golang
diff --git a/‎doc/go1.13.html
+58 b/‎doc/go1.13.html
+58
diff --git a/‎src/cmd/go/internal/modconv/convert_test.go
+1-1 b/‎src/cmd/go/internal/modconv/convert_test.go
+1-1
diff --git a/‎src/cmd/go/internal/modfetch/cache.go
+5-13 b/‎src/cmd/go/internal/modfetch/cache.go
+5-13
diff --git a/‎src/cmd/go/internal/modfetch/codehost/codehost.go
+24-8 b/‎src/cmd/go/internal/modfetch/codehost/codehost.go
+24-8
diff --git a/‎src/cmd/go/internal/modfetch/codehost/git.go
+88-17 b/‎src/cmd/go/internal/modfetch/codehost/git.go
+88-17
diff --git a/‎src/cmd/go/internal/modfetch/codehost/vcs.go
+12-2 b/‎src/cmd/go/internal/modfetch/codehost/vcs.go
+12-2
@@ -161,6 +161,64 @@ <h2 id="tools">Tools</h2>
 TODO
 </p>
 
+<h3 id="modules">Modules</h3>
+
+<h4 id="version-validation">Version validation</h4><!-- CL 181881 -->
+
+<p>
+  When extracting a module from a version control system, the <code>go</code>
+  command now performs additional validation on the requested version string.
+</p>
+
+<p>
+  The <code>+incompatible</code> version annotation bypasses the requirement
+  of <a href="/cmd/go/#hdr-Module_compatibility_and_semantic_versioning">semantic
+  import versioning</a> for repositories that predate the introduction of
+  modules. The <code>go</code> command now verifies that such a version does not
+  include an explicit <code>go.mod</code> file.
+</p>
+
+<p>
+  The <code>go</code> command now verifies the mapping
+  between <a href="/cmd/go#hdr-Pseudo_versions">pseudo-versions</a> and
+  version-control metadata. Specifically:
+  <ul>
+    <li>The version prefix must be derived from a tag on the named revision or
+    one of its ancestors, or be of the form <code>vX.0.0</code>.</li>
+
+    <li>The date string must match the UTC timestamp of the revision.</li>
+
+    <li>The short name of the revision must use the same number of characters as
+    what the <code>go</code> command would generate. (For SHA-1 hashes as used
+    by <code>git</code>, a 12-digit prefix.)</li>
+  </ul>
+</p>
+
+<p>
+  If the main module directly requires a version that fails the above
+  validation, a corrected version can be obtained by redacting the version to
+  just the commit hash and re-running a <code>go</code> command such as <code>go
+  list -m all</code> or <code>go mod tidy</code>. For example,
+  <pre>require github.com/docker/docker v1.14.0-0.20190319215453-e7b5f7dbe98c</pre>
+      can be redacted to
+  <pre>require github.com/docker/docker e7b5f7dbe98c</pre>
+  which resolves to
+  <pre>require github.com/docker/docker v0.7.3-0.20190319215453-e7b5f7dbe98c</pre>
+</p>
+
+<p>
+  If the main module has a transitive requirement on a version that fails
+  validation, the invalid version can still be replaced with a valid one through
+  the use of a <a href="/cmd/go/#hdr-The_go_mod_file"><code>replace</code>
+  directive</a> in the <code>go.mod</code> file of
+  the <a href="/cmd/go/#hdr-The_main_module_and_the_build_list">main module</a>.
+  If the replacement is a commit hash, it will be resolved to the appropriate
+  pseudo-version. For example,
+  <pre>replace github.com/docker/docker v1.14.0-0.20190319215453-e7b5f7dbe98c => github.com/docker/docker e7b5f7dbe98c</pre>
+  resolves to
+  <pre>replace github.com/docker/docker v1.14.0-0.20190319215453-e7b5f7dbe98c => github.com/docker/docker v0.7.3-0.20190319215453-e7b5f7dbe98c</pre>
+</p>
+
 <h3 id="compiler">Compiler toolchain</h3>
 
 <p><!-- CL 170448 -->
 
@@ -128,7 +128,7 @@ func TestConvertLegacyConfig(t *testing.T) {
 
 		{
 			// golang.org/issue/24585 - confusion about v2.0.0 tag in legacy non-v2 module
-			"github.com/fishy/gcsbucket", "v0.0.0-20150410205453-618d60fe84e0",
+			"github.com/fishy/gcsbucket", "v0.0.0-20180217031846-618d60fe84e0",
 			`module github.com/fishy/gcsbucket
 
 			require (
 
@@ -216,29 +216,21 @@ func (r *cachingRepo) Latest() (*RevInfo, error) {
 	return &info, nil
 }
 
-func (r *cachingRepo) GoMod(rev string) ([]byte, error) {
+func (r *cachingRepo) GoMod(version string) ([]byte, error) {
 	type cached struct {
 		text []byte
 		err  error
 	}
-	c := r.cache.Do("gomod:"+rev, func() interface{} {
-		file, text, err := readDiskGoMod(r.path, rev)
+	c := r.cache.Do("gomod:"+version, func() interface{} {
+		file, text, err := readDiskGoMod(r.path, version)
 		if err == nil {
 			// Note: readDiskGoMod already called checkGoMod.
 			return cached{text, nil}
 		}
 
-		// Convert rev to canonical version
-		// so that we use the right identifier in the go.sum check.
-		info, err := r.Stat(rev)
-		if err != nil {
-			return cached{nil, err}
-		}
-		rev = info.Version
-
-		text, err = r.r.GoMod(rev)
+		text, err = r.r.GoMod(version)
 		if err == nil {
-			checkGoMod(r.path, rev, text)
+			checkGoMod(r.path, version, text)
 			if err := writeDiskGoMod(file, text); err != nil {
 				fmt.Fprintf(os.Stderr, "go: writing go.mod cache: %v\n", err)
 			}
 
@@ -79,14 +79,16 @@ type Repo interface {
 	// nested in a single top-level directory, whose name is not specified.
 	ReadZip(rev, subdir string, maxSize int64) (zip io.ReadCloser, actualSubdir string, err error)
 
-	// RecentTag returns the most recent tag at or before the given rev
-	// with the given prefix. It should make a best-effort attempt to
-	// find a tag that is a valid semantic version (following the prefix),
-	// or else the result is not useful to the caller, but it need not
-	// incur great expense in doing so. For example, the git implementation
-	// of RecentTag limits git's search to tags matching the glob expression
-	// "v[0-9]*.[0-9]*.[0-9]*" (after the prefix).
-	RecentTag(rev, prefix string) (tag string, err error)
+	// RecentTag returns the most recent tag on rev or one of its predecessors
+	// with the given prefix and major version.
+	// An empty major string matches any major version.
+	RecentTag(rev, prefix, major string) (tag string, err error)
+
+	// DescendsFrom reports whether rev or any of its ancestors has the given tag.
+	//
+	// DescendsFrom must return true for any tag returned by RecentTag for the
+	// same revision.
+	DescendsFrom(rev, tag string) (bool, error)
 }
 
 // A Rev describes a single revision in a source code repository.
@@ -105,6 +107,20 @@ type FileRev struct {
 	Err  error  // error if any; os.IsNotExist(Err)==true if rev exists but file does not exist in that rev
 }
 
+// UnknownRevisionError is an error equivalent to os.ErrNotExist, but for a
+// revision rather than a file.
+type UnknownRevisionError struct {
+	Rev string
+}
+
+func (e *UnknownRevisionError) Error() string {
+	return "unknown revision " + e.Rev
+}
+
+func (e *UnknownRevisionError) Is(err error) bool {
+	return err == os.ErrNotExist
+}
+
 // AllHex reports whether the revision rev is entirely lower-case hexadecimal digits.
 func AllHex(rev string) bool {
 	for i := 0; i < len(rev); i++ {
 
@@ -10,6 +10,7 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"sort"
 	"strconv"
@@ -318,7 +319,7 @@ func (r *gitRepo) stat(rev string) (*RevInfo, error) {
 			hash = rev
 		}
 	} else {
-		return nil, fmt.Errorf("unknown revision %s", rev)
+		return nil, &UnknownRevisionError{Rev: rev}
 	}
 
 	// Protect r.fetchLevel and the "fetch more and more" sequence.
@@ -378,17 +379,30 @@ func (r *gitRepo) stat(rev string) (*RevInfo, error) {
 
 	// Last resort.
 	// Fetch all heads and tags and hope the hash we want is in the history.
+	if err := r.fetchRefsLocked(); err != nil {
+		return nil, err
+	}
+
+	return r.statLocal(rev, rev)
+}
+
+// fetchRefsLocked fetches all heads and tags from the origin, along with the
+// ancestors of those commits.
+//
+// We only fetch heads and tags, not arbitrary other commits: we don't want to
+// pull in off-branch commits (such as rejected GitHub pull requests) that the
+// server may be willing to provide. (See the comments within the stat method
+// for more detail.)
+//
+// fetchRefsLocked requires that r.mu remain locked for the duration of the call.
+func (r *gitRepo) fetchRefsLocked() error {
 	if r.fetchLevel < fetchAll {
-		// TODO(bcmills): should we wait to upgrade fetchLevel until after we check
-		// err? If there is a temporary server error, we want subsequent fetches to
-		// try again instead of proceeding with an incomplete repo.
-		r.fetchLevel = fetchAll
 		if err := r.fetchUnshallow("refs/heads/*:refs/heads/*", "refs/tags/*:refs/tags/*"); err != nil {
-			return nil, err
+			return err
 		}
+		r.fetchLevel = fetchAll
 	}
-
-	return r.statLocal(rev, rev)
+	return nil
 }
 
 func (r *gitRepo) fetchUnshallow(refSpecs ...string) error {
@@ -411,7 +425,7 @@ func (r *gitRepo) fetchUnshallow(refSpecs ...string) error {
 func (r *gitRepo) statLocal(version, rev string) (*RevInfo, error) {
 	out, err := Run(r.dir, "git", "-c", "log.showsignature=false", "log", "-n1", "--format=format:%H %ct %D", rev, "--")
 	if err != nil {
-		return nil, fmt.Errorf("unknown revision %s", rev)
+		return nil, &UnknownRevisionError{Rev: rev}
 	}
 	f := strings.Fields(string(out))
 	if len(f) < 2 {
@@ -648,7 +662,7 @@ func (r *gitRepo) readFileRevs(tags []string, file string, fileMap map[string]*F
 	return missing, nil
 }
 
-func (r *gitRepo) RecentTag(rev, prefix string) (tag string, err error) {
+func (r *gitRepo) RecentTag(rev, prefix, major string) (tag string, err error) {
 	info, err := r.Stat(rev)
 	if err != nil {
 		return "", err
@@ -681,7 +695,7 @@ func (r *gitRepo) RecentTag(rev, prefix string) (tag string, err error) {
 
 			semtag := line[len(prefix):]
 			// Consider only tags that are valid and complete (not just major.minor prefixes).
-			if c := semver.Canonical(semtag); c != "" && strings.HasPrefix(semtag, c) {
+			if c := semver.Canonical(semtag); c != "" && strings.HasPrefix(semtag, c) && (major == "" || semver.Major(c) == major) {
 				highest = semver.Max(highest, semtag)
 			}
 		}
@@ -716,12 +730,8 @@ func (r *gitRepo) RecentTag(rev, prefix string) (tag string, err error) {
 	}
 	defer unlock()
 
-	if r.fetchLevel < fetchAll {
-		// Fetch all heads and tags and see if that gives us enough history.
-		if err := r.fetchUnshallow("refs/heads/*:refs/heads/*", "refs/tags/*:refs/tags/*"); err != nil {
-			return "", err
-		}
-		r.fetchLevel = fetchAll
+	if err := r.fetchRefsLocked(); err != nil {
+		return "", err
 	}
 
 	// If we've reached this point, we have all of the commits that are reachable
@@ -738,6 +748,67 @@ func (r *gitRepo) RecentTag(rev, prefix string) (tag string, err error) {
 	return tag, err
 }
 
+func (r *gitRepo) DescendsFrom(rev, tag string) (bool, error) {
+	// The "--is-ancestor" flag was added to "git merge-base" in version 1.8.0, so
+	// this won't work with Git 1.7.1. According to golang.org/issue/28550, cmd/go
+	// already doesn't work with Git 1.7.1, so at least it's not a regression.
+	//
+	// git merge-base --is-ancestor exits with status 0 if rev is an ancestor, or
+	// 1 if not.
+	_, err := Run(r.dir, "git", "merge-base", "--is-ancestor", "--", tag, rev)
+
+	// Git reports "is an ancestor" with exit code 0 and "not an ancestor" with
+	// exit code 1.
+	// Unfortunately, if we've already fetched rev with a shallow history, git
+	// merge-base has been observed to report a false-negative, so don't stop yet
+	// even if the exit code is 1!
+	if err == nil {
+		return true, nil
+	}
+
+	// See whether the tag and rev even exist.
+	tags, err := r.Tags(tag)
+	if err != nil {
+		return false, err
+	}
+	if len(tags) == 0 {
+		return false, nil
+	}
+
+	// NOTE: r.stat is very careful not to fetch commits that we shouldn't know
+	// about, like rejected GitHub pull requests, so don't try to short-circuit
+	// that here.
+	if _, err = r.stat(rev); err != nil {
+		return false, err
+	}
+
+	// Now fetch history so that git can search for a path.
+	unlock, err := r.mu.Lock()
+	if err != nil {
+		return false, err
+	}
+	defer unlock()
+
+	if r.fetchLevel < fetchAll {
+		// Fetch the complete history for all refs and heads. It would be more
+		// efficient to only fetch the history from rev to tag, but that's much more
+		// complicated, and any kind of shallow fetch is fairly likely to trigger
+		// bugs in JGit servers and/or the go command anyway.
+		if err := r.fetchRefsLocked(); err != nil {
+			return false, err
+		}
+	}
+
+	_, err = Run(r.dir, "git", "merge-base", "--is-ancestor", "--", tag, rev)
+	if err == nil {
+		return true, nil
+	}
+	if ee, ok := err.(*RunError).Err.(*exec.ExitError); ok && ee.ExitCode() == 1 {
+		return false, nil
+	}
+	return false, err
+}
+
 func (r *gitRepo) ReadZip(rev, subdir string, maxSize int64) (zip io.ReadCloser, actualSubdir string, err error) {
 	// TODO: Use maxSize or drop it.
 	args := []string{}
 
@@ -347,7 +347,7 @@ func (r *vcsRepo) fetch() {
 func (r *vcsRepo) statLocal(rev string) (*RevInfo, error) {
 	out, err := Run(r.dir, r.cmd.statLocal(rev, r.remote))
 	if err != nil {
-		return nil, vcsErrorf("unknown revision %s", rev)
+		return nil, &UnknownRevisionError{Rev: rev}
 	}
 	return r.cmd.parseStat(rev, string(out))
 }
@@ -392,7 +392,7 @@ func (r *vcsRepo) ReadFileRevs(revs []string, file string, maxSize int64) (map[s
 	return nil, vcsErrorf("ReadFileRevs not implemented")
 }
 
-func (r *vcsRepo) RecentTag(rev, prefix string) (tag string, err error) {
+func (r *vcsRepo) RecentTag(rev, prefix, major string) (tag string, err error) {
 	// We don't technically need to lock here since we're returning an error
 	// uncondititonally, but doing so anyway will help to avoid baking in
 	// lock-inversion bugs.
@@ -405,6 +405,16 @@ func (r *vcsRepo) RecentTag(rev, prefix string) (tag string, err error) {
 	return "", vcsErrorf("RecentTag not implemented")
 }
 
+func (r *vcsRepo) DescendsFrom(rev, tag string) (bool, error) {
+	unlock, err := r.mu.Lock()
+	if err != nil {
+		return false, err
+	}
+	defer unlock()
+
+	return false, vcsErrorf("DescendsFrom not implemented")
+}
+
 func (r *vcsRepo) ReadZip(rev, subdir string, maxSize int64) (zip io.ReadCloser, actualSubdir string, err error) {
 	if r.cmd.readZip == nil {
 		return nil, "", vcsErrorf("ReadZip not implemented for %s", r.cmd.vcs)
Original file line number	Diff line number	Diff line change
`@@ -128,7 +128,7 @@ func TestConvertLegacyConfig(t *testing.T) {`
`128`	`128`
`129`	`129`	`{`
`130`	`130`	`// golang.org/issue/24585 - confusion about v2.0.0 tag in legacy non-v2 module`
`131`		`- "github.com/fishy/gcsbucket", "v0.0.0-20150410205453-618d60fe84e0",`
	`131`	`+ "github.com/fishy/gcsbucket", "v0.0.0-20180217031846-618d60fe84e0",`
`132`	`132`	`module github.com/fishy/gcsbucket
`133`	`133`
`134`	`134`	`require (`