Sem: New primitive for code understanding – not LSPs, but entities on top of Git
摘要
标题为 Sem: New primitive for code understanding – not LSPs, but entities on top of Git；正文介绍 Git 之上构建的语义理解原语，包括 diff、blame、impact、log、entities、context 六条命令和一个二进制文件；具体描述 sem diff 是实体级 diff（含重命名检测、结构哈希和单词级内联高亮）、sem blame 显示每个函数/类/方法的最后修改提交、sem impact 展示跨文件依赖图与受影响测试、sem log 记录单个实体的 Git 历史、sem entities 列出路径下所有函数/类/方法/类型及行范围、sem context 给出带依赖关系和依赖者的实体级上下文；所有命令均支持 --json；支持 26 种语言和 5 种数据格式，无需配置；典型 diff 时间 8ms；下载量 4,000+；安装方式为 brew install sem-cli 或 cargo install --git https://github.com/Ataraxy-Labs/sem sem-cli；提到 AI 代理使用 sem 输出比原始行 diff 准确率高 2.3 倍。
荐读理由
用 sem diff 就能把 git diff 换成实体级 diffs、rename detection、structural hashing 和 word-level inline highlights，3 秒内把函数改动看清，8ms 典型时间直接抄到项目里
原文
Know what changed.
Semantic understanding on top of Git. Diff, blame, impact, log. Functions, not lines.
copied $ brew install sem-cli
~/project
Same commit. Different lens.
Left: what git shows you. Right: what actually happened.
git diff
diff --git a/src/auth/login.ts b/src/auth/login.ts
index 4a2b1c0..8f3d2e1 100644
--- a/src/auth/login.ts
+++ b/src/auth/login.ts
@@ -12,6 +12,18 @@
+export function validateToken(token: string) {
+ const decoded = jwt.verify(token, SECRET);
+ if (!decoded.exp || decoded.exp < Date.now()) {
+ throw new TokenExpiredError();
+ }
+ return decoded;
+}
+
@@ -24,8 +36,10 @@
export async function authenticateUser(
- const user = await db.findUser(email);
- if (!user) return null;
+ const user = await db.findUser(email);
+ if (!user) throw new UserNotFoundError();
+ await rateLimiter.check(email);
@@ -45,12 +59,0 @@
-export function legacyAuth(user, pass) {
- return db.query('SELECT * FROM users
- WHERE email = ? AND password = ?',
- [user, pass]);
-}
sem diff
┌─ src/auth/login.ts ────────────────
│
│ ⊕ function validateToken [added]
│ ∆ function authenticateUser [modified]
│ ⊖ function legacyAuth [deleted]
│
└────────────────────────────────────
3 entities changed across 1 file
AI agents are 2.3x more accurate when given sem output vs raw line diffs. See the benchmark.
Six commands. One binary.
Everything works in any Git repo. No config. No plugins.
sem diff
What changed? Entity-level diffs with rename detection, structural hashing, and word-level inline highlights.
│ ⊕ function validateToken [added]
│ ∆ function authenticateUser [modified]
│ ⊖ function legacyAuth [deleted]
sem blame
Who changed it? Per-entity blame showing the last commit that touched each function, class, or method.
│ ⊕ render_inline_diff a1a6fbf Rohan 04-03
│ ⊕ format_terminal a1a6fbf Rohan 04-03
sem impact
What breaks? Cross-file dependency graph shows every entity that depends on a given function, plus affected tests.
⊕ function authenticateUser
→ depends on: db.findUser, rateLimiter
← used by: loginRoute, authMiddleware
! 42 entities transitively affected
sem log
How did it evolve? Git history for a single entity. See every commit that touched a specific function.
│ ae576ab Rohan 02-05 added
│ a105183 Rohan 02-08 modified (logic)
│ a1a6fbf Rohan 04-03 modified (logic)
sem entities
What's under a path? Lists every function, class, method, and type with line ranges.
entities: src/auth/login.ts
function validateToken (L12:24)
function authenticateUser (L26:45)
interface AuthConfig (L47:52)
sem context
Smart context for AI. Token-budgeted context window: the entity, its dependencies, and dependents. Fits in any LLM prompt.
context for authenticateUser (budget: 8000)
target: ~705 tokens
dependencies: ~256 tokens
dependents: ~812 tokens
All commands support --json for machine-readable output. Full reference.
Your stack. Covered.
26 languages. 5 data formats. One binary.
TypeScript
JavaScript
Python
Go
Rust
Java
C
C++
C#
Ruby
PHP
Swift
Kotlin
Elixir
Bash
HCL
Fortran
Vue
Svelte
XML
ERB
Dart
Perl
OCaml
Scala
Zig
JSON
YAML
TOML
CSV
Markdown
8ms typical diff
26 languages
0 config needed
4,000+ downloads
Try it. 10 seconds.
$ brew install sem-cli
$ sem setup
✓ Created wrapper script
✓ Set git config --global diff.external = sem
✓ Pre-commit hook installed
Done! Running git diff in any repo will now use sem.
To revert, run: sem unsetup
One command. Every git diff becomes a sem diff. No config files.
Also: cargo install --git https://github.com/Ataraxy-Labs/sem sem-cli
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