Cherry-pick #9817: Remove database on schema downgrade

platform/default/mbgl/storage/offline_database.cpp

@@ -50,7 +50,7 @@ void OfflineDatabase::ensureSchema() {
             case 3: // no-op and fall through
             case 4: migrateToVersion5(); // fall through
             case 5: return;
-            default: throw std::runtime_error("unknown schema version");
+            default: break; // downgrade, delete the database
             }
 
             removeExisting();

test/storage/offline_database.test.cpp

@@ -634,6 +634,17 @@ static int databaseSyncMode(const std::string& path) {
     return stmt.get<int>(0);
 }
 
+static std::vector<std::string> databaseTableColumns(const std::string& path, const std::string& name) {
+    mapbox::sqlite::Database db(path, mapbox::sqlite::ReadOnly);
+    const auto sql = std::string("pragma table_info(") + name + ")";
+    mapbox::sqlite::Statement stmt = db.prepare(sql.c_str());
+    std::vector<std::string> columns;
+    while (stmt.run()) {
+        columns.push_back(stmt.get<std::string>(1));
+    }
+    return columns;
+}
+
 TEST(OfflineDatabase, MigrateFromV2Schema) {
     using namespace mbgl;
 
@@ -698,3 +709,27 @@ TEST(OfflineDatabase, MigrateFromV4Schema) {
     // Synchronous setting should be FULL (2) after migration to v5.
     EXPECT_EQ(2, databaseSyncMode("test/fixtures/offline_database/v5.db"));
 }
+
+TEST(OfflineDatabase, DowngradeSchema) {
+    using namespace mbgl;
+
+    // v999.db is a v999 database, it should be deleted
+    // and recreated with the current schema.
+
+    deleteFile("test/fixtures/offline_database/migrated.db");
+    writeFile("test/fixtures/offline_database/migrated.db", util::read_file("test/fixtures/offline_database/v999.db"));
+
+    {
+        OfflineDatabase db("test/fixtures/offline_database/migrated.db", 0);
+    }
+
+    EXPECT_EQ(5, databaseUserVersion("test/fixtures/offline_database/migrated.db"));
+
+    EXPECT_EQ((std::vector<std::string>{ "id", "url_template", "pixel_ratio", "z", "x", "y",
+                                         "expires", "modified", "etag", "data", "compressed",
+                                         "accessed" }),
+              databaseTableColumns("test/fixtures/offline_database/migrated.db", "tiles"));
+    EXPECT_EQ((std::vector<std::string>{ "id", "url", "kind", "expires", "modified", "etag", "data",
+                                         "compressed", "accessed" }),
+              databaseTableColumns("test/fixtures/offline_database/migrated.db", "resources"));
+}