put chainrules core in a requires block, rm it from deps

[vpuri3]

fix #106

[codecov]

Codecov Report

Patch coverage: 33.33% and project coverage change: -0.77 ⚠️

Comparison is base (a25656d) 87.08% compared to head (8db7851) 86.32%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
- Coverage   87.08%   86.32%   -0.77%     
==========================================
  Files           3        3              
  Lines         209      212       +3     
==========================================
+ Hits          182      183       +1     
- Misses         27       29       +2     

Impacted Files	Coverage Δ
src/AbstractFFTs.jl	50.00% <33.33%> (-50.00%)	⬇️

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[stevengj]

Why is coverage warning that we don't have test coverage for the requires block?

[vpuri3]

added tests to check conditional loading of ChainRulesCore on ^1.9

[stevengj]

Invalidations test is failing with

ERROR: LoadError: Failed to precompile SnoopCompile [aa65fe97-06da-5843-b5b1-d5d13cad87d2] to "/home/runner/.julia/compiled/v1.9/SnoopCompile/jl_fFICKt".

which seems like not the fault of this PR?

[vpuri3]

correct, that can't be related to this PR. it looks like a compile error in TypedSyntax.jl, Cthulu.jl.

https://github.com/JuliaMath/AbstractFFTs.jl/actions/runs/5300882552/jobs/9594723411?pr=107#step:5:215

[devmotion]

I wonder if this PR was a good idea? ChainRulesCore is (supposed to be) a lightweight interface package (and I've even heard some people argue it should not be put into an extension on Julia >= 1.9 even though that's the common pattern now). Masking it with Requires as done in this PR will 1) break pre-compilation on Julia < 1.9 and 2) add an additional dependency on Julia >= 1.9.

[vpuri3]

My reasoning for putting extension packages in a requires block is that loading CRC in here will prompt loading CRC extensions of every downstream package. As these extensions can be arbitrarily many and arbitrarily large, its worth adding a Requires dependency than paying the cost of all that code loading.

[vpuri3]

break pre-compilation on Julia < 1.9

can you explain?

[devmotion]

Requires breaks pre-compilation.

[devmotion]

My reasoning for putting extension packages in a requires block is that loading CRC in here will prompt loading CRC extensions of every downstream package.

ChainRulesCore will be loaded in most projects with AbstractFFTs on Julia <= 1.8 anyway I assume since e.g. SpecialFunctions and many other core packages depend on ChainRulesCore.

[vpuri3]

Requires breaks pre-compilation.

I'm not aware of this. Is there an issue or discourse on this topic?

[devmotion]

I'm not aware of a "standard" reference (e.g., I just happened to learn about the deficiencies of Requires over the years and I assume many other people also "just know") but there a few open issues in Requires.jl that point to different problems. A few problems, including the issue with precompilation, are listed in JuliaLang/Pkg.jl#1285.