo bool
+	// It is an error to set both FakeImportC and go115UsesCgo.
+	go115UsesCgo bool
 
 	// If Error != nil, it is called with each error found
 	// during type checking; err has dynamic type Error.
@@ -140,6 +140,10 @@ type Config struct {
 	DisableUnusedImportCheck bool
 }
 
+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
diff --git a/src/go/types/check.go b/src/go/types/check.go
index a94770ffef..007babdf9d 100644
--- a/src/go/types/check.go
+++ b/src/go/types/check.go
@@ -248,10 +248,10 @@ func (check *Checker) handleBailout(err *error) {
 // Files checks the provided files as part of the checker's package.
 func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }
 
-var errBadCgo = errors.New("cannot use FakeImportC and UsesCgo together")
+var errBadCgo = errors.New("cannot use FakeImportC and go115UsesCgo together")
 
 func (check *Checker) checkFiles(files []*ast.File) (err error) {
-	if check.conf.FakeImportC && check.conf.UsesCgo {
+	if check.conf.FakeImportC && check.conf.go115UsesCgo {
 		return errBadCgo
 	}
 
diff --git a/src/go/types/resolver.go b/src/go/types/resolver.go
index f80b4ec784..078adc5ec7 100644
--- a/src/go/types/resolver.go
+++ b/src/go/types/resolver.go
@@ -141,10 +141,10 @@ func (check *Checker) importPackage(pos token.Pos, path, dir string) *Package {
 	}
 
 	// no package yet => import it
-	if path == "C" && (check.conf.FakeImportC || check.conf.UsesCgo) {
+	if path == "C" && (check.conf.FakeImportC || check.conf.go115UsesCgo) {
 		imp = NewPackage("C", "C")
 		imp.fake = true // package scope is not populated
-		imp.cgo = check.conf.UsesCgo
+		imp.cgo = check.conf.go115UsesCgo
 	} else {
 		// ordinary import
 		var err error