Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1364 insertions, 0 deletions

diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
new file mode 100644
index 0000000..154fc3c
--- /dev/null
+++ b/src/cmd/go/internal/modload/load.go
@@ -0,0 +1,1364 @@
+// Copyright 2018 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 modload
+
+// This file contains the module-mode package loader, as well as some accessory
+// functions pertaining to the package import graph.
+//
+// There are two exported entry points into package loading — LoadPackages and
+// ImportFromFiles — both implemented in terms of loadFromRoots, which itself
+// manipulates an instance of the loader struct.
+//
+// Although most of the loading state is maintained in the loader struct,
+// one key piece - the build list - is a global, so that it can be modified
+// separate from the loading operation, such as during "go get"
+// upgrades/downgrades or in "go mod" operations.
+// TODO(#40775): It might be nice to make the loader take and return
+// a buildList rather than hard-coding use of the global.
+//
+// Loading is an iterative process. On each iteration, we try to load the
+// requested packages and their transitive imports, then try to resolve modules
+// for any imported packages that are still missing.
+//
+// The first step of each iteration identifies a set of “root” packages.
+// Normally the root packages are exactly those matching the named pattern
+// arguments. However, for the "all" meta-pattern, the final set of packages is
+// computed from the package import graph, and therefore cannot be an initial
+// input to loading that graph. Instead, the root packages for the "all" pattern
+// are those contained in the main module, and allPatternIsRoot parameter to the
+// loader instructs it to dynamically expand those roots to the full "all"
+// pattern as loading progresses.
+//
+// The pkgInAll flag on each loadPkg instance tracks whether that
+// package is known to match the "all" meta-pattern.
+// A package matches the "all" pattern if:
+// 	- it is in the main module, or
+// 	- it is imported by any test in the main module, or
+// 	- it is imported by another package in "all", or
+// 	- the main module specifies a go version ≤ 1.15, and the package is imported
+// 	  by a *test of* another package in "all".
+//
+// When we implement lazy loading, we will record the modules providing packages
+// in "all" even when we are only loading individual packages, so we set the
+// pkgInAll flag regardless of the whether the "all" pattern is a root.
+// (This is necessary to maintain the “import invariant” described in
+// https://golang.org/design/36460-lazy-module-loading.)
+//
+// Because "go mod vendor" prunes out the tests of vendored packages, the
+// behavior of the "all" pattern with -mod=vendor in Go 1.11–1.15 is the same
+// as the "all" pattern (regardless of the -mod flag) in 1.16+.
+// The allClosesOverTests parameter to the loader indicates whether the "all"
+// pattern should close over tests (as in Go 1.11–1.15) or stop at only those
+// packages transitively imported by the packages and tests in the main module
+// ("all" in Go 1.16+ and "go mod vendor" in Go 1.11+).
+//
+// Note that it is possible for a loaded package NOT to be in "all" even when we
+// are loading the "all" pattern. For example, packages that are transitive
+// dependencies of other roots named on the command line must be loaded, but are
+// not in "all". (The mod_notall test illustrates this behavior.)
+// Similarly, if the LoadTests flag is set but the "all" pattern does not close
+// over test dependencies, then when we load the test of a package that is in
+// "all" but outside the main module, the dependencies of that test will not
+// necessarily themselves be in "all". (That configuration does not arise in Go
+// 1.11–1.15, but it will be possible in Go 1.16+.)
+//
+// Loading proceeds from the roots, using a parallel work-queue with a limit on
+// the amount of active work (to avoid saturating disks, CPU cores, and/or
+// network connections). Each package is added to the queue the first time it is
+// imported by another package. When we have finished identifying the imports of
+// a package, we add the test for that package if it is needed. A test may be
+// needed if:
+// 	- the package matches a root pattern and tests of the roots were requested, or
+// 	- the package is in the main module and the "all" pattern is requested
+// 	  (because the "all" pattern includes the dependencies of tests in the main
+// 	  module), or
+// 	- the package is in "all" and the definition of "all" we are using includes
+// 	  dependencies of tests (as is the case in Go ≤1.15).
+//
+// After all available packages have been loaded, we examine the results to
+// identify any requested or imported packages that are still missing, and if
+// so, which modules we could add to the module graph in order to make the
+// missing packages available. We add those to the module graph and iterate,
+// until either all packages resolve successfully or we cannot identify any
+// module that would resolve any remaining missing package.
+//
+// If the main module is “tidy” (that is, if "go mod tidy" is a no-op for it)
+// and all requested packages are in "all", then loading completes in a single
+// iteration.
+// TODO(bcmills): We should also be able to load in a single iteration if the
+// requested packages all come from modules that are themselves tidy, regardless
+// of whether those packages are in "all". Today, that requires two iterations
+// if those packages are not found in existing dependencies of the main module.
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"go/build"
+	"io/fs"
+	"os"
+	"path"
+	pathpkg "path"
+	"path/filepath"
+	"reflect"
+	"runtime"
+	"sort"
+	"strings"
+	"sync"
+	"sync/atomic"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/fsys"
+	"cmd/go/internal/imports"
+	"cmd/go/internal/modfetch"
+	"cmd/go/internal/mvs"
+	"cmd/go/internal/par"
+	"cmd/go/internal/search"
+	"cmd/go/internal/str"
+
+	"golang.org/x/mod/module"
+)
+
+// loaded is the most recently-used package loader.
+// It holds details about individual packages.
+var loaded *loader
+
+// PackageOpts control the behavior of the LoadPackages function.
+type PackageOpts struct {
+	// Tags are the build tags in effect (as interpreted by the
+	// cmd/go/internal/imports package).
+	// If nil, treated as equivalent to imports.Tags().
+	Tags map[string]bool
+
+	// ResolveMissingImports indicates that we should attempt to add module
+	// dependencies as needed to resolve imports of packages that are not found.
+	//
+	// For commands that support the -mod flag, resolving imports may still fail
+	// if the flag is set to "readonly" (the default) or "vendor".
+	ResolveMissingImports bool
+
+	// AllowPackage, if non-nil, is called after identifying the module providing
+	// each package. If AllowPackage returns a non-nil error, that error is set
+	// for the package, and the imports and test of that package will not be
+	// loaded.
+	//
+	// AllowPackage may be invoked concurrently by multiple goroutines,
+	// and may be invoked multiple times for a given package path.
+	AllowPackage func(ctx context.Context, path string, mod module.Version) error
+
+	// LoadTests loads the test dependencies of each package matching a requested
+	// pattern. If ResolveMissingImports is also true, test dependencies will be
+	// resolved if missing.
+	LoadTests bool
+
+	// UseVendorAll causes the "all" package pattern to be interpreted as if
+	// running "go mod vendor" (or building with "-mod=vendor").
+	//
+	// This is a no-op for modules that declare 'go 1.16' or higher, for which this
+	// is the default (and only) interpretation of the "all" pattern in module mode.
+	UseVendorAll bool
+
+	// AllowErrors indicates that LoadPackages should not terminate the process if
+	// an error occurs.
+	AllowErrors bool
+
+	// SilenceErrors indicates that LoadPackages should not print errors
+	// that occur while loading packages. SilenceErrors implies AllowErrors.
+	SilenceErrors bool
+
+	// SilenceMissingStdImports indicates that LoadPackages should not print
+	// errors or terminate the process if an imported package is missing, and the
+	// import path looks like it might be in the standard library (perhaps in a
+	// future version).
+	SilenceMissingStdImports bool
+
+	// SilenceUnmatchedWarnings suppresses the warnings normally emitted for
+	// patterns that did not match any packages.
+	SilenceUnmatchedWarnings bool
+}
+
+// LoadPackages identifies the set of packages matching the given patterns and
+// loads the packages in the import graph rooted at that set.
+func LoadPackages(ctx context.Context, opts PackageOpts, patterns ...string) (matches []*search.Match, loadedPackages []string) {
+	LoadModFile(ctx)
+	if opts.Tags == nil {
+		opts.Tags = imports.Tags()
+	}
+
+	patterns = search.CleanPatterns(patterns)
+	matches = make([]*search.Match, 0, len(patterns))
+	allPatternIsRoot := false
+	for _, pattern := range patterns {
+		matches = append(matches, search.NewMatch(pattern))
+		if pattern == "all" {
+			allPatternIsRoot = true
+		}
+	}
+
+	updateMatches := func(ld *loader) {
+		for _, m := range matches {
+			switch {
+			case m.IsLocal():
+				// Evaluate list of file system directories on first iteration.
+				if m.Dirs == nil {
+					matchLocalDirs(m)
+				}
+
+				// Make a copy of the directory list and translate to import paths.
+				// Note that whether a directory corresponds to an import path
+				// changes as the build list is updated, and a directory can change
+				// from not being in the build list to being in it and back as
+				// the exact version of a particular module increases during
+				// the loader iterations.
+				m.Pkgs = m.Pkgs[:0]
+				for _, dir := range m.Dirs {
+					pkg, err := resolveLocalPackage(dir)
+					if err != nil {
+						if !m.IsLiteral() && (err == errPkgIsBuiltin || err == errPkgIsGorootSrc) {
+							continue // Don't include "builtin" or GOROOT/src in wildcard patterns.
+						}
+
+						// If we're outside of a module, ensure that the failure mode
+						// indicates that.
+						ModRoot()
+
+						if ld != nil {
+							m.AddError(err)
+						}
+						continue
+					}
+					m.Pkgs = append(m.Pkgs, pkg)
+				}
+
+			case m.IsLiteral():
+				m.Pkgs = []string{m.Pattern()}
+
+			case strings.Contains(m.Pattern(), "..."):
+				m.Errs = m.Errs[:0]
+				matchPackages(ctx, m, opts.Tags, includeStd, buildList)
+
+			case m.Pattern() == "all":
+				if ld == nil {
+					// The initial roots are the packages in the main module.
+					// loadFromRoots will expand that to "all".
+					m.Errs = m.Errs[:0]
+					matchPackages(ctx, m, opts.Tags, omitStd, []module.Version{Target})
+				} else {
+					// Starting with the packages in the main module,
+					// enumerate the full list of "all".
+					m.Pkgs = ld.computePatternAll()
+				}
+
+			case m.Pattern() == "std" || m.Pattern() == "cmd":
+				if m.Pkgs == nil {
+					m.MatchPackages() // Locate the packages within GOROOT/src.
+				}
+
+			default:
+				panic(fmt.Sprintf("internal error: modload missing case for pattern %s", m.Pattern()))
+			}
+		}
+	}
+
+	loaded = loadFromRoots(loaderParams{
+		PackageOpts: opts,
+
+		allClosesOverTests: index.allPatternClosesOverTests() && !opts.UseVendorAll,
+		allPatternIsRoot:   allPatternIsRoot,
+
+		listRoots: func() (roots []string) {
+			updateMatches(nil)
+			for _, m := range matches {
+				roots = append(roots, m.Pkgs...)
+			}
+			return roots
+		},
+	})
+
+	// One last pass to finalize wildcards.
+	updateMatches(loaded)
+
+	// Report errors, if any.
+	checkMultiplePaths()
+	for _, pkg := range loaded.pkgs {
+		if pkg.err != nil {
+			if sumErr := (*ImportMissingSumError)(nil); errors.As(pkg.err, &sumErr) {
+				if importer := pkg.stack; importer != nil {
+					sumErr.importer = importer.path
+					sumErr.importerVersion = importer.mod.Version
+					sumErr.importerIsTest = importer.testOf != nil
+				}
+			}
+			silence := opts.SilenceErrors
+			if stdErr := (*ImportMissingError)(nil); errors.As(pkg.err, &stdErr) &&
+				stdErr.isStd && opts.SilenceMissingStdImports {
+				silence = true
+			}
+
+			if !silence {
+				if opts.AllowErrors {
+					fmt.Fprintf(os.Stderr, "%s: %v\n", pkg.stackText(), pkg.err)
+				} else {
+					base.Errorf("%s: %v", pkg.stackText(), pkg.err)
+				}
+			}
+		}
+		if !pkg.isTest() {
+			loadedPackages = append(loadedPackages, pkg.path)
+		}
+	}
+	if !opts.SilenceErrors {
+		// Also list errors in matching patterns (such as directory permission
+		// errors for wildcard patterns).
+		for _, match := range matches {
+			for _, err := range match.Errs {
+				if opts.AllowErrors {
+					fmt.Fprintf(os.Stderr, "%v\n", err)
+				} else {
+					base.Errorf("%v", err)
+				}
+			}
+		}
+	}
+	base.ExitIfErrors()
+
+	if !opts.SilenceUnmatchedWarnings {
+		search.WarnUnmatched(matches)
+	}
+
+	// Success! Update go.mod (if needed) and return the results.
+	WriteGoMod()
+	sort.Strings(loadedPackages)
+	return matches, loadedPackages
+}
+
+// matchLocalDirs is like m.MatchDirs, but tries to avoid scanning directories
+// outside of the standard library and active modules.
+func matchLocalDirs(m *search.Match) {
+	if !m.IsLocal() {
+		panic(fmt.Sprintf("internal error: resolveLocalDirs on non-local pattern %s", m.Pattern()))
+	}
+
+	if i := strings.Index(m.Pattern(), "..."); i >= 0 {
+		// The pattern is local, but it is a wildcard. Its packages will
+		// only resolve to paths if they are inside of the standard
+		// library, the main module, or some dependency of the main
+		// module. Verify that before we walk the filesystem: a filesystem
+		// walk in a directory like /var or /etc can be very expensive!
+		dir := filepath.Dir(filepath.Clean(m.Pattern()[:i+3]))
+		absDir := dir
+		if !filepath.IsAbs(dir) {
+			absDir = filepath.Join(base.Cwd, dir)
+		}
+		if search.InDir(absDir, cfg.GOROOTsrc) == "" && search.InDir(absDir, ModRoot()) == "" && pathInModuleCache(absDir) == "" {
+			m.Dirs = []string{}
+			m.AddError(fmt.Errorf("directory prefix %s outside available modules", base.ShortPath(absDir)))
+			return
+		}
+	}
+
+	m.MatchDirs()
+}
+
+// resolveLocalPackage resolves a filesystem path to a package path.
+func resolveLocalPackage(dir string) (string, error) {
+	var absDir string
+	if filepath.IsAbs(dir) {
+		absDir = filepath.Clean(dir)
+	} else {
+		absDir = filepath.Join(base.Cwd, dir)
+	}
+
+	bp, err := cfg.BuildContext.ImportDir(absDir, 0)
+	if err != nil && (bp == nil || len(bp.IgnoredGoFiles) == 0) {
+		// golang.org/issue/32917: We should resolve a relative path to a
+		// package path only if the relative path actually contains the code
+		// for that package.
+		//
+		// If the named directory does not exist or contains no Go files,
+		// the package does not exist.
+		// Other errors may affect package loading, but not resolution.
+		if _, err := fsys.Stat(absDir); err != nil {
+			if os.IsNotExist(err) {
+				// Canonicalize OS-specific errors to errDirectoryNotFound so that error
+				// messages will be easier for users to search for.
+				return "", &fs.PathError{Op: "stat", Path: absDir, Err: errDirectoryNotFound}
+			}
+			return "", err
+		}
+		if _, noGo := err.(*build.NoGoError); noGo {
+			// A directory that does not contain any Go source files — even ignored
+			// ones! — is not a Go package, and we can't resolve it to a package
+			// path because that path could plausibly be provided by some other
+			// module.
+			//
+			// Any other error indicates that the package “exists” (at least in the
+			// sense that it cannot exist in any other module), but has some other
+			// problem (such as a syntax error).
+			return "", err
+		}
+	}
+
+	if modRoot != "" && absDir == modRoot {
+		if absDir == cfg.GOROOTsrc {
+			return "", errPkgIsGorootSrc
+		}
+		return targetPrefix, nil
+	}
+
+	// Note: The checks for @ here are just to avoid misinterpreting
+	// the module cache directories (formerly GOPATH/src/mod/foo@v1.5.2/bar).
+	// It's not strictly necessary but helpful to keep the checks.
+	if modRoot != "" && strings.HasPrefix(absDir, modRoot+string(filepath.Separator)) && !strings.Contains(absDir[len(modRoot):], "@") {
+		suffix := filepath.ToSlash(absDir[len(modRoot):])
+		if strings.HasPrefix(suffix, "/vendor/") {
+			if cfg.BuildMod != "vendor" {
+				return "", fmt.Errorf("without -mod=vendor, directory %s has no package path", absDir)
+			}
+
+			readVendorList()
+			pkg := strings.TrimPrefix(suffix, "/vendor/")
+			if _, ok := vendorPkgModule[pkg]; !ok {
+				return "", fmt.Errorf("directory %s is not a package listed in vendor/modules.txt", absDir)
+			}
+			return pkg, nil
+		}
+
+		if targetPrefix == "" {
+			pkg := strings.TrimPrefix(suffix, "/")
+			if pkg == "builtin" {
+				// "builtin" is a pseudo-package with a real source file.
+				// It's not included in "std", so it shouldn't resolve from "."
+				// within module "std" either.
+				return "", errPkgIsBuiltin
+			}
+			return pkg, nil
+		}
+
+		pkg := targetPrefix + suffix
+		if _, ok, err := dirInModule(pkg, targetPrefix, modRoot, true); err != nil {
+			return "", err
+		} else if !ok {
+			return "", &PackageNotInModuleError{Mod: Target, Pattern: pkg}
+		}
+		return pkg, nil
+	}
+
+	if sub := search.InDir(absDir, cfg.GOROOTsrc); sub != "" && sub != "." && !strings.Contains(sub, "@") {
+		pkg := filepath.ToSlash(sub)
+		if pkg == "builtin" {
+			return "", errPkgIsBuiltin
+		}
+		return pkg, nil
+	}
+
+	pkg := pathInModuleCache(absDir)
+	if pkg == "" {
+		return "", fmt.Errorf("directory %s outside available modules", base.ShortPath(absDir))
+	}
+	return pkg, nil
+}
+
+var (
+	errDirectoryNotFound = errors.New("directory not found")
+	errPkgIsGorootSrc    = errors.New("GOROOT/src is not an importable package")
+	errPkgIsBuiltin      = errors.New(`"builtin" is a pseudo-package, not an importable package`)
+)
+
+// pathInModuleCache returns the import path of the directory dir,
+// if dir is in the module cache copy of a module in our build list.
+func pathInModuleCache(dir string) string {
+	tryMod := func(m module.Version) (string, bool) {
+		var root string
+		var err error
+		if repl := Replacement(m); repl.Path != "" && repl.Version == "" {
+			root = repl.Path
+			if !filepath.IsAbs(root) {
+				root = filepath.Join(ModRoot(), root)
+			}
+		} else if repl.Path != "" {
+			root, err = modfetch.DownloadDir(repl)
+		} else {
+			root, err = modfetch.DownloadDir(m)
+		}
+		if err != nil {
+			return "", false
+		}
+
+		sub := search.InDir(dir, root)
+		if sub == "" {
+			return "", false
+		}
+		sub = filepath.ToSlash(sub)
+		if strings.Contains(sub, "/vendor/") || strings.HasPrefix(sub, "vendor/") || strings.Contains(sub, "@") {
+			return "", false
+		}
+
+		return path.Join(m.Path, filepath.ToSlash(sub)), true
+	}
+
+	for _, m := range buildList[1:] {
+		if importPath, ok := tryMod(m); ok {
+			// checkMultiplePaths ensures that a module can be used for at most one
+			// requirement, so this must be it.
+			return importPath
+		}
+	}
+	return ""
+}
+
+// ImportFromFiles adds modules to the build list as needed
+// to satisfy the imports in the named Go source files.
+func ImportFromFiles(ctx context.Context, gofiles []string) {
+	LoadModFile(ctx)
+
+	tags := imports.Tags()
+	imports, testImports, err := imports.ScanFiles(gofiles, tags)
+	if err != nil {
+		base.Fatalf("go: %v", err)
+	}
+
+	loaded = loadFromRoots(loaderParams{
+		PackageOpts: PackageOpts{
+			Tags:                  tags,
+			ResolveMissingImports: true,
+		},
+		allClosesOverTests: index.allPatternClosesOverTests(),
+		listRoots: func() (roots []string) {
+			roots = append(roots, imports...)
+			roots = append(roots, testImports...)
+			return roots
+		},
+	})
+	WriteGoMod()
+}
+
+// DirImportPath returns the effective import path for dir,
+// provided it is within the main module, or else returns ".".
+func DirImportPath(dir string) string {
+	if !HasModRoot() {
+		return "."
+	}
+	LoadModFile(context.TODO())
+
+	if !filepath.IsAbs(dir) {
+		dir = filepath.Join(base.Cwd, dir)
+	} else {
+		dir = filepath.Clean(dir)
+	}
+
+	if dir == modRoot {
+		return targetPrefix
+	}
+	if strings.HasPrefix(dir, modRoot+string(filepath.Separator)) {
+		suffix := filepath.ToSlash(dir[len(modRoot):])
+		if strings.HasPrefix(suffix, "/vendor/") {
+			return strings.TrimPrefix(suffix, "/vendor/")
+		}
+		return targetPrefix + suffix
+	}
+	return "."
+}
+
+// TargetPackages returns the list of packages in the target (top-level) module
+// matching pattern, which may be relative to the working directory, under all
+// build tag settings.
+func TargetPackages(ctx context.Context, pattern string) *search.Match {
+	// TargetPackages is relative to the main module, so ensure that the main
+	// module is a thing that can contain packages.
+	LoadModFile(ctx)
+	ModRoot()
+
+	m := search.NewMatch(pattern)
+	matchPackages(ctx, m, imports.AnyTags(), omitStd, []module.Version{Target})
+	return m
+}
+
+// ImportMap returns the actual package import path
+// for an import path found in source code.
+// If the given import path does not appear in the source code
+// for the packages that have been loaded, ImportMap returns the empty string.
+func ImportMap(path string) string {
+	pkg, ok := loaded.pkgCache.Get(path).(*loadPkg)
+	if !ok {
+		return ""
+	}
+	return pkg.path
+}
+
+// PackageDir returns the directory containing the source code
+// for the package named by the import path.
+func PackageDir(path string) string {
+	pkg, ok := loaded.pkgCache.Get(path).(*loadPkg)
+	if !ok {
+		return ""
+	}
+	return pkg.dir
+}
+
+// PackageModule returns the module providing the package named by the import path.
+func PackageModule(path string) module.Version {
+	pkg, ok := loaded.pkgCache.Get(path).(*loadPkg)
+	if !ok {
+		return module.Version{}
+	}
+	return pkg.mod
+}
+
+// PackageImports returns the imports for the package named by the import path.
+// Test imports will be returned as well if tests were loaded for the package
+// (i.e., if "all" was loaded or if LoadTests was set and the path was matched
+// by a command line argument). PackageImports will return nil for
+// unknown package paths.
+func PackageImports(path string) (imports, testImports []string) {
+	pkg, ok := loaded.pkgCache.Get(path).(*loadPkg)
+	if !ok {
+		return nil, nil
+	}
+	imports = make([]string, len(pkg.imports))
+	for i, p := range pkg.imports {
+		imports[i] = p.path
+	}
+	if pkg.test != nil {
+		testImports = make([]string, len(pkg.test.imports))
+		for i, p := range pkg.test.imports {
+			testImports[i] = p.path
+		}
+	}
+	return imports, testImports
+}
+
+// Lookup returns the source directory, import path, and any loading error for
+// the package at path as imported from the package in parentDir.
+// Lookup requires that one of the Load functions in this package has already
+// been called.
+func Lookup(parentPath string, parentIsStd bool, path string) (dir, realPath string, err error) {
+	if path == "" {
+		panic("Lookup called with empty package path")
+	}
+
+	if parentIsStd {
+		path = loaded.stdVendor(parentPath, path)
+	}
+	pkg, ok := loaded.pkgCache.Get(path).(*loadPkg)
+	if !ok {
+		// The loader should have found all the relevant paths.
+		// There are a few exceptions, though:
+		//	- during go list without -test, the p.Resolve calls to process p.TestImports and p.XTestImports
+		//	  end up here to canonicalize the import paths.
+		//	- during any load, non-loaded packages like "unsafe" end up here.
+		//	- during any load, build-injected dependencies like "runtime/cgo" end up here.
+		//	- because we ignore appengine/* in the module loader,
+		//	  the dependencies of any actual appengine/* library end up here.
+		dir := findStandardImportPath(path)
+		if dir != "" {
+			return dir, path, nil
+		}
+		return "", "", errMissing
+	}
+	return pkg.dir, pkg.path, pkg.err
+}
+
+// A loader manages the process of loading information about
+// the required packages for a particular build,
+// checking that the packages are available in the module set,
+// and updating the module set if needed.
+type loader struct {
+	loaderParams
+
+	work *par.Queue
+
+	// reset on each iteration
+	roots    []*loadPkg
+	pkgCache *par.Cache // package path (string) → *loadPkg
+	pkgs     []*loadPkg // transitive closure of loaded packages and tests; populated in buildStacks
+
+	// computed at end of iterations
+	direct map[string]bool // imported directly by main module
+}
+
+// loaderParams configure the packages loaded by, and the properties reported
+// by, a loader instance.
+type loaderParams struct {
+	PackageOpts
+
+	allClosesOverTests bool // Does the "all" pattern include the transitive closure of tests of packages in "all"?
+	allPatternIsRoot   bool // Is the "all" pattern an additional root?
+
+	listRoots func() []string
+}
+
+func (ld *loader) reset() {
+	select {
+	case <-ld.work.Idle():
+	default:
+		panic("loader.reset when not idle")
+	}
+
+	ld.roots = nil
+	ld.pkgCache = new(par.Cache)
+	ld.pkgs = nil
+}
+
+// A loadPkg records information about a single loaded package.
+type loadPkg struct {
+	// Populated at construction time:
+	path   string // import path
+	testOf *loadPkg
+
+	// Populated at construction time and updated by (*loader).applyPkgFlags:
+	flags atomicLoadPkgFlags
+
+	// Populated by (*loader).load:
+	mod         module.Version // module providing package
+	dir         string         // directory containing source code
+	err         error          // error loading package
+	imports     []*loadPkg     // packages imported by this one
+	testImports []string       // test-only imports, saved for use by pkg.test.
+	inStd       bool
+
+	// Populated by (*loader).pkgTest:
+	testOnce sync.Once
+	test     *loadPkg
+
+	// Populated by postprocessing in (*loader).buildStacks:
+	stack *loadPkg // package importing this one in minimal import stack for this pkg
+}
+
+// loadPkgFlags is a set of flags tracking metadata about a package.
+type loadPkgFlags int8
+
+const (
+	// pkgInAll indicates that the package is in the "all" package pattern,
+	// regardless of whether we are loading the "all" package pattern.
+	//
+	// When the pkgInAll flag and pkgImportsLoaded flags are both set, the caller
+	// who set the last of those flags must propagate the pkgInAll marking to all
+	// of the imports of the marked package.
+	//
+	// A test is marked with pkgInAll if that test would promote the packages it
+	// imports to be in "all" (such as when the test is itself within the main
+	// module, or when ld.allClosesOverTests is true).
+	pkgInAll loadPkgFlags = 1 << iota
+
+	// pkgIsRoot indicates that the package matches one of the root package
+	// patterns requested by the caller.
+	//
+	// If LoadTests is set, then when pkgIsRoot and pkgImportsLoaded are both set,
+	// the caller who set the last of those flags must populate a test for the
+	// package (in the pkg.test field).
+	//
+	// If the "all" pattern is included as a root, then non-test packages in "all"
+	// are also roots (and must be marked pkgIsRoot).
+	pkgIsRoot
+
+	// pkgImportsLoaded indicates that the imports and testImports fields of a
+	// loadPkg have been populated.
+	pkgImportsLoaded
+)
+
+// has reports whether all of the flags in cond are set in f.
+func (f loadPkgFlags) has(cond loadPkgFlags) bool {
+	return f&cond == cond
+}
+
+// An atomicLoadPkgFlags stores a loadPkgFlags for which individual flags can be
+// added atomically.
+type atomicLoadPkgFlags struct {
+	bits int32
+}
+
+// update sets the given flags in af (in addition to any flags already set).
+//
+// update returns the previous flag state so that the caller may determine which
+// flags were newly-set.
+func (af *atomicLoadPkgFlags) update(flags loadPkgFlags) (old loadPkgFlags) {
+	for {
+		old := atomic.LoadInt32(&af.bits)
+		new := old | int32(flags)
+		if new == old || atomic.CompareAndSwapInt32(&af.bits, old, new) {
+			return loadPkgFlags(old)
+		}
+	}
+}
+
+// has reports whether all of the flags in cond are set in af.
+func (af *atomicLoadPkgFlags) has(cond loadPkgFlags) bool {
+	return loadPkgFlags(atomic.LoadInt32(&af.bits))&cond == cond
+}
+
+// isTest reports whether pkg is a test of another package.
+func (pkg *loadPkg) isTest() bool {
+	return pkg.testOf != nil
+}
+
+var errMissing = errors.New("cannot find package")
+
+// loadFromRoots attempts to load the build graph needed to process a set of
+// root packages and their dependencies.
+//
+// The set of root packages is returned by the params.listRoots function, and
+// expanded to the full set of packages by tracing imports (and possibly tests)
+// as needed.
+func loadFromRoots(params loaderParams) *loader {
+	ld := &loader{
+		loaderParams: params,
+		work:         par.NewQueue(runtime.GOMAXPROCS(0)),
+	}
+
+	var err error
+	reqs := &mvsReqs{buildList: buildList}
+	buildList, err = mvs.BuildList(Target, reqs)
+	if err != nil {
+		base.Fatalf("go: %v", err)
+	}
+
+	addedModuleFor := make(map[string]bool)
+	for {
+		ld.reset()
+
+		// Load the root packages and their imports.
+		// Note: the returned roots can change on each iteration,
+		// since the expansion of package patterns depends on the
+		// build list we're using.
+		inRoots := map[*loadPkg]bool{}
+		for _, path := range ld.listRoots() {
+			root := ld.pkg(path, pkgIsRoot)
+			if !inRoots[root] {
+				ld.roots = append(ld.roots, root)
+				inRoots[root] = true
+			}
+		}
+
+		// ld.pkg adds imported packages to the work queue and calls applyPkgFlags,
+		// which adds tests (and test dependencies) as needed.
+		//
+		// When all of the work in the queue has completed, we'll know that the
+		// transitive closure of dependencies has been loaded.
+		<-ld.work.Idle()
+
+		ld.buildStacks()
+
+		if !ld.ResolveMissingImports || (!HasModRoot() && !allowMissingModuleImports) {
+			// We've loaded as much as we can without resolving missing imports.
+			break
+		}
+		modAddedBy := ld.resolveMissingImports(addedModuleFor)
+		if len(modAddedBy) == 0 {
+			break
+		}
+
+		// Recompute buildList with all our additions.
+		reqs = &mvsReqs{buildList: buildList}
+		buildList, err = mvs.BuildList(Target, reqs)
+		if err != nil {
+			// If an error was found in a newly added module, report the package
+			// import stack instead of the module requirement stack. Packages
+			// are more descriptive.
+			if err, ok := err.(*mvs.BuildListError); ok {
+				if pkg := modAddedBy[err.Module()]; pkg != nil {
+					base.Fatalf("go: %s: %v", pkg.stackText(), err.Err)
+				}
+			}
+			base.Fatalf("go: %v", err)
+		}
+	}
+	base.ExitIfErrors()
+
+	// Compute directly referenced dependency modules.
+	ld.direct = make(map[string]bool)
+	for _, pkg := range ld.pkgs {
+		if pkg.mod == Target {
+			for _, dep := range pkg.imports {
+				if dep.mod.Path != "" && dep.mod.Path != Target.Path && index != nil {
+					_, explicit := index.require[dep.mod]
+					if allowWriteGoMod && cfg.BuildMod == "readonly" && !explicit {
+						// TODO(#40775): attach error to package instead of using
+						// base.Errorf. Ideally, 'go list' should not fail because of this,
+						// but today, LoadPackages calls WriteGoMod unconditionally, which
+						// would fail with a less clear message.
+						base.Errorf("go: %[1]s: package %[2]s imported from implicitly required module; to add missing requirements, run:\n\tgo get %[2]s@%[3]s", pkg.path, dep.path, dep.mod.Version)
+					}
+					ld.direct[dep.mod.Path] = true
+				}
+			}
+		}
+	}
+	base.ExitIfErrors()
+
+	// If we didn't scan all of the imports from the main module, or didn't use
+	// imports.AnyTags, then we didn't necessarily load every package that
+	// contributes “direct” imports — so we can't safely mark existing
+	// dependencies as indirect-only.
+	// Conservatively mark those dependencies as direct.
+	if modFile != nil && (!ld.allPatternIsRoot || !reflect.DeepEqual(ld.Tags, imports.AnyTags())) {
+		for _, r := range modFile.Require {
+			if !r.Indirect {
+				ld.direct[r.Mod.Path] = true
+			}
+		}
+	}
+
+	return ld
+}
+
+// resolveMissingImports adds module dependencies to the global build list
+// in order to resolve missing packages from pkgs.
+//
+// The newly-resolved packages are added to the addedModuleFor map, and
+// resolveMissingImports returns a map from each newly-added module version to
+// the first package for which that module was added.
+func (ld *loader) resolveMissingImports(addedModuleFor map[string]bool) (modAddedBy map[module.Version]*loadPkg) {
+	var needPkgs []*loadPkg
+	for _, pkg := range ld.pkgs {
+		if pkg.err == nil {
+			continue
+		}
+		if pkg.isTest() {
+			// If we are missing a test, we are also missing its non-test version, and
+			// we should only add the missing import once.
+			continue
+		}
+		if !errors.As(pkg.err, new(*ImportMissingError)) {
+			// Leave other errors for Import or load.Packages to report.
+			continue
+		}
+
+		needPkgs = append(needPkgs, pkg)
+
+		pkg := pkg
+		ld.work.Add(func() {
+			pkg.mod, pkg.err = queryImport(context.TODO(), pkg.path)
+		})
+	}
+	<-ld.work.Idle()
+
+	modAddedBy = map[module.Version]*loadPkg{}
+	for _, pkg := range needPkgs {
+		if pkg.err != nil {
+			continue
+		}
+
+		fmt.Fprintf(os.Stderr, "go: found %s in %s %s\n", pkg.path, pkg.mod.Path, pkg.mod.Version)
+		if addedModuleFor[pkg.path] {
+			// TODO(bcmills): This should only be an error if pkg.mod is the same
+			// version we already tried to add previously.
+			base.Fatalf("go: %s: looping trying to add package", pkg.stackText())
+		}
+		if modAddedBy[pkg.mod] == nil {
+			modAddedBy[pkg.mod] = pkg
+			buildList = append(buildList, pkg.mod)
+		}
+	}
+
+	return modAddedBy
+}
+
+// pkg locates the *loadPkg for path, creating and queuing it for loading if
+// needed, and updates its state to reflect the given flags.
+//
+// The imports of the returned *loadPkg will be loaded asynchronously in the
+// ld.work queue, and its test (if requested) will also be populated once
+// imports have been resolved. When ld.work goes idle, all transitive imports of
+// the requested package (and its test, if requested) will have been loaded.
+func (ld *loader) pkg(path string, flags loadPkgFlags) *loadPkg {
+	if flags.has(pkgImportsLoaded) {
+		panic("internal error: (*loader).pkg called with pkgImportsLoaded flag set")
+	}
+
+	pkg := ld.pkgCache.Do(path, func() interface{} {
+		pkg := &loadPkg{
+			path: path,
+		}
+		ld.applyPkgFlags(pkg, flags)
+
+		ld.work.Add(func() { ld.load(pkg) })
+		return pkg
+	}).(*loadPkg)
+
+	ld.applyPkgFlags(pkg, flags)
+	return pkg
+}
+
+// applyPkgFlags updates pkg.flags to set the given flags and propagate the
+// (transitive) effects of those flags, possibly loading or enqueueing further
+// packages as a result.
+func (ld *loader) applyPkgFlags(pkg *loadPkg, flags loadPkgFlags) {
+	if flags == 0 {
+		return
+	}
+
+	if flags.has(pkgInAll) && ld.allPatternIsRoot && !pkg.isTest() {
+		// This package matches a root pattern by virtue of being in "all".
+		flags |= pkgIsRoot
+	}
+
+	old := pkg.flags.update(flags)
+	new := old | flags
+	if new == old || !new.has(pkgImportsLoaded) {
+		// We either didn't change the state of pkg, or we don't know anything about
+		// its dependencies yet. Either way, we can't usefully load its test or
+		// update its dependencies.
+		return
+	}
+
+	if !pkg.isTest() {
+		// Check whether we should add (or update the flags for) a test for pkg.
+		// ld.pkgTest is idempotent and extra invocations are inexpensive,
+		// so it's ok if we call it more than is strictly necessary.
+		wantTest := false
+		switch {
+		case ld.allPatternIsRoot && pkg.mod == Target:
+			// We are loading the "all" pattern, which includes packages imported by
+			// tests in the main module. This package is in the main module, so we
+			// need to identify the imports of its test even if LoadTests is not set.
+			//
+			// (We will filter out the extra tests explicitly in computePatternAll.)
+			wantTest = true
+
+		case ld.allPatternIsRoot && ld.allClosesOverTests && new.has(pkgInAll):
+			// This variant of the "all" pattern includes imports of tests of every
+			// package that is itself in "all", and pkg is in "all", so its test is
+			// also in "all" (as above).
+			wantTest = true
+
+		case ld.LoadTests && new.has(pkgIsRoot):
+			// LoadTest explicitly requests tests of “the root packages”.
+			wantTest = true
+		}
+
+		if wantTest {
+			var testFlags loadPkgFlags
+			if pkg.mod == Target || (ld.allClosesOverTests && new.has(pkgInAll)) {
+				// Tests of packages in the main module are in "all", in the sense that
+				// they cause the packages they import to also be in "all". So are tests
+				// of packages in "all" if "all" closes over test dependencies.
+				testFlags |= pkgInAll
+			}
+			ld.pkgTest(pkg, testFlags)
+		}
+	}
+
+	if new.has(pkgInAll) && !old.has(pkgInAll|pkgImportsLoaded) {
+		// We have just marked pkg with pkgInAll, or we have just loaded its
+		// imports, or both. Now is the time to propagate pkgInAll to the imports.
+		for _, dep := range pkg.imports {
+			ld.applyPkgFlags(dep, pkgInAll)
+		}
+	}
+}
+
+// load loads an individual package.
+func (ld *loader) load(pkg *loadPkg) {
+	if strings.Contains(pkg.path, "@") {
+		// Leave for error during load.
+		return
+	}
+	if build.IsLocalImport(pkg.path) || filepath.IsAbs(pkg.path) {
+		// Leave for error during load.
+		// (Module mode does not allow local imports.)
+		return
+	}
+
+	if search.IsMetaPackage(pkg.path) {
+		pkg.err = &invalidImportError{
+			importPath: pkg.path,
+			err:        fmt.Errorf("%q is not an importable package; see 'go help packages'", pkg.path),
+		}
+		return
+	}
+
+	pkg.mod, pkg.dir, pkg.err = importFromBuildList(context.TODO(), pkg.path, buildList)
+	if pkg.dir == "" {
+		return
+	}
+	if pkg.mod == Target {
+		// Go ahead and mark pkg as in "all". This provides the invariant that a
+		// package that is *only* imported by other packages in "all" is always
+		// marked as such before loading its imports.
+		//
+		// We don't actually rely on that invariant at the moment, but it may
+		// improve efficiency somewhat and makes the behavior a bit easier to reason
+		// about (by reducing churn on the flag bits of dependencies), and costs
+		// essentially nothing (these atomic flag ops are essentially free compared
+		// to scanning source code for imports).
+		ld.applyPkgFlags(pkg, pkgInAll)
+	}
+	if ld.AllowPackage != nil {
+		if err := ld.AllowPackage(context.TODO(), pkg.path, pkg.mod); err != nil {
+			pkg.err = err
+		}
+	}
+
+	pkg.inStd = (search.IsStandardImportPath(pkg.path) && search.InDir(pkg.dir, cfg.GOROOTsrc) != "")
+
+	var imports, testImports []string
+
+	if cfg.BuildContext.Compiler == "gccgo" && pkg.inStd {
+		// We can't scan standard packages for gccgo.
+	} else {
+		var err error
+		imports, testImports, err = scanDir(pkg.dir, ld.Tags)
+		if err != nil {
+			pkg.err = err
+			return
+		}
+	}
+
+	pkg.imports = make([]*loadPkg, 0, len(imports))
+	var importFlags loadPkgFlags
+	if pkg.flags.has(pkgInAll) {
+		importFlags = pkgInAll
+	}
+	for _, path := range imports {
+		if pkg.inStd {
+			// Imports from packages in "std" and "cmd" should resolve using
+			// GOROOT/src/vendor even when "std" is not the main module.
+			path = ld.stdVendor(pkg.path, path)
+		}
+		pkg.imports = append(pkg.imports, ld.pkg(path, importFlags))
+	}
+	pkg.testImports = testImports
+
+	ld.applyPkgFlags(pkg, pkgImportsLoaded)
+}
+
+// pkgTest locates the test of pkg, creating it if needed, and updates its state
+// to reflect the given flags.
+//
+// pkgTest requires that the imports of pkg have already been loaded (flagged
+// with pkgImportsLoaded).
+func (ld *loader) pkgTest(pkg *loadPkg, testFlags loadPkgFlags) *loadPkg {
+	if pkg.isTest() {
+		panic("pkgTest called on a test package")
+	}
+
+	createdTest := false
+	pkg.testOnce.Do(func() {
+		pkg.test = &loadPkg{
+			path:   pkg.path,
+			testOf: pkg,
+			mod:    pkg.mod,
+			dir:    pkg.dir,
+			err:    pkg.err,
+			inStd:  pkg.inStd,
+		}
+		ld.applyPkgFlags(pkg.test, testFlags)
+		createdTest = true
+	})
+
+	test := pkg.test
+	if createdTest {
+		test.imports = make([]*loadPkg, 0, len(pkg.testImports))
+		var importFlags loadPkgFlags
+		if test.flags.has(pkgInAll) {
+			importFlags = pkgInAll
+		}
+		for _, path := range pkg.testImports {
+			if pkg.inStd {
+				path = ld.stdVendor(test.path, path)
+			}
+			test.imports = append(test.imports, ld.pkg(path, importFlags))
+		}
+		pkg.testImports = nil
+		ld.applyPkgFlags(test, pkgImportsLoaded)
+	} else {
+		ld.applyPkgFlags(test, testFlags)
+	}
+
+	return test
+}
+
+// stdVendor returns the canonical import path for the package with the given
+// path when imported from the standard-library package at parentPath.
+func (ld *loader) stdVendor(parentPath, path string) string {
+	if search.IsStandardImportPath(path) {
+		return path
+	}
+
+	if str.HasPathPrefix(parentPath, "cmd") {
+		if Target.Path != "cmd" {
+			vendorPath := pathpkg.Join("cmd", "vendor", path)
+			if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
+				return vendorPath
+			}
+		}
+	} else if Target.Path != "std" || str.HasPathPrefix(parentPath, "vendor") {
+		// If we are outside of the 'std' module, resolve imports from within 'std'
+		// to the vendor directory.
+		//
+		// Do the same for importers beginning with the prefix 'vendor/' even if we
+		// are *inside* of the 'std' module: the 'vendor/' packages that resolve
+		// globally from GOROOT/src/vendor (and are listed as part of 'go list std')
+		// are distinct from the real module dependencies, and cannot import
+		// internal packages from the real module.
+		//
+		// (Note that although the 'vendor/' packages match the 'std' *package*
+		// pattern, they are not part of the std *module*, and do not affect
+		// 'go mod tidy' and similar module commands when working within std.)
+		vendorPath := pathpkg.Join("vendor", path)
+		if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
+			return vendorPath
+		}
+	}
+
+	// Not vendored: resolve from modules.
+	return path
+}
+
+// computePatternAll returns the list of packages matching pattern "all",
+// starting with a list of the import paths for the packages in the main module.
+func (ld *loader) computePatternAll() (all []string) {
+	for _, pkg := range ld.pkgs {
+		if pkg.flags.has(pkgInAll) && !pkg.isTest() {
+			all = append(all, pkg.path)
+		}
+	}
+	sort.Strings(all)
+	return all
+}
+
+// scanDir is like imports.ScanDir but elides known magic imports from the list,
+// so that we do not go looking for packages that don't really exist.
+//
+// The standard magic import is "C", for cgo.
+//
+// The only other known magic imports are appengine and appengine/*.
+// These are so old that they predate "go get" and did not use URL-like paths.
+// Most code today now uses google.golang.org/appengine instead,
+// but not all code has been so updated. When we mostly ignore build tags
+// during "go vendor", we look into "// +build appengine" files and
+// may see these legacy imports. We drop them so that the module
+// search does not look for modules to try to satisfy them.
+func scanDir(dir string, tags map[string]bool) (imports_, testImports []string, err error) {
+	imports_, testImports, err = imports.ScanDir(dir, tags)
+
+	filter := func(x []string) []string {
+		w := 0
+		for _, pkg := range x {
+			if pkg != "C" && pkg != "appengine" && !strings.HasPrefix(pkg, "appengine/") &&
+				pkg != "appengine_internal" && !strings.HasPrefix(pkg, "appengine_internal/") {
+				x[w] = pkg
+				w++
+			}
+		}
+		return x[:w]
+	}
+
+	return filter(imports_), filter(testImports), err
+}
+
+// buildStacks computes minimal import stacks for each package,
+// for use in error messages. When it completes, packages that
+// are part of the original root set have pkg.stack == nil,
+// and other packages have pkg.stack pointing at the next
+// package up the import stack in their minimal chain.
+// As a side effect, buildStacks also constructs ld.pkgs,
+// the list of all packages loaded.
+func (ld *loader) buildStacks() {
+	if len(ld.pkgs) > 0 {
+		panic("buildStacks")
+	}
+	for _, pkg := range ld.roots {
+		pkg.stack = pkg // sentinel to avoid processing in next loop
+		ld.pkgs = append(ld.pkgs, pkg)
+	}
+	for i := 0; i < len(ld.pkgs); i++ { // not range: appending to ld.pkgs in loop
+		pkg := ld.pkgs[i]
+		for _, next := range pkg.imports {
+			if next.stack == nil {
+				next.stack = pkg
+				ld.pkgs = append(ld.pkgs, next)
+			}
+		}
+		if next := pkg.test; next != nil && next.stack == nil {
+			next.stack = pkg
+			ld.pkgs = append(ld.pkgs, next)
+		}
+	}
+	for _, pkg := range ld.roots {
+		pkg.stack = nil
+	}
+}
+
+// stackText builds the import stack text to use when
+// reporting an error in pkg. It has the general form
+//
+//	root imports
+//		other imports
+//		other2 tested by
+//		other2.test imports
+//		pkg
+//
+func (pkg *loadPkg) stackText() string {
+	var stack []*loadPkg
+	for p := pkg; p != nil; p = p.stack {
+		stack = append(stack, p)
+	}
+
+	var buf bytes.Buffer
+	for i := len(stack) - 1; i >= 0; i-- {
+		p := stack[i]
+		fmt.Fprint(&buf, p.path)
+		if p.testOf != nil {
+			fmt.Fprint(&buf, ".test")
+		}
+		if i > 0 {
+			if stack[i-1].testOf == p {
+				fmt.Fprint(&buf, " tested by\n\t")
+			} else {
+				fmt.Fprint(&buf, " imports\n\t")
+			}
+		}
+	}
+	return buf.String()
+}
+
+// why returns the text to use in "go mod why" output about the given package.
+// It is less ornate than the stackText but contains the same information.
+func (pkg *loadPkg) why() string {
+	var buf strings.Builder
+	var stack []*loadPkg
+	for p := pkg; p != nil; p = p.stack {
+		stack = append(stack, p)
+	}
+
+	for i := len(stack) - 1; i >= 0; i-- {
+		p := stack[i]
+		if p.testOf != nil {
+			fmt.Fprintf(&buf, "%s.test\n", p.testOf.path)
+		} else {
+			fmt.Fprintf(&buf, "%s\n", p.path)
+		}
+	}
+	return buf.String()
+}
+
+// Why returns the "go mod why" output stanza for the given package,
+// without the leading # comment.
+// The package graph must have been loaded already, usually by LoadPackages.
+// If there is no reason for the package to be in the current build,
+// Why returns an empty string.
+func Why(path string) string {
+	pkg, ok := loaded.pkgCache.Get(path).(*loadPkg)
+	if !ok {
+		return ""
+	}
+	return pkg.why()
+}
+
+// WhyDepth returns the number of steps in the Why listing.
+// If there is no reason for the package to be in the current build,
+// WhyDepth returns 0.
+func WhyDepth(path string) int {
+	n := 0
+	pkg, _ := loaded.pkgCache.Get(path).(*loadPkg)
+	for p := pkg; p != nil; p = p.stack {
+		n++
+	}
+	return n
+}