clan select: better error

pkgs/clan-cli/clan_lib/flake/__init__.py

@@ -1 +1 @@
-from .flake import Flake, require_flake  # noqa
+from .flake import Flake, require_flake, ClanSelectError  # noqa

pkgs/clan-cli/clan_lib/flake/flake.py

@@ -11,7 +11,7 @@ from pathlib import Path
 from tempfile import NamedTemporaryFile
 from typing import Any
 
-from clan_lib.errors import ClanError
+from clan_lib.errors import ClanCmdError, ClanError
 
 log = logging.getLogger(__name__)
 
@@ -143,6 +143,42 @@ class Selector:
         raise ValueError(msg)
 
 
+class ClanSelectError(ClanError):
+    selectors: list[str]
+    failed_attr: str | None = None
+    flake_identifier: str
+
+    def __init__(
+        self,
+        flake_identifier: str,
+        selectors: list[str],
+        cmd_error: ClanCmdError | None = None,
+    ) -> None:
+        attribute = None
+        if cmd_error:
+            attribute_match = re.search(r"error: attribute '([^']+)'", str(cmd_error))
+            attribute = attribute_match.group(1) if attribute_match else None
+        if selectors == []:
+            msg = "failed to select []\n"
+        if len(selectors) == 1:
+            msg = f"failed to select {selectors[0]}\n"
+        else:
+            msg = f"failed to select: {'\n'.join(selectors)}\n"
+        msg += f" from {flake_identifier}\n"
+        if attribute:
+            msg += f" '{attribute}' is missing\n"
+        self.selectors = selectors
+        self.failed_attr = attribute
+        self.flake_identifier = flake_identifier
+        super().__init__(msg)
+
+    def __str__(self) -> str:
+        return self.msg
+
+    def __repr__(self) -> str:
+        return f"ClanSelectError({self.failed_attr})"
+
+
 def selectors_as_dict(selectors: list[Selector]) -> list[dict[str, Any]]:
     return [selector.as_dict() for selector in selectors]
 
@@ -180,7 +216,7 @@ def parse_selector(selector: str) -> list[Selector]:
             if c == ".":
                 stack.pop()
                 if stack != []:
-                    msg = "expected empy stack, but got {stack}"
+                    msg = "expected empty stack, but got {stack}"
                     raise ValueError(msg)
             else:
                 msg = "expected ., but got {c}"
@@ -863,12 +899,15 @@ class Flake:
               }}
         """
         trace = os.environ.get("CLAN_DEBUG_NIX_SELECTORS", False) == "1"
-        build_output = Path(
-            run(
-                nix_build(["--expr", nix_code, *nix_options]),
-                RunOpts(log=Log.NONE, trace=trace),
-            ).stdout.strip()
-        )
+        try:
+            build_output = Path(
+                run(
+                    nix_build(["--expr", nix_code, *nix_options]),
+                    RunOpts(log=Log.NONE, trace=trace),
+                ).stdout.strip()
+            )
+        except ClanCmdError as e:
+            raise ClanSelectError(flake_identifier=self.identifier, selectors=selectors, cmd_error=e) from e
 
         if tmp_store := nix_test_store():
             build_output = tmp_store.joinpath(*build_output.parts[1:])

pkgs/clan-cli/clan_lib/machines/machines.py

@@ -1,6 +1,5 @@
 import importlib
 import logging
-import re
 from dataclasses import dataclass
 from functools import cached_property
 from pathlib import Path
@@ -11,8 +10,8 @@ from clan_cli.facts import secret_modules as facts_secret_modules
 from clan_cli.vars._types import StoreBase
 
 from clan_lib.api import API
-from clan_lib.errors import ClanCmdError, ClanError
-from clan_lib.flake import Flake
+from clan_lib.errors import ClanError
+from clan_lib.flake import ClanSelectError, Flake
 from clan_lib.nix_models.clan import InventoryMachine
 from clan_lib.ssh.remote import Remote
 
@@ -77,10 +76,8 @@ class Machine:
             return self.flake.select(
                 f'clanInternals.inventoryClass.inventory.machines."{self.name}".machineClass'
             )
-        except ClanCmdError as e:
-            if re.search(f"error: attribute '{self.name}' missing", e.cmd.stderr):
-                return "nixos"
-            raise
+        except ClanSelectError:
+            return "nixos"
 
     @property
     def system(self) -> str:

pkgs/clan-cli/clan_lib/tests/test_create.py

@@ -19,7 +19,7 @@ from clan_cli.vars.generate import get_generators, run_generators
 from clan_lib.cmd import RunOpts, run
 from clan_lib.dirs import specific_machine_dir
 from clan_lib.errors import ClanError
-from clan_lib.flake import Flake
+from clan_lib.flake import ClanSelectError, Flake
 from clan_lib.machines.machines import Machine
 from clan_lib.nix import nix_command
 from clan_lib.nix_models.clan import (
@@ -278,10 +278,10 @@ def test_clan_create_api(
 
     if in_sandbox:
         # In sandbox: expect build to fail due to network restrictions
-        with pytest.raises(ClanError) as exc_info:
+        with pytest.raises(ClanSelectError) as select_error:
             Path(machine.select("config.system.build.toplevel"))
-        # The error should mention the system derivation name
-        assert "nixos-system-test-clan" in str(exc_info.value)
+        # The error should be a select_error without a failed_attr
+        assert select_error.value.failed_attr is None
     else:
         # Outside sandbox: build should succeed
         toplevel_path = Path(machine.select("config.system.build.toplevel"))