vm_image_util: Share the Vagrant metadata JSON between providers

We currently publish separate metadata for each provider, VirtualBox and
Parallels, but you're supposed to combine these and let Vagrant choose
the provider.

Rewriting an existing output file is a little weird, but this use of jq
makes it relatively safe.

Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>

build_library/vm_image_util.sh

@@ -954,9 +954,15 @@ write_vm_bundle() {
 
 _write_box_bundle() {
     local box=$(_dst_path ".box")
-    local json=$(_dst_path ".json")
     local image=${VM_DST_IMG}
-    local provider="virtualbox"
+
+    # Share the metadata JSON between providers.
+    local json=${VM_SRC_IMG##*/}
+    json=$(_dst_dir)/${json%_image.bin}_vagrant.json
+
+    local -xI FLATCAR_VERSION FLATCAR_VERSION_ID VM_GROUP
+    local -x provider="virtualbox"
+    local -x arch=${BOARD%-usr}
 
     if [[ "${VM_IMG_TYPE}" == vagrant_parallels ]]; then
         provider="parallels"
@@ -966,28 +972,37 @@ _write_box_bundle() {
         mv "$(_dst_path ".pvs")" "${image}"/config.pvs
     fi
 
-    cat > "${VM_TMP_DIR}"/box/metadata.json <<EOF
-{"provider": "${provider}"}
-EOF
+    jq -n '{ provider: env.provider, architecture: env.arch }' > "${VM_TMP_DIR}"/box/metadata.json
 
     mv "${image}" "${VM_TMP_DIR}/box"
     tar -czf "${box}" -C "${VM_TMP_DIR}/box" .
 
-    cat >"${json}" <<EOF
-{
-  "name": "flatcar-${VM_GROUP}",
-  "description": "Flatcar ${VM_GROUP}",
-  "versions": [{
-    "version": "${FLATCAR_VERSION_ID}",
-    "providers": [{
-      "name": "${provider}",
-      "url": "https://${BUILDCACHE_SERVER:-bincache.flatcar-linux.net}/images/${BOARD%-usr}/${FLATCAR_VERSION}/$(_dst_name ".box")",
-      "checksum_type": "sha256",
-      "checksum": "$(sha256sum "${box}" | awk '{print $1}')"
-    }]
-  }]
-}
-EOF
+    local -x checksum=$(sha256sum "${box}")
+    checksum=${checksum%% *}
+
+    # Fetch existing box entries for this Flatcar version that do not match the
+    # provider or architecture we're about to add.
+    local existing="[]"
+    [[ -e ${json} ]] &&
+        existing=$(jq '[ .versions[] | select(.version == env.FLATCAR_VERSION_ID) | .providers[] |
+                         select(.name != env.provider or .architecture != env.arch) ]' "${json}")
+
+    # Generate a new metadata JSON that includes the existing box entries.
+    jq -n --argjson existing "${existing}" --arg server "${BUILDCACHE_SERVER:-bincache.flatcar-linux.net}" --arg box "${box##*/}" '{
+        name: "flatcar-\(env.VM_GROUP)",
+        description: "Flatcar \(env.VM_GROUP)",
+        versions: [{
+            version: env.FLATCAR_VERSION_ID,
+            providers: $existing + [{
+                name: env.provider,
+                url: "https://\($server)/images/\(env.arch)/\(env.FLATCAR_VERSION)/\($box)",
+                checksum_type: "sha256",
+                checksum: env.checksum,
+                architecture: env.arch
+            }]
+        }]
+    }' > "${json}"
+
     VM_GENERATED_FILES+=( "${box}" "${json}" )
 }