bake: composable attributes for attestations support

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

__tests__/.fixtures/bake-03-default.json

@@ -3,6 +3,16 @@
     "default": {
       "context": ".",
       "dockerfile": "Dockerfile",
+      "attest": [
+        {
+          "mode": "max",
+          "type": "provenance"
+        },
+        {
+          "disabled": "true",
+          "type": "sbom"
+        }
+      ],
       "cache-from": [
         {
           "scope": "build",

__tests__/.fixtures/bake-03.hcl

@@ -13,6 +13,10 @@
 // limitations under the License.
 
 target "default" {
+  attest = [
+    "type=provenance,mode=max",
+    "type=sbom,disabled=true",
+  ]
   cache-from = [
     "type=gha,scope=build",
     "user/repo:cache",

src/buildx/bake.ts

@@ -24,7 +24,7 @@ import {Exec} from '../exec';
 import {Util} from '../util';
 
 import {ExecOptions} from '@actions/exec';
-import {BakeDefinition, CacheEntry, ExportEntry, SecretEntry, SSHEntry} from '../types/buildx/bake';
+import {AttestEntry, BakeDefinition, CacheEntry, ExportEntry, SecretEntry, SSHEntry} from '../types/buildx/bake';
 import {BuildMetadata} from '../types/buildx/build';
 import {VertexWarning} from '../types/buildkit/client';
 
@@ -183,6 +183,11 @@ export class Bake {
     // convert to composable attributes: https://github.com/docker/buildx/pull/2758
     for (const name in definition.target) {
       const target = definition.target[name];
+      if (target['attest'] && Array.isArray(target['attest'])) {
+        target['attest'] = target['attest'].map((item: string | AttestEntry): AttestEntry => {
+          return Bake.parseAttestEntry(item);
+        });
+      }
       if (target['cache-from'] && Array.isArray(target['cache-from'])) {
         target['cache-from'] = target['cache-from'].map((item: string | CacheEntry): CacheEntry => {
           return Bake.parseCacheEntry(item);
@@ -213,6 +218,34 @@ export class Bake {
     return definition;
   }
 
+  private static parseAttestEntry(item: AttestEntry | string): AttestEntry {
+    if (typeof item !== 'string') {
+      return item;
+    }
+
+    const attestEntry: AttestEntry = {type: ''};
+    const fields = parse(item, {
+      relaxColumnCount: true,
+      skipEmptyLines: true
+    })[0];
+
+    for (const field of fields) {
+      const [key, value] = field
+        .toString()
+        .split(/(?<=^[^=]+?)=/)
+        .map((item: string) => item.trim());
+      switch (key) {
+        case 'type':
+          attestEntry.type = value;
+          break;
+        default:
+          attestEntry[key] = value;
+      }
+    }
+
+    return attestEntry;
+  }
+
   private static parseCacheEntry(item: CacheEntry | string): CacheEntry {
     if (typeof item !== 'string') {
       return item;

src/types/buildx/bake.ts

@@ -27,7 +27,7 @@ export interface Group {
 export interface Target {
   description?: string;
   args?: Record<string, string>;
-  attest?: Array<string>;
+  attest?: Array<AttestEntry> | Array<string>;
   'cache-from'?: Array<CacheEntry> | Array<string>;
   'cache-to'?: Array<CacheEntry> | Array<string>;
   call?: string;
@@ -50,6 +50,11 @@ export interface Target {
   ulimits?: Array<string>;
 }
 
+export interface AttestEntry {
+  type: string;
+  [key: string]: string;
+}
+
 export interface CacheEntry {
   type: string;
   [key: string]: string;