makefile

Makefile

Goal

Write Makefiles that fail before doing work when required user input is missing. A target that needs a user-provided variable must explain what the variable is for in the Make error, close to the target that needs it.

Required Variable Guard

When adding a target that reads user input from Make variables, include this helper once near the top of the Makefile if an equivalent helper is not already present:

# https://stackoverflow.com/a/10858332
check_defined = \
    $(strip $(foreach 1,$1, \
        $(call __check_defined,$1,$(strip $(value 2)))))
__check_defined = \
    $(if $(value $1),, \
        $(error Undefined $1$(if $2, ($2))$(if $(value @), \
		required by target `$@`)))

Use the helper at the start of each target that requires input:

.PHONY: init_cluster
init_cluster:
	@:$(call check_defined, GIT_USERNAME, username used for Git operations)
	@:$(call check_defined, GIT_TOKEN, access token with required repository permissions)
	@:$(call check_defined, GIT_BRANCH, Git branch to reconcile)
	@:$(call check_defined, KUSTOMIZATION_PATH, path from repo root to the kustomization)
	flux create source git k8s --url=https://github.com/AnthonyPoschen/k8s.git --username="$(GIT_USERNAME)" --password="$(GIT_TOKEN)" --branch="$(GIT_BRANCH)" -n flux-system
	flux create kustomization k8s --source=k8s -n flux-system --path="$(KUSTOMIZATION_PATH)" --interval=1m

Rules

• Validate every required user-provided Make variable before the first command that uses it.
• Give each check_defined call a short, concrete description of what the variable is for, not just "required".
• Keep validation inside the target that needs the variable unless several targets share the exact same required inputs.
• Prefer explicit variable names that do not shadow common environment variables. For example, use KUSTOMIZATION_PATH, CONFIG_PATH, or MANIFEST_PATH instead of PATH.
• Do not check optional variables. Document their defaults near the assignment or in the target help text.
• Use $(VAR) in Make recipes. Avoid ${VAR} unless the command specifically needs shell-style expansion after Make runs.
• Quote variable expansions in shell commands when values may contain special characters or spaces: "$(VAR)".
• Keep .PHONY declarations for command targets.
• Do not print secrets. It is fine to validate that GIT_TOKEN or another secret variable is present, but do not echo the value.