improve support for null entries

[mikaelarguedas]

syntax like 'ubuntu: null' will now be raising ResolutionError with
relevant error message instead of InvalidData

This came up recently with ros/rosdistro#21906
This should also fix / improve error message for issues like #689

Details

before:

root@cd07c77952b3:/# rosdep resolve apparmor --os fedora:30

ERROR: Rosdep experienced an error: rosdep OS definition for [apparmor:fedora] must be a dictionary, string, or list: None
Please go to the rosdep page [1] and file a bug report with the stack trace below.
[1] : http://www.ros.org/wiki/rosdep

rosdep version: 0.17.1

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/rosdep2/main.py", line 144, in rosdep_main
    exit_code = _rosdep_main(args)
  File "/usr/local/lib/python3.6/dist-packages/rosdep2/main.py", line 424, in _rosdep_main
    return _rosdep_args_handler(command, parser, options, args)
  File "/usr/local/lib/python3.6/dist-packages/rosdep2/main.py", line 446, in _rosdep_args_handler
    return command_handlers[command](args, options)
  File "/usr/local/lib/python3.6/dist-packages/rosdep2/main.py", line 865, in command_resolve
    rule_installer, rule = d.get_rule_for_platform(os_name, os_version, installer_keys, default_key)
  File "/usr/local/lib/python3.6/dist-packages/rosdep2/lookup.py", line 151, in get_rule_for_platform
    raise InvalidData('rosdep OS definition for [%s:%s] must be a dictionary, string, or list: %s' % (self.rosdep_key, os_name, data), origin=self.origin)
rosdep2.core.InvalidData: rosdep OS definition for [apparmor:fedora] must be a dictionary, string, or list: None

after:

root@cd07c77952b3:/# rosdep resolve apparmor --os fedora:30

ERROR: [apparmor] defined as "not available" for OS version [30]

[apparmor] defined as "not available" for OS version [30]
	rosdep key : apparmor
	OS name    : fedora
	OS version : 30
	Data: 
debian:
- apparmor
fedora: null
ubuntu:
- apparmor

Second commit improves the formatting, but can be ommitted if disruptive as it;s not really related to this fix

Details

before:

root@cd07c77952b3:/# rosdep resolve apparmor --os fedora:30

ERROR: [apparmor] defined as "not available" for OS version [30]

[apparmor] defined as "not available" for OS version [30]
	rosdep key : apparmor
	OS name    : fedora
	OS version : 30
	Data: debian:
- apparmor
fedora: null
ubuntu:
- apparmor

after:

root@cd07c77952b3:/# rosdep resolve apparmor --os fedora:30

ERROR: [apparmor] defined as "not available" for OS version [30]

[apparmor] defined as "not available" for OS version [30]
	rosdep key : apparmor
	OS name    : fedora
	OS version : 30
	Data: 
debian:
- apparmor
fedora: null
ubuntu:
- apparmor

Signed-off-by: Mikael Arguedas mikael.arguedas@gmail.com

[codecov-io]

Codecov Report

Merging #726 into master will increase coverage by 0.48%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #726      +/-   ##
==========================================
+ Coverage   75.85%   76.34%   +0.48%     
==========================================
  Files          40       40              
  Lines        3148     3293     +145     
==========================================
+ Hits         2388     2514     +126     
- Misses        760      779      +19

Impacted Files	Coverage Δ
src/rosdep2/lookup.py	87.82% <100%> (+0.09%)	⬆️
src/rosdep2/platforms/source.py	90.5% <0%> (-0.06%)	⬇️
src/rosdep2/_version.py	100% <0%> (ø)	⬆️
src/rosdep2/meta.py	100% <0%> (ø)	⬆️
src/rosdep2/platforms/alpine.py	100% <0%> (ø)	⬆️
src/rosdep2/sources_list.py	87.74% <0%> (+1.09%)	⬆️
src/rosdep2/main.py	54.49% <0%> (+5.65%)	⬆️

---

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[cottsay]

This is great. It's come up several times now, and as python 2 packages drop like flies out of Fedora and EPEL, it's only going to get worse.

Thanks!

[mikaelarguedas]

@cottsay @nuclearsandwich friendly 🛎️

[mikaelarguedas]

@cottsay @nuclearsandwich is there anything holding this approved PR ?

[nuclearsandwich]

I think this is much clearer. Love that this has tests. Thanks @mikaelarguedas

[nuclearsandwich]

is there anything holding this approved PR ?

Not from my end. Thanks for the re-ping. I've kicked CI up again and if it comes back 🆗 I'll merge. I think @cottsay has some additional PRs that need review before the next release is made so this may sit on master for a while longer but I'll use this as an impelling force to get those reviewed, merged, and released as well.

[mikaelarguedas]

Sounds good, CI will most likely need #739 to come back ✔️

[tfoote]

This looks good but needs a rebase to pass CI

[mikaelarguedas]

rebased and passing CI