common: allow automatic branch following for extensions

When an application or runtime is updated and its metadata requests a
new branch of an extension, Flatpak should automatically pull the new
branch if the user already has at least one branch of that extension
installed.

This ensures that "no-autodownload" extensions (like GIMP plugins)
stay functional after an update that requires a new branch, while still
respecting the user's explicit opt-in (the existing installation of
a previous branch).

Fixes: https://github.com/flatpak/flatpak/issues/4208

common/flatpak-dir.c

@@ -16573,6 +16573,26 @@ add_related (FlatpakDir        *self,
     flatpak_extension_matches_reason (id, download_if, !no_autodownload) ||
     deploy_data != NULL;
 
+  /* Automatic branch following: if this extension wouldn't normally be
+   * auto-downloaded, still download it if there's already an installed branch
+   * of the same extension for this arch. This handles the case where an app
+   * updates its extension version requirement. */
+  if (!download)
+    {
+      g_autoptr(GPtrArray) installed_branches =
+        flatpak_dir_list_refs_for_name (self, FLATPAK_KINDS_RUNTIME, id, NULL, NULL);
+
+      for (size_t i = 0; installed_branches && i < installed_branches->len; i++)
+        {
+          FlatpakDecomposed *installed_ref = g_ptr_array_index (installed_branches, i);
+          if (flatpak_decomposed_is_arch (installed_ref, arch))
+            {
+              download = TRUE;
+              break;
+            }
+        }
+    }
+
   if (!flatpak_extension_matches_reason (id, autoprune_unless, TRUE))
     auto_prune = TRUE;
 

tests/test-extension-branch-follow.sh

@@ -0,0 +1,107 @@
+#!/bin/bash
+
+set -euo pipefail
+
+# shellcheck source=tests/libtest.sh
+# shellcheck disable=SC1091
+. "$(dirname "$0")/libtest.sh"
+
+skip_without_bwrap
+
+echo "1..1"
+
+setup_repo () {
+    mkdir -p repos
+    ostree init --repo=repos/test --mode=archive-z2
+}
+
+make_extension () {
+    local ID=$1
+    local VERSION=$2
+
+    local DIR
+    DIR=$(mktemp -d)
+
+    cat > "${DIR}/metadata" <<EOF
+[Runtime]
+name=${ID}
+EOF
+    mkdir -p "${DIR}/usr"
+    mkdir -p "${DIR}/files"
+    touch "${DIR}/usr/extension-$ID:$VERSION"
+
+    # shellcheck disable=SC2086
+    ${FLATPAK} build-export --no-update-summary --runtime ${GPGARGS-} repos/test "${DIR}" "${VERSION}" >&2
+    update_repo
+    rm -rf "${DIR}"
+}
+
+setup_repo
+
+"$(dirname "$0")/make-test-runtime.sh" repos/test org.test.Platform master "" "" bash ls cat echo readlink > /dev/null
+
+# Create app version 1 with extension version 1.0
+mkdir -p hello
+cat > hello/metadata <<EOF
+[Application]
+name=org.test.Hello
+runtime=org.test.Platform/$(uname -m)/master
+sdk=org.test.Platform/$(uname -m)/master
+
+[Extension org.test.Extension]
+directory=files/ext
+version=1.0
+no-autodownload=true
+EOF
+mkdir -p hello/files/ext
+${FLATPAK} build-finish --no-inherit-permissions hello >&2
+${FLATPAK} build-export --no-update-summary --disable-sandbox repos/test hello master >&2
+update_repo
+
+# Create extension branch 1.0
+make_extension org.test.Extension 1.0
+
+# Install app and extension 1.0
+${FLATPAK} remote-add --user --no-gpg-verify test-repo repos/test >&2
+${FLATPAK} --user install -y test-repo org.test.Hello master >&2
+${FLATPAK} --user install -y test-repo org.test.Extension 1.0 >&2
+
+if ! ${FLATPAK} --user list --runtime | grep -q "org.test.Extension.*1.0"; then
+    ${FLATPAK} --user list --runtime >&2
+    assert_not_reached "Extension 1.0 not installed"
+fi
+echo "# Extension 1.0 installed successfully" >&2
+
+# Create app version 2 with extension version 2.0
+mkdir -p hello2
+cat > hello2/metadata <<EOF
+[Application]
+name=org.test.Hello
+runtime=org.test.Platform/$(uname -m)/master
+sdk=org.test.Platform/$(uname -m)/master
+
+[Extension org.test.Extension]
+directory=files/ext
+version=2.0
+no-autodownload=true
+EOF
+mkdir -p hello2/files/ext
+${FLATPAK} build-finish --no-inherit-permissions hello2 >&2
+${FLATPAK} build-export --no-update-summary --disable-sandbox repos/test hello2 master >&2
+update_repo
+
+# Create extension branch 2.0
+make_extension org.test.Extension 2.0
+
+# Update the app
+${FLATPAK} --user update -y --verbose org.test.Hello master >&2
+
+# Check if extension 2.0 was installed
+${FLATPAK} --user list --runtime >&2
+if ${FLATPAK} --user list --runtime | grep -q "org.test.Extension.*2.0"; then
+    echo "# Success: Extension 2.0 installed automatically after branch follow"
+else
+    assert_not_reached "Extension 2.0 NOT installed automatically"
+fi
+
+ok "extension branch follow"

tests/test-matrix/meson.build

@@ -40,6 +40,7 @@ wrapped_tests += {'name' : 'test-history.sh', 'script' : 'test-history.sh'}
 wrapped_tests += {'name' : 'test-default-remotes.sh', 'script' : 'test-default-remotes.sh'}
 wrapped_tests += {'name' : 'test-metadata-validation.sh', 'script' : 'test-metadata-validation.sh'}
 wrapped_tests += {'name' : 'test-extensions.sh', 'script' : 'test-extensions.sh'}
+wrapped_tests += {'name' : 'test-extension-branch-follow.sh', 'script' : 'test-extension-branch-follow.sh'}
 wrapped_tests += {'name' : 'test-oci.sh', 'script' : 'test-oci.sh'}
 wrapped_tests += {'name' : 'test-override.sh', 'script' : 'test-override.sh'}
 wrapped_tests += {'name' : 'test-auth.sh', 'script' : 'test-auth.sh'}

tests/update-test-matrix

@@ -21,6 +21,7 @@ TEST_MATRIX_SOURCE=(
 	'tests/test-default-remotes.sh' \
 	'tests/test-metadata-validation.sh' \
 	'tests/test-extensions.sh' \
+	'tests/test-extension-branch-follow.sh' \
 	'tests/test-bundle.sh{user+system+system-norevokefs}' \
 	'tests/test-oci.sh' \
 	'tests/test-oci-registry.sh{{user+system},{http+https}}' \