https://github.com/werediver/dart-reptr-rs

Fast code generation for Dart. Eventually. Maybe.
https://github.com/werediver/dart-reptr-rs

Last synced: 11 months ago
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Fast code generation for Dart. Eventually. Maybe.

• Host: GitHub
• URL: https://github.com/werediver/dart-reptr-rs
• Owner: werediver
• License: mit
• Created: 2022-11-13T21:06:59.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2023-09-20T17:40:32.000Z (over 2 years ago)
• Last Synced: 2024-10-19T07:54:29.115Z (over 1 year ago)
• Language: Rust
• Size: 143 KB
• Stars: 5
• Watchers: 3
• Forks: 3
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
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# Dart repointer

Dart repointer (`reptr`) ~~puts the sharp part in your Dart~~ aims to facilitate _fast_ code generation for Dart. It consists of [the tool itself](reptr/) and a [Dart parser library](dart-parser).

## Motivation

`build_runner`-based code generation for a single package can take a couple minutes. This translates to unreasonably long code generation time for large Dart and Flutter projects (e.g. over 45 minutes 🤯). This is predominantly due to inefficiencies in the code generation infrastructure, the `build_runner`. A faster implementation should allow 20–50x speed-up.

## Project structure

The key components of this project that are already functional are:

- Filesystem scanner

  - Identifies Dart packages and source files on the filesystem

- File loader

  - Loads a file into memory, performs UTF-8 validation

- Parser (lexerless)

  - Constructs an abstract syntax tree from the loaded Dart code

```mermaid

flowchart LR

  CLI --> Scanner[F/s scanner] --> Loader --> Parser["Parser\n(lexerless)"] --> Gen1 & Gen2 --> Combiner --> Writer --> Formatter[External formatter]

  CLI --> Reporter[Status / progress reporter]

  CLI --> Watcher[F/s watcher]

  subgraph Generator 1

    Gen1[...]

  end

  subgraph Generator 2

    Gen2[...]

  end

  style Reporter stroke-dasharray: 5 5

  style Watcher stroke-dasharray: 5 5

  style Gen1 stroke-dasharray: 5 5

  style Gen2 stroke-dasharray: 5 5

  style Combiner stroke-dasharray: 5 5

  style Writer stroke-dasharray: 5 5

  style Formatter stroke-dasharray: 5 5

```

## Design notes

- Loading source files

  - Loading the complete file for parsing is fine

  - Memory-mapping is not faster per se

    - May play nicely with a lazy tokenizer with lazy UTF-8 validation

- Parsing

  - The parser is a _partial_ parser: it recognizes certain parts of the target language and can skip over the rest

  - Capturing slices of the source (`&str`) is extremely cheap (doesn't cause memory allocation), so take advantage of that

  - When feasible, avoid memory allocation (namely, the use of `Vec` and co.)

  - When implementing a parser as a function

    - Do not start parsing with whitespace

      - E.g. the import-stmt. parser should start with consuming `import`, not whitespace

    - Do not consume the trailing whitespace after a construct (e.g. in `import 'dart:math';\n\n` do not consume `\n\n`)

  - When combining parsers

    - Prefer consuming whitespace in trailing position, not leading

- A tempting feature: in-place code generation / code transformation

  - Requires accurate back-to-source transformation

- Output formatting

  - Delegate to [dart format](https://dart.dev/tools/dart-format) (it's fast enough)