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ANTLR4 Language Target, Runtime for Swift

Performance Note

To use ANTLR4 Swift target in production environment, make sure to turn on compiler optimizations by following these instructions if you use SwiftPM to build your project. If you are using Xcode to build your project, it's unlikely you will not use release build for production build.

Conclusion is, you need to turn on release mode (which will have all the optimization pre configured for you) so the ANTLR4 Swift target can have reasonable parsing speed.

Install ANTLR4

Make sure you have the ANTLR installed. The getting started guide should get you started.

Create a Swift lexer or parser

This is pretty much the same as creating a Java lexer or parser, except you need to specify the language target, for example:

$ antlr4 -Dlanguage=Swift MyGrammar.g4 

If you integrate this as a build step inside Xcode, then you should use the "gnu" message format to have any error messages parsed by Xcode. You may also want to use the -o option to put the autogenerated files in a separate subdirectory.

antlr4 -Dlanguage=Swift -message-format gnu -o Autogen MyGrammar.g4

For a full list of antlr4 tool options, please visit the tool documentation page.

Build your Swift project with ANTLR runtime

Note

We use boot.py script located at the root of the Swift runtime folder antlr4/runtime/Swift to provide additional support for both Xcode-based projects and SPM-based projects. Below sections are organized for both of the flavors. If you want to quickly get started, try:

python boot.py --help

for information about this script.

Xcode Projects

Note that even if you are otherwise using ANTLR from a binary distribution, you should compile the ANTLR Swift runtime from source, because the Swift language does not yet have a stable ABI.

ANTLR uses Swift Package Manager to generate Xcode project files. Note that Swift Package Manager does not currently support iOS, watchOS, or tvOS, so if you wish to use those platforms, you will need to alter the project build settings manually as appropriate.

Download source code for ANTLR

git clone https://github.com/antlr/antlr4

Generate Xcode project for ANTLR runtime

The boot.py script includes a wrapper around swift package generate-xcodeproj. Use this to generate Antlr4.xcodeproj for the ANTLR Swift runtime. (using swift package generate-xcodeproj is not recommended) since the project is dependent on some parser files generated by boot.py.

cd antlr4/runtime/Swift
python boot.py --gen-xcodeproj

Import ANTLR Swift runtime into your project

Open your own project in Xcode.

Open Finder in the runtime/Swift directory:

# From antlr4/runtime/Swift
open .

Drag Antlr4.xcodeproj into your project.

After this is done, your Xcode project navigator will be something like the screenshot below. In this example, your own project is "Smalltalk", and you will be able to see Antlr4.xcodeproj shown as a contained project.

Edit the build settings if necessary

Swift Package Manager currently does not support iOS, watchOS, or tvOS. If you wish to build for those platforms, you will need to alter the project build settings manually.

Add generated parser and lexer to project

Make sure the parsers/lexers generated in step 2 are added to the project. To do this, you can drag the generated files from Finder to the Xcode IDE. Remember to check Copy items if needed to make sure the files are actually moved into the project folder instead of symbolic links (see the screenshot below). After moving you will be able to see your files in the project navigator. Make sure that the Target Membership settings are correct for your project.

Add the ANTLR Swift runtime as a dependency

Select your own project in Xcode and go to the Build Phases settings panel. Add the ANTLR runtime under Target Dependencies and Link Binary With Libraries.

Build your project

The runtime and generated grammar should now build correctly.

Swift Package Manager Projects

Since we cannot have a separate repository for Swift target (see issue #1774), and Swift is currently not ABI stable. We currently support support SPM-based projects by creating temporary local repository.

For people using Swift Package Manager, the boot.py script supports generating local repository that can be used as a dependency to your project. Simply run:

python boot.py --gen-spm-module

The prompt will show something like below:

Put the SPM directive that contains the url to temporary repository to your project's Package.swift. And run swift build in your project.

The project is generated in your system's /tmp/ directory, if you find it inconvenient, consider copy that generated ANTLR repository to some place that won't be cleaned automatically and update url parameter in your Package.swift file.

Swift access levels

You may use the accessLevel option to control the access levels on generated code. This option can either be specified with -DaccessLevel=value on the antlr4 command line, or inside your .g4 file like this:

options {
    accessLevel = 'value';
}

By default (with the accessLevel option unspecified) the generated code uses the following access levels:

  • open for anything that you can feasibly extend with subclassing: the generated parser, lexer, and context classes, the the listener and visitor base classes, and all their accessor and setter functions.
  • public for anything that should not be subclassed, but otherwise is useful to client code: protocols, initializers, and static definitions such as the lexer tokens, symbol names, and so on.
  • internal or private for anything that should not be accessed directly.

If you specify accessLevel = 'public' then all items that are open by default will use public instead. Otherwise, the behavior is the same as the default.

If you specify accessLevel = '' or accessLevel='internal' then all items that are open or public by default will use Swift's default (internal) access level instead.

Those are the only supported values for accessLevel when using the Swift code-generator.

We recommend using accessLevel = ''. Even if you are creating a parser as part of a library, you would usually want to wrap it in an API of your own and keep the ANTLR-generated parser internal to your module. You only need to use the less restrictive access levels if you need to expose the parser directly as part of your own module's API.