cmd/go/internal/modload: support go.mod retract directive

The go command now recognizes 'retract' directives in go.mod. A
retract directive may be used by a module author to indicate a
version should not be used. The go command will not automatically
upgrade to a retracted version. Retracted versions will not be
considered when resolving version queries like "latest" that don't
refer to a specific version.

Internally, when the go command resolves a version query, it will find
the highest release version (or pre-release if no release is
available), then it will load retractions from the go.mod file for
that version. Comments on retractions are treated as a rationale and
may appear in error messages. Retractions are only loaded when a query
is resolved, so this should have no impact on performance for most
builds, except when go.mod is incomplete.

For #24031

Change-Id: I17d643b9e03a3445676dbf1a5a351090c6ff6914
Reviewed-on: https://go-review.googlesource.com/c/go/+/228380
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/src/cmd/go/internal/modinfo/info.go b/src/cmd/go/internal/modinfo/info.go
index 07248d1a61..897be56397 100644
--- a/src/cmd/go/internal/modinfo/info.go
+++ b/src/cmd/go/internal/modinfo/info.go
@@ -21,6 +21,7 @@ type ModulePublic struct {
 	Dir       string        `json:",omitempty"` // directory holding local copy of files, if any
 	GoMod     string        `json:",omitempty"` // path to go.mod file describing module, if any
 	GoVersion string        `json:",omitempty"` // go version used in module
+	Retracted []string      `json:",omitempty"` // retraction information, if any (with -retracted or -u)
 	Error     *ModuleError  `json:",omitempty"` // error loading module
 }
 
@@ -30,18 +31,26 @@ type ModuleError struct {
 
 func (m *ModulePublic) String() string {
 	s := m.Path
+	versionString := func(mm *ModulePublic) string {
+		v := mm.Version
+		if len(mm.Retracted) == 0 {
+			return v
+		}
+		return v + " (retracted)"
+	}
+
 	if m.Version != "" {
-		s += " " + m.Version
+		s += " " + versionString(m)
 		if m.Update != nil {
-			s += " [" + m.Update.Version + "]"
+			s += " [" + versionString(m.Update) + "]"
 		}
 	}
 	if m.Replace != nil {
 		s += " => " + m.Replace.Path
 		if m.Replace.Version != "" {
-			s += " " + m.Replace.Version
+			s += " " + versionString(m.Replace)
 			if m.Replace.Update != nil {
-				s += " [" + m.Replace.Update.Version + "]"
+				s += " [" + versionString(m.Replace.Update) + "]"
 			}
 		}
 	}