Fix #100: strip lines before parsing with Requirement() (#101)

* Add failing test for issue #100

packaging 26.3 rejects requirement strings with trailing whitespace.
process_line() passes the raw line including its newline to Requirement(),
the resulting InvalidRequirement is silently swallowed, and source
packages are no longer commented out in the generated constraints.

* Fix #100: strip lines before parsing with Requirement()

packaging 26.3 made requirement parsing strict: a trailing newline now
raises InvalidRequirement. process_line() parsed the raw line straight
from file iteration, the error was silently swallowed, and source
packages stayed pinned in the generated constraints.

Parse the stripped line instead, and log unparseable lines at debug
level so parser-behavior changes surface under -v instead of silently
producing downstream resolver errors.

* Update CHANGES.md for #100

Author: jensens

CHANGES.md

@@ -4,6 +4,11 @@
 
 <!-- Add future changes here -->
 
+- Fix #100: With packaging >= 26.3, packages configured as sources were no longer
+  commented out in the generated requirements/constraints, because `Requirement()`
+  now rejects the trailing newline and the error was silently swallowed. Lines are
+  now stripped before parsing and unparseable lines are logged at debug level. [jensens]
+
 
 ## 5.4.0 (2026-06-01)
 

src/mxdev/processing.py

@@ -122,9 +122,9 @@ def process_line(
             cache_dir=cache_dir,
         )
     try:
-        parsed = Requirement(line)
+        parsed = Requirement(line.strip())
     except Exception:
-        pass
+        logger.debug(f"Line is not a requirement specifier: {line.strip()!r}")
     else:
         parsed_name_lower = parsed.name.lower()
         if parsed_name_lower in [k.lower() for k in package_keys]:

tests/test_processing.py

@@ -109,6 +109,65 @@ def test_process_line_blank():
     assert constraints == []
 
 
+@pytest.mark.parametrize("eol", ["\n", "\r\n"])
+def test_process_line_source_package_with_trailing_newline(eol):
+    """Regression test for #100: lines read from files carry a trailing newline.
+
+    packaging >= 26.3 rejects requirement strings with trailing whitespace, so
+    process_line must strip before parsing.
+    """
+    from mxdev.processing import process_line
+
+    requirements, constraints = process_line(
+        f"my.package==1.0.0{eol}",
+        package_keys=["my.package"],
+        override_keys=[],
+        ignore_keys=[],
+        variety="r",
+    )
+    assert requirements == ["# my.package==1.0.0 -> mxdev disabled (source)\n"]
+    assert constraints == []
+
+
+@pytest.mark.parametrize("eol", ["\n", "\r\n"])
+def test_process_line_source_constraint_with_trailing_newline(eol):
+    """Regression test for #100: constraints variety must also strip before parsing."""
+    from mxdev.processing import process_line
+
+    requirements, constraints = process_line(
+        f"my.package==1.0.0{eol}",
+        package_keys=["my.package"],
+        override_keys=[],
+        ignore_keys=[],
+        variety="c",
+    )
+    assert requirements == []
+    assert constraints == ["# my.package==1.0.0 -> mxdev disabled (source)\n"]
+
+
+def test_resolve_dependencies_source_package_commented(tmp_path):
+    """Regression test for #100 through the real file-reading path."""
+    from mxdev.processing import resolve_dependencies
+
+    req_file = tmp_path / "requirements.txt"
+    req_file.write_text("my.package==1.0.0\nrequests>=2.28.0\n")
+
+    old_cwd = os.getcwd()
+    os.chdir(tmp_path)
+    try:
+        requirements, constraints = resolve_dependencies(
+            "requirements.txt",
+            package_keys=["my.package"],
+            override_keys=[],
+            ignore_keys=[],
+            variety="r",
+        )
+        assert "# my.package==1.0.0 -> mxdev disabled (source)\n" in requirements
+        assert any("requests>=2.28.0" in line for line in requirements)
+    finally:
+        os.chdir(old_cwd)
+
+
 def test_resolve_dependencies_missing_file(tmp_path):
     """Test resolve_dependencies with a missing requirements file."""
     from mxdev.processing import resolve_dependencies