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109 lines
4.5 KiB
Markdown
109 lines
4.5 KiB
Markdown
# Semantic
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`semantic` is a Haskell library and command line tool for parsing, analyzing, and comparing source code.
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In a hurry? Check out our documentation of [example uses for the `semantic` command line tool](docs/examples.md).
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| Table of Contents |
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| :------------- |
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| [Usage](#usage) |
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| [Language support](#language-support) |
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| [Development](#development) |
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| [Technology and architecture](#technology-and-architecture) |
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| [Licensing](#licensing) |
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## Usage
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Run `semantic --help` for complete list of up-to-date options.
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#### Parse
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```
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Usage: semantic parse [--sexpression | (--json-symbols|--symbols) |
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--proto-symbols | --show | --quiet] [FILES...]
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Generate parse trees for path(s)
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Available options:
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--sexpression Output s-expression parse trees (default)
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--json-symbols,--symbols Output JSON symbol list
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--proto-symbols Output protobufs symbol list
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--show Output using the Show instance (debug only, format
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subject to change without notice)
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--quiet Don't produce output, but show timing stats
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-h,--help Show this help text
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```
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## Language support
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| Language | Parse | AST Symbols† | Stack graphs |
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| :------------- | :---: | :---: | :---: |
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| Ruby | ✅ | ✅ | |
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| JavaScript | ✅ | ✅ | |
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| TypeScript | ✅ | ✅ | 🚧 |
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| Python | ✅ | ✅ | 🚧 |
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| Go | ✅ | ✅ | |
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| PHP | ✅ | ✅ | |
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| Java | 🚧 | ✅ | |
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| JSON | ✅ | ⬜️ | ⬜️ |
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| JSX | ✅ | ✅ | |
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| TSX | ✅ | ✅ | |
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| CodeQL | ✅ | ✅ | |
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| Haskell | 🚧 | 🚧 | |
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† Used for [code navigation](https://help.github.com/en/github/managing-files-in-a-repository/navigating-code-on-github) on github.com.
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* ✅ — Supported
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* 🔶 — Partial support
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* 🚧 — Under development
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* ⬜ - N/A ️
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## Development
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`semantic` requires at least GHC 8.8.1 and Cabal 3.0. We strongly recommend using [`ghcup`][ghcup] to sandbox GHC versions, as GHC packages installed through your OS's package manager may not install statically-linked versions of the GHC boot libraries. `semantic` currently builds only on Unix systems; users of other operating systems may wish to use the [Docker images](https://github.com/github/semantic/packages/11609).
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We use `cabal's` [Nix-style local builds][nix] for development. To get started quickly:
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```bash
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git clone git@github.com:github/semantic.git
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cd semantic
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script/bootstrap
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cabal v2-build all
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cabal v2-test
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cabal v2-run semantic -- --help
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```
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`stack` as a build tool is not officially supported; there is [unofficial `stack.yaml` support](https://github.com/jkachmar/semantic-stack-yaml) available, though we cannot make guarantees as to its stability.
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[nix]: https://www.haskell.org/cabal/users-guide/nix-local-build-overview.html
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[ghcup]: https://www.haskell.org/ghcup/
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## Technology and architecture
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Architecturally, `semantic`:
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1. Reads blobs.
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2. Generates parse trees for those blobs with [tree-sitter][tree-sitter] (an incremental parsing system for programming tools).
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3. Assigns those trees into a generalized representation of syntax.
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4. Performs analysis, computes diffs, or just returns parse trees.
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5. Renders output in one of many supported formats.
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Semantic leverages a number of interesting algorithms and techniques:
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- Myers' algorithm (SES) as described in the paper [*An O(ND) Difference Algorithm and Its Variations*][SES]
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- RWS as described in the paper [*RWS-Diff: Flexible and Efficient Change Detection in Hierarchical Data*][RWS].
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- Open unions and [data types à la carte](http://www.cs.ru.nl/~W.Swierstra/Publications/DataTypesALaCarte.pdf).
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- An implementation of [Abstracting Definitional Interpreters][adi] extended to work with an à la carte representation of syntax terms.
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[SES]: http://www.xmailserver.org/diff2.pdf
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[RWS]: https://db.in.tum.de/~finis/papers/RWS-Diff.pdf
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[adi]: https://plum-umd.github.io/abstracting-definitional-interpreters/
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[tree-sitter]: https://github.com/tree-sitter/tree-sitter
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## Contributions
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Contributions are welcome! Please see our [contribution
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guidelines](CONTRIBUTING.md) and our [code of conduct](CODE_OF_CONDUCT.md) for
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details on how to participate in our community.
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## Licensing
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Semantic is licensed under the [MIT license](LICENSE).
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