| // 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 mvs implements Minimal Version Selection. |
| // See https://research.swtch.com/vgo-mvs. |
| package mvs |
| |
| import ( |
| "fmt" |
| "sort" |
| "sync" |
| |
| "cmd/go/internal/module" |
| "cmd/go/internal/par" |
| ) |
| |
| // A Reqs is the requirement graph on which Minimal Version Selection (MVS) operates. |
| // |
| // The version strings are opaque except for the special version "none" |
| // (see the documentation for module.Version). In particular, MVS does not |
| // assume that the version strings are semantic versions; instead, the Max method |
| // gives access to the comparison operation. |
| // |
| // It must be safe to call methods on a Reqs from multiple goroutines simultaneously. |
| // Because a Reqs may read the underlying graph from the network on demand, |
| // the MVS algorithms parallelize the traversal to overlap network delays. |
| type Reqs interface { |
| // Required returns the module versions explicitly required by m itself. |
| // The caller must not modify the returned list. |
| Required(m module.Version) ([]module.Version, error) |
| |
| // Max returns the maximum of v1 and v2 (it returns either v1 or v2). |
| // |
| // For all versions v, Max(v, "none") must be v, |
| // and for the tanget passed as the first argument to MVS functions, |
| // Max(target, v) must be target. |
| // |
| // Note that v1 < v2 can be written Max(v1, v2) != v1 |
| // and similarly v1 <= v2 can be written Max(v1, v2) == v2. |
| Max(v1, v2 string) string |
| |
| // Upgrade returns the upgraded version of m, |
| // for use during an UpgradeAll operation. |
| // If m should be kept as is, Upgrade returns m. |
| // If m is not yet used in the build, then m.Version will be "none". |
| // More typically, m.Version will be the version required |
| // by some other module in the build. |
| // |
| // If no module version is available for the given path, |
| // Upgrade returns a non-nil error. |
| // TODO(rsc): Upgrade must be able to return errors, |
| // but should "no latest version" just return m instead? |
| Upgrade(m module.Version) (module.Version, error) |
| |
| // Previous returns the version of m.Path immediately prior to m.Version, |
| // or "none" if no such version is known. |
| Previous(m module.Version) (module.Version, error) |
| } |
| |
| type MissingModuleError struct { |
| Module module.Version |
| } |
| |
| func (e *MissingModuleError) Error() string { |
| return fmt.Sprintf("missing module: %v", e.Module) |
| } |
| |
| // BuildList returns the build list for the target module. |
| func BuildList(target module.Version, reqs Reqs) ([]module.Version, error) { |
| return buildList(target, reqs, nil) |
| } |
| |
| func buildList(target module.Version, reqs Reqs, upgrade func(module.Version) module.Version) ([]module.Version, error) { |
| // Explore work graph in parallel in case reqs.Required |
| // does high-latency network operations. |
| var work par.Work |
| work.Add(target) |
| var ( |
| mu sync.Mutex |
| min = map[string]string{target.Path: target.Version} |
| firstErr error |
| ) |
| work.Do(10, func(item interface{}) { |
| m := item.(module.Version) |
| required, err := reqs.Required(m) |
| |
| mu.Lock() |
| if err != nil && firstErr == nil { |
| firstErr = err |
| } |
| if firstErr != nil { |
| mu.Unlock() |
| return |
| } |
| if v, ok := min[m.Path]; !ok || reqs.Max(v, m.Version) != v { |
| min[m.Path] = m.Version |
| } |
| mu.Unlock() |
| |
| for _, r := range required { |
| work.Add(r) |
| } |
| |
| if upgrade != nil { |
| work.Add(upgrade(m)) |
| } |
| }) |
| |
| if firstErr != nil { |
| return nil, firstErr |
| } |
| if v := min[target.Path]; v != target.Version { |
| panic(fmt.Sprintf("mistake: chose version %q instead of target %+v", v, target)) // TODO: Don't panic. |
| } |
| |
| list := []module.Version{target} |
| listed := map[string]bool{target.Path: true} |
| for i := 0; i < len(list); i++ { |
| m := list[i] |
| required, err := reqs.Required(m) |
| if err != nil { |
| return nil, err |
| } |
| for _, r := range required { |
| v := min[r.Path] |
| if r.Path != target.Path && reqs.Max(v, r.Version) != v { |
| panic(fmt.Sprintf("mistake: version %q does not satisfy requirement %+v", v, r)) // TODO: Don't panic. |
| } |
| if !listed[r.Path] { |
| list = append(list, module.Version{Path: r.Path, Version: v}) |
| listed[r.Path] = true |
| } |
| } |
| } |
| |
| tail := list[1:] |
| sort.Slice(tail, func(i, j int) bool { |
| return tail[i].Path < tail[j].Path |
| }) |
| return list, nil |
| } |
| |
| // Req returns the minimal requirement list for the target module |
| // that results in the given build list. |
| func Req(target module.Version, list []module.Version, reqs Reqs) ([]module.Version, error) { |
| // Note: Not running in parallel because we assume |
| // that list came from a previous operation that paged |
| // in all the requirements, so there's no I/O to overlap now. |
| |
| // Compute postorder, cache requirements. |
| var postorder []module.Version |
| reqCache := map[module.Version][]module.Version{} |
| reqCache[target] = nil |
| var walk func(module.Version) error |
| walk = func(m module.Version) error { |
| _, ok := reqCache[m] |
| if ok { |
| return nil |
| } |
| required, err := reqs.Required(m) |
| if err != nil { |
| return err |
| } |
| reqCache[m] = required |
| for _, m1 := range required { |
| if err := walk(m1); err != nil { |
| return err |
| } |
| } |
| postorder = append(postorder, m) |
| return nil |
| } |
| for _, m := range list { |
| if err := walk(m); err != nil { |
| return nil, err |
| } |
| } |
| |
| // Walk modules in reverse post-order, only adding those not implied already. |
| have := map[string]string{} |
| walk = func(m module.Version) error { |
| if v, ok := have[m.Path]; ok && reqs.Max(m.Version, v) == v { |
| return nil |
| } |
| have[m.Path] = m.Version |
| for _, m1 := range reqCache[m] { |
| walk(m1) |
| } |
| return nil |
| } |
| max := map[string]string{} |
| for _, m := range list { |
| if v, ok := max[m.Path]; ok { |
| max[m.Path] = reqs.Max(m.Version, v) |
| } else { |
| max[m.Path] = m.Version |
| } |
| } |
| var min []module.Version |
| for i := len(postorder) - 1; i >= 0; i-- { |
| m := postorder[i] |
| if max[m.Path] != m.Version { |
| // Older version. |
| continue |
| } |
| if have[m.Path] != m.Version { |
| min = append(min, m) |
| walk(m) |
| } |
| } |
| sort.Slice(min, func(i, j int) bool { |
| return min[i].Path < min[j].Path |
| }) |
| return min, nil |
| } |
| |
| // UpgradeAll returns a build list for the target module |
| // in which every module is upgraded to its latest version. |
| func UpgradeAll(target module.Version, reqs Reqs) ([]module.Version, error) { |
| return buildList(target, reqs, func(m module.Version) module.Version { |
| if m.Path == target.Path { |
| return target |
| } |
| |
| latest, err := reqs.Upgrade(m) |
| if err != nil { |
| panic(err) // TODO |
| } |
| m.Version = latest.Version |
| return m |
| }) |
| } |
| |
| // Upgrade returns a build list for the target module |
| // in which the given additional modules are upgraded. |
| func Upgrade(target module.Version, reqs Reqs, upgrade ...module.Version) ([]module.Version, error) { |
| list, err := reqs.Required(target) |
| if err != nil { |
| panic(err) // TODO |
| } |
| // TODO: Maybe if an error is given, |
| // rerun with BuildList(upgrade[0], reqs) etc |
| // to find which ones are the buggy ones. |
| list = append([]module.Version(nil), list...) |
| list = append(list, upgrade...) |
| return BuildList(target, &override{target, list, reqs}) |
| } |
| |
| // Downgrade returns a build list for the target module |
| // in which the given additional modules are downgraded. |
| // |
| // The versions to be downgraded may be unreachable from reqs.Latest and |
| // reqs.Previous, but the methods of reqs must otherwise handle such versions |
| // correctly. |
| func Downgrade(target module.Version, reqs Reqs, downgrade ...module.Version) ([]module.Version, error) { |
| list, err := reqs.Required(target) |
| if err != nil { |
| panic(err) // TODO |
| } |
| max := make(map[string]string) |
| for _, r := range list { |
| max[r.Path] = r.Version |
| } |
| for _, d := range downgrade { |
| if v, ok := max[d.Path]; !ok || reqs.Max(v, d.Version) != d.Version { |
| max[d.Path] = d.Version |
| } |
| } |
| |
| var ( |
| added = make(map[module.Version]bool) |
| rdeps = make(map[module.Version][]module.Version) |
| excluded = make(map[module.Version]bool) |
| ) |
| var exclude func(module.Version) |
| exclude = func(m module.Version) { |
| if excluded[m] { |
| return |
| } |
| excluded[m] = true |
| for _, p := range rdeps[m] { |
| exclude(p) |
| } |
| } |
| var add func(module.Version) |
| add = func(m module.Version) { |
| if added[m] { |
| return |
| } |
| added[m] = true |
| if v, ok := max[m.Path]; ok && reqs.Max(m.Version, v) != v { |
| exclude(m) |
| return |
| } |
| list, err := reqs.Required(m) |
| if err != nil { |
| panic(err) // TODO |
| } |
| for _, r := range list { |
| add(r) |
| if excluded[r] { |
| exclude(m) |
| return |
| } |
| rdeps[r] = append(rdeps[r], m) |
| } |
| } |
| |
| var out []module.Version |
| out = append(out, target) |
| List: |
| for _, r := range list { |
| add(r) |
| for excluded[r] { |
| p, err := reqs.Previous(r) |
| if err != nil { |
| return nil, err // TODO |
| } |
| // If the target version is a pseudo-version, it may not be |
| // included when iterating over prior versions using reqs.Previous. |
| // Insert it into the right place in the iteration. |
| // If v is excluded, p should be returned again by reqs.Previous on the next iteration. |
| if v := max[r.Path]; reqs.Max(v, r.Version) != v && reqs.Max(p.Version, v) != p.Version { |
| p.Version = v |
| } |
| if p.Version == "none" { |
| continue List |
| } |
| add(p) |
| r = p |
| } |
| out = append(out, r) |
| } |
| |
| return out, nil |
| } |
| |
| type override struct { |
| target module.Version |
| list []module.Version |
| Reqs |
| } |
| |
| func (r *override) Required(m module.Version) ([]module.Version, error) { |
| if m == r.target { |
| return r.list, nil |
| } |
| return r.Reqs.Required(m) |
| } |