Add error message to autofold

[nomisRev]

This closes #462

@JorgeCastilloPrz @raulraja As discussed in #766 I am not sure how we should proceed with throwing KnownException. I did a small spike with the scenario handled in this PR and had to rely on MonadError and Traverse for it to be somewhat manageable.

[nomisRev]

@jereksel I tried adding some tests for the processor but ran into some issues. If I understand correctly I should.

1. Add annotated targets to :arrow-annotation-processor-test-models
2. Add expected generated result to arrow-annotation-processor/src/test/resources
3. Add test under arrow-annotation-processor/src/test

Since @autofold generates extension functions I have a dependency on :arrow-annotation-processor-test-models in resources. This was not working for me.

Any ideas? Am I missing something?

[codecov]

Codecov Report

Merging #806 into master will decrease coverage by 0.05%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master     #806      +/-   ##
============================================
- Coverage     44.71%   44.66%   -0.06%     
  Complexity      623      623              
============================================
  Files           298      298              
  Lines          7657     7669      +12     
  Branches        831      832       +1     
============================================
+ Hits           3424     3425       +1     
- Misses         3930     3942      +12     
+ Partials        303      302       -1

Impacted Files	Coverage Δ	Complexity Δ
...ssor/src/main/java/arrow/fold/AutoFoldProcessor.kt	0% <0%> (ø)	0 <0> (ø)	⬇️
.../src/main/java/arrow/fold/AutoFoldFileGenerator.kt	0% <0%> (ø)	0 <0> (ø)	⬇️
...ics/src/main/kotlin/arrow/optics/instances/mapk.kt	91.66% <0%> (+4.16%)	0% <0%> (ø)	⬇️

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[andrzejressel]

@nomisRev Try removing "build" directory in models. When you add new classes kapt often doesn't transform them.

[raulraja]

I think it's ok to throw exceptions since this should fail fast at compile time but I don't have an strong opinion since I'm actually more interested in removing the entire kapt API we use all together for something that wraps the Proto stuff which is tedious as hell to deal with. I'm also realizing that arrow-generic will provide also this same feature when we have @coproduct sealed ... since fold is one of the ops in @coproduct and soon will be in @product because of the HList <-> data class Iso.

Maybe then we should consider merging these processors and annotations to be part of arrow-generic

[nomisRev]

@jereksel I doubled checked everything but still get FileNotFoundException. Although I can see the java stub under .../models/build/tmp/kapt3/stubs/main/arrow/ap/objects/autofold.

Test fail with following error java.io.FileNotFoundException: /var/folders/y6/3f_jn1qd2xg6kkgsnmf2_p680000gp/T/1524998582721-0/autofold (Is a directory)

I am unsure why it's trying to look in that location. Any ideas?

[andrzejressel]

@nomisRev That means that AP passed fine, but checking of output file failed (this directory is for AP output files).

[nomisRev]

@jereksel I have no clue how to make it find the directory. The same thing is done for Optics. I'd like to close this PR, if we cannot fix tests I prefer to remove them for now.