cmd/go/internal/modfetch: return structured errors from proxy operations

CL 181881 added structured error types for direct fetches.
Use those same structured errors to format proxy errors consistently.

Also ensure that an empty @v/list is treated as equivalent to the module
not existing at all.

Updates #27173
Updates #32715

Change-Id: I203fd8259bc4f28b3389745f1a1fde936b0fa24d
Reviewed-on: https://go-review.googlesource.com/c/go/+/183619
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/modfetch/codehost/codehost.go

@@ -116,8 +116,20 @@ type UnknownRevisionError struct {
 func (e *UnknownRevisionError) Error() string {
 	return "unknown revision " + e.Rev
 }
+func (UnknownRevisionError) Is(err error) bool {
+	return err == os.ErrNotExist
+}
+
+// ErrNoCommits is an error equivalent to os.ErrNotExist indicating that a given
+// repository or module contains no commits.
+var ErrNoCommits error = noCommitsError{}
 
-func (e *UnknownRevisionError) Is(err error) bool {
+type noCommitsError struct{}
+
+func (noCommitsError) Error() string {
+	return "no commits"
+}
+func (noCommitsError) Is(err error) bool {
 	return err == os.ErrNotExist
 }
 

src/cmd/go/internal/modfetch/codehost/git.go

@@ -222,7 +222,7 @@ func (r *gitRepo) Latest() (*RevInfo, error) {
 		return nil, r.refsErr
 	}
 	if r.refs["HEAD"] == "" {
-		return nil, fmt.Errorf("no commits")
+		return nil, ErrNoCommits
 	}
 	return r.Stat(r.refs["HEAD"])
 }

src/cmd/go/internal/modfetch/proxy.go

@@ -196,6 +196,26 @@ func (p *proxyRepo) ModulePath() string {
 	return p.path
 }
 
+// versionError returns err wrapped in a ModuleError for p.path.
+func (p *proxyRepo) versionError(version string, err error) error {
+	if version != "" && version != module.CanonicalVersion(version) {
+		return &module.ModuleError{
+			Path: p.path,
+			Err: &module.InvalidVersionError{
+				Version: version,
+				Pseudo:  IsPseudoVersion(version),
+				Err:     err,
+			},
+		}
+	}
+
+	return &module.ModuleError{
+		Path:    p.path,
+		Version: version,
+		Err:     err,
+	}
+}
+
 func (p *proxyRepo) getBytes(path string) ([]byte, error) {
 	body, err := p.getBody(path)
 	if err != nil {
@@ -226,7 +246,7 @@ func (p *proxyRepo) getBody(path string) (io.ReadCloser, error) {
 func (p *proxyRepo) Versions(prefix string) ([]string, error) {
 	data, err := p.getBytes("@v/list")
 	if err != nil {
-		return nil, err
+		return nil, p.versionError("", err)
 	}
 	var list []string
 	for _, line := range strings.Split(string(data), "\n") {
@@ -242,7 +262,7 @@ func (p *proxyRepo) Versions(prefix string) ([]string, error) {
 func (p *proxyRepo) latest() (*RevInfo, error) {
 	data, err := p.getBytes("@v/list")
 	if err != nil {
-		return nil, err
+		return nil, p.versionError("", err)
 	}
 	var best time.Time
 	var bestVersion string
@@ -257,7 +277,7 @@ func (p *proxyRepo) latest() (*RevInfo, error) {
 		}
 	}
 	if bestVersion == "" {
-		return nil, fmt.Errorf("no commits")
+		return nil, p.versionError("", codehost.ErrNoCommits)
 	}
 	info := &RevInfo{
 		Version: bestVersion,
@@ -271,21 +291,21 @@ func (p *proxyRepo) latest() (*RevInfo, error) {
 func (p *proxyRepo) Stat(rev string) (*RevInfo, error) {
 	encRev, err := module.EncodeVersion(rev)
 	if err != nil {
-		return nil, err
+		return nil, p.versionError(rev, err)
 	}
 	data, err := p.getBytes("@v/" + encRev + ".info")
 	if err != nil {
-		return nil, err
+		return nil, p.versionError(rev, err)
 	}
 	info := new(RevInfo)
 	if err := json.Unmarshal(data, info); err != nil {
-		return nil, err
+		return nil, p.versionError(rev, err)
 	}
 	if info.Version != rev && rev == module.CanonicalVersion(rev) && module.Check(p.path, rev) == nil {
 		// If we request a correct, appropriate version for the module path, the
 		// proxy must return either exactly that version or an error — not some
 		// arbitrary other version.
-		return nil, fmt.Errorf("requested canonical version %s, but proxy returned info for version %s", rev, info.Version)
+		return nil, p.versionError(rev, fmt.Errorf("proxy returned info for version %s instead of requested version", info.Version))
 	}
 	return info, nil
 }
@@ -298,48 +318,48 @@ func (p *proxyRepo) Latest() (*RevInfo, error) {
 	}
 	info := new(RevInfo)
 	if err := json.Unmarshal(data, info); err != nil {
-		return nil, err
+		return nil, p.versionError("", err)
 	}
 	return info, nil
 }
 
 func (p *proxyRepo) GoMod(version string) ([]byte, error) {
 	if version != module.CanonicalVersion(version) {
-		return nil, fmt.Errorf("version %s is not canonical", version)
+		return nil, p.versionError(version, fmt.Errorf("internal error: version passed to GoMod is not canonical"))
 	}
 
 	encVer, err := module.EncodeVersion(version)
 	if err != nil {
-		return nil, err
+		return nil, p.versionError(version, err)
 	}
 	data, err := p.getBytes("@v/" + encVer + ".mod")
 	if err != nil {
-		return nil, err
+		return nil, p.versionError(version, err)
 	}
 	return data, nil
 }
 
 func (p *proxyRepo) Zip(dst io.Writer, version string) error {
 	if version != module.CanonicalVersion(version) {
-		return fmt.Errorf("version %s is not canonical", version)
+		return p.versionError(version, fmt.Errorf("internal error: version passed to Zip is not canonical"))
 	}
 
 	encVer, err := module.EncodeVersion(version)
 	if err != nil {
-		return err
+		return p.versionError(version, err)
 	}
 	body, err := p.getBody("@v/" + encVer + ".zip")
 	if err != nil {
-		return err
+		return p.versionError(version, err)
 	}
 	defer body.Close()
 
 	lr := &io.LimitedReader{R: body, N: codehost.MaxZipFile + 1}
 	if _, err := io.Copy(dst, lr); err != nil {
-		return err
+		return p.versionError(version, err)
 	}
 	if lr.N <= 0 {
-		return fmt.Errorf("downloaded zip file too large")
+		return p.versionError(version, fmt.Errorf("downloaded zip file too large"))
 	}
 	return nil
 }

src/cmd/go/internal/modload/query.go

@@ -243,9 +243,14 @@ func queryProxy(proxy, path, query, current string, allowed func(module.Version)
 	if mayUseLatest {
 		// Special case for "latest": if no tags match, use latest commit in repo,
 		// provided it is not excluded.
-		if latest, err := repo.Latest(); err == nil && allowed(module.Version{Path: path, Version: latest.Version}) {
+		latest, err := repo.Latest()
+		if err == nil {
+			if allowed(module.Version{Path: path, Version: latest.Version}) {
 				return lookup(latest.Version)
 			}
+		} else if !errors.Is(err, os.ErrNotExist) {
+			return nil, err
+		}
 	}
 
 	return nil, &NoMatchingVersionError{query: query, current: current}

src/cmd/go/internal/module/module.go

@@ -536,7 +536,10 @@ func EncodePath(path string) (encoding string, err error) {
 // and not contain exclamation marks.
 func EncodeVersion(v string) (encoding string, err error) {
 	if err := checkElem(v, true); err != nil || strings.Contains(v, "!") {
-		return "", fmt.Errorf("disallowed version string %q", v)
+		return "", &InvalidVersionError{
+			Version: v,
+			Err:     fmt.Errorf("disallowed version string"),
+		}
 	}
 	return encodeString(v)
 }

src/cmd/go/testdata/script/mod_query_empty.txt

+env GO111MODULE=on
+env GOSUMDB=off
+
+go mod download example.com/join@v1.1.0
+
+# If the proxy serves a bogus result for the @latest version,
+# reading that version should cause 'go get' to fail.
+env GOPROXY=file:///$WORK/badproxy
+cp go.mod.orig go.mod
+! go get -d example.com/join/subpkg
+stderr 'go get example.com/join/subpkg: example.com/join/subpkg@v0.0.0-20190624000000-123456abcdef: .*'
+
+# If @v/list is empty, the 'go' command should still try to resolve
+# other module paths.
+env GOPROXY=file:///$WORK/emptysub
+cp go.mod.orig go.mod
+go get -d example.com/join/subpkg
+go list -m example.com/join/...
+! stdout 'example.com/join/subpkg'
+stdout 'example.com/join v1.1.0'
+
+# If @v/list includes a version that the proxy does not actually serve,
+# that version is treated as nonexistent.
+env GOPROXY=file:///$WORK/notfound
+cp go.mod.orig go.mod
+go get -d example.com/join/subpkg
+go list -m example.com/join/...
+! stdout 'example.com/join/subpkg'
+stdout 'example.com/join v1.1.0'
+
+-- go.mod.orig --
+module example.com/othermodule
+go 1.13
+-- $WORK/badproxy/example.com/join/subpkg/@v/list --
+v0.0.0-20190624000000-123456abcdef
+-- $WORK/badproxy/example.com/join/subpkg/@v/v0.0.0-20190624000000-123456abcdef.info --
+This file is not valid JSON.
+-- $WORK/badproxy/example.com/join/@v/list --
+v1.1.0
+-- $WORK/badproxy/example.com/join/@v/v1.1.0.info --
+{"Version": "v1.1.0"}
+-- $WORK/emptysub/example.com/join/subpkg/@v/list --
+-- $WORK/emptysub/example.com/join/@v/list --
+v1.1.0
+-- $WORK/emptysub/example.com/join/@v/v1.1.0.info --
+{"Version": "v1.1.0"}
+-- $WORK/notfound/example.com/join/subpkg/@v/list --
+v1.0.0-does-not-exist
+-- $WORK/notfound/example.com/join/@v/list --
+v1.1.0
+-- $WORK/notfound/example.com/join/@v/v1.1.0.info --
+{"Version": "v1.1.0"}