reduce unset script_env variable to warning

conda_build/build.py

@@ -1923,9 +1923,12 @@ def bundle_conda(output, metadata: MetaData, env, stats, **kw):
  val = var.split("=", 1)[1]
  var = var.split("=", 1)[0]
  elif var not in os.environ:
- raise ValueError(
- f"env var '{var}' specified in script_env, but is not set."
+ warnings.warn(
+ "The environment variable '%s' specified in script_env is undefined."
+ % var,
+ UserWarning,
  )
+ val = ""
  else:
  val = os.environ[var]
  env_output[var] = val

conda_build/environ.py

@@ -491,7 +491,9 @@ def meta_vars(meta: MetaData, skip_build_id=False):
  value = os.getenv(var_name)
  if value is None:
  warnings.warn(
- "The environment variable '%s' is undefined." % var_name, UserWarning
+ "The environment variable '%s' specified in script_env is undefined."
+ % var_name,
+ UserWarning,
  )
  else:
  d[var_name] = value

news/5105-script-env-warn

@@ -0,0 +1,20 @@
+### Enhancements
+
+* Relax script_env error in outputs when variable referenced in script_env is not defined.
+ This unifies current behavior with the top-level build. (#5105)
+
+### Bug fixes
+
+* <news item>
+
+### Deprecations
+
+* <news item>
+
+### Docs
+
+* <news item>
+
+### Other
+
+* <news item>

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

@@ -0,0 +1,9 @@
+package:
+ name: test_build_script_in_output
+ version: 1.0
+
+outputs:
+ - name: test_1
+ build:
+ script_env:
+ - TEST_FN

tests/test_subpackages.py

@@ -335,6 +335,16 @@ def test_build_script_and_script_env(testing_config):
  api.build(recipe, config=testing_config)
 
 
+@pytest.mark.sanity
+def test_build_script_and_script_env_warn_empty_script_env(testing_config):
+ recipe = os.path.join(subpackage_dir, "_build_script_missing_var")
+ with pytest.warns(
+ UserWarning,
+ match="The environment variable 'TEST_FN' specified in script_env is undefined",
+ ):
+ api.build(recipe, config=testing_config)
+
+
 @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):