Fix parsing environment definitions per issue #290

docs/stack-files.md

@@ -363,6 +363,8 @@ A service can pick up the same variable from more than one place.  Later sources
 This is the order Docker Compose uses, and it is applied identically for Kubernetes deployments, so a pod file
 hands its containers the same values whichever target it is deployed to.  A pod file that wants a deployment-time
 value to reach the container can forward it explicitly, e.g. `environment: {SOME_VAR: "${SOME_VAR}"}`.
+In the sequence form, a bare `- SOME_VAR` does the same thing: it names a variable to take from the sources
+listed above it, and passes nothing at all when none of them set it.
 
 The consequence worth knowing is that an inline default beats a value the deployer supplied with `--config`: the
 composefile wins, and the deployment is wrong rather than failed.  So `stack deploy` reports it, naming the service

src/stack/deploy/k8s/helpers.py

@@ -350,9 +350,18 @@ def _expand_shell_vars(raw_val: str, environ=os.environ) -> str:
 # TODO: handle the case where the same env var is defined in multiple places
 def envs_from_compose_file(compose_file_envs: Mapping[str, str], environ=os.environ) -> Mapping[str, str]:
     result = {}
-    if isinstance(compose_file_envs, CommentedSeq):
+    if isinstance(compose_file_envs, list):
         for item in compose_file_envs:
-            env_var, env_val = item.split("=", 2)
+            # Only the first "=" separates the name from the value: a value is free to
+            # contain more of them.  An entry with none at all is compose's pass-through
+            # form, which names a variable to take from the surrounding environment and
+            # is omitted entirely when that variable is unset.
+            env_var, separator, env_val = _env_value_to_str(item).partition("=")
+            if not separator:
+                if env_var not in environ:
+                    continue
+                result.update({env_var: _env_value_to_str(environ[env_var])})
+                continue
             expanded_env_val = _expand_shell_vars(env_val, environ)
             result.update({env_var: expanded_env_val})
     else:

tests/unit/test_deploy_helpers.py

@@ -18,9 +18,11 @@
 import re
 
 import pytest
+from ruamel.yaml.comments import CommentedSeq
 
 from stack.deploy.deploy_util import convert_to_seconds
 from stack.deploy.deployment_create import _get_mapped_ports, _parse_config_variables
+from stack.deploy.k8s.helpers import envs_from_compose_file
 from stack.init.init import _parse_http_proxy
 
 
@@ -180,3 +182,49 @@ def test_parse_http_proxy_rejects_non_numeric_port(value):
     # The path leads: the reversed 'svc:port:path' form must fail rather than reach the spec.
     with pytest.raises(SystemExit):
         _parse_http_proxy(value)
+
+
+# ---------------------------------------------------------------------------
+# envs_from_compose_file
+# ---------------------------------------------------------------------------
+
+
+def _seq(*items):
+    # The composefile is parsed by ruamel, so a sequence arrives as a CommentedSeq.
+    seq = CommentedSeq()
+    seq.extend(items)
+    return seq
+
+
+def test_envs_from_compose_file_mapping_form():
+    assert envs_from_compose_file({"A": "1", "B": True}, {}) == {"A": "1", "B": "true"}
+
+
+def test_envs_from_compose_file_sequence_form():
+    assert envs_from_compose_file(_seq("A=1", "B=2"), {}) == {"A": "1", "B": "2"}
+
+
+def test_envs_from_compose_file_value_containing_equals():
+    # Only the first "=" separates name from value; the rest belongs to the value.
+    assert envs_from_compose_file(_seq("URL=a=b"), {}) == {"URL": "a=b"}
+
+
+def test_envs_from_compose_file_pass_through_takes_surrounding_value():
+    # The bare form names a variable to pick up from the environment it is merged into.
+    assert envs_from_compose_file(_seq("SOME_VAR"), {"SOME_VAR": "from-config"}) == {"SOME_VAR": "from-config"}
+
+
+def test_envs_from_compose_file_pass_through_omitted_when_unset():
+    # Compose passes nothing at all rather than an empty string, so neither does this.
+    assert envs_from_compose_file(_seq("SOME_VAR"), {}) == {}
+
+
+def test_envs_from_compose_file_forwarding_form_expands():
+    assert envs_from_compose_file(_seq("SOME_VAR=${SOME_VAR}"), {"SOME_VAR": "from-config"}) == {
+        "SOME_VAR": "from-config"
+    }
+
+
+def test_envs_from_compose_file_plain_list_form():
+    # A sequence that did not come from ruamel is still a sequence.
+    assert envs_from_compose_file(["A=1", "SOME_VAR"], {"SOME_VAR": "x"}) == {"A": "1", "SOME_VAR": "x"}