[LNT] Update to match API change in PIP

[ostannard]

Summary

The parse_requirements function in PIP now (as of version 20.1) returns a list of ParsedRequirements, where it was previously a list of InstallRequirements. Update our setup.py to work with either one.

This is an internal function of pip, so we shouldn't really be depending on it, the recommended solution seems to be to hard-code the dependency list in setup.py. However, according to a comment on D45211 the requirements.*.txt files are needed for some cloud setups, and this avoids duplicating the dependency list between these files and setup.py.

[DavidSpickett]

LGTM

[ostannard]

Committed as 5acafc540ad61c4cab90fbe3323c795d5210b72f.

setup.py

     # In old PIP the session flag cannot be passed.
     install_reqs = parse_requirements(req_file)
 
-reqs = [str(ir.req) for ir in install_reqs]
+try:
+    # Filter out git dependencies, which can't be handled by setuptools.
+    reqs = [ir.requirement for ir in install_reqs
+            if not ir.requirement.startswith("git+")]
+except AttributeError:
+    # Old versions of pip (<20.1) returned a List[InstallRequirement] instead
+    # of a List[ParsedRequirement], which has different member names, and does
+    # not include git dependencies.
+    reqs = [str(ir.req) for ir in install_reqs]
 
 setup(
     name="LNT",