blob: 18dada495ca8acd709942e508c6b6ce76d5ab7ef [file] [log] [blame]
// 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"
"sync"
"golang.org/x/tools/internal/gopathwalk"
)
// To find packages to import, the resolver needs to know about all of the
// 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
)
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.
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.
//
// TODO(suzmue): consider other concurrency strategies and data structures (RWLocks, sync.Map, etc)
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
}
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()
_, 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
}