Sem – Semantic version control. Entity-level diffs on top of Git

Source: Hacker News

Overview

Semantic version control. Entity‑level diffs on top of Git.

Instead of line 43 changed, sem tells you function validateToken was added in src/auth.ts.

sem diff

┌─ src/auth/login.ts ──────────────────────────────────
│
│  ⊕ function  validateToken          [added]
│  ∆ function  authenticateUser       [modified]
│  ⊖ function  legacyAuth             [deleted]
│
└──────────────────────────────────────────────────────

┌─ config/database.yml ─────────────────────────────────
│
│  ∆ property  production.pool_size   [modified]
│    - 5
│    + 20
│
└──────────────────────────────────────────────────────

Summary: 1 added, 1 modified, 1 deleted across 2 files

Install

Build from source (requires Rust):

git clone https://github.com/Ataraxy-Labs/sem
cd sem/crates
cargo install --path sem-cli

Or grab a binary from GitHub Releases.

Usage

Works in any Git repo. No setup required.

• Semantic diff of working changes

  sem diff

• Staged changes only

  sem diff --staged

• Specific commit

  sem diff --commit abc1234

• Commit range

  sem diff --from HEAD~5 --to HEAD

• JSON output (for AI agents, CI pipelines)

  sem diff --format json

• Read file changes from stdin (no git repo needed)

  echo '[{"filePath":"src/main.rs","status":"modified","beforeContent":"...","afterContent":"..."}]' \
    | sem diff --stdin --format json

• Only specific file types

  sem diff --file-exts .py .rs

• Entity dependency graph

  sem graph

• Impact analysis (what breaks if this entity changes?)

  sem impact validateToken

• Entity‑level blame

  sem blame src/auth.ts

What it parses

Programming languages (13)

Structured data formats

Everything else falls back to chunk‑based diffing.

How matching works

Three‑phase entity matching:

1. Exact ID match – same entity in before/after → modified or unchanged.
2. Structural hash match – same AST structure, different name → renamed or moved (ignores whitespace/comments).
3. Fuzzy similarity – > 80 % token overlap → probable rename.

This allows sem to detect renames and moves, not just additions and deletions. Structural hashing also distinguishes cosmetic changes (whitespace, formatting) from real logic changes.

JSON output

{
  "summary": {
    "fileCount": 2,
    "added": 1,
    "modified": 1,
    "deleted": 1,
    "total": 3
  },
  "changes": [
    {
      "entityId": "src/auth.ts::function::validateToken",
      "changeType": "added",
      "entityType": "function",
      "entityName": "validateToken",
      "filePath": "src/auth.ts"
    }
  ]
}

As a library

sem-core can be used as a Rust library dependency:

[dependencies]
sem-core = { git = "https://github.com/Ataraxy-Labs/sem", version = "0.3" }

Used by weave (semantic merge driver) and inspect (entity‑level code review).

Architecture

• tree‑sitter for code parsing (native Rust, not WASM)
• git2 for Git operations
• rayon for parallel file processing
• xxhash for structural hashing
• Plugin system for adding new languages and formats

Star History

License

MIT OR Apache‑2.0