[PATCH RFC] docker: automatic dependencies for dockerfiles

[John Snow <jsnow@redhat.com>]

This is a demo for using makefile dependencies for image requisites.
Honestly, I don't like it -- Makefile sorcery is a bit beyond my
comprehension.

This is as near as I could stab, and it has the unfortunate requisite
that it will generate all of the *.d files at first run and not in an
on-demand way. Boo.

But, I wanted to raise the point that manually managing the variables
is not long-term viable -- we should manage them automatically if we
can.

As far as "partial" images vs "full" images, we should manage this
too; perhaps by subdirectory on the dockerfiles -- that way these
won't get out of date, either.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 tests/docker/Makefile.include | 37 ++++++++-------------------------
 tests/docker/deputil.py       | 39 +++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 28 deletions(-)
 create mode 100755 tests/docker/deputil.py

diff --git a/tests/docker/Makefile.include b/tests/docker/Makefile.include
index 50a400b573..266395d927 100644
--- a/tests/docker/Makefile.include
+++ b/tests/docker/Makefile.include
@@ -21,6 +21,7 @@ DOCKER_TOOLS := travis
 ENGINE := auto
 
 DOCKER_SCRIPT=$(SRC_PATH)/tests/docker/docker.py --engine $(ENGINE)
+DEPTOOL=$(SRC_PATH)/tests/docker/deputil.py
 
 TESTS ?= %
 IMAGES ?= %
@@ -47,12 +48,12 @@ docker-image: ${DOCKER_TARGETS}
 # invoked with SKIP_DOCKER_BUILD we still check the image is up to date
 # though
 ifdef SKIP_DOCKER_BUILD
-docker-image-%: $(DOCKER_FILES_DIR)/%.docker
+docker-image-%: $(DOCKER_FILES_DIR)/%.docker %.d
 	$(call quiet-command, \
 		$(DOCKER_SCRIPT) check --quiet qemu:$* $<, \
 		"CHECK", "$*")
 else
-docker-image-%: $(DOCKER_FILES_DIR)/%.docker
+docker-image-%: $(DOCKER_FILES_DIR)/%.docker %.d
 	$(call quiet-command,\
 		$(DOCKER_SCRIPT) build qemu:$* $< \
 		$(if $V,,--quiet) $(if $(NOCACHE),--no-cache) \
@@ -88,23 +89,17 @@ docker-binfmt-image-debian-%: $(DOCKER_FILES_DIR)/debian-bootstrap.docker
 endif
 
 # Enforce dependencies for composite images
-docker-image-debian9-mxe: docker-image-debian9
+%.d: $(DOCKER_FILES_DIR)/%.docker
+	$(call quiet-command, $(DEPTOOL) $(DOCKER_FILES_DIR)/$*.docker > $@)
+
+DEPFILES := $(DOCKER_IMAGES:%=%.d)
+include $(DEPFILES)
+
 ifeq ($(ARCH),x86_64)
-docker-image-debian-amd64: docker-image-debian9
 DOCKER_PARTIAL_IMAGES += debian-amd64-cross
 else
-docker-image-debian-amd64-cross: docker-image-debian10
 DOCKER_PARTIAL_IMAGES += debian-amd64
 endif
-docker-image-debian-armel-cross: docker-image-debian9
-docker-image-debian-armhf-cross: docker-image-debian9
-docker-image-debian-mips-cross: docker-image-debian9
-docker-image-debian-mipsel-cross: docker-image-debian9
-docker-image-debian-mips64el-cross: docker-image-debian9
-docker-image-debian-ppc64el-cross: docker-image-debian9
-docker-image-debian-s390x-cross: docker-image-debian9
-docker-image-debian-win32-cross: docker-image-debian9-mxe
-docker-image-debian-win64-cross: docker-image-debian9-mxe
 
 # For non-x86 hosts not all cross-compilers have been packaged
 ifneq ($(ARCH),x86_64)
@@ -115,22 +110,8 @@ DOCKER_PARTIAL_IMAGES += debian-win32-cross debian-win64-cross
 DOCKER_PARTIAL_IMAGES += fedora travis
 endif
 
-docker-image-debian-alpha-cross: docker-image-debian10
-docker-image-debian-arm64-cross: docker-image-debian10
-docker-image-debian-hppa-cross: docker-image-debian10
-docker-image-debian-m68k-cross: docker-image-debian10
-docker-image-debian-mips64-cross: docker-image-debian10
-docker-image-debian-powerpc-cross: docker-image-debian10
-docker-image-debian-ppc64-cross: docker-image-debian10
-docker-image-debian-riscv64-cross: docker-image-debian10
-docker-image-debian-sh4-cross: docker-image-debian10
-docker-image-debian-sparc64-cross: docker-image-debian10
-
 docker-image-travis: NOUSER=1
 
-# Specialist build images, sometimes very limited tools
-docker-image-tricore-cross: docker-image-debian9
-
 # These images may be good enough for building tests but not for test builds
 DOCKER_PARTIAL_IMAGES += debian-alpha-cross
 DOCKER_PARTIAL_IMAGES += debian-hppa-cross
diff --git a/tests/docker/deputil.py b/tests/docker/deputil.py
new file mode 100755
index 0000000000..69711cf85e
--- /dev/null
+++ b/tests/docker/deputil.py
@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+import os
+import re
+import sys
+from typing import IO, Optional
+
+def get_dep(infile: IO[str]) -> Optional[str]:
+    """Get a dependency as a string from a dockerfile."""
+    for line in infile:
+        match = re.match(r'FROM (.+)', line)
+        if match:
+            return match[1]
+    return None
+
+def get_qemu_dep(infile: IO[str]) -> Optional[str]:
+    """Get a dependency on the qemu: namespace from a dockerfile."""
+    dep = get_dep(infile) or ''
+    match = re.match(r'qemu:(.+)', dep)
+    return match[1] if match else None
+
+def main() -> None:
+    filename = sys.argv[1]
+    basefile = os.path.basename(filename)
+    base = os.path.splitext(basefile)[0]
+    depfile = f"{base}.d"
+    deps = [filename]
+
+    print(f"{depfile}: {filename}")
+    with open(filename, "r") as infile:
+        match = get_qemu_dep(infile) or ''
+        if match:
+            deps.append(f"docker-image-{match}")
+    print("{}: {}".format(
+        f"docker-image-{base}",
+        " ".join(deps)
+    ))
+
+if __name__ == '__main__':
+    main()
-- 
2.21.0