parser: warn user on multiple global gateway (LP: #1901836) (FR-728)

[schopin-pro]

Description

It doesn't make sense for the user to have multiple global gateways. This patch introduces a consistency check at the end of the parsing stage, and only emits a warning in order not to break current configurations.

Addresses LP #1901836

Checklist

• Runs make check successfully.
• Retains 100% code coverage (make check-coverage).
• New/changed keys in YAML format are documented.
• (Optional) Adds example YAML for new feature.
• (Optional) Closes an open bug in Launchpad.

[schopin-pro]

Note that #216 and this PR are in slight conflict, as merging one of them will lead to the tests failing on the other. To solve this is only a matter of changing the keywords from gateway4/6 to gateway in the tests introduced in this PR.

[slyon]

Please mention LP: #1901836 in the PR description and title.

[slyon]

Thank you for another great PR! Contrary to the PR description, we do actually support multiple routing tables (table: setting) – maybe you could update that accordingly.

This patch introduces a consistency check at the end of the parsing stage, and only emits a
warning in order not to break current configurations.

Yes that's good. We do not want to break existing configurations in the field. Although, arguably configuration defining multiple gateways are already broken (in a different way).

So I like your changes: Clean functions and straight forward testing.
I just want to ask for two small changes see inline comments):

• Logical order of execution of the validate_gateway_consistency() function
• Verbosity of the error message, please feel free to extend/modify the example I gave below

[codecov-commenter]

Codecov Report

Merging #217 (dd7e09e) into master (2fd3fc2) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #217   +/-   ##
=======================================
  Coverage   99.00%   99.01%           
=======================================
  Files          55       55           
  Lines        9178     9200   +22     
=======================================
+ Hits         9087     9109   +22     
  Misses         91       91           

Impacted Files	Coverage Δ
src/parse.c	100.00% <100.00%> (ø)
src/validation.c	99.48% <100.00%> (+0.04%)	⬆️
tests/generator/test_errors.py	100.00% <100.00%> (ø)

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[slyon]

Thank you Simon, LGTM! 👀

I've cleaned up some whitespace in the warning message log and I think it's ready for merging, independently of #216