bake: add attest field

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

bake/bake.go

@@ -551,6 +551,7 @@ type Target struct {
 	// Inherits is the only field that cannot be overridden with --set
 	Inherits []string `json:"inherits,omitempty" hcl:"inherits,optional"`
 
+	Attest           []string          `json:"attest,omitempty" hcl:"attest,optional"`
 	Context          *string           `json:"context,omitempty" hcl:"context,optional"`
 	Contexts         map[string]string `json:"contexts,omitempty" hcl:"contexts,optional"`
 	Dockerfile       *string           `json:"dockerfile,omitempty" hcl:"dockerfile,optional"`
@@ -576,6 +577,7 @@ type Target struct {
 }
 
 func (t *Target) normalize() {
+	t.Attest = removeDupes(t.Attest)
 	t.Tags = removeDupes(t.Tags)
 	t.Secrets = removeDupes(t.Secrets)
 	t.SSH = removeDupes(t.SSH)
@@ -629,6 +631,9 @@ func (t *Target) Merge(t2 *Target) {
 	if t2.Target != nil {
 		t.Target = t2.Target
 	}
+	if t2.Attest != nil { // merge
+		t.Attest = append(t.Attest, t2.Attest...)
+	}
 	if t2.Secrets != nil { // merge
 		t.Secrets = append(t.Secrets, t2.Secrets...)
 	}
@@ -711,6 +716,8 @@ func (t *Target) AddOverrides(overrides map[string]Override) error {
 			t.Platforms = o.ArrValue
 		case "output":
 			t.Outputs = o.ArrValue
+		case "attest":
+			t.Attest = o.ArrValue
 		case "no-cache":
 			noCache, err := strconv.ParseBool(value)
 			if err != nil {
@@ -964,6 +971,12 @@ func toBuildOpt(t *Target, inp *Input) (*build.Options, error) {
 	}
 	bo.Exports = outputs
 
+	attests, err := buildflags.ParseAttests(t.Attest)
+	if err != nil {
+		return nil, err
+	}
+	bo.Attests = attests
+
 	return bo, nil
 }