src

mod_cache.go (10426B)

---

 // Copyright 2019 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 imports
 
 import (
 	"context"
 	"fmt"
 	"path"
 	"path/filepath"
 	"strings"
 	"sync"
 
 	"golang.org/x/mod/module"
 	"golang.org/x/tools/internal/gopathwalk"
 	"golang.org/x/tools/internal/stdlib"
 )
 
 // To find packages to import, the resolver needs to know about all of
 // the packages that could be imported. This includes packages that are
 // already in modules that are in (1) the current module, (2) replace targets,
 // and (3) packages in the module cache. Packages in (1) and (2) may change over
 // time, as the client may edit the current module and locally replaced modules.
 // The module cache (which includes all of the packages in (3)) can only
 // ever be added to.
 //
 // The resolver can thus save state about packages in the module cache
 // and guarantee that this will not change over time. To obtain information
 // about new modules added to the module cache, the module cache should be
 // rescanned.
 //
 // It is OK to serve information about modules that have been deleted,
 // as they do still exist.
 // TODO(suzmue): can we share information with the caller about
 // what module needs to be downloaded to import this package?
 
 type directoryPackageStatus int
 
 const (
 	_ directoryPackageStatus = iota
 	directoryScanned
 	nameLoaded
 	exportsLoaded
 )
 
 // directoryPackageInfo holds (possibly incomplete) information about packages
 // contained in a given directory.
 type directoryPackageInfo struct {
 	// status indicates the extent to which this struct has been filled in.
 	status directoryPackageStatus
 	// err is non-nil when there was an error trying to reach status.
 	err error
 
 	// Set when status >= directoryScanned.
 
 	// dir is the absolute directory of this package.
 	dir      string
 	rootType gopathwalk.RootType
 	// nonCanonicalImportPath is the package's expected import path. It may
 	// not actually be importable at that path.
 	nonCanonicalImportPath string
 
 	// Module-related information.
 	moduleDir  string // The directory that is the module root of this dir.
 	moduleName string // The module name that contains this dir.
 
 	// Set when status >= nameLoaded.
 
 	packageName string // the package name, as declared in the source.
 
 	// Set when status >= exportsLoaded.
 	// TODO(rfindley): it's hard to see this, but exports depend implicitly on
 	// the default build context GOOS and GOARCH.
 	//
 	// We can make this explicit, and key exports by GOOS, GOARCH.
 	exports []stdlib.Symbol
 }
 
 // reachedStatus returns true when info has a status at least target and any error associated with
 // an attempt to reach target.
 func (info *directoryPackageInfo) reachedStatus(target directoryPackageStatus) (bool, error) {
 	if info.err == nil {
 		return info.status >= target, nil
 	}
 	if info.status == target {
 		return true, info.err
 	}
 	return true, nil
 }
 
 // DirInfoCache is a concurrency-safe map for storing information about
 // directories that may contain packages.
 //
 // The information in this cache is built incrementally. Entries are initialized in scan.
 // No new keys should be added in any other functions, as all directories containing
 // packages are identified in scan.
 //
 // Other functions, including loadExports and findPackage, may update entries in this cache
 // as they discover new things about the directory.
 //
 // The information in the cache is not expected to change for the cache's
 // lifetime, so there is no protection against competing writes. Users should
 // take care not to hold the cache across changes to the underlying files.
 type DirInfoCache struct {
 	mu sync.Mutex
 	// dirs stores information about packages in directories, keyed by absolute path.
 	dirs      map[string]*directoryPackageInfo
 	listeners map[*int]cacheListener
 }
 
 func NewDirInfoCache() *DirInfoCache {
 	return &DirInfoCache{
 		dirs:      make(map[string]*directoryPackageInfo),
 		listeners: make(map[*int]cacheListener),
 	}
 }
 
 type cacheListener func(directoryPackageInfo)
 
 // ScanAndListen calls listener on all the items in the cache, and on anything
 // newly added. The returned stop function waits for all in-flight callbacks to
 // finish and blocks new ones.
 func (d *DirInfoCache) ScanAndListen(ctx context.Context, listener cacheListener) func() {
 	ctx, cancel := context.WithCancel(ctx)
 
 	// Flushing out all the callbacks is tricky without knowing how many there
 	// are going to be. Setting an arbitrary limit makes it much easier.
 	const maxInFlight = 10
 	sema := make(chan struct{}, maxInFlight)
 	for range maxInFlight {
 		sema <- struct{}{}
 	}
 
 	cookie := new(int) // A unique ID we can use for the listener.
 
 	// We can't hold mu while calling the listener.
 	d.mu.Lock()
 	var keys []string
 	for key := range d.dirs {
 		keys = append(keys, key)
 	}
 	d.listeners[cookie] = func(info directoryPackageInfo) {
 		select {
 		case <-ctx.Done():
 			return
 		case <-sema:
 		}
 		listener(info)
 		sema <- struct{}{}
 	}
 	d.mu.Unlock()
 
 	stop := func() {
 		cancel()
 		d.mu.Lock()
 		delete(d.listeners, cookie)
 		d.mu.Unlock()
 		for range maxInFlight {
 			<-sema
 		}
 	}
 
 	// Process the pre-existing keys.
 	for _, k := range keys {
 		select {
 		case <-ctx.Done():
 			return stop
 		default:
 		}
 		if v, ok := d.Load(k); ok {
 			listener(v)
 		}
 	}
 
 	return stop
 }
 
 // Store stores the package info for dir.
 func (d *DirInfoCache) Store(dir string, info directoryPackageInfo) {
 	d.mu.Lock()
 	// TODO(rfindley, golang/go#59216): should we overwrite an existing entry?
 	// That seems incorrect as the cache should be idempotent.
 	_, old := d.dirs[dir]
 	d.dirs[dir] = &info
 	var listeners []cacheListener
 	for _, l := range d.listeners {
 		listeners = append(listeners, l)
 	}
 	d.mu.Unlock()
 
 	if !old {
 		for _, l := range listeners {
 			l(info)
 		}
 	}
 }
 
 // Load returns a copy of the directoryPackageInfo for absolute directory dir.
 func (d *DirInfoCache) Load(dir string) (directoryPackageInfo, bool) {
 	d.mu.Lock()
 	defer d.mu.Unlock()
 	info, ok := d.dirs[dir]
 	if !ok {
 		return directoryPackageInfo{}, false
 	}
 	return *info, true
 }
 
 // Keys returns the keys currently present in d.
 func (d *DirInfoCache) Keys() (keys []string) {
 	d.mu.Lock()
 	defer d.mu.Unlock()
 	for key := range d.dirs {
 		keys = append(keys, key)
 	}
 	return keys
 }
 
 func (d *DirInfoCache) CachePackageName(info directoryPackageInfo) (string, error) {
 	if loaded, err := info.reachedStatus(nameLoaded); loaded {
 		return info.packageName, err
 	}
 	if scanned, err := info.reachedStatus(directoryScanned); !scanned || err != nil {
 		return "", fmt.Errorf("cannot read package name, scan error: %v", err)
 	}
 	info.packageName, info.err = packageDirToName(info.dir)
 	info.status = nameLoaded
 	d.Store(info.dir, info)
 	return info.packageName, info.err
 }
 
 func (d *DirInfoCache) CacheExports(ctx context.Context, env *ProcessEnv, info directoryPackageInfo) (string, []stdlib.Symbol, error) {
 	if reached, _ := info.reachedStatus(exportsLoaded); reached {
 		return info.packageName, info.exports, info.err
 	}
 	if reached, err := info.reachedStatus(nameLoaded); reached && err != nil {
 		return "", nil, err
 	}
 	info.packageName, info.exports, info.err = loadExportsFromFiles(ctx, env, info.dir, false)
 	if info.err == context.Canceled || info.err == context.DeadlineExceeded {
 		return info.packageName, info.exports, info.err
 	}
 	// The cache structure wants things to proceed linearly. We can skip a
 	// step here, but only if we succeed.
 	if info.status == nameLoaded || info.err == nil {
 		info.status = exportsLoaded
 	} else {
 		info.status = nameLoaded
 	}
 	d.Store(info.dir, info)
 	return info.packageName, info.exports, info.err
 }
 
 // ScanModuleCache walks the given directory, which must be a GOMODCACHE value,
 // for directory package information, storing the results in cache.
 func ScanModuleCache(dir string, cache *DirInfoCache, logf func(string, ...any)) {
 	// Note(rfindley): it's hard to see, but this function attempts to implement
 	// just the side effects on cache of calling PrimeCache with a ProcessEnv
 	// that has the given dir as its GOMODCACHE.
 	//
 	// Teasing out the control flow, we see that we can avoid any handling of
 	// vendor/ and can infer module info entirely from the path, simplifying the
 	// logic here.
 
 	root := gopathwalk.Root{
 		Path: filepath.Clean(dir),
 		Type: gopathwalk.RootModuleCache,
 	}
 
 	directoryInfo := func(root gopathwalk.Root, dir string) directoryPackageInfo {
 		// This is a copy of ModuleResolver.scanDirForPackage, trimmed down to
 		// logic that applies to a module cache directory.
 
 		subdir := ""
 		if dir != root.Path {
 			subdir = dir[len(root.Path)+len("/"):]
 		}
 
 		matches := modCacheRegexp.FindStringSubmatch(subdir)
 		if len(matches) == 0 {
 			return directoryPackageInfo{
 				status: directoryScanned,
 				err:    fmt.Errorf("invalid module cache path: %v", subdir),
 			}
 		}
 		modPath, err := module.UnescapePath(filepath.ToSlash(matches[1]))
 		if err != nil {
 			if logf != nil {
 				logf("decoding module cache path %q: %v", subdir, err)
 			}
 			return directoryPackageInfo{
 				status: directoryScanned,
 				err:    fmt.Errorf("decoding module cache path %q: %v", subdir, err),
 			}
 		}
 		importPath := path.Join(modPath, filepath.ToSlash(matches[3]))
 		index := strings.Index(dir, matches[1]+"@"+matches[2])
 		modDir := filepath.Join(dir[:index], matches[1]+"@"+matches[2])
 		modName := readModName(filepath.Join(modDir, "go.mod"))
 		return directoryPackageInfo{
 			status:                 directoryScanned,
 			dir:                    dir,
 			rootType:               root.Type,
 			nonCanonicalImportPath: importPath,
 			moduleDir:              modDir,
 			moduleName:             modName,
 		}
 	}
 
 	add := func(root gopathwalk.Root, dir string) {
 		info := directoryInfo(root, dir)
 		cache.Store(info.dir, info)
 	}
 
 	skip := func(_ gopathwalk.Root, dir string) bool {
 		// Skip directories that have already been scanned.
 		//
 		// Note that gopathwalk only adds "package" directories, which must contain
 		// a .go file, and all such package directories in the module cache are
 		// immutable. So if we can load a dir, it can be skipped.
 		info, ok := cache.Load(dir)
 		if !ok {
 			return false
 		}
 		packageScanned, _ := info.reachedStatus(directoryScanned)
 		return packageScanned
 	}
 
 	gopathwalk.WalkSkip([]gopathwalk.Root{root}, add, skip, gopathwalk.Options{Logf: logf, ModulesEnabled: true})
 }