build-sys: Add BOOTC_nocache option to force rebuild without cache

This is useful when debugging issues with stale cached layers,
such as package version skew between base images and repos.

Signed-off-by: Colin Walters <walters@verbum.org>

Author: cgwalters

Justfile

@@ -28,6 +28,8 @@ buildroot_base := env("BOOTC_buildroot_base", "quay.io/centos/centos:stream10")
 extra_src := env("BOOTC_extra_src", "")
 
 # Internal variables
+nocache := env("BOOTC_nocache", "")
+_nocache_arg := if nocache != "" { "--no-cache" } else { "" }
 testimage_label := "bootc.testimage=1"
 lbi_images := "quay.io/curl/curl:latest quay.io/curl/curl-base:latest registry.access.redhat.com/ubi9/podman:latest"
 fedora-coreos := "quay.io/fedora/fedora-coreos:testing-devel"
@@ -79,7 +81,7 @@ build: package _keygen && _pull-lbi-images
     set -xeuo pipefail
     test -d target/packages
     pkg_path=$(realpath target/packages)
-    podman build --build-context "packages=${pkg_path}" -t {{base_img}} {{buildargs}} .
+    podman build {{_nocache_arg}} --build-context "packages=${pkg_path}" -t {{base_img}} {{buildargs}} .
 
 # Build a sealed composefs image (alias for variant=composefs-sealeduki-sdboot)
 [group('core')]