solve: use comparables instead of reflection in result struct

Since go 1.20, interfaces (that can be compared) now implement the
comparable interface. The use of reflection in solver/result was a
workaround for this limitation, however, we can remove this with the
upstream fix.

Signed-off-by: Justin Chadwell <me@jedevc.com>

frontend/attestations/sbom/sbom.go

@@ -31,7 +31,7 @@ const (
 // build-contexts or multi-stage builds. Handling these separately allows the
 // scanner to optionally ignore these or to mark them as such in the
 // attestation.
-type Scanner func(ctx context.Context, name string, ref llb.State, extras map[string]llb.State, opts ...llb.ConstraintsOpt) (result.Attestation[llb.State], error)
+type Scanner func(ctx context.Context, name string, ref llb.State, extras map[string]llb.State, opts ...llb.ConstraintsOpt) (result.Attestation[*llb.State], error)
 
 func CreateSBOMScanner(ctx context.Context, resolver llb.ImageMetaResolver, scanner string) (Scanner, error) {
 	if scanner == "" {
@@ -55,7 +55,7 @@ func CreateSBOMScanner(ctx context.Context, resolver llb.ImageMetaResolver, scan
 		return nil, errors.Errorf("scanner %s does not have cmd", scanner)
 	}
 
-	return func(ctx context.Context, name string, ref llb.State, extras map[string]llb.State, opts ...llb.ConstraintsOpt) (result.Attestation[llb.State], error) {
+	return func(ctx context.Context, name string, ref llb.State, extras map[string]llb.State, opts ...llb.ConstraintsOpt) (result.Attestation[*llb.State], error) {
 		var env []string
 		env = append(env, cfg.Config.Env...)
 		env = append(env, "BUILDKIT_SCAN_DESTINATION="+outDir)
@@ -86,9 +86,9 @@ func CreateSBOMScanner(ctx context.Context, resolver llb.ImageMetaResolver, scan
 		}
 
 		stsbom := runscan.AddMount(outDir, llb.Scratch())
-		return result.Attestation[llb.State]{
+		return result.Attestation[*llb.State]{
 			Kind: gatewaypb.AttestationKindBundle,
-			Ref:  stsbom,
+			Ref:  &stsbom,
 			Metadata: map[string][]byte{
 				result.AttestationReasonKey: []byte(result.AttestationReasonSBOM),
 				result.AttestationSBOMCore:  []byte(CoreSBOMName),
@@ -100,7 +100,7 @@ func CreateSBOMScanner(ctx context.Context, resolver llb.ImageMetaResolver, scan
 	}, nil
 }
 
-func HasSBOM[T any](res *result.Result[T]) bool {
+func HasSBOM[T comparable](res *result.Result[T]) bool {
 	for _, as := range res.Attestations {
 		for _, a := range as {
 			if a.InToto.PredicateType == intoto.PredicateSPDX {

frontend/dockerfile/builder/build.go

@@ -169,7 +169,7 @@ func Build(ctx context.Context, c client.Client) (_ *client.Result, err error) {
 				return err
 			}
 
-			attSolve, err := result.ConvertAttestation(&att, func(st llb.State) (client.Reference, error) {
+			attSolve, err := result.ConvertAttestation(&att, func(st *llb.State) (client.Reference, error) {
 				def, err := st.Marshal(ctx)
 				if err != nil {
 					return nil, err

solver/llbsolver/proc/sbom.go

@@ -52,7 +52,7 @@ func SBOMProcessor(scannerRef string, useCache bool) llbsolver.Processor {
 			if err != nil {
 				return nil, err
 			}
-			attSolve, err := result.ConvertAttestation(&att, func(st llb.State) (solver.ResultProxy, error) {
+			attSolve, err := result.ConvertAttestation(&att, func(st *llb.State) (solver.ResultProxy, error) {
 				def, err := st.Marshal(ctx)
 				if err != nil {
 					return nil, err

solver/result/attestation.go

@@ -1,8 +1,6 @@
 package result
 
 import (
-	"reflect"
-
 	pb "github.com/moby/buildkit/frontend/gateway/pb"
 	digest "github.com/opencontainers/go-digest"
 )
@@ -58,9 +56,11 @@ func FromDigestMap(m map[string]string) []digest.Digest {
 	return ds
 }
 
-func ConvertAttestation[U any, V any](a *Attestation[U], fn func(U) (V, error)) (*Attestation[V], error) {
+func ConvertAttestation[U comparable, V comparable](a *Attestation[U], fn func(U) (V, error)) (*Attestation[V], error) {
+	var zero U
+
 	var ref V
-	if reflect.ValueOf(a.Ref).IsValid() {
+	if a.Ref != zero {
 		var err error
 		ref, err = fn(a.Ref)
 		if err != nil {

solver/result/result.go

@@ -1,13 +1,12 @@
 package result
 
 import (
-	"reflect"
 	"sync"
 
 	"github.com/pkg/errors"
 )
 
-type Result[T any] struct {
+type Result[T comparable] struct {
 	mu           sync.Mutex
 	Ref          T
 	Refs         map[string]T
@@ -50,7 +49,8 @@ func (r *Result[T]) SingleRef() (T, error) {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
-	if r.Refs != nil && !reflect.ValueOf(r.Ref).IsValid() {
+	var zero T
+	if r.Refs != nil && r.Ref == zero {
 		var t T
 		return t, errors.Errorf("invalid map result")
 	}
@@ -77,11 +77,12 @@ func (r *Result[T]) FindRef(key string) (T, bool) {
 }
 
 func (r *Result[T]) EachRef(fn func(T) error) (err error) {
-	if reflect.ValueOf(r.Ref).IsValid() {
+	var zero T
+	if r.Ref != zero {
 		err = fn(r.Ref)
 	}
 	for _, r := range r.Refs {
-		if reflect.ValueOf(r).IsValid() {
+		if r != zero {
 			if err1 := fn(r); err1 != nil && err == nil {
 				err = err1
 			}
@@ -89,7 +90,7 @@ func (r *Result[T]) EachRef(fn func(T) error) (err error) {
 	}
 	for _, as := range r.Attestations {
 		for _, a := range as {
-			if reflect.ValueOf(a.Ref).IsValid() {
+			if a.Ref != zero {
 				if err1 := fn(a.Ref); err1 != nil && err == nil {
 					err = err1
 				}
@@ -102,8 +103,12 @@ func (r *Result[T]) EachRef(fn func(T) error) (err error) {
 // EachRef iterates over references in both a and b.
 // a and b are assumed to be of the same size and map their references
 // to the same set of keys
-func EachRef[U any, V any](a *Result[U], b *Result[V], fn func(U, V) error) (err error) {
-	if reflect.ValueOf(a.Ref).IsValid() && reflect.ValueOf(b.Ref).IsValid() {
+func EachRef[U comparable, V comparable](a *Result[U], b *Result[V], fn func(U, V) error) (err error) {
+	var (
+		zeroU U
+		zeroV V
+	)
+	if a.Ref != zeroU && b.Ref != zeroV {
 		err = fn(a.Ref, b.Ref)
 	}
 	for k, r := range a.Refs {
@@ -111,7 +116,7 @@ func EachRef[U any, V any](a *Result[U], b *Result[V], fn func(U, V) error) (err
 		if !ok {
 			continue
 		}
-		if reflect.ValueOf(r).IsValid() && reflect.ValueOf(r2).IsValid() {
+		if r != zeroU && r2 != zeroV {
 			if err1 := fn(r, r2); err1 != nil && err == nil {
 				err = err1
 			}
@@ -127,7 +132,7 @@ func EachRef[U any, V any](a *Result[U], b *Result[V], fn func(U, V) error) (err
 				break
 			}
 			att2 := atts2[i]
-			if reflect.ValueOf(att.Ref).IsValid() && reflect.ValueOf(att2.Ref).IsValid() {
+			if att.Ref != zeroU && att2.Ref != zeroV {
 				if err1 := fn(att.Ref, att2.Ref); err1 != nil && err == nil {
 					err = err1
 				}
@@ -137,11 +142,13 @@ func EachRef[U any, V any](a *Result[U], b *Result[V], fn func(U, V) error) (err
 	return err
 }
 
-func ConvertResult[U any, V any](r *Result[U], fn func(U) (V, error)) (*Result[V], error) {
+func ConvertResult[U comparable, V comparable](r *Result[U], fn func(U) (V, error)) (*Result[V], error) {
+	var zero U
+
 	r2 := &Result[V]{}
 	var err error
 
-	if reflect.ValueOf(r.Ref).IsValid() {
+	if r.Ref != zero {
 		r2.Ref, err = fn(r.Ref)
 		if err != nil {
 			return nil, err
@@ -152,7 +159,7 @@ func ConvertResult[U any, V any](r *Result[U], fn func(U) (V, error)) (*Result[V
 		r2.Refs = map[string]V{}
 	}
 	for k, r := range r.Refs {
-		if !reflect.ValueOf(r).IsValid() {
+		if r == zero {
 			continue
 		}
 		r2.Refs[k], err = fn(r)