Enable show subverb to print yamllint compliant YAML.

[leander-dsouza]

Basic Info

Info	Result
Primary OS tested on	Ubuntu

Description of contribution in a few bullet points

• Enabled colcon mixin show to print in a YAML that is compliant with the onboard yamllint linter.
• Included a custom IndentDumper so that yaml.dump would print indentation that is suited to the linter.
• Reformatted all the strings to f-strings for brevity.

Description of how this change was tested

• Add the mixins from the sample colcon-mixin-repository:

  colcon mixin add default https://raw.githubusercontent.com/colcon/colcon-mixin-repository/master/index.yaml
  colcon mixin update default

• Without this change, the show subverb would yield the following:

  colcon mixin show test

  - coverage-pytest
    pytest-args: ['--cov-report=term']
    pytest-with-coverage: True
  - linters-only
    ctest-args: ['-L', 'linter']
    pytest-args: ['-m', 'linter']
  - linters-skip
    ctest-args: ['-LE', 'linter']
    pytest-args: ['-m', 'not linter']
  - memcheck
    ctest-args: ['-D', 'ExperimentalMemCheck']

  This is printed in a non-standard format, and is not a YAML file.

• After incorporating this PR, the output is as follows:

  ---
  test:
    coverage-pytest:
      pytest-args:
        - --cov-report=term
      pytest-with-coverage: true
    linters-only:
      ctest-args:
        - -L
        - linter
      pytest-args:
        - -m
        - linter
    linters-skip:
      ctest-args:
        - -LE
        - linter
      pytest-args:
        - -m
        - not linter
    memcheck:
      ctest-args:
        - -D
        - ExperimentalMemCheck

• You can verify the sanctity of this output by testing it against yamllint:

  colcon mixin show test > test.yaml && yamllint test.yaml 

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 15.32%. Comparing base (ebedd27) to head (b82b79e).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
colcon_mixin/subverb/show.py	0.00%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #58      +/-   ##
==========================================
+ Coverage   15.30%   15.32%   +0.02%     
==========================================
  Files          11       11              
  Lines         562      561       -1     
  Branches       94       91       -3     
==========================================
  Hits           86       86              
+ Misses        474      473       -1     
  Partials        2        2              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[knmcguire]

Tested it and I get this as well:

> colcon mixin show test
---
test:
  coverage-pytest:
    pytest-args:
      - --cov-report=term
    pytest-with-coverage: true
  linters-only:
    ctest-args:
      - -L
      - linter
    pytest-args:
      - -m
      - linter
  linters-skip:
    ctest-args:
      - -LE
      - linter
    pytest-args:
      - -m
      - not linter
  memcheck:
    ctest-args:
      - -D
      - ExperimentalMemCheck

An added benefit is that if there are any mixins with malformed yaml formats, it will fail here, which I'm not sure it would have failed with colcon mixin before. Perhaps an good thing to add in another PR to the other functions than show (not part of this PR)

[KmoM88]

I'm getting the same results testing with the colcon-mixin-repository example

$ colcon mixin show test                                                                                       [9:55:31]
---
test:
  coverage-pytest:
    pytest-args:
      - --cov-report=term
    pytest-with-coverage: true
  linters-only:
    ctest-args:
      - -L
      - linter
    pytest-args:
      - -m
      - linter
  linters-skip:
    ctest-args:
      - -LE
      - linter
    pytest-args:
      - -m
      - not linter
  memcheck:
    ctest-args:
      - -D
      - ExperimentalMemCheck

Also tested that with this feature it produces a valid yamllint while the previous version fails that validation.