Semantic : Parsing, Analysing & Comparing Source Code Across Many Languages

Semantic is a Haskell library and command line tool for parsing, analysing, and comparing source code.

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

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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

Development

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

git clone git@github.com:github/semantic.git
cd semantic
git submodule sync –recursive && git submodule update –init –recursive –force
cabal new-update
cabal new-build
cabal new-test
cabal new-run semantic — –help

It requires at least GHC 8.6.4 and Cabal 2.4. We recommend using ghcup to sandbox GHC versions. 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:

• Reads blobs.
• Generates parse trees for those blobs with tree-sitter (an incremental parsing system for programming tools).
• Assigns those trees into a generalized representation of syntax.
• Performs analysis, computes diffs, or just returns parse trees.
• 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.