#431 Recognizers often ascribe wrong file type

[tfesenko]

Fix contentType for an empty YAML file, now it returns a more generic YEdit editor. Why this fix works

1. An empty file always returns INDETERMINATE as description. Note that it's not the VALID which is returned when a content describer actually accepts the input. See com.reprezen.swagedit.core.editor.TextContentDescriber.describe(InputStream, IContentDescription):

       String content = CharStreams.toString(new
   InputStreamReader(contents));
       if (content.trim().isEmpty()) {
           return INDETERMINATE;
       }
   
       return isSupported(content) ? VALID : INVALID;

2. All ContentDescriber for a given file extensions are equally important. Because all the ContentDescriber return INDETERMINATE, they are treated equally important, see org.eclipse.core.internal.content.ContentTypeCatalog.collectMatchingByContents(int, IContentType[], List<ContentType>, ILazySource, Map<String, Object>)

3. Then IContentType are sorted and the first one wins org.eclipse.core.internal.content.ContentTypeCatalog.internalFindContentTypesFor(ILazySource, IContentType[][], Comparator<IContentType>, Comparator<IContentType>) sorts the inputs. In case of INDETERMINATE, ContentTypeCatalog.policyConstantGeneralIsBetter is used which is...

   A sorting policy where the more generic content type wins. Lexicographical comparison is done as a last resort when all other criteria fail.

where more generic content type means, getDepth() is based on the hierarchy defined by the base-type:

// first criteria: depth - the lower, the better
int depthCriteria = type1.getDepth() - type2.getDepth();

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By using YEdit as the base-type, we make the YEdit the more generic content type => it will be used in case of empty files.