Hack Building Rules

Core Commands

✅ Main build target:

buck build @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:hh_single_type_check

✅ Type check single file:

buck run @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:hh_single_type_check -- $THE_FILE

✅ View typed abstract syntax tree:

buck run @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:hh_single_type_check -- --tast $THE_FILE

✅ Run tests:

You can consult BUCK files and existing tests to find the best test target to run.

Examples:

buck test @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/test/typecheck:typecheck

buck test @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/test/nast/...

To update snapshots (.exp files):

buck test @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/test/ --config hack.update=always

❌ NEVER run all tests unless the user asks you to

❌ buck test @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/test/...

Command Restrictions

❌ NEVER use these (require approval):

• buck clean - Buck's output is trustworthy, if the build is broken then fix it. If you doubt your changes are taking effect, just make a code change and observe the result.
• Bash redirects: >, >>
• timeout command
• Risky globs

Examples

✅ GOOD - Building before making changes:

# Always build first to verify clean state
buck build @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:hh_single_type_check
# Make your changes
# Build again to verify
buck build @fbcode//mode/dev-nosan-lg fbcode//hphp/hack/src:hh_single_type_check

❌ BAD - Using prohibited commands:

# DON'T DO THIS
buck clean
buck build ... > build.log 2>&1
timeout 30 buck build ...
ocamlc ...

Development Workflow

1. Build frequently - OCaml IDE diagnostics are often wrong, trust builds
2. You can make one-off tests and run them with buck run
3. Commit working states - Use succinct commit messages
4. Use specific targets - Find in BUCK files

Success Pattern

✅ Build succeeds ✅ No unintended behavior changes ✅ Tests pass (with updated snapshots if needed)