Report a compilation error for invalid placeholders [Part I]

[yevhenii-nadtochii]

This PR addresses #213 for boolean options that use a companion option to specify custom error messages.

The following options have received this compilation check: (distinct), (required), (set_once).

Their companion policies now extract and check the error messages on their own. Instead of a single event, the main and companion policies now emit their own events that are accumulated in the view:

1. RequiredFieldDiscovered → RequiredFieldDiscovered and IfMissingOptionDiscovered.
2. DistinctFieldDiscovered → DistinctFieldDiscovered and IfHasDuplicatesOptionDiscovered.
3. SetOnceFieldDiscovered → SetOnceFieldDiscovered and IfSetAgainOptionDiscovered.

Note that we usually emit the following event: ${OptionName}{OptionTarget}Discovered. I kept this convention for the main options, but emitting something like IfMissingFieldDiscovered makes no sense because this is actually an option that affects another, its main option, not the field itself.

Having these checks in :model required the following changes:

1. The ErrorPlaceholder enum has been moved to :model.
2. resolveErrorMessage() function is no longer needed. Companion policies now unpack the option and extract the message in a typed manner.
3. CompanionPolicy has been replaced in favor of the checkBothApplied() function.

As for now, I haven't extracted a common checkPlaceholders() function to check for placeholders. I'll do in the next PR when the rest of options will be given such a check.

Non-related changes

ChoiceView has been renamed to ChoiceGroupView to fix naming consistency: ${OptionName}{OptionTarget}View.

[codecov]

Codecov Report

Attention: Patch coverage is 68.86792% with 33 lines in your changes missing coverage. Please review.

Project coverage is 26.14%. Comparing base (b266ea3) to head (fe9a0d7).
Report is 20 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #216      +/-   ##
============================================
+ Coverage     23.67%   26.14%   +2.47%     
- Complexity      240      241       +1     
============================================
  Files           137      137              
  Lines          3177     3236      +59     
  Branches        241      247       +6     
============================================
+ Hits            752      846      +94     
+ Misses         2392     2351      -41     
- Partials         33       39       +6     

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[yevhenii-nadtochii]

@armiol @alexander-yevsyukov PTAL

[armiol]

@yevhenii-nadtochii LGMT in general. Please see my comment though.

[armiol]

Instead of having a function taking two very similar arguments (in which I would have the primary first, BTW), I'd rather have an extension function to GeneratedExtension.

The reason is that the invocations of callFunction(someparameter, someotherparameter) in which both of the arguments are of the same type, are prone to errors with the parameters swapped.

[yevhenii-nadtochii]

@armiol PTAL