cmd/go/internal/modload: allow 'go get' to use replaced versions

'go mod tidy' has been able to use replaced versions since CL 152739,
but 'go get' failed for many of the same paths. Now that we are
recommending 'go get' more aggressively due to #40728, we should make
that work too.

In the future, we might consider factoring out the new replacementRepo
type so that 'go list' can report the new versions as well.

For #41577
For #41416
For #37438
Updates #26241

Change-Id: I9140c556424b584fdd9bdd0a747842774664a7d8
Reviewed-on: https://go-review.googlesource.com/c/go/+/258220
Trust: Bryan C. Mills <bcmills@google.com>
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 41 insertions, 13 deletions

diff --git a/src/cmd/go/internal/modload/modfile.go b/src/cmd/go/internal/modload/modfile.go
index 6457a7d968..d15da892e6 100644
--- a/src/cmd/go/internal/modload/modfile.go
+++ b/src/cmd/go/internal/modload/modfile.go
@@ -35,13 +35,14 @@ var modFile *modfile.File
 // A modFileIndex is an index of data corresponding to a modFile
 // at a specific point in time.
 type modFileIndex struct {
-	data         []byte
-	dataNeedsFix bool // true if fixVersion applied a change while parsing data
-	module       module.Version
-	goVersionV   string // GoVersion with "v" prefix
-	require      map[module.Version]requireMeta
-	replace      map[module.Version]module.Version
-	exclude      map[module.Version]bool
+	data            []byte
+	dataNeedsFix    bool // true if fixVersion applied a change while parsing data
+	module          module.Version
+	goVersionV      string // GoVersion with "v" prefix
+	require         map[module.Version]requireMeta
+	replace         map[module.Version]module.Version
+	highestReplaced map[string]string // highest replaced version of each module path; empty string for wildcard-only replacements
+	exclude         map[module.Version]bool
 }
 
 // index is the index of the go.mod file as of when it was last read or written.
@@ -117,7 +118,7 @@ func checkRetractions(ctx context.Context, m module.Version) error {
 		// v2.0.0+incompatible is not "latest" if v1.0.0 is current.
 		rev, err := Query(ctx, path, "latest", findCurrentVersion(path), nil)
 		if err != nil {
-			return &entry{err: err}
+			return &entry{nil, err}
 		}
 
 		// Load go.mod for that version.
@@ -138,13 +139,19 @@ func checkRetractions(ctx context.Context, m module.Version) error {
 		}
 		summary, err := rawGoModSummary(rm)
 		if err != nil {
-			return &entry{err: err}
+			return &entry{nil, err}
 		}
-		return &entry{retract: summary.retract}
+		return &entry{summary.retract, nil}
 	}).(*entry)
 
-	if e.err != nil {
-		return fmt.Errorf("loading module retractions: %v", e.err)
+	if err := e.err; err != nil {
+		// Attribute the error to the version being checked, not the version from
+		// which the retractions were to be loaded.
+		var mErr *module.ModuleError
+		if errors.As(err, &mErr) {
+			err = mErr.Err
+		}
+		return &retractionLoadingError{m: m, err: err}
 	}
 
 	var rationale []string
@@ -158,7 +165,7 @@ func checkRetractions(ctx context.Context, m module.Version) error {
 		}
 	}
 	if isRetracted {
-		return &retractedError{rationale: rationale}
+		return module.VersionError(m, &retractedError{rationale: rationale})
 	}
 	return nil
 }
@@ -183,6 +190,19 @@ func (e *retractedError) Is(err error) bool {
 	return err == ErrDisallowed
 }
 
+type retractionLoadingError struct {
+	m   module.Version
+	err error
+}
+
+func (e *retractionLoadingError) Error() string {
+	return fmt.Sprintf("loading module retractions for %v: %v", e.m, e.err)
+}
+
+func (e *retractionLoadingError) Unwrap() error {
+	return e.err
+}
+
 // ShortRetractionRationale returns a retraction rationale string that is safe
 // to print in a terminal. It returns hard-coded strings if the rationale
 // is empty, too long, or contains non-printable characters.
@@ -255,6 +275,14 @@ func indexModFile(data []byte, modFile *modfile.File, needsFix bool) *modFileInd
 		i.replace[r.Old] = r.New
 	}
 
+	i.highestReplaced = make(map[string]string)
+	for _, r := range modFile.Replace {
+		v, ok := i.highestReplaced[r.Old.Path]
+		if !ok || semver.Compare(r.Old.Version, v) > 0 {
+			i.highestReplaced[r.Old.Path] = r.Old.Version
+		}
+	}
+
 	i.exclude = make(map[module.Version]bool, len(modFile.Exclude))
 	for _, x := range modFile.Exclude {
 		i.exclude[x.Mod] = true