geant4-build

geant4-build — compile a Geant4 app in the container

Purpose

Compile the user's Geant4 application from src/ into ./build/ using CMake inside the pinned apptainer image. The single bridge from source to a runnable executable — never call cmake, g++, or make on the host directly.

Inputs (all optional)

Flag	Default	Meaning
--src <dir>	src	Source dir; must contain a top-level CMakeLists.txt.
--build <dir>	build	Build dir; created if missing.
--clean	off	Delete <build> before configuring.

Steps

1. Resolve the engine (every skill starts with this; written by geant4-init):

   G4C="$PWD"; while [ "$G4C" != "/" ] && [ ! -d "$G4C/.g4c" ]; do G4C="$(dirname "$G4C")"; done
   [ -f "$G4C/.g4c/env" ] && . "$G4C/.g4c/env"; G4RUN="${G4RUN:-$G4C/.g4c/g4run}"
   

   If .g4c/ is missing, stop and tell the user to run the geant4-init skill first.

2. Validate source:

   test -f "${SRC}/CMakeLists.txt" || { echo "no ${SRC}/CMakeLists.txt"; exit 1; }
   

   If missing, suggest the geant4-example skill (drops in a working sample) or bringing your own and pointing --src at it.

3. Optional clean. If --clean: rm -rf "${BUILD}".

4. Build:

   "${G4RUN}" build "${SRC}" "${BUILD}"
   

   Both paths are passed to apptainer as canonical (symlink-resolved) paths and bound automatically — CWD-relative paths work.

5. Report. Show the build dir and the executables now under it (find "${BUILD}" -maxdepth 3 -type f -executable -not -path '*CMakeFiles*'), and point at the geant4-run skill. If the build wrote no executable, that's a likely missing add_executable in the user's CMakeLists.txt.

Outputs

• <build>/ populated with CMake artifacts and the compiled binary(ies).

Failure modes

Symptom	Likely cause	Fix
.g4c/ missing	Workspace not initialized.	Run the geant4-init skill first.
no src/CMakeLists.txt	No source yet.	Use the geant4-example skill, or bring your own.
Could not find a package configuration file provided by "Geant4"	find_package(Geant4 …) missing or misspelled.	Mirror ${GEANT4_CLAUDE_ROOT}/templates/example/src/CMakeLists.txt.
error: 'FTFP_BERT.hh' file not found	Header not in include path.	The container's find_package(Geant4) brings includes in; check typos and include(${Geant4_USE_FILE}).
Build succeeds but no executable	No add_executable directive.	Add it to src/CMakeLists.txt and rebuild.
Linker undefined references to ROOT::*	find_package(ROOT …) missing or wrong components.	Add find_package(ROOT REQUIRED COMPONENTS Tree RIO) and link ROOT::Core ROOT::RIO ROOT::Tree.

Notes

• ./build/ is gitignored by the workspace .gitignore from the geant4-init step.
• Idempotent. CMake's incremental builds rebuild only what changed; pass --clean for a from-scratch rebuild.
• Need a different toolchain or extra cmake flags? Use "${G4RUN}" shell to enter the container and run cmake by hand — this skill stays minimal.