be more relaxed about attribute casing

[Rich-Harris]

fixes #1062

[codecov-io]

Codecov Report

Merging #1095 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1095      +/-   ##
==========================================
+ Coverage   91.53%   91.54%   +0.01%     
==========================================
  Files         123      123              
  Lines        4477     4483       +6     
  Branches     1443     1444       +1     
==========================================
+ Hits         4098     4104       +6     
  Misses        162      162              
  Partials      217      217

Impacted Files	Coverage Δ
src/generators/nodes/Attribute.ts	85.92% <100%> (+0.43%)	⬆️

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[Conduitry]

Do you think it makes more sense to do this normalization during parsing instead of during generation? I don't think it actually currently matters, but in the future it might be good to know we always have canonically-cased attributes in the AST.

[Rich-Harris]

I wondered about that. I think it might cause problems with components though — you don't know at parse time whether something is an element or a component (at least until v2 when we insist that components are capitalised and elements are not), and if we 'corrected' <Widget viewbox='...'> then it would break stuff.

[Conduitry]

Ah I wasn't thinking about that, makes sense.