Add support for multiple file validation

[greyli]

Add MultipleFileField, FilesRequired, FilesAllowed to support multiple files validation.

Closes #337

[codecov-io]

Codecov Report

Merging #338 into master will increase coverage by 0.02%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #338      +/-   ##
==========================================
+ Coverage   99.67%   99.69%   +0.02%     
==========================================
  Files          18       18              
  Lines         911      986      +75     
  Branches       74       82       +8     
==========================================
+ Hits          908      983      +75     
  Misses          3        3

Impacted Files	Coverage Δ
tests/test_file.py	100% <100%> (ø)	:arrow_up:
flask_wtf/file.py	100% <100%> (ø)	:arrow_up:

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[davidism]

I experimented with this back when I made the WTForms PR, I'm trying to remember the design decisions I made.

I think that while the fields were separate so it was clear what was intended, I was trying to make the validators work for both single and multiple files (rather than adding extra validators or a multiple=True flag). Do you or @lepture agree with that?

Also might be interesting to add a test of the Length validator on the multiple field.

[greyli]

Sounds good to me.

[theomega]

I'd love to see this merged. Anything I can help with?

[codecov-commenter]

Codecov Report

Merging #338 into master will decrease coverage by 1.33%. The diff coverage is 81.01%.

@@            Coverage Diff             @@
##           master     #338      +/-   ##
==========================================
- Coverage   97.97%   96.63%   -1.34%     
==========================================
  Files          18       18              
  Lines         936     1011      +75     
  Branches       73       81       +8     
==========================================
+ Hits          917      977      +60     
- Misses         17       31      +14     
- Partials        2        3       +1     

Impacted Files	Coverage Δ
tests/test_file.py	78.18% <76.00%> (-2.78%)	:arrow_down:
flask_wtf/file.py	90.62% <89.65%> (-1.05%)	:arrow_down:

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[misilot]

Any chance of this being merged? :)

[PanderMusubi]

Any chance of this being merged? :)

Hoping the same. @azmeuk can you review this please?

[greyli]

This PR may not be merged.

I was planning to implement what David recommended as an alternative to this PR in January, but I was too busy with work. Maybe I will have time to make another PR next month. BTW, I'm also happy to review a PR!

[greyli]

Hi guys, I finally re-implemented this in #556. With the new PR, the FileRequired, FileAllowed, and FileSize can be used for both single or multiple files.