Take the list of arches for -build Koji tag from buildrequired modules.

Currently, we are using just `conf.arches` and `conf.base_module_arches`
to define the list of arches for which the RPMs in a submitted module are
built. This is not enough, because RCM needs to generate modules based
on the base modules which should use different arches.

This commit changes the MBS to take the list of arches from the buildrequired
module build. It checks the buildrequires for "privileged" module or base
module and if it finds such module, it queries the Koji to find out the list
of arches to set for the module.

The "privileged" module is a module which can override base module arches
or disttag. Previously, these modules have been defined by
`allowed_disttag_marking_module_names` config option. In this commit,
this has been renamed to `allowed_privileged_module_names`.

The list of arches are stored per module build in new table represented
by ModuleArch class and are m:n mapped to ModuleBuild.

module_build_service/utils/general.py

@@ -325,7 +325,7 @@ def get_rpm_release(module_build):
         # Looping through all the non-base modules that are allowed to set the disttag_marking
         # and the base modules to see what the disttag marking should be. Doing it this way
         # preserves the order in the configurations.
-        for module in conf.allowed_disttag_marking_module_names + conf.base_module_names:
+        for module in conf.allowed_privileged_module_names + conf.base_module_names:
             module_in_xmd = buildrequires.get(module)
 
             if not module_in_xmd:
@@ -350,7 +350,7 @@ def get_rpm_release(module_build):
                     if module not in conf.base_module_names:
                         continue
                     # If we've made it past all the modules in
-                    # conf.allowed_disttag_marking_module_names, and the base module doesn't have
+                    # conf.allowed_privileged_module_names, and the base module doesn't have
                     # the disttag_marking set, then default to the stream of the first base module
                     marking = module_obj.stream
                 br_module_marking = marking + "+"
@@ -674,16 +674,70 @@ def get_build_arches(mmd, config):
     :param config: config (module_build_service.config.Config instance)
     :return list of architectures
     """
-    arches = config.arches
+    # Imported here to allow import of utils in GenericBuilder.
+    import module_build_service.builder
+    nsvc = mmd.get_nsvc()
 
-    # Handle BASE_MODULE_ARCHES. Find out the base modules in buildrequires
-    # section of XMD and set the Koji tag arches according to it.
+    # At first, handle BASE_MODULE_ARCHES - this overrides any other option.
+    # Find out the base modules in buildrequires section of XMD and
+    # set the Koji tag arches according to it.
     if "mbs" in mmd.get_xmd():
         for req_name, req_data in mmd.get_xmd()["mbs"]["buildrequires"].items():
             ns = ":".join([req_name, req_data["stream"]])
             if ns in config.base_module_arches:
                 arches = config.base_module_arches[ns]
-                break
+                log.info("Setting build arches of %s to %r based on the BASE_MODULE_ARCHES." % (
+                    nsvc, arches))
+                return arches
+
+    # Check whether the module contains the `koji_tag_arches`. This is used only
+    # by special modules defining the layered products.
+    try:
+        arches = mmd.get_xmd()["mbs"]["koji_tag_arches"]
+        log.info("Setting build arches of %s to %r based on the koji_tag_arches." % (
+            nsvc, arches))
+        return arches
+    except KeyError:
+        pass
+
+    # Check the base/layered-product module this module buildrequires and try to get the
+    # list of arches from there.
+    try:
+        buildrequires = mmd.get_xmd()["mbs"]["buildrequires"]
+    except (ValueError, KeyError):
+        log.warning(
+            "Module {0} does not have buildrequires in its xmd".format(mmd.get_nsvc()))
+        buildrequires = None
+    if buildrequires:
+        # Looping through all the privileged modules that are allowed to set koji tag arches
+        # and the base modules to see what the koji tag arches should be. Doing it this way
+        # preserves the order in the configurations.
+        with models.make_session(conf) as session:
+            for module in conf.allowed_privileged_module_names + conf.base_module_names:
+                module_in_xmd = buildrequires.get(module)
+
+                if not module_in_xmd:
+                    continue
+
+                module_obj = models.ModuleBuild.get_build_from_nsvc(
+                    session,
+                    module,
+                    module_in_xmd["stream"],
+                    module_in_xmd["version"],
+                    module_in_xmd["context"],
+                )
+                if not module_obj:
+                    continue
+                arches = module_build_service.builder.GenericBuilder.get_module_build_arches(
+                    module_obj)
+                if arches:
+                    log.info("Setting build arches of %s to %r based on the buildrequired "
+                             "module %r." % (nsvc, arches, module_obj))
+                    return arches
+
+    # As a last resort, return just the preconfigured list of arches.
+    arches = config.arches
+    log.info("Setting build arches of %s to %r based on default ARCHES." % (nsvc, arches))
     return arches