internal/exportdata: introduce shared library for exportdata

Deduplicates FindPkg and FindExportData which were shared by
go/internal/gcimporter and cmd/compile/internal/importer into
a new package internal/exportdata.

This change only moves code.

Change-Id: I1daf24dd79fafbe9014b2b15671dcde46b54711e
Reviewed-on: https://go-review.googlesource.com/c/go/+/626700
Commit-Queue: Tim King <taking@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: timothy-king

src/cmd/compile/internal/importer/exportdata.go

@@ -2,155 +2,23 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file contains the FindPkg and Import functions for tests
-// to use gc-generated object files.
+// This file implements the Import function for tests to use gc-generated object files.
 
 package importer
 
 import (
 	"bufio"
-	"bytes"
-	"errors"
 	"fmt"
-	"go/build"
+	"internal/exportdata"
 	"internal/pkgbits"
 	"internal/saferio"
 	"io"
 	"os"
-	"os/exec"
-	"path/filepath"
 	"strings"
-	"sync"
 
 	"cmd/compile/internal/types2"
 )
 
-var exportMap sync.Map // package dir → func() (string, error)
-
-// lookupGorootExport returns the location of the export data
-// (normally found in the build cache, but located in GOROOT/pkg
-// in prior Go releases) for the package located in pkgDir.
-//
-// (We use the package's directory instead of its import path
-// mainly to simplify handling of the packages in src/vendor
-// and cmd/vendor.)
-func lookupGorootExport(pkgDir string) (string, error) {
-	f, ok := exportMap.Load(pkgDir)
-	if !ok {
-		var (
-			listOnce   sync.Once
-			exportPath string
-			err        error
-		)
-		f, _ = exportMap.LoadOrStore(pkgDir, func() (string, error) {
-			listOnce.Do(func() {
-				cmd := exec.Command(filepath.Join(build.Default.GOROOT, "bin", "go"), "list", "-export", "-f", "{{.Export}}", pkgDir)
-				cmd.Dir = build.Default.GOROOT
-				cmd.Env = append(os.Environ(), "PWD="+cmd.Dir, "GOROOT="+build.Default.GOROOT)
-				var output []byte
-				output, err = cmd.Output()
-				if err != nil {
-					if ee, ok := err.(*exec.ExitError); ok && len(ee.Stderr) > 0 {
-						err = errors.New(string(ee.Stderr))
-					}
-					return
-				}
-
-				exports := strings.Split(string(bytes.TrimSpace(output)), "\n")
-				if len(exports) != 1 {
-					err = fmt.Errorf("go list reported %d exports; expected 1", len(exports))
-					return
-				}
-
-				exportPath = exports[0]
-			})
-
-			return exportPath, err
-		})
-	}
-
-	return f.(func() (string, error))()
-}
-
-var pkgExts = [...]string{".a", ".o"} // a file from the build cache will have no extension
-
-// FindPkg returns the filename and unique package id for an import
-// path based on package information provided by build.Import (using
-// the build.Default build.Context). A relative srcDir is interpreted
-// relative to the current working directory.
-//
-// This function should only be used in tests.
-func FindPkg(path, srcDir string) (filename, id string, err error) {
-	// TODO(taking): move FindPkg into src/internal and dedup src/go/internal/gcimporter.FindPkg
-
-	if path == "" {
-		return "", "", errors.New("path is empty")
-	}
-
-	var noext string
-	switch {
-	default:
-		// "x" -> "$GOPATH/pkg/$GOOS_$GOARCH/x.ext", "x"
-		// Don't require the source files to be present.
-		if abs, err := filepath.Abs(srcDir); err == nil { // see issue 14282
-			srcDir = abs
-		}
-		var bp *build.Package
-		bp, err = build.Import(path, srcDir, build.FindOnly|build.AllowBinary)
-		if bp.PkgObj == "" {
-			if bp.Goroot && bp.Dir != "" {
-				filename, err = lookupGorootExport(bp.Dir)
-				if err == nil {
-					_, err = os.Stat(filename)
-				}
-				if err == nil {
-					return filename, bp.ImportPath, nil
-				}
-			}
-			goto notfound
-		} else {
-			noext = strings.TrimSuffix(bp.PkgObj, ".a")
-		}
-		id = bp.ImportPath
-
-	case build.IsLocalImport(path):
-		// "./x" -> "/this/directory/x.ext", "/this/directory/x"
-		noext = filepath.Join(srcDir, path)
-		id = noext
-
-	case filepath.IsAbs(path):
-		// for completeness only - go/build.Import
-		// does not support absolute imports
-		// "/x" -> "/x.ext", "/x"
-		noext = path
-		id = path
-	}
-
-	if false { // for debugging
-		if path != id {
-			fmt.Printf("%s -> %s\n", path, id)
-		}
-	}
-
-	// try extensions
-	for _, ext := range pkgExts {
-		filename = noext + ext
-		f, statErr := os.Stat(filename)
-		if statErr == nil && !f.IsDir() {
-			return filename, id, nil
-		}
-		if err == nil {
-			err = statErr
-		}
-	}
-
-notfound:
-	if err == nil {
-		return "", path, fmt.Errorf("can't find import: %q", path)
-	}
-	return "", path, fmt.Errorf("can't find import: %q: %w", path, err)
-}
-
 // Import imports a gc-generated package given its import path and srcDir, adds
 // the corresponding package object to the packages map, and returns the object.
 // The packages map must contain all packages already imported.
@@ -178,7 +46,7 @@ func Import(packages map[string]*types2.Package, path, srcDir string, lookup fun
 		rc = f
 	} else {
 		var filename string
-		filename, id, err = FindPkg(path, srcDir)
+		filename, id, err = exportdata.FindPkg(path, srcDir)
 		if filename == "" {
 			if path == "unsafe" {
 				return types2.Unsafe, nil
@@ -207,7 +75,7 @@ func Import(packages map[string]*types2.Package, path, srcDir string, lookup fun
 	defer rc.Close()
 
 	buf := bufio.NewReader(rc)
-	hdr, size, err := FindExportData(buf)
+	hdr, size, err := exportdata.FindExportData(buf)
 	if err != nil {
 		return
 	}

src/cmd/compile/internal/importer/gcimporter.go

@@ -10,6 +10,7 @@ import (
 	"cmd/compile/internal/types2"
 	"fmt"
 	"go/build"
+	"internal/exportdata"
 	"internal/testenv"
 	"os"
 	"os/exec"
@@ -101,7 +102,7 @@ func TestImportTestdata(t *testing.T) {
 
 		importMap := map[string]string{}
 		for _, pkg := range wantImports {
-			export, _, err := FindPkg(pkg, "testdata")
+			export, _, err := exportdata.FindPkg(pkg, "testdata")
 			if export == "" {
 				t.Fatalf("no export data found for %s: %v", pkg, err)
 			}
@@ -278,7 +279,7 @@ var importedObjectTests = []struct {
 	{"math.Pi", "const Pi untyped float"},
 	{"math.Sin", "func Sin(x float64) float64"},
 	{"go/ast.NotNilFilter", "func NotNilFilter(_ string, v reflect.Value) bool"},
-	{"go/internal/gcimporter.FindPkg", "func FindPkg(path string, srcDir string) (filename string, id string, err error)"},
+	{"internal/exportdata.FindPkg", "func FindPkg(path string, srcDir string) (filename string, id string, err error)"},
 
 	// interfaces
 	{"context.Context", "type Context interface{Deadline() (deadline time.Time, ok bool); Done() <-chan struct{}; Err() error; Value(key any) any}"},
@@ -440,7 +441,7 @@ func TestIssue13566(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	jsonExport, _, err := FindPkg("encoding/json", "testdata")
+	jsonExport, _, err := exportdata.FindPkg("encoding/json", "testdata")
 	if jsonExport == "" {
 		t.Fatalf("no export data found for encoding/json: %v", err)
 	}

src/cmd/compile/internal/importer/gcimporter_test.go

@@ -73,6 +73,7 @@ var bootstrapDirs = []string{
 	"cmd/internal/cov/covcmd",
 	"internal/bisect",
 	"internal/buildcfg",
+	"internal/exportdata",
 	"internal/goarch",
 	"internal/godebugs",
 	"internal/goexperiment",

src/cmd/dist/buildtool.go

@@ -549,7 +549,7 @@ var depsRules = `
 	# crypto-aware packages
 
 	DEBUG, go/build, go/types, text/scanner, crypto/md5
-	< internal/pkgbits
+	< internal/pkgbits, internal/exportdata
 	< go/internal/gcimporter, go/internal/gccgoimporter, go/internal/srcimporter
 	< go/importer;