Best library for generating Dart code?

[James deBoer]

We are building a tool that will automatically generate Dart code.  What is the best library for generating an AST and producing sane Dart source code?

A few months ago we were working on a project that used analyzer_experimental for reading Dart (http://pub.dartlang.org/packages/analyzer_experimental).  In this case, we want to *write* Dart. Is analyzer_experimental still the way to go or is there something else out there?

Thanks,

James.

[Dan Grove]

+sig...@google.com and justin...@google.com, who have both been working on codegen

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[Erik Grimes]

Hey James!

I haven't found any libraries for this sort of thing, but I've found using mirrors to analyze the source dart code and mustache4dart templates (http://pub.dartlang.org/packages/mustache4dart) to generate the resulting code fairly straightforward. If you need access to more than just source metadata this approach won't work for you. I particularly like using templates for the code generation. I find it makes it easy to visualize and evolve the generated code.

Erik

[Justin Fagnani]

I used dart2js to parse the code and do AST transformations. Fro outputting the code I walked the AST, but to re-create files like they were in the input I had to do a bit of extra bookkeeping on libraries and parts, and pull out source spans if tokens we're contiguous to grab comments and whitespace in certain locations.

You could also using a templating library like mustaches if you're purely generating code, but it won't be much help if you're transforming code.

Cheers,

  Justin

[Peter Ahé]

We added 'BackDoor.compilationUnitsOf(library)' to make it easier to
find compilation units. It's used in this sample:

https://code.google.com/p/dart/source/browse/branches/bleeding_edge/dart/sdk/lib/_internal/compiler/samples/darttags/darttags.dart

Cheers,
Peter

[Siggi Cherem]

We've done a bit of codegen in web_ui/polymer. Both creating code from scratch (for example generating brand new code after interpreting html + MDV bindings), and modifying code in-place (for example the observable transform that changes @observable classes to notify changes proactively).

In both cases we decided to work directly on the text instead of manipulating AST nodes. More specifically, we take code written in Dart, parse it with analyzer experimental and use the AST to understand the code and find where we need to inject our changes. Based on the offset positions that the analyzer gives us, we create a transaction of text edits which we finally commit to generate the final result (see TextEditTransaction below). 

Here are some links to some of our code and a description of what they do. I've been refactoring some of this code recently, so I'm mixing here pointers from new and old code:

• the observable transformer: we recently rewrote the code transformation for @observable as run standalone barback[1] transformer. The code can be found in the observe package: https://github.com/dart-lang/bleeding_edge/blob/master/dart/pkg/observe/lib/transform.dart
  
  
• the old web_ui compiler had a lot of code emitters here https://github.com/dart-lang/web-ui/blob/master/lib/src/emitters.dart. This code used a code generation helper 'CodePrinter'  that helps keep track of indentation, nesting, and source maps. I've recently refactored out common parts of that type and named it NestedPrinter in the source-maps package (more below).

We added to the source_maps package a few handy types that can help generate and transform code:

• TextEditTransaction in refactor.dart: has the logic to help with in-place edits. This type can check that you don't have conflicts in your edits, which is especially useful if you want to do more than 1 change in a file and you want to split the logic of those changes in multiple phases. 
  
• NestedPrinter in printer.dart: has logic for generating text: append text, new lines, track indentation, track source map locations, and nest printers (for example so you can create a printer with the contents of a method, and you want to insert it inside a printer that generates a class).

Hope you find these useful!

Cheers,

Siggi

[1]: barback is the system that pub will use internally to do codegen and code transformations before serving or deploying an app.

On Wed, Aug 21, 2013 at 8:50 AM, Dan Grove <dgr...@google.com> wrote:

[James deBoer]

Sweet, thanks for the responses.  I hope the code we are writing is not that complicated.  Just printing text may be the easiest route.

[Sean Eagan]

I actually just uploaded a codegen pub package yesterday:

pub: http://pub.dartlang.org/packages/codegen

github: https://github.com/seaneagan/codegen

It basically focuses on generating library level stuff (library, part of, import directives, package: URIs, the files themselves, not classes, methods, fields, etc.) so far.  I'm using it to generate locale data code for intlx, cldr, and intl.

Would love to get feedback on it!

Cheers,
Sean Eagan

[Daniel Davidson]

I have a code generation library, maybe similar to Sean Eagan's. The package is called ebisu and it only focuses on the structure, libraries, parts, classes, members, enums etc. It provides protect blocks so code can be regenerated without destroying hand written code. I use it to generate Dart code, D code (ebisu_dlang) and I started using it to generate Web UI components - before switch to polymer. 

The project is: https://github.com/patefacio/ebisu

To get a feel for it, see this which generates the structure of ebisu using ebisu:

https://github.com/patefacio/ebisu/blob/master/bin/ebisu.ebisu.dart

Thanks,

Dan

On Tuesday, August 20, 2013 5:24:00 PM UTC-5, James deBoer wrote:

[Günter Zöchbauer]

I'm looking for a way to generate Dart code or AST programmatically.

Did some new things emerge since this discussion took place?

[Panneerselvam V.]

Hi Günter Zöchbauer,

      I am looking for generating flutter code from scratch, did you find feasible option for generating dart code? Any lead on this topic will be very helpful to me. Thanks!!!

[Samuel Rawlins]

Hi Panneerselvam,

That post is pretty old :) Dart has changed a lot in the last 4.5 years. Luckily it's only gotten better in the code generation story.

The best resource for you is probably the build_runner package. It has a great README. Paired with the build package, you should be able to do some great code generation.

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