build-check

name	build-check
description	Auto-detects the project's build system and runs compile/type-check after file changes, auto-fixing straightforward errors (max 3 attempts). Use after completing a multi-file feature or when asked to build or check compilation.

Build Check Skill

Purpose

Auto-detect the project's build system and run compilation/type-checking after creating or modifying files. Catches errors (missing imports, type mismatches, DI failures) before the user discovers them at runtime.

Activation

Run once per logical change set — after completing a multi-file feature or a self-contained modification, NOT after each individual file:

• After completing a multi-file feature (run once at the end)
• After a single-file change that could affect compilation (run once for that change)
• When the user asks to build or check compilation

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How It Works

This skill does NOT hardcode build commands. It detects them from the project.

Results cached in .codex/idev/build-check/cache.json after first detection.

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Phase 1: Detect Build System

Scan for build configuration files. Check ALL — do not assume any stack:

.NET:
  Glob for *.sln → dotnet build {solution.sln}
  Glob for *.csproj (if no .sln) → dotnet build {project.csproj}
  Check for specific project to build (API project .csproj for faster builds)

Node.js/TypeScript:
  Read package.json → check scripts section:
    "build" → npm run build / yarn build / pnpm build
    "typecheck" or "tsc" → npm run typecheck (preferred — faster than full build)
    "check" → npm run check (Svelte)
  Detect package manager: look for yarn.lock, pnpm-lock.yaml, or package-lock.json

Python:
  Glob for pyproject.toml → check for build tool (poetry, setuptools, hatch)
  Check for mypy.ini or pyproject.toml [tool.mypy] → mypy for type checking
  Check for ruff.toml or pyproject.toml [tool.ruff] → ruff check

Java:
  Glob for pom.xml → mvn compile
  Glob for build.gradle → gradle compileJava / ./gradlew compileJava

Go:
  Glob for go.mod → go build ./...

Rust:
  Glob for Cargo.toml → cargo check (faster than cargo build)

Ruby:
  Glob for Gemfile → bundle exec ruby -c (syntax check)
  Check for sorbet → srb tc (type check)

PHP:
  Glob for composer.json → check for phpstan or psalm → phpstan analyse / psalm

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Phase 2: Generate Cache

Write detected build commands to .codex/idev/build-check/cache.json:

{
  "generated": "YYYY-MM-DD",
  "projects": [
    {
      "name": "ProjectName",
      "root": "relative/path/to/project",
      "layer": "backend|frontend",
      "buildCommand": "dotnet build path/to/project.csproj",
      "typeCheckCommand": "npm run typecheck (if different from build)",
      "lintCommand": "npm run lint (if available)",
      "workingDirectory": "relative/path (if command must run from specific dir)",
      "timeout": 120000
    }
  ],
  "quickChecks": {
    "backend": "dotnet build path/to/api.csproj --no-restore",
    "frontend": "npx tsc --noEmit"
  }
}

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Phase 3: When to Run

After creating a NEW feature (multi-file):

1. Wait until ALL files are created (entity, DTOs, service, controller, etc.)
2. Run the backend build command
3. If frontend files were also created, run frontend type-check
4. Report results: success or list of errors

After modifying a SINGLE file:

1. Determine which project the file belongs to (use architecture-scanner)
2. Run ONLY that project's build/type-check
3. Use quick check command (--no-restore, --noEmit) for speed

When NOT to run:

- After reading files (no changes made)
- After modifying only .md, .json, .txt, .css files (non-compiled)
- When user explicitly says "don't build" or "skip build"
- When creating skill/config files (not source code)

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Phase 4: Handle Build Errors

If build succeeds:

Report: "Build passed ✓" (brief, one line)

If build fails:

1. Parse error output for:
   - File path and line number
   - Error code and message
   - Missing reference or type
2. Categorize the error:
   - Missing using/import → Add it
   - Missing registration (DI) → Use post-creation-verify skill
   - Type mismatch → Fix the type
   - Missing file → Check if it was created
3. Fix the error automatically if it's straightforward
4. Re-run build to verify fix
5. If fix is unclear, report the error to the user

Error fix limits:

- Max 3 auto-fix attempts per build
- If still failing after 3 attempts, report all errors to user
- Never suppress or ignore build errors

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Phase 5: Usage Commands

The user can trigger builds manually:

• "build" or "check build" → Run all project builds
• "build backend" → Run backend build only
• "build frontend" → Run frontend type-check only
• "skip build" → Suppress auto-build for current task

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Integration with Other Skills

After creating a new backend feature:
  1. post-creation-verify → Check all registrations exist
  2. build-check → Run dotnet build
  3. If errors → auto-fix → re-build
  4. Report final status

After creating a new frontend feature:
  1. build-check → Run tsc --noEmit
  2. If errors → auto-fix → re-check
  3. Report final status

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Anti-Patterns

1. Do NOT run build after every single file in a multi-file creation — wait until done
2. Do NOT run full build when a quick check (--noEmit, --no-restore) suffices
3. Do NOT hardcode build commands — always detect from project config
4. Do NOT ignore build failures — always report or fix
5. Do NOT run builds for non-compiled file changes