formats: extract manifest loading into module

Extract the code that loads a pipeline from a pipeline description,
i.e. a manifest, into a new module inside a new 'formats' package.
The idea is to have different descriptions, i.e. different formats,
for the same internal representation. This allows changing the
internal representation, i.e. data structures, but still having the
same external description.
Later a new description might be added that better matches the new
internal representation.

osbuild/__init__.py

@@ -8,8 +8,8 @@ The utility module `osbuild.util` provides access to common functionality
 independent of osbuild but used across the osbuild codebase.
 """
 
-
-from .pipeline import Assembler, load, load_build, Pipeline, Stage
+from .formats.v1 import load, load_build
+from .pipeline import Assembler, Pipeline, Stage
 
 
 __all__ = [

osbuild/formats/__init__.py

@@ -0,0 +1,3 @@
+"""
+Concrete representation of manifest descriptions
+"""

osbuild/formats/v1.py

@@ -0,0 +1,32 @@
+# Version 1 of the manifest description
+
+from ..pipeline import Pipeline, detect_host_runner
+
+
+def load_build(description, sources_options):
+    pipeline = description.get("pipeline")
+    if pipeline:
+        build_pipeline = load(pipeline, sources_options)
+    else:
+        build_pipeline = None
+
+    return build_pipeline, description["runner"]
+
+
+def load(description, sources_options):
+    build = description.get("build")
+    if build:
+        build_pipeline, runner = load_build(build, sources_options)
+    else:
+        build_pipeline, runner = None, detect_host_runner()
+
+    pipeline = Pipeline(runner, build_pipeline)
+
+    for s in description.get("stages", []):
+        pipeline.add_stage(s["name"], sources_options, s.get("options", {}))
+
+    a = description.get("assembler")
+    if a:
+        pipeline.set_assembler(a["name"], a.get("options", {}))
+
+    return pipeline

osbuild/pipeline.py

@@ -363,32 +363,3 @@ def detect_host_runner():
     """Use os-release(5) to detect the runner for the host"""
     osname = osrelease.describe_os(*osrelease.DEFAULT_PATHS)
     return "org.osbuild." + osname
-
-
-def load_build(description, sources_options):
-    pipeline = description.get("pipeline")
-    if pipeline:
-        build_pipeline = load(pipeline, sources_options)
-    else:
-        build_pipeline = None
-
-    return build_pipeline, description["runner"]
-
-
-def load(description, sources_options):
-    build = description.get("build")
-    if build:
-        build_pipeline, runner = load_build(build, sources_options)
-    else:
-        build_pipeline, runner = None, detect_host_runner()
-
-    pipeline = Pipeline(runner, build_pipeline)
-
-    for s in description.get("stages", []):
-        pipeline.add_stage(s["name"], sources_options, s.get("options", {}))
-
-    a = description.get("assembler")
-    if a:
-        pipeline.set_assembler(a["name"], a.get("options", {}))
-
-    return pipeline