vcs.go

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package codehost
     6  
     7  import (
     8  	"context"
     9  	"errors"
    10  	"fmt"
    11  	"internal/lazyregexp"
    12  	"io"
    13  	"io/fs"
    14  	"os"
    15  	"path/filepath"
    16  	"sort"
    17  	"strconv"
    18  	"strings"
    19  	"sync"
    20  	"sync/atomic"
    21  	"time"
    22  
    23  	"cmd/go/internal/base"
    24  	"cmd/go/internal/cfg"
    25  	"cmd/go/internal/lockedfile"
    26  	"cmd/go/internal/str"
    27  	"cmd/internal/par"
    28  
    29  	"golang.org/x/mod/semver"
    30  )
    31  
    32  // A VCSError indicates an error using a version control system.
    33  // The implication of a VCSError is that we know definitively where
    34  // to get the code, but we can't access it due to the error.
    35  // The caller should report this error instead of continuing to probe
    36  // other possible module paths.
    37  //
    38  // TODO(golang.org/issue/31730): See if we can invert this. (Return a
    39  // distinguished error for “repo not found” and treat everything else
    40  // as terminal.)
    41  type VCSError struct {
    42  	Err error
    43  }
    44  
    45  func (e *VCSError) Error() string { return e.Err.Error() }
    46  
    47  func (e *VCSError) Unwrap() error { return e.Err }
    48  
    49  func vcsErrorf(format string, a ...any) error {
    50  	return &VCSError{Err: fmt.Errorf(format, a...)}
    51  }
    52  
    53  type vcsCacheKey struct {
    54  	vcs    string
    55  	remote string
    56  	local  bool
    57  }
    58  
    59  func NewRepo(ctx context.Context, vcs, remote string, local bool) (Repo, error) {
    60  	return vcsRepoCache.Do(vcsCacheKey{vcs, remote, local}, func() (Repo, error) {
    61  		repo, err := newVCSRepo(ctx, vcs, remote, local)
    62  		if err != nil {
    63  			return nil, &VCSError{err}
    64  		}
    65  		return repo, nil
    66  	})
    67  }
    68  
    69  var vcsRepoCache par.ErrCache[vcsCacheKey, Repo]
    70  
    71  type vcsRepo struct {
    72  	mu lockedfile.Mutex // protects all commands, so we don't have to decide which are safe on a per-VCS basis
    73  
    74  	remote string
    75  	cmd    *vcsCmd
    76  	dir    string
    77  	local  bool
    78  
    79  	tagsOnce sync.Once
    80  	tags     map[string]bool
    81  
    82  	branchesOnce sync.Once
    83  	branches     map[string]bool
    84  
    85  	fetchOnce sync.Once
    86  	fetchErr  error
    87  	fetched   atomic.Bool
    88  
    89  	repoSumOnce sync.Once
    90  	repoSum     string
    91  
    92  	statCache     par.ErrCache[string, *RevInfo]  // cache key is revision
    93  	readFileCache par.ErrCache[[2]string, []byte] // cache key is revision and file path
    94  }
    95  
    96  func newVCSRepo(ctx context.Context, vcs, remote string, local bool) (Repo, error) {
    97  	if vcs == "git" {
    98  		return newGitRepo(ctx, remote, local)
    99  	}
   100  	r := &vcsRepo{remote: remote, local: local}
   101  	cmd := vcsCmds[vcs]
   102  	if cmd == nil {
   103  		return nil, fmt.Errorf("unknown vcs: %s %s", vcs, remote)
   104  	}
   105  	r.cmd = cmd
   106  	if local {
   107  		info, err := os.Stat(remote)
   108  		if err != nil {
   109  			return nil, err
   110  		}
   111  		if !info.IsDir() {
   112  			return nil, fmt.Errorf("%s exists but is not a directory", remote)
   113  		}
   114  		r.dir = remote
   115  		r.mu.Path = r.dir + ".lock"
   116  		return r, nil
   117  	}
   118  	if !strings.Contains(remote, "://") {
   119  		return nil, fmt.Errorf("invalid vcs remote: %s %s", vcs, remote)
   120  	}
   121  	var err error
   122  	r.dir, r.mu.Path, err = WorkDir(ctx, vcsWorkDirType+vcs, r.remote)
   123  	if err != nil {
   124  		return nil, err
   125  	}
   126  
   127  	if cmd.init == nil {
   128  		return r, nil
   129  	}
   130  
   131  	unlock, err := r.mu.Lock()
   132  	if err != nil {
   133  		return nil, err
   134  	}
   135  	defer unlock()
   136  
   137  	if _, err := os.Stat(filepath.Join(r.dir, "."+vcs)); err != nil {
   138  		release, err := base.AcquireNet()
   139  		if err != nil {
   140  			return nil, err
   141  		}
   142  		_, err = Run(ctx, r.dir, cmd.init(r.remote))
   143  		if err == nil && cmd.postInit != nil {
   144  			err = cmd.postInit(ctx, r)
   145  		}
   146  		release()
   147  
   148  		if err != nil {
   149  			os.RemoveAll(r.dir)
   150  			return nil, err
   151  		}
   152  	}
   153  	return r, nil
   154  }
   155  
   156  const vcsWorkDirType = "vcs1."
   157  
   158  type vcsCmd struct {
   159  	vcs                string                                            // vcs name "hg"
   160  	init               func(remote string) []string                      // cmd to init repo to track remote
   161  	postInit           func(context.Context, *vcsRepo) error             // func to init repo after .init runs
   162  	repoSum            func(remote string) []string                      // cmd to calculate reposum of remote repo
   163  	lookupRef          func(remote, ref string) []string                 // cmd to look up ref in remote repo
   164  	tags               func(remote string) []string                      // cmd to list local tags
   165  	tagsNeedsFetch     bool                                              // run fetch before tags
   166  	tagRE              *lazyregexp.Regexp                                // regexp to extract tag names from output of tags cmd
   167  	branches           func(remote string) []string                      // cmd to list local branches
   168  	branchesNeedsFetch bool                                              // run branches before tags
   169  	branchRE           *lazyregexp.Regexp                                // regexp to extract branch names from output of tags cmd
   170  	badLocalRevRE      *lazyregexp.Regexp                                // regexp of names that must not be served out of local cache without doing fetch first
   171  	statLocal          func(rev, remote string) []string                 // cmd to stat local rev
   172  	parseStat          func(rev, out string) (*RevInfo, error)           // func to parse output of statLocal
   173  	fetch              []string                                          // cmd to fetch everything from remote
   174  	latest             string                                            // name of latest commit on remote (tip, HEAD, etc)
   175  	descendsFrom       func(rev, tag string) []string                    // cmd to check whether rev descends from tag
   176  	recentTags         func(rev string) []string                         // cmd to print tag ancestors of rev
   177  	readFile           func(rev, file, remote string) []string           // cmd to read rev's file
   178  	readZip            func(rev, subdir, remote, target string) []string // cmd to read rev's subdir as zip file
   179  
   180  	// arbitrary function to read rev's subdir as zip file
   181  	doReadZip func(ctx context.Context, dst io.Writer, workDir, rev, subdir, remote string) error
   182  }
   183  
   184  var re = lazyregexp.New
   185  
   186  var vcsCmds = map[string]*vcsCmd{
   187  	"hg": {
   188  		vcs: "hg",
   189  		repoSum: func(remote string) []string {
   190  			return []string{
   191  				"hg",
   192  				"--config=extensions.goreposum=" + filepath.Join(cfg.GOROOT, "lib/hg/goreposum.py"),
   193  				"goreposum",
   194  				"--",
   195  				remote,
   196  			}
   197  		},
   198  		lookupRef: func(remote, ref string) []string {
   199  			return []string{
   200  				"hg",
   201  				"--config=extensions.goreposum=" + filepath.Join(cfg.GOROOT, "lib/hg/goreposum.py"),
   202  				"golookup",
   203  				"--",
   204  				remote,
   205  				ref,
   206  			}
   207  		},
   208  		init: func(remote string) []string {
   209  			return []string{"hg", "init", "."}
   210  		},
   211  		postInit: hgAddRemote,
   212  		tags: func(remote string) []string {
   213  			return []string{"hg", "tags", "-q"}
   214  		},
   215  		tagsNeedsFetch: true,
   216  		tagRE:          re(`(?m)^[^\n]+$`),
   217  		branches: func(remote string) []string {
   218  			return []string{"hg", "branches", "-c", "-q"}
   219  		},
   220  		branchesNeedsFetch: true,
   221  		branchRE:           re(`(?m)^[^\n]+$`),
   222  		badLocalRevRE:      re(`(?m)^(tip)$`),
   223  		statLocal: func(rev, remote string) []string {
   224  			return []string{"hg", "log", "-l1", fmt.Sprintf("--rev=%s", rev), "--template", "{node} {date|hgdate} {tags}"}
   225  		},
   226  		parseStat: hgParseStat,
   227  		fetch:     []string{"hg", "pull", "-f"},
   228  		latest:    "tip",
   229  		descendsFrom: func(rev, tag string) []string {
   230  			return []string{"hg", "log", "--rev=ancestors(" + rev + ") and " + tag}
   231  		},
   232  		recentTags: func(rev string) []string {
   233  			return []string{"hg", "log", "--rev=ancestors(" + rev + ") and tag()", "--template", "{tags}\n"}
   234  		},
   235  		readFile: func(rev, file, remote string) []string {
   236  			return []string{"hg", "cat", fmt.Sprintf("--rev=%s", rev), "--", file}
   237  		},
   238  		readZip: func(rev, subdir, remote, target string) []string {
   239  			pattern := []string{}
   240  			if subdir != "" {
   241  				pattern = []string{fmt.Sprintf("--include=%s", subdir+"/**")}
   242  			}
   243  			return str.StringList("hg", "archive", "-t", "zip", "--no-decode", fmt.Sprintf("--rev=%s", rev), "--prefix=prefix/", pattern, "--", target)
   244  		},
   245  	},
   246  
   247  	"svn": {
   248  		vcs:  "svn",
   249  		init: nil, // no local checkout
   250  		tags: func(remote string) []string {
   251  			return []string{"svn", "list", "--", strings.TrimSuffix(remote, "/trunk") + "/tags"}
   252  		},
   253  		tagRE: re(`(?m)^(.*?)/?$`),
   254  		statLocal: func(rev, remote string) []string {
   255  			suffix := "@" + rev
   256  			if rev == "latest" {
   257  				suffix = ""
   258  			}
   259  			return []string{"svn", "log", "-l1", "--xml", "--", remote + suffix}
   260  		},
   261  		parseStat: svnParseStat,
   262  		latest:    "latest",
   263  		readFile: func(rev, file, remote string) []string {
   264  			return []string{"svn", "cat", "--", remote + "/" + file + "@" + rev}
   265  		},
   266  		doReadZip: svnReadZip,
   267  	},
   268  
   269  	"bzr": {
   270  		vcs: "bzr",
   271  		init: func(remote string) []string {
   272  			return []string{"bzr", "branch", "--use-existing-dir", "--", remote, "."}
   273  		},
   274  		fetch: []string{
   275  			"bzr", "pull", "--overwrite-tags",
   276  		},
   277  		tags: func(remote string) []string {
   278  			return []string{"bzr", "tags"}
   279  		},
   280  		tagRE:         re(`(?m)^\S+`),
   281  		badLocalRevRE: re(`^revno:-`),
   282  		statLocal: func(rev, remote string) []string {
   283  			return []string{"bzr", "log", "-l1", "--long", "--show-ids", fmt.Sprintf("--revision=%s", rev)}
   284  		},
   285  		parseStat: bzrParseStat,
   286  		latest:    "revno:-1",
   287  		readFile: func(rev, file, remote string) []string {
   288  			return []string{"bzr", "cat", fmt.Sprintf("--revision=%s", rev), "--", file}
   289  		},
   290  		readZip: func(rev, subdir, remote, target string) []string {
   291  			extra := []string{}
   292  			if subdir != "" {
   293  				extra = []string{"./" + subdir}
   294  			}
   295  			return str.StringList("bzr", "export", "--format=zip", fmt.Sprintf("--revision=%s", rev), "--root=prefix/", "--", target, extra)
   296  		},
   297  	},
   298  
   299  	"fossil": {
   300  		vcs: "fossil",
   301  		init: func(remote string) []string {
   302  			return []string{"fossil", "clone", "--", remote, ".fossil"}
   303  		},
   304  		fetch: []string{"fossil", "pull", "-R", ".fossil"},
   305  		tags: func(remote string) []string {
   306  			return []string{"fossil", "tag", "-R", ".fossil", "list"}
   307  		},
   308  		tagRE: re(`XXXTODO`),
   309  		statLocal: func(rev, remote string) []string {
   310  			return []string{"fossil", "info", "-R", ".fossil", "--", rev}
   311  		},
   312  		parseStat: fossilParseStat,
   313  		latest:    "trunk",
   314  		readFile: func(rev, file, remote string) []string {
   315  			return []string{"fossil", "cat", "-R", ".fossil", fmt.Sprintf("-r=%s", rev), "--", file}
   316  		},
   317  		readZip: func(rev, subdir, remote, target string) []string {
   318  			extra := []string{}
   319  			if subdir != "" && !strings.ContainsAny(subdir, "*?[],") {
   320  				extra = []string{fmt.Sprintf("--include=%s", subdir)}
   321  			}
   322  			// Note that vcsRepo.ReadZip below rewrites this command
   323  			// to run in a different directory, to work around a fossil bug.
   324  			return str.StringList("fossil", "zip", "-R", ".fossil", "--name", "prefix", extra, "--", rev, target)
   325  		},
   326  	},
   327  }
   328  
   329  func (r *vcsRepo) loadTags(ctx context.Context) {
   330  	if r.cmd.tagsNeedsFetch {
   331  		r.fetchOnce.Do(func() { r.fetch(ctx) })
   332  	}
   333  
   334  	out, err := Run(ctx, r.dir, r.cmd.tags(r.remote))
   335  	if err != nil {
   336  		return
   337  	}
   338  
   339  	// Run tag-listing command and extract tags.
   340  	r.tags = make(map[string]bool)
   341  	for _, tag := range r.cmd.tagRE.FindAllString(string(out), -1) {
   342  		if r.cmd.badLocalRevRE != nil && r.cmd.badLocalRevRE.MatchString(tag) {
   343  			continue
   344  		}
   345  		r.tags[tag] = true
   346  	}
   347  }
   348  
   349  func (r *vcsRepo) loadBranches(ctx context.Context) {
   350  	if r.cmd.branches == nil {
   351  		return
   352  	}
   353  
   354  	if r.cmd.branchesNeedsFetch {
   355  		r.fetchOnce.Do(func() { r.fetch(ctx) })
   356  	}
   357  
   358  	out, err := Run(ctx, r.dir, r.cmd.branches(r.remote))
   359  	if err != nil {
   360  		return
   361  	}
   362  
   363  	r.branches = make(map[string]bool)
   364  	for _, branch := range r.cmd.branchRE.FindAllString(string(out), -1) {
   365  		if r.cmd.badLocalRevRE != nil && r.cmd.badLocalRevRE.MatchString(branch) {
   366  			continue
   367  		}
   368  		r.branches[branch] = true
   369  	}
   370  }
   371  
   372  func (r *vcsRepo) loadRepoSum(ctx context.Context) {
   373  	if r.cmd.repoSum == nil {
   374  		return
   375  	}
   376  	where := r.remote
   377  	if r.fetched.Load() {
   378  		where = "." // use local repo
   379  	}
   380  	out, err := Run(ctx, r.dir, r.cmd.repoSum(where))
   381  	if err != nil {
   382  		return
   383  	}
   384  	r.repoSum = strings.TrimSpace(string(out))
   385  }
   386  
   387  func (r *vcsRepo) lookupRef(ctx context.Context, ref string) (string, error) {
   388  	if r.cmd.lookupRef == nil {
   389  		return "", fmt.Errorf("no lookupRef")
   390  	}
   391  	out, err := Run(ctx, r.dir, r.cmd.lookupRef(r.remote, ref))
   392  	if err != nil {
   393  		return "", err
   394  	}
   395  	return strings.TrimSpace(string(out)), nil
   396  }
   397  
   398  // repoSumOrigin returns an Origin containing a RepoSum.
   399  func (r *vcsRepo) repoSumOrigin(ctx context.Context) *Origin {
   400  	origin := &Origin{
   401  		VCS:     r.cmd.vcs,
   402  		URL:     r.remote,
   403  		RepoSum: r.repoSum,
   404  	}
   405  	r.repoSumOnce.Do(func() { r.loadRepoSum(ctx) })
   406  	origin.RepoSum = r.repoSum
   407  	return origin
   408  }
   409  
   410  func (r *vcsRepo) CheckReuse(ctx context.Context, old *Origin, subdir string) error {
   411  	if old == nil {
   412  		return fmt.Errorf("missing origin")
   413  	}
   414  	if old.VCS != r.cmd.vcs || old.URL != r.remote {
   415  		return fmt.Errorf("origin moved from %v %q to %v %q", old.VCS, old.URL, r.cmd.vcs, r.remote)
   416  	}
   417  	if old.Subdir != subdir {
   418  		return fmt.Errorf("origin moved from %v %q %q to %v %q %q", old.VCS, old.URL, old.Subdir, r.cmd.vcs, r.remote, subdir)
   419  	}
   420  
   421  	if old.Ref == "" && old.RepoSum == "" && old.Hash != "" {
   422  		// Hash has to remain in repo.
   423  		hash, err := r.lookupRef(ctx, old.Hash)
   424  		if err == nil && hash == old.Hash {
   425  			return nil
   426  		}
   427  		if err != nil {
   428  			return fmt.Errorf("looking up hash: %v", err)
   429  		}
   430  		return fmt.Errorf("hash changed") // weird but maybe they made a tag
   431  	}
   432  
   433  	if old.Ref != "" && old.RepoSum == "" {
   434  		hash, err := r.lookupRef(ctx, old.Ref)
   435  		if err == nil && hash != "" && hash == old.Hash {
   436  			return nil
   437  		}
   438  	}
   439  
   440  	r.repoSumOnce.Do(func() { r.loadRepoSum(ctx) })
   441  	if r.repoSum != "" {
   442  		if old.RepoSum == "" {
   443  			return fmt.Errorf("non-specific origin")
   444  		}
   445  		if old.RepoSum != r.repoSum {
   446  			return fmt.Errorf("repo changed")
   447  		}
   448  		return nil
   449  	}
   450  	return fmt.Errorf("vcs %s: CheckReuse: %w", r.cmd.vcs, errors.ErrUnsupported)
   451  }
   452  
   453  func (r *vcsRepo) Tags(ctx context.Context, prefix string) (*Tags, error) {
   454  	unlock, err := r.mu.Lock()
   455  	if err != nil {
   456  		return nil, err
   457  	}
   458  	defer unlock()
   459  
   460  	r.tagsOnce.Do(func() { r.loadTags(ctx) })
   461  	tags := &Tags{
   462  		Origin: r.repoSumOrigin(ctx),
   463  		List:   []Tag{},
   464  	}
   465  	for tag := range r.tags {
   466  		if strings.HasPrefix(tag, prefix) {
   467  			tags.List = append(tags.List, Tag{tag, ""})
   468  		}
   469  	}
   470  	sort.Slice(tags.List, func(i, j int) bool {
   471  		return tags.List[i].Name < tags.List[j].Name
   472  	})
   473  	return tags, nil
   474  }
   475  
   476  func (r *vcsRepo) Stat(ctx context.Context, rev string) (*RevInfo, error) {
   477  	return r.statCache.Do(rev, func() (*RevInfo, error) {
   478  		unlock, err := r.mu.Lock()
   479  		if err != nil {
   480  			return nil, err
   481  		}
   482  		defer unlock()
   483  
   484  		if rev == "latest" {
   485  			rev = r.cmd.latest
   486  		}
   487  		r.branchesOnce.Do(func() { r.loadBranches(ctx) })
   488  		if r.local {
   489  			// Ignore the badLocalRevRE precondition in local only mode.
   490  			// We cannot fetch latest upstream changes so only serve what's in the local cache.
   491  			return r.statLocal(ctx, rev)
   492  		}
   493  		revOK := (r.cmd.badLocalRevRE == nil || !r.cmd.badLocalRevRE.MatchString(rev)) && !r.branches[rev]
   494  		if revOK {
   495  			if info, err := r.statLocal(ctx, rev); err == nil {
   496  				return info, nil
   497  			}
   498  		}
   499  
   500  		r.fetchOnce.Do(func() { r.fetch(ctx) })
   501  		if r.fetchErr != nil {
   502  			return nil, r.fetchErr
   503  		}
   504  		info, err := r.statLocal(ctx, rev)
   505  		if err != nil {
   506  			return info, err
   507  		}
   508  		if !revOK {
   509  			info.Version = info.Name
   510  		}
   511  		return info, nil
   512  	})
   513  }
   514  
   515  func (r *vcsRepo) fetch(ctx context.Context) {
   516  	if len(r.cmd.fetch) > 0 {
   517  		release, err := base.AcquireNet()
   518  		if err != nil {
   519  			r.fetchErr = err
   520  			return
   521  		}
   522  		_, r.fetchErr = Run(ctx, r.dir, r.cmd.fetch)
   523  		release()
   524  		r.fetched.Store(true)
   525  	}
   526  }
   527  
   528  func (r *vcsRepo) statLocal(ctx context.Context, rev string) (*RevInfo, error) {
   529  	out, err := Run(ctx, r.dir, r.cmd.statLocal(rev, r.remote))
   530  	if err != nil {
   531  		info := &RevInfo{Origin: r.repoSumOrigin(ctx)}
   532  		return info, &UnknownRevisionError{Rev: rev}
   533  	}
   534  	info, err := r.cmd.parseStat(rev, string(out))
   535  	if err != nil {
   536  		return nil, err
   537  	}
   538  	if info.Origin == nil {
   539  		info.Origin = new(Origin)
   540  	}
   541  	info.Origin.VCS = r.cmd.vcs
   542  	info.Origin.URL = r.remote
   543  	info.Origin.Ref = rev
   544  	if strings.HasPrefix(info.Name, rev) && len(rev) >= 12 {
   545  		info.Origin.Ref = "" // duplicates Hash
   546  	}
   547  	return info, nil
   548  }
   549  
   550  func (r *vcsRepo) Latest(ctx context.Context) (*RevInfo, error) {
   551  	return r.Stat(ctx, "latest")
   552  }
   553  
   554  func (r *vcsRepo) ReadFile(ctx context.Context, rev, file string, maxSize int64) ([]byte, error) {
   555  	return r.readFileCache.Do([2]string{rev, file}, func() ([]byte, error) {
   556  		if rev == "latest" {
   557  			rev = r.cmd.latest
   558  		}
   559  		_, err := r.Stat(ctx, rev) // download rev into local repo
   560  		if err != nil {
   561  			return nil, err
   562  		}
   563  
   564  		// r.Stat acquires r.mu, so lock after that.
   565  		unlock, err := r.mu.Lock()
   566  		if err != nil {
   567  			return nil, err
   568  		}
   569  		defer unlock()
   570  
   571  		out, err := Run(ctx, r.dir, r.cmd.readFile(rev, file, r.remote))
   572  		if err != nil {
   573  			return nil, fs.ErrNotExist
   574  		}
   575  		return out, nil
   576  	})
   577  }
   578  
   579  func (r *vcsRepo) RecentTag(ctx context.Context, rev, prefix string, allowed func(string) bool) (tag string, err error) {
   580  	// Only lock for the subprocess execution, not for the tag scan.
   581  	// allowed may call other methods that acquire the lock.
   582  	unlock, err := r.mu.Lock()
   583  	if err != nil {
   584  		return "", err
   585  	}
   586  
   587  	if r.cmd.recentTags == nil {
   588  		unlock()
   589  		return "", vcsErrorf("vcs %s: RecentTag: %w", r.cmd.vcs, errors.ErrUnsupported)
   590  	}
   591  	out, err := Run(ctx, r.dir, r.cmd.recentTags(rev))
   592  	unlock()
   593  	if err != nil {
   594  		return "", err
   595  	}
   596  
   597  	highest := ""
   598  	for _, tag := range strings.Fields(string(out)) {
   599  		if !strings.HasPrefix(tag, prefix) || !allowed(tag) {
   600  			continue
   601  		}
   602  		semtag := tag[len(prefix):]
   603  		if semver.Compare(semtag, highest) > 0 {
   604  			highest = semtag
   605  		}
   606  	}
   607  	if highest != "" {
   608  		return prefix + highest, nil
   609  	}
   610  	return "", nil
   611  }
   612  
   613  func (r *vcsRepo) DescendsFrom(ctx context.Context, rev, tag string) (bool, error) {
   614  	unlock, err := r.mu.Lock()
   615  	if err != nil {
   616  		return false, err
   617  	}
   618  	defer unlock()
   619  
   620  	if r.cmd.descendsFrom == nil {
   621  		return false, vcsErrorf("vcs %s: DescendsFrom: %w", r.cmd.vcs, errors.ErrUnsupported)
   622  	}
   623  
   624  	out, err := Run(ctx, r.dir, r.cmd.descendsFrom(rev, tag))
   625  	if err != nil {
   626  		return false, err
   627  	}
   628  	return strings.TrimSpace(string(out)) != "", nil
   629  }
   630  
   631  func (r *vcsRepo) ReadZip(ctx context.Context, rev, subdir string, maxSize int64) (zip io.ReadCloser, err error) {
   632  	if r.cmd.readZip == nil && r.cmd.doReadZip == nil {
   633  		return nil, vcsErrorf("vcs %s: ReadZip: %w", r.cmd.vcs, errors.ErrUnsupported)
   634  	}
   635  
   636  	if rev == "latest" {
   637  		rev = r.cmd.latest
   638  	}
   639  	_, err = r.Stat(ctx, rev) // download rev into local repo
   640  	if err != nil {
   641  		return nil, err
   642  	}
   643  
   644  	unlock, err := r.mu.Lock()
   645  	if err != nil {
   646  		return nil, err
   647  	}
   648  	defer unlock()
   649  
   650  	f, err := os.CreateTemp("", "go-readzip-*.zip")
   651  	if err != nil {
   652  		return nil, err
   653  	}
   654  	if r.cmd.doReadZip != nil {
   655  		lw := &limitedWriter{
   656  			W:               f,
   657  			N:               maxSize,
   658  			ErrLimitReached: errors.New("ReadZip: encoded file exceeds allowed size"),
   659  		}
   660  		err = r.cmd.doReadZip(ctx, lw, r.dir, rev, subdir, r.remote)
   661  		if err == nil {
   662  			_, err = f.Seek(0, io.SeekStart)
   663  		}
   664  	} else if r.cmd.vcs == "fossil" {
   665  		// If you run
   666  		//	fossil zip -R .fossil --name prefix trunk /tmp/x.zip
   667  		// fossil fails with "unable to create directory /tmp" [sic].
   668  		// Change the command to run in /tmp instead,
   669  		// replacing the -R argument with an absolute path.
   670  		args := r.cmd.readZip(rev, subdir, r.remote, filepath.Base(f.Name()))
   671  		for i := range args {
   672  			if args[i] == ".fossil" {
   673  				args[i] = filepath.Join(r.dir, ".fossil")
   674  			}
   675  		}
   676  		_, err = Run(ctx, filepath.Dir(f.Name()), args)
   677  	} else {
   678  		_, err = Run(ctx, r.dir, r.cmd.readZip(rev, subdir, r.remote, f.Name()))
   679  	}
   680  	if err != nil {
   681  		f.Close()
   682  		os.Remove(f.Name())
   683  		return nil, err
   684  	}
   685  	return &deleteCloser{f}, nil
   686  }
   687  
   688  // deleteCloser is a file that gets deleted on Close.
   689  type deleteCloser struct {
   690  	*os.File
   691  }
   692  
   693  func (d *deleteCloser) Close() error {
   694  	defer os.Remove(d.File.Name())
   695  	return d.File.Close()
   696  }
   697  
   698  func hgAddRemote(ctx context.Context, r *vcsRepo) error {
   699  	// Write .hg/hgrc with remote URL in it.
   700  	return os.WriteFile(filepath.Join(r.dir, ".hg/hgrc"), []byte(fmt.Sprintf("[paths]\ndefault = %s\n", r.remote)), 0666)
   701  }
   702  
   703  func hgParseStat(rev, out string) (*RevInfo, error) {
   704  	f := strings.Fields(out)
   705  	if len(f) < 3 {
   706  		return nil, vcsErrorf("unexpected response from hg log: %q", out)
   707  	}
   708  	hash := f[0]
   709  	version := rev
   710  	if strings.HasPrefix(hash, version) {
   711  		version = hash // extend to full hash
   712  	}
   713  	t, err := strconv.ParseInt(f[1], 10, 64)
   714  	if err != nil {
   715  		return nil, vcsErrorf("invalid time from hg log: %q", out)
   716  	}
   717  
   718  	var tags []string
   719  	for _, tag := range f[3:] {
   720  		if tag != "tip" {
   721  			tags = append(tags, tag)
   722  		}
   723  	}
   724  	sort.Strings(tags)
   725  
   726  	info := &RevInfo{
   727  		Origin:  &Origin{Hash: hash},
   728  		Name:    hash,
   729  		Short:   ShortenSHA1(hash),
   730  		Time:    time.Unix(t, 0).UTC(),
   731  		Version: version,
   732  		Tags:    tags,
   733  	}
   734  	return info, nil
   735  }
   736  
   737  func bzrParseStat(rev, out string) (*RevInfo, error) {
   738  	var revno int64
   739  	var tm time.Time
   740  	var tags []string
   741  	for line := range strings.SplitSeq(out, "\n") {
   742  		if line == "" || line[0] == ' ' || line[0] == '\t' {
   743  			// End of header, start of commit message.
   744  			break
   745  		}
   746  		if line[0] == '-' {
   747  			continue
   748  		}
   749  		before, after, found := strings.Cut(line, ":")
   750  		if !found {
   751  			// End of header, start of commit message.
   752  			break
   753  		}
   754  		key, val := before, strings.TrimSpace(after)
   755  		switch key {
   756  		case "revno":
   757  			if j := strings.Index(val, " "); j >= 0 {
   758  				val = val[:j]
   759  			}
   760  			i, err := strconv.ParseInt(val, 10, 64)
   761  			if err != nil {
   762  				return nil, vcsErrorf("unexpected revno from bzr log: %q", line)
   763  			}
   764  			revno = i
   765  		case "timestamp":
   766  			j := strings.Index(val, " ")
   767  			if j < 0 {
   768  				return nil, vcsErrorf("unexpected timestamp from bzr log: %q", line)
   769  			}
   770  			t, err := time.Parse("2006-01-02 15:04:05 -0700", val[j+1:])
   771  			if err != nil {
   772  				return nil, vcsErrorf("unexpected timestamp from bzr log: %q", line)
   773  			}
   774  			tm = t.UTC()
   775  		case "tags":
   776  			tags = strings.Split(val, ", ")
   777  		}
   778  	}
   779  	if revno == 0 || tm.IsZero() {
   780  		return nil, vcsErrorf("unexpected response from bzr log: %q", out)
   781  	}
   782  
   783  	info := &RevInfo{
   784  		Name:    strconv.FormatInt(revno, 10),
   785  		Short:   fmt.Sprintf("%012d", revno),
   786  		Time:    tm,
   787  		Version: rev,
   788  		Tags:    tags,
   789  	}
   790  	return info, nil
   791  }
   792  
   793  func fossilParseStat(rev, out string) (*RevInfo, error) {
   794  	for line := range strings.SplitSeq(out, "\n") {
   795  		if strings.HasPrefix(line, "uuid:") || strings.HasPrefix(line, "hash:") {
   796  			f := strings.Fields(line)
   797  			if len(f) != 5 || len(f[1]) != 40 || f[4] != "UTC" {
   798  				return nil, vcsErrorf("unexpected response from fossil info: %q", line)
   799  			}
   800  			t, err := time.Parse(time.DateTime, f[2]+" "+f[3])
   801  			if err != nil {
   802  				return nil, vcsErrorf("unexpected response from fossil info: %q", line)
   803  			}
   804  			hash := f[1]
   805  			version := rev
   806  			if strings.HasPrefix(hash, version) {
   807  				version = hash // extend to full hash
   808  			}
   809  			info := &RevInfo{
   810  				Origin:  &Origin{Hash: hash},
   811  				Name:    hash,
   812  				Short:   ShortenSHA1(hash),
   813  				Time:    t,
   814  				Version: version,
   815  			}
   816  			return info, nil
   817  		}
   818  	}
   819  	return nil, vcsErrorf("unexpected response from fossil info: %q", out)
   820  }
   821  
   822  type limitedWriter struct {
   823  	W               io.Writer
   824  	N               int64
   825  	ErrLimitReached error
   826  }
   827  
   828  func (l *limitedWriter) Write(p []byte) (n int, err error) {
   829  	if l.N > 0 {
   830  		max := len(p)
   831  		if l.N < int64(max) {
   832  			max = int(l.N)
   833  		}
   834  		n, err = l.W.Write(p[:max])
   835  		l.N -= int64(n)
   836  		if err != nil || n >= len(p) {
   837  			return n, err
   838  		}
   839  	}
   840  
   841  	return n, l.ErrLimitReached
   842  }
   843
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