cmd/go: ignore retracted versions when converting revisions to versions

When a module author retracts a version, the go command should act as
if it doesn't exist unless it's specifically requested.

When converting a revision to a version, we should ignore tags for
retracted versions. For example, if the tag v1.0.0 is retracted, and
branch B points to the same revision, we should convert B to a
pseudo-version, not v1.0.0. Similarly, if B points to a commit after
v1.0.0, we should not use v1.0.0 as the base; we can use an earlier
non-retracted tag or no base.

Fixes #41700

Change-Id: Ia596b05b0780e5acfe6616a04e94d24bd342fbae
Reviewed-on: https://go-review.googlesource.com/c/go/+/261079
Run-TryBot: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Jay Conrod <jayconrod@google.com>

5 files changed, 143 insertions, 11 deletions

diff --git a/src/cmd/go/internal/modfetch/codehost/codehost.go b/src/cmd/go/internal/modfetch/codehost/codehost.go
index d85eddf767b..df4cfdab1af 100644
--- a/src/cmd/go/internal/modfetch/codehost/codehost.go
+++ b/src/cmd/go/internal/modfetch/codehost/codehost.go
@@ -79,9 +79,8 @@ type Repo interface {
 	ReadZip(rev, subdir string, maxSize int64) (zip io.ReadCloser, 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)
+	// with the given prefix. allowed may be used to filter out unwanted versions.
+	RecentTag(rev, prefix string, allowed func(string) bool) (tag string, err error)
 
 	// DescendsFrom reports whether rev or any of its ancestors has the given tag.
 	//
diff --git a/src/cmd/go/internal/modfetch/codehost/git.go b/src/cmd/go/internal/modfetch/codehost/git.go
index 31921324a7d..5a35829c98c 100644
--- a/src/cmd/go/internal/modfetch/codehost/git.go
+++ b/src/cmd/go/internal/modfetch/codehost/git.go
@@ -644,7 +644,7 @@ func (r *gitRepo) readFileRevs(tags []string, file string, fileMap map[string]*F
 	return missing, nil
 }
 
-func (r *gitRepo) RecentTag(rev, prefix, major string) (tag string, err error) {
+func (r *gitRepo) RecentTag(rev, prefix string, allowed func(string) bool) (tag string, err error) {
 	info, err := r.Stat(rev)
 	if err != nil {
 		return "", err
@@ -680,7 +680,10 @@ func (r *gitRepo) RecentTag(rev, prefix, major string) (tag string, err error) {
 			// NOTE: Do not replace the call to semver.Compare with semver.Max.
 			// We want to return the actual tag, not a canonicalized version of it,
 			// and semver.Max currently canonicalizes (see golang.org/issue/32700).
-			if c := semver.Canonical(semtag); c != "" && strings.HasPrefix(semtag, c) && (major == "" || semver.Major(c) == major) && semver.Compare(semtag, highest) > 0 {
+			if c := semver.Canonical(semtag); c == "" || !strings.HasPrefix(semtag, c) || !allowed(semtag) {
+				continue
+			}
+			if semver.Compare(semtag, highest) > 0 {
 				highest = semtag
 			}
 		}
diff --git a/src/cmd/go/internal/modfetch/codehost/vcs.go b/src/cmd/go/internal/modfetch/codehost/vcs.go
index 7284557f4ba..6278cb21e13 100644
--- a/src/cmd/go/internal/modfetch/codehost/vcs.go
+++ b/src/cmd/go/internal/modfetch/codehost/vcs.go
@@ -395,7 +395,7 @@ func (r *vcsRepo) ReadFileRevs(revs []string, file string, maxSize int64) (map[s
 	return nil, vcsErrorf("ReadFileRevs not implemented")
 }
 
-func (r *vcsRepo) RecentTag(rev, prefix, major string) (tag string, err error) {
+func (r *vcsRepo) RecentTag(rev, prefix string, allowed func(string) bool) (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.
diff --git a/src/cmd/go/internal/modfetch/coderepo.go b/src/cmd/go/internal/modfetch/coderepo.go
index d043903336c..d99a31d3605 100644
--- a/src/cmd/go/internal/modfetch/coderepo.go
+++ b/src/cmd/go/internal/modfetch/coderepo.go
@@ -419,9 +419,14 @@ func (r *codeRepo) convert(info *codehost.RevInfo, statVers string) (*RevInfo, e
 		tagPrefix = r.codeDir + "/"
 	}
 
+	isRetracted, err := r.retractedVersions()
+	if err != nil {
+		isRetracted = func(string) bool { return false }
+	}
+
 	// tagToVersion returns the version obtained by trimming tagPrefix from tag.
-	// If the tag is invalid or a pseudo-version, tagToVersion returns an empty
-	// version.
+	// If the tag is invalid, retracted, or a pseudo-version, tagToVersion returns
+	// an empty version.
 	tagToVersion := func(tag string) (v string, tagIsCanonical bool) {
 		if !strings.HasPrefix(tag, tagPrefix) {
 			return "", false
@@ -436,6 +441,9 @@ func (r *codeRepo) convert(info *codehost.RevInfo, statVers string) (*RevInfo, e
 		if v == "" || !strings.HasPrefix(trimmed, v) {
 			return "", false // Invalid or incomplete version (just vX or vX.Y).
 		}
+		if isRetracted(v) {
+			return "", false
+		}
 		if v == trimmed {
 			tagIsCanonical = true
 		}
@@ -500,15 +508,24 @@ func (r *codeRepo) convert(info *codehost.RevInfo, statVers string) (*RevInfo, e
 		return checkGoMod()
 	}
 
+	// Find the highest tagged version in the revision's history, subject to
+	// major version and +incompatible constraints. Use that version as the
+	// pseudo-version base so that the pseudo-version sorts higher. Ignore
+	// retracted versions.
+	allowedMajor := func(major string) func(v string) bool {
+		return func(v string) bool {
+			return (major == "" || semver.Major(v) == major) && !isRetracted(v)
+		}
+	}
 	if pseudoBase == "" {
 		var tag string
 		if r.pseudoMajor != "" || canUseIncompatible() {
-			tag, _ = r.code.RecentTag(info.Name, tagPrefix, r.pseudoMajor)
+			tag, _ = r.code.RecentTag(info.Name, tagPrefix, allowedMajor(r.pseudoMajor))
 		} else {
 			// Allow either v1 or v0, but not incompatible higher versions.
-			tag, _ = r.code.RecentTag(info.Name, tagPrefix, "v1")
+			tag, _ = r.code.RecentTag(info.Name, tagPrefix, allowedMajor("v1"))
 			if tag == "" {
-				tag, _ = r.code.RecentTag(info.Name, tagPrefix, "v0")
+				tag, _ = r.code.RecentTag(info.Name, tagPrefix, allowedMajor("v0"))
 			}
 		}
 		pseudoBase, _ = tagToVersion(tag) // empty if the tag is invalid
@@ -869,6 +886,57 @@ func (r *codeRepo) modPrefix(rev string) string {
 	return r.modPath + "@" + rev
 }
 
+func (r *codeRepo) retractedVersions() (func(string) bool, error) {
+	versions, err := r.Versions("")
+	if err != nil {
+		return nil, err
+	}
+
+	for i, v := range versions {
+		if strings.HasSuffix(v, "+incompatible") {
+			versions = versions[:i]
+			break
+		}
+	}
+	if len(versions) == 0 {
+		return func(string) bool { return false }, nil
+	}
+
+	var highest string
+	for i := len(versions) - 1; i >= 0; i-- {
+		v := versions[i]
+		if semver.Prerelease(v) == "" {
+			highest = v
+			break
+		}
+	}
+	if highest == "" {
+		highest = versions[len(versions)-1]
+	}
+
+	data, err := r.GoMod(highest)
+	if err != nil {
+		return nil, err
+	}
+	f, err := modfile.ParseLax("go.mod", data, nil)
+	if err != nil {
+		return nil, err
+	}
+	retractions := make([]modfile.VersionInterval, len(f.Retract))
+	for _, r := range f.Retract {
+		retractions = append(retractions, r.VersionInterval)
+	}
+
+	return func(v string) bool {
+		for _, r := range retractions {
+			if semver.Compare(r.Low, v) <= 0 && semver.Compare(v, r.High) <= 0 {
+				return true
+			}
+		}
+		return false
+	}, nil
+}
+
 func (r *codeRepo) Zip(dst io.Writer, version string) error {
 	if version != module.CanonicalVersion(version) {
 		return fmt.Errorf("version %s is not canonical", version)
diff --git a/src/cmd/go/testdata/script/mod_retract_pseudo_base.txt b/src/cmd/go/testdata/script/mod_retract_pseudo_base.txt
new file mode 100644
index 00000000000..93609f36c95
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_retract_pseudo_base.txt
@@ -0,0 +1,62 @@
+# When converting a commit to a pseudo-version, don't use a retracted version
+# as the base.
+# Verifies golang.org/issue/41700.
+
+[!net] skip
+[!exec:git] skip
+env GOPROXY=direct
+env GOSUMDB=off
+go mod init m
+
+# Control: check that v1.0.0 is the only version and is retracted.
+go list -m -versions vcs-test.golang.org/git/retract-pseudo.git
+stdout '^vcs-test.golang.org/git/retract-pseudo.git$'
+go list -m -versions -retracted vcs-test.golang.org/git/retract-pseudo.git
+stdout '^vcs-test.golang.org/git/retract-pseudo.git v1.0.0$'
+
+# 713affd19d7b is a commit after v1.0.0. Don't use v1.0.0 as the base.
+go list -m vcs-test.golang.org/git/retract-pseudo.git@713affd19d7b
+stdout '^vcs-test.golang.org/git/retract-pseudo.git v0.0.0-20201009173747-713affd19d7b$'
+
+# 64c061ed4371 is the commit v1.0.0 refers to. Don't convert to v1.0.0.
+go list -m vcs-test.golang.org/git/retract-pseudo.git@64c061ed4371
+stdout '^vcs-test.golang.org/git/retract-pseudo.git v0.0.0-20201009173747-64c061ed4371'
+
+# A retracted version is a valid base. Retraction should not validate existing
+# pseudo-versions, nor should it turn invalid pseudo-versions valid.
+go get -d vcs-test.golang.org/git/retract-pseudo.git@v1.0.1-0.20201009173747-713affd19d7b
+go list -m vcs-test.golang.org/git/retract-pseudo.git
+stdout '^vcs-test.golang.org/git/retract-pseudo.git v1.0.1-0.20201009173747-713affd19d7b$'
+
+! go get -d vcs-test.golang.org/git/retract-pseudo.git@v1.0.1-0.20201009173747-64c061ed4371
+stderr '^go get vcs-test.golang.org/git/retract-pseudo.git@v1.0.1-0.20201009173747-64c061ed4371: vcs-test.golang.org/git/retract-pseudo.git@v1.0.1-0.20201009173747-64c061ed4371: invalid pseudo-version: tag \(v1.0.0\) found on revision 64c061ed4371 is already canonical, so should not be replaced with a pseudo-version derived from that tag$'
+
+-- retract-pseudo.sh --
+#!/bin/bash
+
+# This is not part of the test.
+# Run this to generate and update the repository on vcs-test.golang.org.
+
+set -euo pipefail
+
+rm -rf retract-pseudo
+mkdir retract-pseudo
+cd retract-pseudo
+git init
+
+# Create the module.
+# Retract v1.0.0 and tag v1.0.0 at the same commit.
+# The module has no unretracted release versions.
+go mod init vcs-test.golang.org/git/retract-pseudo.git
+go mod edit -retract v1.0.0
+echo 'package p' >p.go
+git add -A
+git commit -m 'create module retract-pseudo'
+git tag v1.0.0
+
+# Commit a trivial change so the default branch does not point to v1.0.0.
+git mv p.go q.go
+git commit -m 'trivial change'
+
+zip -r ../retract-pseudo.zip .
+gsutil cp ../retract-pseudo.zip gs://vcs-test/git/retract-pseudo.zip