Rebuild package also on upstream updates

So far, we skipped rebuilding a package if it didn't change.
However, we also need to consider any upstream changes.

src/build.sh

@@ -137,11 +137,11 @@ function pkg_exists {
   local pkg_version="${2%"$DEB_DISTRO"}"
   local available; available=$(LANG=C apt-cache policy "$1" | sed -n "s#^\s*Candidate:\s\(.*\)$DEB_DISTRO\..*#\1#p")
   if [ "$SKIP_EXISTING" == "true" ] && [ -n "$available" ] && [ "$available" != "(none)" ] && \
-     dpkg --compare-versions "$available" ">=" "$pkg_version"; then
+     dpkg --compare-versions "$available" ">=" "$pkg_version" && ! "$SRC_PATH/scripts/upstream_rebuilds.py" "$DEBS_PATH"; then
     echo "Skipped (existing version $available >= $pkg_version)"
     return 0
   fi
-  echo "Building version $pkg_version"
+  echo "Building version $pkg_version (old: $available)"
   return 1
 }
 

src/scripts/upstream_rebuilds.py

@@ -0,0 +1,70 @@
+#!/usr/bin/env python3
+
+from catkin_pkg.package import _get_package_xml, parse_package_string
+from rosdep2.main import (
+    _get_default_RosdepLookup,
+    create_default_installer_context,
+    configure_installer_context,
+    get_default_installer,
+)
+from rosdep2.rospkg_loader import DEFAULT_VIEW_KEY
+from rosdep2.sources_list import get_sources_cache_dir
+
+from dataclasses import dataclass, field
+from pathlib import Path
+import os, sys
+
+
+@dataclass
+class Options:
+    as_root: dict = field(default_factory=lambda: {})
+    dependency_types: list[str] = field(default_factory=lambda: [])
+    os_override: str = None
+    sources_cache_dir: str = get_sources_cache_dir()
+    verbose: bool = False
+
+
+debs = Path(sys.argv[1])
+folder = Path(sys.argv[2] if len(sys.argv) > 2 else ".")
+
+xml, file = _get_package_xml(folder)
+pkg = parse_package_string(xml, filename=file)
+pkg.evaluate_conditions(os.environ)
+
+options = Options()
+lookup = _get_default_RosdepLookup(options)
+installer_context = create_default_installer_context(verbose=options.verbose)
+configure_installer_context(installer_context, options)
+
+installer, installer_keys, default_key, os_name, os_version = get_default_installer(
+    installer_context=installer_context, verbose=options.verbose
+)
+
+view = lookup.get_rosdep_view(DEFAULT_VIEW_KEY, verbose=options.verbose)
+
+
+def resolve(rosdep_name):
+    "Resolve rosdep package name to required system package name(s)"
+    try:
+        d = view.lookup(rosdep_name)
+    except KeyError:
+        return []
+
+    rule_installer, rule = d.get_rule_for_platform(
+        os_name, os_version, installer_keys, default_key
+    )
+
+    installer = installer_context.get_installer(rule_installer)
+    resolved = installer.resolve(rule)
+    return resolved
+
+
+for dep in pkg.build_depends:
+    if dep.evaluated_condition:
+        for name in resolve(dep.name):
+            # check whether file debs/name*.deb exists
+            if any(debs.glob(f"{name}*.deb")):
+                print(f"Rebuild needed due to {name}")
+                exit(0)  # rebuild needed
+
+exit(1)  # no rebuild needed