Limit pyparsing to major version 2

[moyiz]

pyparsing released a new major version (3.0.0) with breaking changes.

Package: https://github.com/pyparsing/pyparsing/
Changelog: https://github.com/pyparsing/pyparsing/blob/master/docs/whats_new_in_3_0_0.rst
Notable changes relate to renaming originalTextFor, stringEnd, stringStart.

This change limits pyparsing to not installl / upgrade to 3.0.0 and resolves the failing test_parseexception_error_msg:

self = <tests.test_requirements.TestRequirements object at 0x7f418a028160>
                                                                               
    def test_parseexception_error_msg(self):                                                                                                                  
        with pytest.raises(InvalidRequirement) as e:                                                                                                          
            Requirement("toto 42")                            
>       assert "Expected stringEnd" in str(e.value)         
E       assert 'Expected stringEnd' in 'Parse error at "\'42\'": Expected string_end'                                                                         
E        +  where 'Parse error at "\'42\'": Expected string_end' = str(InvalidRequirement('Parse error at "\'42\'": Expected string_end'))
E        +    where InvalidRequirement('Parse error at "\'42\'": Expected string_end') = <ExceptionInfo InvalidRequirement('Parse error at "\'42\'": Expected string_end') tblen=2>.value
                                                                                                                                                              
tests/test_requirements.py:195: AssertionError   

[pradyunsg]

(approved the CI run again)

[moyiz]

@pradyunsg Thanks. The tests currently fail because the workflow installs pytest which depends on packaging which sneaks pyparsing==3.0.0 into the test phase. Should the GitHub action be updated to install packaging from "current" branch?

Edit: Meant nox. Added a session.install(".") to use current packaging dependencies. UTs pass in my fork now.

[henryiii]

Capping this means that packages that use packaging cannot be installed in the same environment as any library that uses pyparsing>=3.0 - with the renames and fairly large changes, this will probably be quite popular (I was just considering it a day or two ago). This really needs to be fixed to support the newly renamed methods, not capped, not for a library like packaging. Adding a version cap does have consequences.

[henryiii]

Also, isn't this really just breaking tests that are looking for exact strings in exception messages? Is it breaking any real code? And who's tests are it breaking other than ours?

[layday]

This does only seem to break the one test which is comparing the error message. The release notes say:

Backward-compatibility synonyms for all names and arguments have been included, to allow parsers written using the old names to run without change.

[henryiii]

Could we just correct this one test to look for both synonyms and then yank 21.2?