conf: log clearer and less verbose error on validation failure

rust2rpm/conf.py

@@ -526,7 +526,22 @@ def load_config(features: set[str], target: str) -> TomlConf:
     except FileNotFoundError as exc:
         tomlconf = None
 
-    except (ConfError, jsonschema.ValidationError) as exc:
+    except jsonschema.ValidationError as exc:
+        if not exc.path:
+            log.error("Invalid rust2rpm.toml file (unknown setting or table):")
+            log.error(exc.message)
+        else:
+            err_path = ""
+            for elem in exc.path:
+                if isinstance(elem, int):
+                    err_path += f"[{elem}]"
+                else:
+                    err_path += f"/{elem}"
+            log.error(f"Invalid rust2rpm.toml file (invalid setting at {err_path!r}):")
+            log.error(exc.message)
+        sys.exit(1)
+
+    except ConfError as exc:
         log.error("Invalid rust2rpm.toml file:")
         log.error(str(exc))
         sys.exit(1)