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pr-description skill

Generate a pull request description from the current git diff.

Trigger

Use this skill when the user runs /pr-description or asks to "generate a PR description", "write a PR description", or "describe this PR".

Instructions

Step 1: Get the diff

Run the following to determine what changed:

git diff main 2>/dev/null

If that returns nothing (no commits on main yet, or branch is main), fall back to:

git diff --staged

If that also returns nothing, try:

git diff HEAD~1 2>/dev/null

Also collect commit messages for context:

git log main..HEAD --oneline 2>/dev/null || git log --oneline -10 2>/dev/null

If there are many commits on the branch, use git log main..HEAD (without --oneline) to read the full message bodies — they often contain context that improves the summary.

Step 2: Detect the language and ecosystem

Before parsing the diff, identify what kind of project this is. This affects type detection, test commands, and "How to test" steps.

Indicator files Ecosystem
package.json, *.ts, *.tsx, *.js JavaScript / TypeScript
pyproject.toml, setup.py, requirements.txt, *.py Python
go.mod, *.go Go
Cargo.toml, *.rs Rust
build.sbt, *.scala Scala / JVM
pom.xml, build.gradle, *.java Java / JVM
build.gradle.kts, *.kt, *.kts Kotlin
*.rb, Gemfile Ruby
*.swift, Package.swift Swift
pubspec.yaml, *.dart Dart / Flutter
composer.json, *.php PHP
*.csproj, *.sln, *.cs C# / .NET
CMakeLists.txt, Makefile, *.cpp, *.c, *.h C / C++
mix.exs, *.ex, *.exs Elixir
*.cabal, stack.yaml, *.hs Haskell
project.clj, deps.edn, *.clj, *.cljs Clojure
*.cbl, *.cob, *.cpy COBOL
*.tf, *.hcl Terraform / Infrastructure
*.yaml, *.yml in .github/workflows/ CI/CD (GitHub Actions)

Use the detected ecosystem to choose the right test commands in Step 3.

Step 3: Parse the diff

Analyze the diff output to identify:

  1. Files changed — group by area (e.g., src/auth/, tests/, config files)
  2. Commit type — infer from commit messages first; fall back to file-path patterns in references/conventional-commits.md
  3. Scope — if present in commit messages (e.g., feat(auth):), include in summary context
  4. Breaking changes — look for BREAKING CHANGE: in commits, removed exports, renamed public APIs, changed function signatures, removed CLI flags, changed config keys
  5. What actually changed — summarize the intent of each change, not just the mechanics

Type detection by file path (language-aware)

JavaScript / TypeScript

  • package.json, *.lock, .nvmrc → chore
  • *.test.ts, *.spec.ts, __tests__/ → test
  • .github/workflows/ → ci
  • *.md → docs
  • New exported function/class/hook → feat
  • Bugfix in existing function body → fix

Python

  • pyproject.toml, requirements*.txt, setup.cfg → chore
  • test_*.py, *_test.py, tests/ → test
  • *.md, docstring-only changes → docs
  • New function/class definition → feat
  • Fix in conditional, exception handling → fix

Go

  • go.mod, go.sum → chore
  • *_test.go → test
  • .github/workflows/ → ci
  • New exported function (func [A-Z]) → feat
  • Fix to error handling, nil checks → fix

Rust

  • Cargo.toml, Cargo.lock → chore
  • #[cfg(test)] blocks, tests/ → test
  • New pub fn, pub struct, pub trait → feat
  • Fix to unwrap, expect, error propagation → fix

Scala / JVM

  • build.sbt, pom.xml, build.gradle, *.conf → chore
  • *Test.scala, *Spec.scala, *Suite.scala → test
  • New class, object, trait, def → feat
  • Fix to pattern match, Option handling → fix

Kotlin

  • build.gradle.kts, *.kts → chore
  • *Test.kt, *Spec.kt → test
  • New fun, class, interface, object → feat
  • Fix to null safety (?., !!), exception handling → fix

Dart / Flutter

  • pubspec.yaml, pubspec.lock → chore
  • *_test.dart, test/ → test
  • New Widget, StatefulWidget, StatelessWidget → feat
  • Fix to null handling, async/await → fix

PHP

  • composer.json, composer.lock → chore
  • *Test.php, tests/ → test
  • New class, interface, trait → feat
  • Fix to conditionals, exception handling → fix

C# / .NET

  • *.csproj, *.sln, NuGet.Config → chore
  • *Tests.cs, *Test.cs, Tests/ → test
  • New public class, interface, record → feat
  • Fix to null checks, exception handling → fix
  • Run tests: dotnet test | Run app: dotnet run

C / C++

  • CMakeLists.txt, Makefile, conanfile.txt → chore
  • *_test.cpp, *_test.c, tests/ → test
  • New function declaration in header → feat
  • Fix to pointer handling, bounds checks, memory management → fix
  • Run tests: make test or ctest | Build: make or cmake --build .

Elixir

  • mix.exs, mix.lock → chore
  • *_test.exs, test/ → test
  • New def, defmodule, defmacro → feat
  • Fix to pattern match, error tuple handling → fix
  • Run tests: mix test | Run app: mix run or iex -S mix

Haskell

  • *.cabal, stack.yaml, package.yaml → chore
  • *Spec.hs, test/ → test
  • New top-level function, typeclass instance → feat
  • Fix to pattern match, Maybe/Either handling → fix
  • Run tests: stack test or cabal test | Run app: stack run

Clojure

  • project.clj, deps.edn, shadow-cljs.edn → chore
  • *_test.clj, test/ → test
  • New defn, defprotocol, defrecord → feat
  • Fix to nil handling, exception catching → fix
  • Run tests: lein test or clj -M:test | Run app: lein run

COBOL

  • *.cbl, *.cob, *.cpy are all source files — no separate test file convention; note test procedures inline
  • Changes to WORKING-STORAGE SECTION → data structure change (feat or refactor)
  • Changes to PROCEDURE DIVISION → logic change (feat or fix)
  • Changes to COPY statements or copybooks (*.cpy) → chore or refactor
  • Breaking changes: renamed COPY members, removed 01 level fields used by callers, changed LINKAGE SECTION interface
  • Run/compile: cobc -x program.cbl && ./program (GnuCOBOL) or per-mainframe JCL

Infrastructure / Terraform

  • *.tf, *.tfvars → chore or feat depending on whether it's new infra
  • *.yaml in .github/workflows/ → ci
  • Dockerfile, docker-compose.yml → chore or ci

Step 4: Generate the PR description

Output exactly the following markdown structure. Check the correct box for the detected commit type (replace [ ] with [x]). If multiple types apply, check all that match.

## Summary
{1-2 sentences describing what this PR does and why}

## Type of change
- [ ] feat: new feature
- [ ] fix: bug fix
- [ ] refactor: code change that doesn't add features or fix bugs
- [ ] chore: dependency updates, config, tooling
- [ ] docs: documentation only
- [ ] perf: performance improvement
- [ ] test: adding or updating tests
- [ ] ci: CI/CD changes

## What changed
{Bullet points grouped by file or feature area. Be specific about what changed, not just that a file changed.}

## How to test
{Numbered steps a reviewer would take to verify the changes work correctly}

## Breaking changes
{List breaking changes, or write "None"}

"How to test" commands by ecosystem

Use the right command for the project type:

Ecosystem Run tests Start / build
JavaScript / TypeScript npm test or pnpm test or bun test npm run dev
Python pytest or python -m pytest uvicorn main:app or python manage.py runserver
Go go test ./... go run .
Rust cargo test cargo run
Scala (sbt) sbt test sbt run
Java (Maven) mvn test mvn spring-boot:run
Java (Gradle) ./gradlew test ./gradlew bootRun
Kotlin (Gradle) ./gradlew test ./gradlew run
Ruby bundle exec rspec rails server
Swift swift test swift run
Dart / Flutter flutter test flutter run
PHP ./vendor/bin/phpunit php artisan serve (Laravel) or php -S localhost:8000
C# / .NET dotnet test dotnet run
C / C++ make test or ctest make or cmake --build .
Elixir mix test iex -S mix
Haskell stack test or cabal test stack run
Clojure lein test or clj -M:test lein run
COBOL (GnuCOBOL) Manual procedure walkthrough cobc -x program.cbl && ./program

If multiple package managers are possible (e.g., npm vs pnpm), check for a lockfile: pnpm-lock.yaml → pnpm, bun.lockb → bun, yarn.lock → yarn, package-lock.json → npm.

Common scenarios

Scenario: dependency update only

  • All changes are in package.json / go.mod / Cargo.toml / requirements.txt
  • Type: chore
  • "How to test": install deps and run the test suite

Scenario: new feature with tests

  • New source file + new test file
  • Type: feat + test
  • Group source and test files together in "What changed"

Scenario: bug fix

  • Change is inside an existing function — conditional logic, null check, error handling
  • Type: fix
  • "How to test": describe the specific scenario that previously failed

Scenario: config or infrastructure change

  • Changes to .conf, .env.example, *.tf, docker-compose.yml
  • Type: chore (or ci if CI/CD related)
  • "How to test": describe how to verify the config takes effect

Scenario: large PR with many commits

  • Run git log main..HEAD (full messages) to understand intent across commits
  • Summarize the overall goal in "Summary", not each individual commit
  • Group "What changed" by feature area, not by commit

Scenario: breaking change

  • Removed export, renamed public API, changed function signature, removed config key
  • Check BREAKING CHANGE: in commit footers
  • List specifics in "Breaking changes": what was removed/renamed and what replaces it

Edge cases

  • On main with no upstream branch — use git diff --staged to pick up staged changes; if nothing staged, use git diff HEAD~1
  • Merge commits in the diff — ignore them; focus on the actual file changes
  • Binary files changed (images, fonts) — note them briefly in "What changed" but don't describe the binary contents
  • Generated files (e.g., *.pb.go, package-lock.json, yarn.lock, migration files) — note that they are auto-generated and skip detailed analysis of their contents
  • Whitespace-only changes — classify as style, not refactor
  • Empty diff — tell the user: "No changes detected. Make sure you have uncommitted changes or commits ahead of main."

Output checklist (self-review before responding)

Before outputting the PR description, verify:

  • Summary is 1-2 sentences and written from a reviewer's perspective
  • At least one type checkbox is checked
  • Every bullet in "What changed" corresponds to an actual file or group of files in the diff
  • "How to test" steps use the correct commands for this project's ecosystem
  • "Breaking changes" is either a specific list or "None" — never left blank

Guidelines

  • Write the Summary from the perspective of a reviewer seeing this PR for the first time
  • In "What changed", group related files together (e.g., group test files with the code they test)
  • In "How to test", be concrete — include commands to run, UI interactions to try, or API calls to make
  • Do not include the diff itself in the output
  • Do not mention the language or ecosystem explicitly unless it adds clarity
  • Reference references/conventional-commits.md for full type detection rules