Treat a missing notes ref as no attestations

pkg/attest/provenance.go

@@ -15,6 +15,7 @@ import (
 	"github.com/carabiner-dev/collector/filters"
 	"github.com/carabiner-dev/collector/repository/github"
 	"github.com/carabiner-dev/collector/repository/note"
+	"github.com/go-git/go-git/v5"
 	vsa "github.com/in-toto/attestation/go/predicates/vsa/v1"
 	intoto "github.com/in-toto/attestation/go/v1"
 	"google.golang.org/protobuf/encoding/protojson"
@@ -151,6 +152,21 @@ func (a *Attester) getCollector(branch *models.Branch) (*collector.Agent, error)
 	return agent, nil
 }
 
+// notesRefMissing reports whether an attestation fetch failed only because the
+// git notes ref does not exist yet. A repository that has never been attested
+// has no such ref, so this is an empty attestation set rather than an error:
+// without it the first attestation can never be written, because writing it
+// requires reading the attestations that would have created the ref.
+func notesRefMissing(err error) bool {
+	if errors.Is(err, git.NoMatchingRefSpecError{}) {
+		return true
+	}
+	// The collector aggregates per-locator failures in a vcslocator.ErrorList,
+	// which has no Unwrap, so on that path the go-git error is only reachable
+	// through the message.
+	return strings.Contains(err.Error(), "couldn't find remote ref")
+}
+
 // GetRevisionVSA returns a revision's VSA attestation
 func (a *Attester) GetRevisionVSA(ctx context.Context, branch *models.Branch, revision models.Revision) (attestation.Envelope, *vsa.VerificationSummary, error) {
 	if revision.GetCommit() == nil {
@@ -176,12 +192,16 @@ func (a *Attester) GetRevisionVSA(ctx context.Context, branch *models.Branch, re
 			ctx, []attestation.Subject{revision.GetCommit().ToResourceDescriptor()},
 			collector.WithQuery(attestation.NewQuery().WithFilter(matcher)),
 		)
-		if attErr == nil {
+		if attErr == nil || notesRefMissing(attErr) {
 			break
 		}
 		time.Sleep(time.Duration(i*5) * time.Second)
 	}
 	if attErr != nil {
+		if notesRefMissing(attErr) {
+			Debugf("notes ref not created yet, treating as no attestations")
+			return nil, nil, nil
+		}
 		return nil, nil, fmt.Errorf("fetching attestations: %w", attErr)
 	}
 
@@ -257,12 +277,16 @@ func (a *Attester) GetRevisionProvenance(ctx context.Context, branch *models.Bra
 			ctx, []attestation.Subject{commit.ToResourceDescriptor()},
 			collector.WithQuery(attestation.NewQuery().WithFilter(matcher)),
 		)
-		if attErr == nil {
+		if attErr == nil || notesRefMissing(attErr) {
 			break
 		}
 		time.Sleep(time.Duration(i*5) * time.Second)
 	}
 	if attErr != nil {
+		if notesRefMissing(attErr) {
+			Debugf("notes ref not created yet, treating as no attestations")
+			return nil, nil
+		}
 		return nil, fmt.Errorf("fetching attestations: %w", attErr)
 	}
 

pkg/attest/provenance_notesref_test.go

@@ -0,0 +1,53 @@
+// SPDX-FileCopyrightText: Copyright 2026 The SLSA Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package attest
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/go-git/go-git/v5"
+)
+
+// errorList stands in for vcslocator.ErrorList, which renders its members but
+// does not implement Unwrap, so errors.Is cannot see through it.
+type errorList struct {
+	errs []error
+}
+
+func (e *errorList) Error() string {
+	return errors.Join(e.errs...).Error()
+}
+
+func TestNotesRefMissing(t *testing.T) {
+	fetchFailure := fmt.Errorf("fetching ref %q: %w", "refs/notes/commits", git.NoMatchingRefSpecError{})
+	// The same failure as it renders once the aggregate has flattened it to
+	// text: go-git's NoMatchingRefSpecError prints the ref it could not find.
+	rendered := errors.New(`fetching ref "refs/notes/commits": couldn't find remote ref "refs/notes/commits"`)
+
+	for name, tc := range map[string]struct {
+		err  error
+		want bool
+	}{
+		"wrapped go-git error": {
+			err:  fmt.Errorf("fetching attestations: %w", fetchFailure),
+			want: true,
+		},
+		"aggregated without an unwrap": {
+			err:  fmt.Errorf("error cloning repositories: %w", &errorList{errs: []error{rendered, nil}}),
+			want: true,
+		},
+		"some other failure": {
+			err:  fmt.Errorf("fetching attestations: %w", errors.New("connection refused")),
+			want: false,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			if got := notesRefMissing(tc.err); got != tc.want {
+				t.Errorf("notesRefMissing(%v) = %v, want %v", tc.err, got, tc.want)
+			}
+		})
+	}
+}