2201.2.0 (Swan Lake)

Overview of Ballerina 2201.2.0 (Swan Lake)

2201.2.0 (Swan Lake) is the second major release of 2022, and it includes a new set of features and significant improvements to the compiler, runtime, standard library, and developer tooling. It is based on the 2022R3 version of the Language Specification.

Update Ballerina

If you are already using Ballerina 2201.0.0 (Swan Lake), run either of the commands below to directly update to 2201.2.0 using the Ballerina Update Tool.

bal dist update (or bal dist pull 2201.2.0)

If you are using a version below 2201.0.0 (Swan Lake), run the commands below to update to 2201.2.0.

  1. Run bal update to get the latest version of the Update Tool.

  2. Run bal dist update ( or bal dist pull 2201.2.0) to update your Ballerina version to 2201.2.0.

However, if you are using a version below 2201.0.0 (Swan Lake) and if you already ran bal dist update (or bal dist pull 2201.2.0) before bal update, see Troubleshooting to recover your installation.

Install Ballerina

If you have not installed Ballerina, then download the installers to install.

Migrate from Swan Lake Beta releases

Info: If you have been using Swan Lake Beta releases, delete the Dependencies.toml files in your Ballerina packages when migrating to Ballerina 2201.2.0 (Swan Lake).

A few backward-incompatible changes have been introduced during the Swan Lake Beta program, and thereby, some of your existing packages may not compile with Ballerina 2201.2.0 (Swan Lake). Therefore, you need to delete the Dependencies.toml file to force the dependency resolver to use the latest versions of your dependencies.

Language Updates

New features

Support for resource methods in client objects

Client objects can now contain resource methods. These resource methods can only be accessed by client resource access actions. With this feature, resource methods are also allowed in object-type descriptors.

In the above example, the greeting/[string name] resource in clientObj is accessed with the ->/ call syntax. This notation signifies that it is a resource access action on a client object.

The greeting/James resource access path segments after ->/ specify the target resource to access on the clientObj. The default resource method name will beget if it is not specified in the client resource access action.

Support for creating maps with query expressions

Maps can now be constructed using query expressions. A query expression that constructs a map must start with the map keyword. Further, the type of the select expression must be a tuple [string, T]. Then the query expression will create a value of type map<T>. Duplicate keys will be handled similarly to a query expression constructing a table.

Support for running new strands safely on separate threads

The isolated feature has been extended to identify cases where strands created by a start action or a named worker can be run safely on separate threads.

A start action is isolated if the function or method it calls has a type that is isolated and the expression for every argument is an isolated expression. The object whose method is called by the method call or remote method call is treated as an argument. An isolated start action is allowed in an isolated function and the strand created by the start action will run in a separate thread from the current thread.

The strand created by a named worker can run on a separate thread from the default worker if the body of the worker satisfies the requirements for an isolated function.


Use xml as the contextually-expected type for interpolations in XML template expressions

The contextually-expected type for interpolations in XML template expressions has been changed to xml. This ensures that a query expression as an interpolation works as expected. However, it is not an error for the static type to not be a subtype of the contextually-expected type.

Allow query expressions with readonly contextually-expected types

Query expressions are now allowed with readonly contextually-expected types. Such query expressions create immutable structural values.

Make the variable declaration in the on-fail clause optional

Previously, a variable needed to be declared in the on-fail clause (e.g., on fail error err). It has now been made optional.

Allow actions inside queries

The grammar now allows an action such as a remote method call to occur inside a query.

Add the call langlib function to dynamically call a function

The lang.function:call() langlib function is introduced to call a function dynamically, passing a function value and optionally argument(s) .

If the arguments do not match the parameters expected by the function, the function call results in a panic.

Bug fixes

  • A bug that resulted in allowing access to non-public error intersection types outside the module has been fixed.
  • Fixed a bug that resulted in a compilation error not being logged for invalid usage of an on-conflict clause in a query with inner queries.
  • A bug that resulted in a compilation error not being logged when a spread field is used in a table member to specify a field that is part of the key sequence has been fixed. For every field name in the key sequence of a table, a mapping constructor member must have a specific field corresponding to the field.

To view bug fixes, see the GitHub milestone for 2201.2.0 (Swan Lake).

Runtime updates

New features

Strand dump

Allows getting the status of strands and strand groups during the execution of a Ballerina program.

This can be used to troubleshoot runtime errors. The Ballerina runtime will emit the strand dump to the standard output stream in the text format if it receives a SIGTRAP signal (SIGTRAP is not available on Windows).

E.g., if the PID of the running Ballerina program is $PID, you can get the strand dump by executing either kill -SIGTRAP $PID or kill -5 $PID command.

StopHandler Object

Allows registering a function that will be called during a graceful shutdown.

A call to onGracefulStop will result in one call to the handler function that was passed as an argument; the handler functions will be called after calling gracefulStop on all registered listeners, in the reverse order of the corresponding calls to onGracefulStop.

E.g., a foo function can be called during the graceful shutdown by registering it as follows.



Type-reference type support at runtime

When a type is defined referring to another type, it will now be passed to the runtime as a BTypeReferenceType instance.

For example, the following code contains the Integer and Student type reference types.

Modified existing runtime APIs

The following runtime Java APIs are now supported to return the BTypeReferenceType instances.

New runtime Java API

The following new runtime APIs are added to provide the referred type of a type reference type.

  • TypeUtils.getReferredType()
  • getReferredType() in ReferenceType

In the above example of the Quantity type,
the TypeUtils.getReferredType() call will return the int type instance.
The getReferredType() call on the ReferenceType will return another BTypeReferenceType instance with the Integer name.

Bug fixes

To view bug fixes, see the GitHub milestone for 2201.2.0 (Swan Lake).

Standard library updates

New features

io package
  • Added support for data mapping between Ballerina Records and CSV in CSV read/write APIs.
constraint package
  • Introduced the constraint standard library package, which provides features to validate the values that have been assigned to Ballerina types
http package
  • Implemented the immediateStop() function for the HTTP listener
  • Added the initial support for HATEOAS
  • Added support for client resource methods in the HTTP client
  • Added IP addresses to both local and remote addresses
  • Added proxy support for the HTTP2 client
  • Added constraint validation to HTTP payload binding
websocket package
  • Added constraint validation to WebSocket payload binding
graphql package
  • Added the support for deprecation of fields and enum values
  • Added the support for GraphQL interceptors
serdes package
  • Introduced the serdes standard library package for serializing and deserializing Ballerina anydata subtypes
  • Proto3 is the underlying technology used by this package to achieve serialization and deserialization
os Package
  • Introduced the exec() function to support OS command execution in Ballerina
xmldata package
  • Introduced new APIs such as fromXml and toXml to perform conversions between XML and map<anydata>. The toRecord API is being deprecated by introducing this fromXml API
  • Introduced a new config named rootTag in the JsonOptions to configure the name of the XML root element tag
sql Package
  • Added schema client abstraction to support metadata retrieval from SQL databases. The implementation for the connectors will be added soon
grpc Package
  • Introduced message-level annotations for the proto descriptor instead of a centralized proto descriptor
  • Introduced packaging support
  • Added stub generation support for nested directories
kafka Package
  • Added constraint validation support for payload binding
rabbitmq Package
  • Added constraint validation support for payload binding
nats Package
  • Added constraint validation support for payload binding


http package
  • Made HTTP2 the default transport for the http package
  • Updated the default response status as HTTP 201 for POST resources
random Package
  • Updated the createDecimal() function to be cryptographically secure
grpc Package
  • Added sample client calls with dummy values to generated client files
  • Removed caller client object when generating code in client mode
  • Added a new grpc:Descriptor annotation for services as a replacement for the current grpc:ServiceDescriptor. Both annotations are supported now to maintain backward compatibility. The grpc:ServiceDescriptor will be removed in the future. (Please update the service annotation if stub files are regenerated for the existing gRPC services)

Bug Fixes

To view bug fixes, see the GitHub milestone for 2201.2.0 (Swan Lake).

Code to Cloud updates


The base image was updated to ballerina/jvm-runtime:1.0 based on Alpine 3.15 with the necessary libraries.

Bug fixes

To view bug fixes, see the GitHub milestone for 2201.2.0 (Swan Lake).

Developer tools updates

New features

Language Server
  • Added API docs reference support on hover. Now when you hover over a construct (class, type, function), the hover documentation will include a link to view the API docs specific to that construct
  • Added new code actions to extract anonymous records into records and to generate undefined record types
  • Introduced new source actions to generate getters and setters for class-level variables
  • Added a new code action to make annotation declarations with the source attach point(s) constant
  • Moved the Optimize imports code action to Source action and it no longer appears under the code action bulb. Source actions are displayed under Source action in the context menu
OpenAPI Tool

Added support for generating client resource methods in the client generation command. The preferred client method type can be chosen using the --client-methods=<remote(default)|resource> option.

  • $ bal openapi -i <OpenAPI contract> --client-methods=resource
  • $ bal openapi -i <OpenAPI contract> --mode client --client-methods=resource
SemVer validator CLI tool (Experimental)

Introduced the bal semver CLI command, which attempts to validate Semantic Versioning compatibility of the local package changes against any previously published version(s) in Ballerina Central. Currently, the tool can be used to:

  • list down the source code differences (along with its compatibility impact) between the local and any published versions in Ballerina central
  • suggest the new package version based on the compatibility impact of source code changes

Refer to the examples below which demonstrate a few key functionalities of the SemVer CLI tool.

  • version suggestions
$bal semver             
checking for the latest compatible release version available in central...

current version: 1.2.2-SNAPSHOT
compatibility impact (compared with the release version '1.2.1'): backward-incompatible changes detected
suggested version: 2.0.0
  • version suggestions with the list of source code changes
$bal semver --show-diff
checking for the latest compatible release version available in central...

 Comparing version '1.2.2-SNAPSHOT'(local) with version '1.2.1'(central) 
[+-] package 'io' is modified [version impact: MAJOR]
  [+-] module 'io' is modified [version impact: MAJOR]
    [++] function 'printlnNew' is added [version impact: MINOR]
    [+-] function 'println' is modified [version impact: MAJOR]
      [+-] documentation is modified [version impact: PATCH]
      [--] 'isolated' qualifier is removed [version impact: AMBIGUOUS]
      [++] 'transactional' qualifier is added [version impact: AMBIGUOUS]
      [++] new required parameter 'a' is added [version impact: MAJOR]
      [++] new defaultable parameter 'b' is added [version impact: MINOR]
      [+-] parameter type changed from 'Printable' to 'string' [version impact: AMBIGUOUS]
      [+-] function body is modified [version impact: PATCH]

current version: 1.2.2-SNAPSHOT
compatibility impact (compared with the release version '1.2.1'): backward-incompatible changes detected
suggested version: 2.0.0

Introduced the bal graph CLI command, which resolves the dependencies of the current package and prints the dependency graph in the console. This produces the textual representation of the dependency graph using the DOT graph description language.

Compiler API
  • Introduced a set of builders in the Types API, which are used to construct complex types that have varying components
Ballerina Update Tool


Language Server
  • Improved the Create variable code action in the async send action
  • Added completion support for the resource access action context
OpenAPI Tool

Added support for OpenAPI schema constraint properties in client/service generation. With this improvement, the OpenAPI constraints will be applied as ballerina/constraint standard library package annotations when generating Ballerina clients and services from the OpenAPI definition. The following OpenAPI properties are currently supported in the Ballerina OpenAPI generation tool.

  • minimum, maximum, exclusiveMinimum, and exclusiveMaximum for integer and number types
  • minLength and maxLength for string type
  • minItems and maxItems for array type

To view bug fixes, see the GitHub milestone for 2201.2.0 (Swan Lake) of the repositories below.

JSON to record converter

Improved JSON value to Ballerina record conversion logic, to enhance the conversion experience of Paste JSON as record feature in Ballerina VSCode extension.

Handling of array of elements/objects

Instead of looking at the first object of the array, all elements/objects would be looked at to generate the record field.

Handling optional fields

If an element is present in a JSON object and not in another (in an array of objects), that field would be treated as an optional field.

Handling null values

JSON null fields would be treated as required fields with the anydata type.

Note: The entire JSON value to Ballerina record conversion logic is rewritten to enhance the conversion experience. The above-mentioned scenarios are a few noticeable, important changes.

Compiler API
  • Added semantic API support for the client resource access action

Breaking changes

Ballerina packages updates

New features

Introduced an include field under the [package] table in Ballerina.toml. It accepts a string array of paths to any additional files and directories, which need to be packed in the BALA file. The path should be relative to the package root directory.