/
mod_cache.go
330 lines (292 loc) · 10.2 KB
/
mod_cache.go
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// 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"
"cuelang.org/go/internal/golangorgx/tools/gopathwalk"
"golang.org/x/mod/module"
)
// 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 []string
}
// 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 i := 0; i < maxInFlight; i++ {
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 i := 0; i < maxInFlight; i++ {
<-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, []string, 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})
}