fix: resolve linked resources against the plain file's directory

file_utils.py

@@ -180,6 +180,20 @@ def open_from(dirs, file_name):
     return None
 
 
+def resolve_linked_resource(dirs, file_name):
+    """Return the first existing path for file_name across dirs, or None if not found.
+
+    Mirrors the search order used by open_from so that validating a linked resource and
+    loading it can never disagree.
+    """
+    for dir in dirs:
+        full_file_name = os.path.join(dir, file_name)
+        if os.path.exists(full_file_name):
+            return full_file_name
+
+    return None
+
+
 def load_linked_resources(template_dirs: list[str], resources_list, module_name: str):
     linked_resources = {}
 

plain_file.py

@@ -90,7 +90,7 @@ def remove_quotes(token):
     token.children = tuple(new_children)
 
 
-def check_section_for_linked_resources(section):
+def check_section_for_linked_resources(section, template_dirs):
     linked_resources = []
     for link in traverse(section, klass=Link):
         parsed_url = urlparse(link.node.target)
@@ -99,11 +99,19 @@ def check_section_for_linked_resources(section):
                 f"Plain syntax error: Only relative links are allowed (text: {link.node.children[0].content}, target: {link.node.target})."
             )
 
-        if not os.path.exists(link.node.target):
-            raise PlainSyntaxError(f"Plain syntax error: Link {link.node.target} does not exist.")
+        resolved_target = file_utils.resolve_linked_resource(template_dirs, link.node.target)
+        if resolved_target is None:
+            searched_dirs = "\n".join(f"  {position}. {dir}" for position, dir in enumerate(template_dirs, start=1))
+            raise PlainSyntaxError(
+                f"Plain syntax error: Link {link.node.target} does not exist. "
+                f"Linked resources are looked up relative to the following directories "
+                f"(highest to lowest precedence):\n{searched_dirs}"
+            )
 
-        if not os.path.isfile(link.node.target):
-            raise PlainSyntaxError(f"Plain syntax error: Link {link.node.target} must be a file.")
+        if not os.path.isfile(resolved_target):
+            raise PlainSyntaxError(
+                f"Plain syntax error: Link {link.node.target} must be a file (resolved to {resolved_target})."
+            )
 
         if len(link.node.children) != 1:
             raise PlainSyntaxError(f"Plain syntax error: Link must have text specified (link: {link.node.target}).")
@@ -122,15 +130,15 @@ def check_section_for_linked_resources(section):
         section.linked_resources = linked_resources
 
 
-def check_for_linked_resources(plain_source):
+def check_for_linked_resources(plain_source, template_dirs):
     for specification_heading in plain_spec.ALLOWED_SPECIFICATION_HEADINGS:
         if specification_heading in plain_source and hasattr(plain_source[specification_heading], "children"):
             for requirement in plain_source[specification_heading].children:
-                check_section_for_linked_resources(requirement)
+                check_section_for_linked_resources(requirement, template_dirs)
 
                 if hasattr(requirement, plain_spec.ACCEPTANCE_TESTS):
                     for acceptance_test in requirement.acceptance_tests:
-                        check_section_for_linked_resources(acceptance_test)
+                        check_section_for_linked_resources(acceptance_test, template_dirs)
 
 
 def process_section_code_variables(section, code_variables):
@@ -845,7 +853,7 @@ def plain_file_parser(  # noqa: C901
 
     process_acceptance_tests(plain_file_parse_result.plain_source)
 
-    check_for_linked_resources(plain_file_parse_result.plain_source)
+    check_for_linked_resources(plain_file_parse_result.plain_source, template_dirs)
 
     marshalled_plain_source = marshall_plain_source(plain_file_parse_result.plain_source)
 

tests/data/plainfile/plain_source_with_missing_link.plain

@@ -0,0 +1,9 @@
+***definitions***
+
+***implementation reqs***
+
+- Implementation should be written in Python.
+
+***functional specs***
+
+- Links must point at an existing file [missing resource](resources/missing_resource.yaml).

tests/data/plainfile/task_manager_with_reference_links.plain

@@ -29,9 +29,9 @@
 
 - Implement the entry point for :App:.
 
-- Show :TaskList:. The details of the user interface are provided in the file [task_list_ui_specification.yaml](tests/data/plainfile/task_list_ui_specification.yaml).
+- Show :TaskList:. The details of the user interface are provided in the file [task_list_ui_specification.yaml](task_list_ui_specification.yaml).
 
-- :User: should be able to add :Task:. Only valid :Task: items can be added. The details of the user interface are provided in the file [add_new_task_modal_specification.yaml](tests/data/plainfile/add_new_task_modal_specification.yaml).
+- :User: should be able to add :Task:. Only valid :Task: items can be added. The details of the user interface are provided in the file [add_new_task_modal_specification.yaml](add_new_task_modal_specification.yaml).
 
 - :User: should be able to delete :Task:.
 

tests/test_plainfileparser.py

@@ -146,14 +146,30 @@ def test_invalid_absolute_link(get_test_data_path):
         )
 
 
+def test_missing_link_error_lists_searched_directories(get_test_data_path):
+    """The error tells the user which directories were searched for the linked resource."""
+    plain_file_dir = get_test_data_path("data/plainfile")
+
+    with pytest.raises(PlainSyntaxError) as exception_info:
+        plain_file.plain_file_parser(
+            "plain_source_with_missing_link.plain",
+            [plain_file_dir],
+        )
+
+    message = str(exception_info.value)
+    assert "resources/missing_resource.yaml does not exist" in message
+    assert "highest to lowest precedence" in message
+    assert plain_file_dir in message
+
+
 def test_reference_link_parsing(get_test_data_path):
     _, plain_sections, _ = plain_file.plain_file_parser(
         "task_manager_with_reference_links.plain",
         [get_test_data_path("data/plainfile")],
     )
     asserted_resources = [
-        "tests/data/plainfile/task_list_ui_specification.yaml",
-        "tests/data/plainfile/add_new_task_modal_specification.yaml",
+        "task_list_ui_specification.yaml",
+        "add_new_task_modal_specification.yaml",
     ]
     for functional_requirement in plain_sections[plain_spec.FUNCTIONAL_REQUIREMENTS]:
         if "linked_resources" not in functional_requirement:
@@ -180,13 +196,36 @@ def test_reference_link_parsing(get_test_data_path):
     assert plain_sections[plain_spec.FUNCTIONAL_REQUIREMENTS][1]["linked_resources"] == [
         {
             "text": "task_list_ui_specification.yaml",
-            "target": "tests/data/plainfile/task_list_ui_specification.yaml",
+            "target": "task_list_ui_specification.yaml",
+        }
+    ]
+    assert plain_sections[plain_spec.FUNCTIONAL_REQUIREMENTS][2]["linked_resources"] == [
+        {
+            "text": "add_new_task_modal_specification.yaml",
+            "target": "add_new_task_modal_specification.yaml",
+        }
+    ]
+
+
+def test_reference_link_parsing_independent_of_working_directory(get_test_data_path, monkeypatch, tmp_path):
+    """Linked resources resolve against the plain file's directory, not the invocation cwd."""
+    monkeypatch.chdir(tmp_path)
+
+    _, plain_sections, _ = plain_file.plain_file_parser(
+        "task_manager_with_reference_links.plain",
+        [get_test_data_path("data/plainfile")],
+    )
+
+    assert plain_sections[plain_spec.FUNCTIONAL_REQUIREMENTS][1]["linked_resources"] == [
+        {
+            "text": "task_list_ui_specification.yaml",
+            "target": "task_list_ui_specification.yaml",
         }
     ]
     assert plain_sections[plain_spec.FUNCTIONAL_REQUIREMENTS][2]["linked_resources"] == [
         {
             "text": "add_new_task_modal_specification.yaml",
-            "target": "tests/data/plainfile/add_new_task_modal_specification.yaml",
+            "target": "add_new_task_modal_specification.yaml",
         }
     ]