[release-branch.go1.19] cmd/go: avoid overwriting cached Origin metadata

Fixes #54633.
Updates #54631.

Change-Id: I17d2fa282642aeb1ae2a6e29a0756b8960bea34b
Reviewed-on: https://go-review.googlesource.com/c/go/+/425255
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
(cherry picked from commit e3004d96b6899945d76e5dd373756324c8ff98fb)
Reviewed-on: https://go-review.googlesource.com/c/go/+/425211

4 files changed, 43 insertions, 17 deletions

diff --git a/src/cmd/go/internal/modfetch/codehost/codehost.go b/src/cmd/go/internal/modfetch/codehost/codehost.go
index 747022759e..3a6e55e9a3 100644
--- a/src/cmd/go/internal/modfetch/codehost/codehost.go
+++ b/src/cmd/go/internal/modfetch/codehost/codehost.go
@@ -37,7 +37,9 @@ const (
 // A Repo represents a code hosting source.
 // Typical implementations include local version control repositories,
 // remote version control servers, and code hosting sites.
-// A Repo must be safe for simultaneous use by multiple goroutines.
+//
+// A Repo must be safe for simultaneous use by multiple goroutines,
+// and callers must not modify returned values, which may be cached and shared.
 type Repo interface {
 	// CheckReuse checks whether the old origin information
 	// remains up to date. If so, whatever cached object it was
diff --git a/src/cmd/go/internal/modfetch/codehost/git.go b/src/cmd/go/internal/modfetch/codehost/git.go
index 35f77e870e..ac2dc2348e 100644
--- a/src/cmd/go/internal/modfetch/codehost/git.go
+++ b/src/cmd/go/internal/modfetch/codehost/git.go
@@ -348,12 +348,21 @@ func (r *gitRepo) Latest() (*RevInfo, error) {
 	if refs["HEAD"] == "" {
 		return nil, ErrNoCommits
 	}
-	info, err := r.Stat(refs["HEAD"])
+	statInfo, err := r.Stat(refs["HEAD"])
 	if err != nil {
 		return nil, err
 	}
+
+	// Stat may return cached info, so make a copy to modify here.
+	info := new(RevInfo)
+	*info = *statInfo
+	info.Origin = new(Origin)
+	if statInfo.Origin != nil {
+		*info.Origin = *statInfo.Origin
+	}
 	info.Origin.Ref = "HEAD"
 	info.Origin.Hash = refs["HEAD"]
+
 	return info, nil
 }
 
@@ -560,7 +569,7 @@ func (r *gitRepo) fetchRefsLocked() error {
 	return nil
 }
 
-// statLocal returns a RevInfo describing rev in the local git repository.
+// statLocal returns a new RevInfo describing rev in the local git repository.
 // It uses version as info.Version.
 func (r *gitRepo) statLocal(version, rev string) (*RevInfo, error) {
 	out, err := Run(r.dir, "git", "-c", "log.showsignature=false", "log", "--no-decorate", "-n1", "--format=format:%H %ct %D", rev, "--")
diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go
index 555d4b3c63..bbece3f849 100644
--- a/src/cmd/go/internal/modload/build.go
+++ b/src/cmd/go/internal/modload/build.go
@@ -182,23 +182,27 @@ func mergeOrigin(m1, m2 *codehost.Origin) *codehost.Origin {
 	if !m2.Checkable() {
 		return m2
 	}
+
+	merged := new(codehost.Origin)
+	*merged = *m1 // Clone to avoid overwriting fields in cached results.
+
 	if m2.TagSum != "" {
 		if m1.TagSum != "" && (m1.TagSum != m2.TagSum || m1.TagPrefix != m2.TagPrefix) {
-			m1.ClearCheckable()
-			return m1
+			merged.ClearCheckable()
+			return merged
 		}
-		m1.TagSum = m2.TagSum
-		m1.TagPrefix = m2.TagPrefix
+		merged.TagSum = m2.TagSum
+		merged.TagPrefix = m2.TagPrefix
 	}
 	if m2.Hash != "" {
 		if m1.Hash != "" && (m1.Hash != m2.Hash || m1.Ref != m2.Ref) {
-			m1.ClearCheckable()
-			return m1
+			merged.ClearCheckable()
+			return merged
 		}
-		m1.Hash = m2.Hash
-		m1.Ref = m2.Ref
+		merged.Hash = m2.Hash
+		merged.Ref = m2.Ref
 	}
-	return m1
+	return merged
 }
 
 // addVersions fills in m.Versions with the list of known versions.
diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
index 01df14fca4..9f9674c26b 100644
--- a/src/cmd/go/internal/modload/query.go
+++ b/src/cmd/go/internal/modload/query.go
@@ -220,6 +220,17 @@ func queryProxy(ctx context.Context, proxy, path, query, current string, allowed
 		return revErr, err
 	}
 
+	mergeRevOrigin := func(rev *modfetch.RevInfo, origin *codehost.Origin) *modfetch.RevInfo {
+		merged := mergeOrigin(rev.Origin, origin)
+		if merged == rev.Origin {
+			return rev
+		}
+		clone := new(modfetch.RevInfo)
+		*clone = *rev
+		clone.Origin = merged
+		return clone
+	}
+
 	lookup := func(v string) (*modfetch.RevInfo, error) {
 		rev, err := repo.Stat(v)
 		// Stat can return a non-nil rev and a non-nil err,
@@ -227,7 +238,7 @@ func queryProxy(ctx context.Context, proxy, path, query, current string, allowed
 		if rev == nil && err != nil {
 			return revErr, err
 		}
-		rev.Origin = mergeOrigin(rev.Origin, versions.Origin)
+		rev = mergeRevOrigin(rev, versions.Origin)
 		if err != nil {
 			return rev, err
 		}
@@ -256,12 +267,12 @@ func queryProxy(ctx context.Context, proxy, path, query, current string, allowed
 				if err := allowed(ctx, module.Version{Path: path, Version: current}); errors.Is(err, ErrDisallowed) {
 					return revErr, err
 				}
-				info, err := repo.Stat(current)
-				if info == nil && err != nil {
+				rev, err = repo.Stat(current)
+				if rev == nil && err != nil {
 					return revErr, err
 				}
-				info.Origin = mergeOrigin(info.Origin, versions.Origin)
-				return info, err
+				rev = mergeRevOrigin(rev, versions.Origin)
+				return rev, err
 			}
 		}