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packaging 26.3 breaks disabling of source-package constraints (Requirement() now rejects trailing newline) #100
Description
Symptom
With packaging==26.3 (released 2026-08-04), mxdev no longer comments out constraints for packages declared as sources. The pin survives into constraints-mxdev.txt, and installation then fails because the editable source (a different version) masks the index:
× No solution found when resolving dependencies:
╰─▶ Because there is no version of edutap-wallet-apple==1.0.0a3 and
you require edutap-wallet-apple==1.0.0a3, we can conclude that your
requirements are unsatisfiable.
Any CI that installs mxdev fresh (unpinned toolchain) went red the moment packaging 26.3 hit PyPI. mxdev 5.4.0, identical inputs:
- packaging 26.2 →
# edutap.wallet_apple==1.0.0a3 -> mxdev disabled (source) - packaging 26.3 →
edutap.wallet_apple==1.0.0a3(kept!)
Root cause
processing.py (5.4.0, ~lines 124–131) parses the raw requirements/constraints line including the trailing newline:
try:
parsed = Requirement(line)
except Exception:
pass
else:
parsed_name_lower = parsed.name.lower()
if parsed_name_lower in [k.lower() for k in package_keys]:
line = f"# {line.strip()} -> mxdev disabled (source)\n"packaging 26.3 made Requirement parsing stricter — a trailing newline now raises:
>>> Requirement('edutap.wallet_apple==1.0.0a3\n')
# packaging 26.2: parses fine
# packaging 26.3: InvalidRequirement: Expected comma (within version specifier), ...The bare except Exception: pass swallows it, so the line is silently treated as "not a source package".
Suggested fix
parsed = Requirement(line.strip()) — and possibly log a warning instead of passing silently, so the next parser-behavior change surfaces instead of producing downstream resolver errors.
Happy to send a PR if wanted.
Activity
jensens commentedon Aug 4, 2026
Confirmed. Root cause verified in
src/mxdev/processing.pyline 125 (process_line()): the raw line — still carrying its trailing newline from file iteration inprocess_io()— is passed topackaging.requirements.Requirement. packaging 26.3's stricter parser raisesInvalidRequirementon the trailing whitespace, and the bareexcept Exception: pass(lines 126-127) swallows it, so the line is treated as not-a-requirement and never matched against the configured source packages. The other twoRequirement()call sites (uv.py:53,config.py:98) already parse stripped strings and are not affected. The existing tests only pass lines without trailing newlines, which is why the suite never caught this.Fix #100: strip lines before parsing with Requirement()
Update CHANGES.md for #100
Fix #100: strip lines before parsing with Requirement() (#101)