Semantic

semantic is a Haskell library and command line tool for parsing, analyzing, and comparing source code.

In a hurry? Check out our documentation of example uses for the semantic command line tool.

Table of Contents
Usage
Language support
Development
Technology and architecture
Licensing

Usage

Run semantic --help for complete list of up-to-date options.

Parse

Usage: semantic parse ([--sexpression] | [--json] | [--json-graph] | [--symbols]
                      | [--dot] | [--show] | [--quiet]) [FILES...]
  Generate parse trees for path(s)

Available options:
  --sexpression            Output s-expression parse trees (default)
  --json                   Output JSON parse trees
  --json-graph             Output JSON adjacency list
  --symbols                Output JSON symbol list
  --dot                    Output DOT graph parse trees
  --show                   Output using the Show instance (debug only, format
                           subject to change without notice)
  --quiet                  Don't produce output, but show timing stats

Diff

Usage: semantic diff ([--sexpression] | [--json] | [--json-graph] | [--toc] |
                     [--dot] | [--show]) [FILE_A] [FILE_B]
  Compute changes between paths

Available options:
  --sexpression            Output s-expression diff tree (default)
  --json                   Output JSON diff trees
  --json-graph             Output JSON diff trees
  --toc                    Output JSON table of contents diff summary
  --dot                    Output the diff as a DOT graph
  --show                   Output using the Show instance (debug only, format
                           subject to change without notice)

Graph

Usage: semantic graph ([--imports] | [--calls]) [--packages] ([--dot] | [--json]
                      | [--show]) ([--root DIR] [--exclude-dir DIR]
                      DIR:LANGUAGE | FILE | --language ARG (FILES... | --stdin))
  Compute a graph for a directory or from a top-level entry point module

Available options:
  --imports                Compute an import graph (default)
  --calls                  Compute a call graph
  --packages               Include a vertex for the package, with edges from it
                           to each module
  --dot                    Output in DOT graph format (default)
  --json                   Output JSON graph
  --show                   Output using the Show instance (debug only, format
                           subject to change without notice)
  --root DIR               Root directory of project. Optional, defaults to
                           entry file/directory.
  --exclude-dir DIR        Exclude a directory (e.g. vendor)
  --language ARG           The language for the analysis.
  --stdin                  Read a list of newline-separated paths to analyze
                           from stdin.

Language support

Priority	Language	Parse	Assign	Diff	ToC	Symbols	Import graph	Call graph	Control flow graph
1	Ruby	✅	✅	✅	✅	✅	✅	🚧
2	JavaScript	✅	✅	✅	✅	✅	✅	🚧
3	TypeScript	✅	✅	✅	✅	✅	✅	🚧
4	Python	✅	✅	✅	✅	✅	✅	🚧
5	Go	✅	✅	✅	✅	✅	✅	🚧
	PHP	🚧	🚧	🚧	🚧	🚧
	Java	🚧	N/A	🚧	🚧	✅
	JSON	✅	N/A	✅	N/A	N/A	N/A	N/A
	JSX	✅	✅	✅	🔶
	Haskell	🚧	🚧	🚧	🔶	🚧
	Markdown	🚧	🚧	🚧	🚧	N/A	N/A	N/A

• ✅ — Supported
• 🔶 — Partial support
• 🚧 — Under development

Development

semantic requires at least GHC 8.8.1 and Cabal 3.0. We strongly recommend using 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.

We use cabal's Nix-style local builds for development. To get started quickly:

git clone git@github.com:github/semantic.git
cd semantic
script/bootstrap
cabal v2-build
cabal v2-test
cabal v2-run semantic -- --help

stack as a build tool is not officially supported; there is an unofficial stack.yaml available, though we cannot make guarantees as to its stability.

Technology and architecture

Architecturally, semantic:

1. Reads blobs.
2. Generates parse trees for those blobs with tree-sitter (an incremental parsing system for programming tools).
3. Assigns those trees into a generalized representation of syntax.
4. Performs analysis, computes diffs, or just returns parse trees.
5. Renders output in one of many supported formats.

Semantic leverages a number of interesting algorithms and techniques:

• Myers' algorithm (SES) as described in the paper An O(ND) Difference Algorithm and Its Variations
• RWS as described in the paper RWS-Diff: Flexible and Efficient Change Detection in Hierarchical Data.
• Open unions and data types à la carte.
• An implementation of Abstracting Definitional Interpreters extended to work with an à la carte representation of syntax terms.

Contributions

Contributions are welcome! Please see our contribution guidelines and our code of conduct for details on how to participate in our community.

Licensing

Semantic is licensed under the MIT license.