Improve error message for missing "command" entry in containerize (#37590)

fixes #21242

1 files changed, 25 insertions, 4 deletions

diff --git a/lib/spack/spack/container/writers/__init__.py b/lib/spack/spack/container/writers/__init__.py
index 7508a67fd7..69a4b7f443 100644
--- a/lib/spack/spack/container/writers/__init__.py
+++ b/lib/spack/spack/container/writers/__init__.py
@@ -10,10 +10,12 @@ import copy
 from typing import Optional
 
 import spack.environment as ev
+import spack.error
 import spack.schema.env
 import spack.tengine as tengine
 import spack.util.spack_yaml as syaml
-from spack.container.images import (
+
+from ..images import (
     bootstrap_template_for,
     build_info,
     checkout_command,
@@ -205,12 +207,20 @@ class PathContext(tengine.Context):
     @tengine.context_property
     def os_packages_final(self):
         """Additional system packages that are needed at run-time."""
-        return self._os_packages_for_stage("final")
+        try:
+            return self._os_packages_for_stage("final")
+        except Exception as e:
+            msg = f"an error occurred while rendering the 'final' stage of the image: {e}"
+            raise spack.error.SpackError(msg) from e
 
     @tengine.context_property
     def os_packages_build(self):
         """Additional system packages that are needed at build-time."""
-        return self._os_packages_for_stage("build")
+        try:
+            return self._os_packages_for_stage("build")
+        except Exception as e:
+            msg = f"an error occurred while rendering the 'build' stage of the image: {e}"
+            raise spack.error.SpackError(msg) from e
 
     @tengine.context_property
     def os_package_update(self):
@@ -243,13 +253,24 @@ class PathContext(tengine.Context):
         if image is None:
             os_pkg_manager = os_package_manager_for(image_config["os"])
         else:
-            os_pkg_manager = self.container_config["os_packages"]["command"]
+            os_pkg_manager = self._os_pkg_manager()
 
         update, install, clean = commands_for(os_pkg_manager)
 
         Packages = collections.namedtuple("Packages", ["update", "install", "list", "clean"])
         return Packages(update=update, install=install, list=package_list, clean=clean)
 
+    def _os_pkg_manager(self):
+        try:
+            os_pkg_manager = self.container_config["os_packages"]["command"]
+        except KeyError:
+            msg = (
+                "cannot determine the OS package manager to use.\n\n\tPlease add an "
+                "appropriate 'os_packages:command' entry to the spack.yaml manifest file\n"
+            )
+            raise spack.error.SpackError(msg)
+        return os_pkg_manager
+
     @tengine.context_property
     def extra_instructions(self):
         Extras = collections.namedtuple("Extra", ["build", "final"])