ensure undefined script_env variables are undefined in multi-output build environment

conda_build/build.py

@@ -1762,15 +1762,14 @@ def bundle_conda(
  if "=" in var:
  val = var.split("=", 1)[1]
  var = var.split("=", 1)[0]
+ env_output[var] = val
  elif var not in os.environ:
  warnings.warn(
  f"The environment variable '{var}' specified in script_env is undefined.",
  UserWarning,
  )
- val = ""
  else:
- val = os.environ[var]
- env_output[var] = val
+ env_output[var] = os.environ[var]
  dest_file = os.path.join(metadata.config.work_dir, output["script"])
  utils.copy_into(os.path.join(metadata.path, output["script"]), dest_file)
  from os import stat

news/5322-undefine-build-vars

@@ -0,0 +1,20 @@
+### Enhancements
+
+* <news item>
+
+### Bug fixes
+
+* Ensures that variables mentioned in `script_env` are undefined in multi-output build environment
+ if undefined in the environment `conda-build` is invoked from.
+
+### Deprecations
+
+* <news item>
+
+### Docs
+
+* <news item>
+
+### Other
+
+* <news item>

tests/test-recipes/split-packages/_build_script_relying_on_missing_var/meta.yaml

@@ -0,0 +1,14 @@
+package:
+ name: test_build_script_relying_on_missing_var
+ version: 1.0
+
+outputs:
+ - name: test_1
+ build:
+ script_env:
+ - TEST_FN_DOESNT_EXIST
+ script:
+ - python -c "import os; print('val...' + os.environ['TEST_FN_DOESNT_EXIST'])"
+ requirements:
+ host:
+ - python

tests/test_subpackages.py

@@ -11,7 +11,7 @@
 from conda.base.context import context
 
 from conda_build import api, utils
-from conda_build.exceptions import CondaBuildUserError
+from conda_build.exceptions import BuildScriptException, CondaBuildUserError
 from conda_build.metadata import MetaDataTuple
 from conda_build.render import finalize_metadata
 
@@ -354,6 +354,18 @@ def test_build_script_and_script_env_warn_empty_script_env(testing_config):
  api.build(recipe, config=testing_config)
 
 
+@pytest.mark.sanity
+def test_build_script_does_not_set_env_from_script_env_if_missing(
+ testing_config, capfd, monkeypatch
+):
+ monkeypatch.delenv("TEST_FN_DOESNT_EXIST", raising=False)
+ recipe = os.path.join(subpackage_dir, "_build_script_relying_on_missing_var")
+ with pytest.raises(BuildScriptException):
+ api.build(recipe, config=testing_config)
+ captured = capfd.readouterr()
+ assert "KeyError: 'TEST_FN_DOESNT_EXIST'" in captured.err
+
+
 @pytest.mark.sanity
 @pytest.mark.skipif(sys.platform != "darwin", reason="only implemented for mac")
 def test_strong_run_exports_from_build_applies_to_host(testing_config):