Better error messages when using unsupported compose file syntax

[jcsirot]

- What I did Docker App prints a more specific error messages when the template uses one of these compose file syntax

• ${VARIABLE:-default}
• ${VARIABLE-default}
• ${VARIABLE:?err}
• ${VARIABLE?err}

- A picture of a cute animal (not mandatory but encouraged)

[codecov[bot]]

Codecov Report

Merging #651 into master will decrease coverage by 0.04%. The diff coverage is 87.23%.

@@            Coverage Diff             @@
##           master     #651      +/-   ##
==========================================
- Coverage   72.19%   72.14%   -0.05%     
==========================================
  Files          51       52       +1     
  Lines        2658     2675      +17     
==========================================
+ Hits         1919     1930      +11     
- Misses        490      497       +7     
+ Partials      249      248       -1

Impacted Files	Coverage Δ
internal/commands/root.go	72.11% <0%> (ø)	:arrow_up:
internal/store/bundle.go	71% <100%> (ø)	:arrow_up:
internal/commands/image/list.go	81.81% <100%> (-1.79%)	:arrow_down:
internal/yaml/yaml.go	80% <100%> (ø)	:arrow_up:
internal/commands/image/command.go	100% <100%> (ø)	:arrow_up:
internal/commands/image/rm.go	61.29% <83.33%> (-8.48%)	:arrow_down:
internal/commands/image/tag.go	88.23% <88.23%> (ø)
types/parameters/parameters.go	92.06% <0%> (-4.77%)	:arrow_down:

---

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[GordonTheTurtle]

Please sign your commits following these rules: https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work The easiest way to do this is to amend the last commit:

$ git clone -b "composefile-syntax-improved-error-messages" git@github.com:jcsirot/docker-app.git somewhere
$ cd somewhere
$ git rebase -i HEAD~842354106912
editor opens
change each 'pick' to 'edit'
save the file and quit
$ git commit --amend -s --no-edit
$ git rebase --continue # and repeat the amend for each commit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[silvin-lubecki]

@jcsirot can you squash?

[jcsirot]

@silvin-lubecki done

[silvin-lubecki]

@jcsirot I see that the errors are capitalised which I thought was against Go best practices. @silvin-lubecki what do we do in the CLI?

You are right @chris-crone nice catch. Indeed the docker/cli error messages are not capitalized.

[jcsirot]

@chris-crone @silvin-lubecki Here the error message is composed of several sentences ending with ponctuation. So maybe we should keep it capitalised?