include offending mapping identifiers in exception when unable to resolve dependencies

1 files changed, 15 insertions, 7 deletions

diff --git a/src/hydrilla/proxy/simple_dependency_satisfying.py b/src/hydrilla/proxy/simple_dependency_satisfying.py
index f1371db..78a1197 100644
--- a/src/hydrilla/proxy/simple_dependency_satisfying.py
+++ b/src/hydrilla/proxy/simple_dependency_satisfying.py
@@ -25,7 +25,11 @@
 # in a proprietary program, I am not going to enforce this in court.
 
 """
-.....
+This module contains logic to construct the dependency graph of Haketilo
+packages and to perform dependency resolution.
+
+The approach taken here is a very simplified one. Hopefully, this will at some
+point be replaced by a solution based on some SAT solver.
 """
 
 # Enable using with Python 3.7.
@@ -39,8 +43,9 @@ from .. import item_infos
 from .. import url_patterns
 
 
+@dc.dataclass(frozen=True)
 class ImpossibleSituation(HaketiloException):
-    pass
+    bad_mapping_identifiers: frozenset[str]
 
 
 @dc.dataclass(frozen=True)
@@ -219,13 +224,16 @@ class _ComputationData:
             if self.mappings.get(depended_identifier) not in choices:
                 _mark_mappings(depended_identifier, reverse_deps, bad_mappings)
 
-        if any(identifier in self.required for identifier in bad_mappings):
-            raise ImpossibleSituation()
+        bad_required_mappings: list[str] = []
 
-        for identifier in bad_mappings:
-            if identifier in self.required:
-                raise ImpossibleSituation()
+        for identifier in self.required:
+            if identifier in bad_mappings or identifier not in choices:
+                bad_required_mappings.append(identifier)
+
+        if len(bad_required_mappings) > 0:
+            raise ImpossibleSituation(frozenset(bad_required_mappings))
 
+        for identifier in bad_mappings:
             if identifier in self.mappings:
                 choices.pop(identifier, None)