add async callbacks support to parse

[mtabbasi]

Fixes #5424

[codecov]

Codecov Report

Merging #5577 (824babb) into master (737f396) will decrease coverage by 0.21%.
The diff coverage is 14.28%.

❗ Current head 824babb differs from pull request most recent head 628f53e. Consider uploading reports for the commit 628f53e to get more accurate results

@@            Coverage Diff             @@
##           master    #5577      +/-   ##
==========================================
- Coverage   88.70%   88.49%   -0.22%     
==========================================
  Files         162      162              
  Lines       10787    10796       +9     
  Branches     1851     1851              
==========================================
- Hits         9569     9554      -15     
- Misses        942      966      +24     
  Partials      276      276              

Impacted Files	Coverage Δ
scrapy/commands/parse.py	28.19% <14.28%> (+0.25%)	⬆️
scrapy/robotstxt.py	75.30% <0.00%> (-22.23%)	⬇️

[Gallaecio]

Looks good to me, but I wonder why the coverage data suggest the new test is not reaching the moved code.

[wRAR]

@Gallaecio the test launches a separate scrapy parse process, and I guess coverage for subprocesses is not collected?

[Gallaecio]

Indeed. I thought coverage was able to pick that up anyway, but it seems not. The same code before the changes was not in coverage either.

[Gallaecio]

Thank you!