Parse flow nested array type annotations like number[][]

[bxt]

Q	A
Bug fix?	yes
Breaking change?	no
New feature?	yes
Deprecations?	no
Spec compliancy?	yes?
Tests added/pass?	yes
Fixed tickets	#217
License	MIT

Flow supports nested array types like number[][], while babylon throws a syntax error, as noted in #217 . This error caused problems upstream, e.g. when trying to strip the types with babel, see babel/babel#4831. The workaround was to use Array<number[]>. To solve this, I adjusted the flowParsePostfixType method to parse 0-n [] postfixes and return the correct AST. I added test cases with:

var a: number[][]

var a: number[][][]

For the tests' expected.jsons I copied flow's ASTs from astexplorer.net and adjusted the range keys etc. to match babylon's format. I was curious if there could be any interference with JS arrays, so I checked with the code of flow's parser. And indeed – they check for line terminators there, so I added another test case with:

var a: number
[]

And made sure this parses as a program with a body of a VariableDeclaration and an ExpressionStatement.

Let me know what you think. ☺️

[codecov-io]

Current coverage is 97.69% (diff: 100%)

Merging #219 into master will increase coverage by <.01%

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  Methods         336        336          
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  Branches        838        838          
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+ Hits           3138       3140     +2   
  Misses           30         30          
  Partials         44         44          

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[danez]

Awesome, thanks for the contribution. Looks good, but I'm currently on my phone will check later when I'm home.

[danez]

Thanks, looks perfect.

[hzoo]

Awesome contribution @bxt (also your issue description was beautiful)

[bxt]

@danez @hzoo Thank you ☺️ nice to work with you.